The URL can be used to link to this page

20130320 Stormwater Pollution Prev Plan 12032013 Larson&Associates Land Surveyors&Engineers,Inc. 4401 South 66th Street Tacoma,WA 98409 CONSTRUCTION STORMWATER POLLUTION PREVENTION PLAN PROPONENT: BENJAMIN RYAN COMMUNITIES 10011 BRIDGEPORT WAY SW SUITE #1500-212 LAKEWOOD,WA. 98499 ��a...�. �'� � M��Jf�� c W s �f s P . �,,,ft8 �I'� � � .�'.��' �, � / L' .,,. � � � ;i I � n �i z' % + � A� �Q / w ,,, ��,�F�IST e1�� ' �� S,tiyC iq P,N�� `�\\\��'' PREPARED BY: Larson & Associates Land Surveyors and Engineers, Inc. 4401 South 66th Street Tacoma, WA 98409 (253) 474-3404 November 13, 2013 �'��Z��D DECO22013 , .K' i ,....+� �.d. ,��_:. . , . � ��... PROJECTENGINEER'S CERTIFICATION.........................................................................................................1 STORMWATER POLLUTION PREVENTION PLAN SECT�oN 1 -CONSTRUCTION STORMWATER POLLUTION PREVENTION ELEMENTS......................2-17 SECTtorr 2-PROJECT DESCRIPTION...............................................................................................................17 SECTiorr 3-EXISTING SITE CONDITIONS.................................................................................................17-18 SECT1orr4-ADJACENT AREAS........................................................................................................................18 SEC1'�oN 5-CRITICAL AREAS..........................................................................................................................18 SECTION6-SOILS...............................................................................................................................................18 SECT1orr 7-EROSION PROBLEM AREAS .......................................................................................................18 SeCTiorr 8-CONSTRUCTION PHASING....................................................................................................18-19 SECT1orr 9-CONSTRUCTION SCHEDULE......................................................................................................19 SECTiorr 10-FINANCIAL/OWNERSHIP RESPONSIBILITIES.......................................................................19 SECT[oN I 1 -ENGINEERING CALCULATIONS..............................................................................................20 SECT[orr 12-EROSION CONTROL SPECIALIST............................................................................................20 APPENDIX��A��.............................................................................................................................................BMPs APPENDIX��B��.........................................................................................MISCELLANEOUS INFORMATION � � ��,; .: . � _ i�. . � I hereby state that this Stormwater Pollution Prevention Plan for River Run Apartments has been prepared by me or under my supervision and meets the standard of care and expertise which is usual and customary in this community for professional engineers. I understand that the City of Yelm and Washington State does not and will not assume liability for the sufficiency, suitability, or performance of drainage facilities prepared by me. �� , � a �/' Grant J. Middleto , �.E. ''��`, s•� � MI Dljl�� I '� i' � �` �i`' ,�cy ` � so �,'° �� ',fl / � '�\ / � � � � �n / / �� % � ti C a,, ,�; r1� . �>� �• �rr IST � m ! \�', ��S5'j N A I EN''�� -_'] 9�\\ �o � �°°��:�-`��.��=�� . . ��."�:._�,��: �-;�,�::� �:_�, ��:�`T�.�ry�.�� _ � �` �� :=�,`� � � �� ° � �:.;�� :�: p �� SECTION 1 —CONSTRUCTION STORMWATER POLLUTION PREVENTION ELEMENTS Stormwater pollution prevention will be maintained during the construction of this site by incorporating standard erosion control methods such as temporary construction entrances, temporary interceptor swales, rock check dams, mirafi siltation fences, seeding/mulching and gravel surfacing. The following devices will be used to trap sediment from the cleared areas and prevent it from leaving the site. A construction entrance will be installed at the entrance to the site to keep sediment from being tracked out of the site and onto the City streets. Mirafi silt fences will be installed along all low areas onsite. Inlet protection will also be installed within all existing and proposed stormwater catch basins to minimize the possibility of pollution downstream. The following general Washington State Elements shall be upheld at all times during the construction process. Please reference the BMP section in this report. Element#1: Preserve Vegetation/Mark Clearing Limits • Prior to beginning land disturbing activities, including clearing and grading, clearly mark all clearing limits and vegetated buffer areas to be preserved within the construction area. These shall be marked, both in the field and on the plans, to prevent damage and offsite impacts. • The duff layer, native topsoil, and natural vegetation shall be retained in an undisturbed state to the maximum degree practicable. • Plastic, metal, or stake wire fence may be used to mark the clearing limits. • Suggested BMPs: - BMP C103: High Visibility Plastic or Metal Fence - BMP C 104: Stake and Wire Fence Element#2: Establish Construction Access • Construction vehicle access and exit shall be limited to one route, if possible. • Access points shall be stabilized with a pad of quarry spalls, crushed rock or other equivalent BMP, to minimize the tracking of sediment onto public roads. • Wheel wash or tire baths should be located on site, if the stabilized construction entrance is not effective in preventing sediment from being tracked onto public/State roads. 2 • If sediment is tracked off site onto public roads/ State highway shall be cleaned thoroughly at the end of each day, or more frequently during wet weather. Sediment shall be removed from roads by shoveling or pickup sweeping and shall be transported to a controlled sediment disposal area. • Street washing is allowed only after sediment is removed in accordance with S9.D.2.d. Street wash wastewater shall be controlled by pumping back on site or otherwise be prevented from discharging into systems tributary to waters of the state. • Construction access restoration shall be equal to or better than the pre- construction condition. • Suggested BMPs: - BMP C 105: Stabilized Construction Entrance - BMP C 106: Wheel Wash - BMP C 107: Construction Road/Parking Area Stabilization Element#3: Control Flow Rates • Properties and waterways downstream from development sites shall be protected from erosion due to increases in the velocity and peak volumetric flow rate of stormwater runoff from the project site, as required by local plan approval authority. • Native vegetation retention buffer areas onsite will attenuate potential stormwater runoff flows that could otherwise potentially leave the site. Element#4: Install Sediment Controls • Stormwater runoff from disturbed areas shall pass through an appropriate sediment removal BMP, prior to leaving a construction site. Runoff from fully stabilized areas may be discharged without a sediment removal BMP, but shall meet the flow control performance standard of S9.D.3.a. • Sediment control BMPs (sediment ponds, traps, filters, etc.) shall be constructed as one of the first steps in grading. These BMPs shall be functional before other land disturbing activities take place. • BMPs intended to trap sediment on site shall be located in a manner to avoid interference with the movement of juvenile salmonids attempting to enter off- channel areas or drainages. � Suggested BMPs: - BMP C233: Silt Fence BMP C 102: Buffer Zones 3 Element#5: Stabilize Soils • Exposed and unworked soils shall be stabilized by application of effective BMPs that prevent erosion. Applicable BMPs include, but are not limited to: temporary and permanent seeding, sodding, mulching, plastic covering, erosion control fabrics and matting, soil application of polyacrylamide (PAM), the early application of gravel base on areas to be paved, and dust control. • Depending on the geographic location of the project, no soils shall remain exposed and unworked for more than the time periods set forth below to prevent erosion: West of the Cascade Mountains Crest: During the dry season(May 1 —Sept. 30): 7 days During the wet season (October 1 —April 30): 2 days The time period may be adjusted by a local jurisdiction, if the Jurisdiction can show that local precipitation data justify a different standard. • Soils shall be stabilized at the end of the shift before a holiday or weekend if needed based on the weather forecast. • Soil stockpiles must be stabilized from erosion, protected with sediment trapping measures, and where possible, be located away from storm drain inlets, waterways, and drainage channels. • Suggested BMPs: - BMP C 120: Temporary and Permanent Seeding - BMP C 121: Mulching - BMP C 124: Sodding - BMP C 125: Topsoiling - BMP C 140: Dust Control Element#6: Protect Slopes • Design and construct cut and fill slopes in a manner that will minimize erosion. Applicable practices include, but are not limited to, reducing continuous length of slope with terracing and diversions, reducing slope steepness, and roughening slope surfaces (e.g., track walking). • A tightlined stormwater pipe "bypass" system will be installed to properly route existing stormwater flows through the site as in the existing condition along it's existing alignment back to the portion of existing ditch line that will remain for continued routing. � � At the top of slopes, collect drainage in pipe slope drains or protected channels to prevent erosion. West of the Cascade Mountains Crest: Temporary pipe slope drains shall handle the peak 10-minute velocity of flow from a Type 1 A, 10-year, 24-hour frequency storm for the developed condition. Alternatively, the 10-year, 1-hour flow rate predicted by an approved continuous runoff model, increased by a factor of 1.6, may be used. The hydrologic analysis shall use the existing land cover condition for predicting flow rates from tributary areas outside the project limits. For tributary areas on the project site, the analysis shall use the temporary or permanent project land cover condition, whichever will produce the highest flow rates. If using the WWHM to predict flows, bare soil areas should be modeled as "landscaped area." • Excavated material shall be placed on the uphill side of trenches, consistent with safety and space considerations. • Check dams shall be placed at regular intervals within constructed channels that are cut down a slope. • Suggested BMPs: - BMP C120: Temporary and Permanent Seeding Element#7: Protect Drain Inlets • All storm drain inlets shall be protected so that stormwater runoff does not enter the conveyance system without first being filtered or treated to remove sediment. • Inlet protection devices shall be cleaned or removed and replaced when sediment has filled one-third of the available storage (unless a different standard is specified by the product manufacturer). • Suggested BMPs: - BMP C220: Storm Drain Inlet Protection Element#8: Stabilize Channels and Outlets • Stabilization, including armoring material, adequate to prevent erosion of outlets, adjacent stream banks, slopes, and downstream reaches shall be provided at the outlets of all conveyance systems. • Suggested BMPs: - BMP C202: Channel Lining - BMP C209: Outlet Protection 5 Element#9: Control Pollutants • All pollutants, including waste materials and demolition debris, that occur on site during construction shall be handled and disposed of in a manner that does not cause contamination of surface water. • Cover, containment, and protection from vandalism shall be provided for all chemicals, liquid products, petroleum products, and other materials that have the potential to pose a threat to human health or the environment. On-site fueling tanks shall include secondary containment. • Maintenance, fueling, and repair of heavy equipment and vehicles shall be conducted using spill prevention and control measures. Contaminated surfaces shall be cleaned immediately following any spill incident. � Wheel wash or tire bath wastewater shall be discharged to a separate on-site treatment system or to the sanitary sewer with local sewer district approval. • Application of fertilizers and pesticides, shall be conducted in a manner and at application rates that will not result in loss of chemical to stormwater runoff. Manufacturers' label requirements for application rates and procedures shall be followed. • BMPs shall be used to prevent or treat contamination of stormwater runoff by pH modifying sources. These sources include, but are not limited to: bulk cement, cement kiln dust, fly ash, new concrete washing and curing waters, waste streams generated from concrete grinding and sawing, exposed aggregate processes, dewatering concrete vaults, concrete pumping and mixer washout waters. Permittees shall adjust the pH of stormwater if necessary to prevent violations of water quality standards. • Permittees shall obtain written approval from Ecology prior to using chemical treatment, other than COZ or dry ice to adjust pH. Element#10: Control Dewatering • Foundation, vault, and trench dewatering water, which have similar characteristics to stormwater runoff at the site, shall be discharged into a controlled conveyance system prior to discharge to a sediment trap or sediment pond. • Clean, non-turbid dewatering water, such as well-point ground water, can be discharged to systems tributary to, or directly into surface waters of the state, as specified in S9.D.8, provided the de-watering flow does not cause erosion or (o flooding of receiving waters. Clean de-watering water should not be routed through stormwater sediment ponds. • Other disposal options may include: 1. Infiltration; 2. Transport off-site in a vehicle, such as a vacuum flush truck, for legal disposal in a manner that does not pollute state waters; 3. Ecology-approved on-site chemical or other suitable treatment technologies; 4. Sanitary sewer discharge with local sewer district approval, if there is no other option; or 5. Use of a sedimentation bag with outfall to a ditch or swale for small volumes of localized de-watering. • Highly turbid or contaminated dewatering water shall be handled separately from stormwater. Element#11: Maintain BMPs • All temporary and permanent erosion and sediment control BMPs shall be maintained and repaired as needed to assure continued performance of their intended function in accordance with BMP specifications. • All temporary erosion and sediment control BMPs shall be removed within 30 days after final site stabilization is achieved or after the temporary BMPs are no longer needed. Element#12: Manage the Project • Development projects shall be phased to the maximum degree practicable and shall take into account seasonal work limitations. • Inspection and Monitoring All BMPs shall be inspected, maintained, and repaired as needed to assure continued performance of their intended function. Site inspections and monitoring shall be conducted in accordance with S4. • Maintaining an Updated Construction SWPPP The SWPPP shall be maintained, updated, and implemented in accordance with Conditions S3, S4 and S9. Monitoring Requirements The primary monitoring requirements are summarized in Table 3 (below): '7 Table 3. Summa of Monitorin Re uirements Size of Soils Disturbance Weekly Weekly Weekly Weekly Site Sampling Sampling w/ pH Inspections w/ Transparency sampling3 Turbidity Tube Meter Sites which disturb less Required Not Not Required Not than 1 acre Required Re uired Sites which disturb 1 acre or more, but less than 5 Required Sampling Requir4d—either Re uired acres method q Sites which disturb 5 acres Re uired Re uired or more q q Requ�reds Required 1 Additional monitoring requirements may apply for: 1) discharges to 303(d) listed waterbodies and waterbodies with applicable TMDLs for turbidity, fine sediment, high pH, or phosphorus—see Condition S8; and 2) sites required to perform additional monitoring by Ecology order—see Condition G13. 2 Soil disturbance is calculated by adding together all areas affected by construction activity. Construction Activity means clearing, grading, excavation, and any other activity which disturbs the surface of the land, including ingress/egress from the site. 3 Beginning October l, 2006, if construction activity involves significant concrete work or the use of engineered soils, and stormwater from the affected area drains to a stormwater collection system or other surface water, the Permittee shall conduct pH sampling in accordance with Condition S4.D. 4 Beginning October 1, 2008, sites with one or more acres, but less than 5 acres of soil disturbance, shall conduct turbidity or transparency sampling in accordance with Condition S4.C. 5 Beginning October l, 2006, sites greater than or equal to 5 acres of soil disturbance shall conduct turbidity sampling using a turbidity meter in accordance with Condition S4.C. A. Site Log Book The Permittee shall maintain a site log book that contains a record of the implementation of the SWPPP and other permit requirements including the installation and maintenance of BMPs, site inspections, and stormwater monitoring. � B. Site Ins ections l. Site inspections shall include all areas disturbed by construction activities, all BMPs, and all stormwater discharge points. Stormwater shall be visually examined for the presence of suspended sediment, turbidity, discoloration, and oil sheen. Inspectors shall evaluate the effectiveness of BMPs and determine if it is necessary to install, maintain, or repair BMPs to improve the quality of stormwater discharges. Based on the results of the inspection, the Permittee shall correct the problems identified as follows: a. Review the SWPPP for compliance with Condition S9 and make appropriate revisions within 7 days of the inspection; and b. Fully implement and maintain appropriate source control and/or treatment BMPs as soon as possible, but no later than 10 days of the inspection; and c. Document BMP implementation and maintenance in the site log book. 2. The site inspections shall be conducted at least once every calendar week and within 24 hours of any discharge from the site. The inspection frequency for temporarily stabilized, inactive sites may be reduced to once every calendar month. 3. Site inspections shall be conducted by a person who is knowledgeable in the principles and practices of erosion and sediment control. The inspector shall have the skills to: a. Assess the site conditions and construction activities that could impact the quality of stormwater, and b. Assess the effectiveness of erosion and sediment control measures used to control the quality of stormwater discharges. 4. Beginning October 1, 2006, construction sites one acre or larger that discharge stormwater to surface waters of the state, shall have site inspections conducted by a Certified Erosion and Sediment Control Lead (CESCL). The CESCL shall be identified in the SWPPP and shall be present on-site or on-call at all times. Certification shall be obtained through an approved erosion and sediment control training program that meets the minimum training standards established by Ecology (see BMP C 160 in the Manual). � 5. The inspector shall summarize the results of each inspection in an inspection report or checklist and be entered into, or attached to, the site log book. At a minimum, each inspection report or checklist shall include: a. Inspection date and time. b. Weather information; general conditions during inspection and approximate amount of precipitation since the last inspection, and within the last 24 hours. c. A summary or list of all BMPs which have been implemented, including observations of all erosion/sediment control structures or practices. d. The following shall be noted: i. locations of BMPs inspected, ii. locations of BMPs that need maintenance, iii. the reason maintenance is needed, iv. locations of BMPs that failed to operate as designed or intended, and v. locations where additional or different BMPs are needed, and the reason(s) why. e. A description of stormwater discharged from the site. The inspector shall note the presence of suspended sediment, turbid water, discoloration, and/or oil sheen, as applicable. f. Any water quality monitoring performed during inspection. g. General comments and notes, including a brief description of any BMP repairs, maintenance or installations made as a result of the inspection. h. A statement that, in the judgment of the person conducting the site inspection, the site is either in compliance or out of compliance with the terms and conditions of the SWPPP and the permit. If the site inspection indicates that the site is out of compliance, the inspection report shall include a summary of the remedial actions required to bring the site back into compliance, as well as a schedule of implementation. ta i. Name, title, and signature of the person conducting site inspection; and the following statement: "I certify that this report is true, accurate, and complete, to the best of my knowledge and belief'. C. Turbiditv/Transparencv Sam�g ReQUirements 1. Sampling Methods/Effective Dates a. Beginning October 1, 2006, if construction activity will involve the disturbance of 5 acres or more, the Permittee shall conduct turbidity sampling per Condition S4.C. b. Beginning October 1, 2008, if construction activity will involve greater than or equal to 1 acre, but less than 5 acres of soil disturbance, the Permittee shall conduct transparency sampling or turbidity sampling per Condition S4.C. 2. Sampling Frequency a. Sampling shall be conducted at least once every calendar week, when there is a discharge of stormwater (or authorized non-stormwater) from the site. Samples shall be representative of the flow and characteristics of the discharge. b. When there is no discharge during a calendar week, sampling is not required. c. Sampling is not required outside of normal working hours or during unsafe conditions. If a Permittee is unable to sample during a monitoring period, the Discharge Monitoring Report (DMR) shall include a brief explanation. 3. Sampling Locations a. Sampling is required at all discharge points where stormwater (or authorized non-stormwater) is discharged off-site. b. All sampling point(s) shall be identified on the SWPPP site map and be clearly marked in the field with a flag, tape, stake or other visible marker. 4. Sampling and Analysis Methods a. Turbidity analysis shall be performed with a calibrated turbidity meter (turbidimeter), either on-site or at an accredited lab. The lt results shall be recorded in the site log book in Nephelometric Turbidity Units (NTU). b. Transparency analysis shall be performed on-site with a 1 3/4 inch diameter, 60 centimeter(cm) long Transparency Tube. The results shall be recorded in the site log book in centimeters (cm). Transparency Tubes are available from: http://watermonitorin�quip com/pages/stream html Analytical Sampling Benchmark Parameter Units Method Fre uenc Value Turbidity NTU SM2130 or Weekly, if 25 NTU EPA 180.1 discharging Transparency cm Manufacturer Weekly, if 31 cm Instructions, or discharging Ecology Guidance 5. Turbidity/Transparency Benchmark Values The benchmark value for turbidity is 25 NTU (Nephelometric Turbidity Units); and the benchmark value for transparency is 31 cm. a. Turbiditv 26—249 NTU or Trans arency 30—7 cm• If discharge turbidity is greater than 25 NTU, but less than 250 NTU; or if discharge transparency is less than 31 cm, but greater than 6 cm, the CESCL shall: i. Review the SWPPP far compliance with Condition S9 and make appropriate revisions within 7 days of the discharge that exceeded the benchmark; and ii. Fully implement and maintain appropriate source control andJor treatment BMPs as soon as possible, but within 10 days of the discharge that exceeded the benchmark; and iii. Document BMP implementation and maintenance in the site log book. b. Turbiditv 250 NTU or �reater or Transparency 6 cm or less• If discharge turbidity is greater than or equal to 250 NTU; or if discharge transparency is less than or equal to 6 cm, the CESCL shall: IZ. i. Notify Ecology by phone in accordance with Condition SS.A.; and ii. Review the SWPPP for compliance with Condition S9 and make appropriate revisions within 7 days of the discharge that exceeded the benchmark; and iii. Fully implement and maintain appropriate source control and/or treatment BMPs as soon as possible, but within 10 days of the discharge that exceeded the benchmark; iv. Document BMP implementation and maintenance in the site log book; and v. Continue to sample discharges daily until: 1. turbidity is 25 NTU (or lower); or 2. transparency is 31 cm (or greater);or 3. the CESCL has demonstrated compliance with the water quality standard for turbidity: a. no more than 5 NTU over background turbidity, if background is less than 50 NTU, or b. no more than 10% over background turbidity, if background is 50 NTU or greater; or 4. the discharge stops or is eliminated. D. pH Monitorin�: Sites with Significant Concrete Work or Engineered Soils Beginning October 1, 2006, if construction activity will result in the disturbance of 1 acre or more, and involves significant concrete work or the use of engineered soils, and stormwater from the affected area drains to surface waters of the state or to a storm sewer system that drains to surface waters of the state, the Permittee shall conduct pH monitoring as set forth below: 1. For sites with significant concrete work, the pH monitoring period shall commence when the concrete is first exposed to precipitation and continue weekly until stormwater pH is 8.5 or less. a. "Significant concrete work" means greater than 1000 cubic yards poured concrete or recycled concrete. t3 2. For sites with engineered soils, the pH monitoring period shall commence when the soil amendments are first exposed to precipitation and shall continue until the area of engineered soils is fully stabilized. a. "Engineered soils" means soil amendments including, but not limited, to Portland cement treated base (CTB), cement kiln dust(CKD), or fly ash. 3. During the pH monitoring period, the Permittee shall obtain a representative sample of stormwater and conduct pH analysis at least once per week. 4. The Permittee shall monitor pH in the sediment trap/pond(s) or other locations that receive stormwater runoff from the area of significant concrete work or engineered soils prior to discharge to surface waters. 5. The benchmark value for pH is 8.5 standard units. Any time sampling indicates pH is 8.5 or greater, the Permittee shall: a. Prevent the high pH water(8.5 or above) from entering storm sewer systems or surface waters; and b. If necessary, adjust or neutralize the high pH water using an appropriate treatment BMP such as COZ sparging or dry ice. The Permittee shall obtain written approval from Ecology prior to using any form of chemical treatment other than CO2 sparging or dry ice. 6. The Permittee shall perform pH analysis on-site with a calibrated pH meter, pH test kit, or wide range pH indicator paper. The Permittee shall record pH monitoring results in the site log book. Renortin� and Recordkeeping Repuirements A. Hi�h Turbidity Phone Re orting Any time sampling performed in accordance with Special Condition S4.0 indicates turbidity is 250 NTU or greater(or transparency is 6 cm or less) the Permittee shall notify the appropriate Ecology regional office by phone within 24 hours of analysis. B. Dischar�e Monitorin�Reports 1. Permittees required to conduct water quality sampling in accordance with Special Conditions S.4.0 (Turbidity/Transparency), S4.D (pH) and/or S8 [303(d)/TMDL sampling] shall submit the results to Ecology monthly on Discharge Monitoring Report (DMR) forms provided by Ecology. Permittees are authorized and encouraged to submit electronic DMRs using the "E-DMR Form" on Ecology's Construction Stormwater web site: I�} http://wu-�v.ecv.wa.�ov/�rograms/wq/stormwater/constrcution/. 2. The Permittee shall submit DMR forms electronically or by mail to be received by Ecology within 15 days following the end of each month. If there was no discharge during a given monitoring period, the Permittee shall submit the form as required with the words "no discharge" entered in place of the monitoring results. If the Permittee is unable to submit discharge monitoring reports electronically, the Permittee may mail reports to the address listed below: Department of Ecology Water Quality Program—Construction Stormwater P.O. Box 47696 Olympia, Washington 98504-7696 C. Records Retention The Permittee shall retain records of all monitoring information (site log book, sampling results, inspection reports/checklists, etc.), Stormwater Pollution Prevention Plan, and any other documentation of compliance with permit requirements during the life of the construction project and for a minimum of three years following the termination of permit coverage. Such information shall include all calibration and maintenance records, and records of all data used to complete the application for this permit. This period of retention shall be extended during the course of any unresolved litigation regarding the discharge of pollutants by the Permittee or when requested by Ecology. D. Recording of Results For each measurement or sample taken, the Permittee shall record the following information: 1. Date, place, method, and time of sampling or measurement; 2. The individual who performed the sampling or measurement; 3. The dates the analyses were performed; 4. The individual who performed the analyses; 5. The analytical techniques or methods used; and 6. The results of all analyses. E. Additional Monitorin�by the Permittee 1'� If the Permittee monitors any pollutant more frequently than required by this permit using test procedures specified by Condition S4 of this permit, the results of this monitoring shall be included in the calculation and reporting of the data submitted in the Permittee's DMR. F. Noncompliance Notification In the event the Permittee is unable to comply with any of the terms and conditions of this permit which may cause a threat to human health or the environment, the Permittee sha1L• 1. Immediately notify Ecology of the failure to comply. 2. Immediately take action to prevent the discharge/pollution, or otherwise stop or correct the noncompliance, and, if applicable, repeat sampling and analysis of any noncompliance immediately and submit the results to Ecology within five (5) days after becoming aware of the violation. 3. Submit a detailed written report to Ecology within five (5) days, unless requested earlier by Ecology. The report shall contain a description of the noncompliance, including exact dates and times, and if the noncompliance has not been corrected, the anticipated time it is expected to continue; and the steps taken or planned to reduce, eliminate, and prevent reoccurrence of the noncompliance. Compliance with these requirements does not relieve the Permittee from responsibility to maintain continuous compliance with the terms and conditions of this permit or the resulting liability for failure to comply. G. Access to Plans and Records 1. The Permittee shall retain the following permit documentation (plans and records) on-site, or within reasonable access to the site, for use by the operator; or on-site review by Ecology ar the local jurisdiction: a. General Permit; b. Permit Coverage Letter; c. Stormwater Pollution Prevention Plan(SWPPP); and d. Site Log Book 2. The Permittee(s) shall address written requests for plans and records listed above (Condition SS.G.I) as follows: « a. A copy of plans and records shall be provided to Ecology within 14 days of receipt of a written request from Ecology. b. A copy of plans and records shall be provided to the public when requested in writing. Upon receiving a written request from the public for the Permittee's plans and records, the Permittee shall either: i. Provide a copy of the plans and records to the requestor within 14 days of a receipt of the written request; or ii. Notify the requestor within 10 days of receipt of the written request of the location and times within normal business hours when the plans and records may be viewed, and provide access to the plans and records within 14 days of receipt of the written request; or iii. Within 14 days of receipt of the written request, the Permittee may submit a copy of the plans and records to Ecology for viewing and/or copying by the requestor at an Ecology office, or a mutually agreed upon location. If plans and records are viewed and/or copied at a location other than at an Ecology office, the Permittee will provide reasonable access to copying services for which a reasonable fee may be charged. The Permittee shall notify the requestor within 10 days of receipt of the request where the plans and records may be viewed and/or copied. SECTION 2—PROJECT DESCRIPTION The "Yelm Apartments"project is located in the NE1/4 of the SE1/4 of Section 24, Township 17 North, Range 1 East of the Willamette Meridian in the City of Yelm in Thurston County, Washington. The proposal consists of construction of(2) 8 unit apartment buildings for a total of 16 proposed units and associated parking/access and open space areas onsite. The property is approximately 1.14 acres in size located at the site address of 304 Longmire St. on parcel #21724410200. Surrounding properties consist of a golf course to the south and existing Multi-Family complexes. This site will be served by the City of Yelm for water and sanitary sewer. Additional utilities include Puget Sound Energy for power and Qwest Communications for telephone. SECTION 3—EXISTING SITE CONDITIONS The site is located east of the intersection of Longmire St. SE and Berry valley Dr. The project area is currently vacant land and sloping from southwest to northeast. A high point is situated in the northwest corner at an approximate elevation of 345. The site then slopes to the northeast to an approximate low point elevation of 340 along the northeastern property boundary line. The site is presently covered in trees and prairie grasses/brush. Stormwater runoff presently sheet flows across the site from the southwest to the northeast and is infiltrated through the "good" onsite soils located across the site. IT7 Per the S.C.S. soils map, on-site soils consist of Spanaway gravelly sandy loam which will very conducive to infiltration of stormwater for proposed improvements onsite. Pacific Geo Engineering, LLC performed an onsite soil investigation on August 6, 2013 at (9) test pit locations onsite to approximate depth of 11 feet and performed field percolation testing at (3) of these (9)total test pit locations. It was determined from there testing that an"in field" infiltration rate of 12 in/hr exists onsite within the native soils. We have taken this information and applied a factor of safety of(2) for a design infiltration rate for onsite infiltration trench facilities of 6 in/hr which we utilized for our Final Stormwater Quantity Control design. SECTION 4—ADJACENT AREAS Surrounding properties consist of a golf course to the south and existing Multi-Family complexes. SECTION 5—CRITICAL AREAS To the best of our knowledge no know critical areas exist on or in the direct vicinity of the site. SECTION 6 - SOILS Per the S.C.S. soils map, on-site soils consist of Spanaway gravelly sandy loam which will very conducive to infiltration of stormwater for proposed improvements onsite. Pacific Geo Engineering, LLC performed an onsite soil investigation on August 6, 2013 at(9) test pit locations onsite to approximate depth of 11 feet and performed field percolation testing at (3) of these (9) total test pit locations. It was determined from there testing that an "in field" infiltration rate of 12 in/hr exists onsite within the native soils. We have taken this information and applied a factor of safety of(2) for a design infiltration rate for onsite infiltration trench facilities of 6 in/hr which we utilized for our Final Stormwater Quantity Control design. SECTION 7—EROSION PROBLEM AREAS There are no areas of particular concern on this project site with regards to erosion problems. SECTION 8—CONSTRUCTION PHASING The proposed construction sequence will be as follows: 1. Call City of Yelm Inspector for pre-construction meeting. 2. Clearly flag all limits of clearing and grading per approved plans. 18 3. Install temporary construction entrance as shown and per notes and details. 4. Install temporary mirafi filter fences as shown and per notes and details. 5. Clear, fill & grade site per approved plans. 6. Any vegetation or other materials taken off site shall be hauled to an Approved dump site. 7. Construct asphalt parking/access area per the approved plans. 8. Provide onsite C.B. protection until onsite improvements are completed and all exposed slopes are seeded & stabilized for erosion & sedimentation. 9. Note: The contractor is responsible for maintenance of storm system during building and landscape construction. 10. Hydroseed and/or mulch slopes and other exposed areas immediately after grading is completed as outlined in"erosion control notes". 11. Clean out and test all storm drain facilities. 12. Inspect and maintain all erosion control facilities at regular intervals & complete required report. Clean as required until risk of sedimentation has passed. �: SECTION 9—CONSTRUCTION SCHEDULE Construction of this project is planned to begin and end in the Winter/Spring of 2014. During the wet season from October 1 through March 31, no soils shall remain exposed and unworked for more than 2 days at a time. SECTION 10—FINANCIAL/OWNERSHIP RESPONSIBLITIES The property owner's agent responsible for the initiation of any necessary bonds and/or other financial securities is: Mt. Terrace Builders Contact: Tony Trunk 6524 Cromwell Beach Drive N.W. Gig Harbor, WA. 98335 Ph: (253) 310-5078 I"1 SECTION 11 —ENGINEERING CALCULATIONS See separate report entitled"Storm Drainage Report" for stormwater calculations associated with Stormwater Infiltration Facility sizing and Conveyance pipe sizing. SECTION 12 --EROSION CONTROL SPECIALIST No erosion control specialist has been appointed at this time. Once one is established, he/she will be reported to the City of Yelm. Zo APPENDIX `�A" BMP'S LARSON & ASS�CIATES INC. � 4401 S. 66TH STREET TACOMA, WA. 98409 ��. BMP C102: Buffer Zones Purpose An undisturbed area or strip of natural vegetation or an established suitable planting that will provide a living filter to reduce soil erosion and runoff velocities. Conditions of Use Natural buffer zones are used along streams, wetlands and other bodies of water that need protection from erosion and sedimentation. Vegetative buffer zones can be used to protect natural swales and can be incorporated into the natural landscaping of an area. Critical-areas buffer zones should not be used as sediment treatment areas. These areas shall remain completely undisturbed. The local pernutting authority may expand the buffer widths temporarily to allow the use of the expanded area for removal of sediment. Design and • Preserving natural vegetation or plantings in clumps,blocks, or strips Installation is generally the easiest and most successful method. Specifications Leave all unstable steep slopes in natural vegetation. . • Mark clearing limits and keep all equipment and construction debris out of the natural areas. Steel construction fencing is the most effective method in protecting sensitive areas and buffers. Alternatively, wire-backed silt fence on steel posts is marginally effective. Flagging alone is typically not effective. • Keep all excavations outside the dripline of trees and shrubs. • Do not push debris or extra soil into the buffer zone area because it will cause damage from burying and smothering. • Vegetative buffer zones for streams, lakes or other waterways shall be established by the local permitting authority or other state or federal permits or approvals. Maintenance • Inspect the area frequently to make sure flagging remains in place Standards and the area remains undisturbed. February 2005 Volume ll— Construction Stormwater Pollution Prevention 4-5 p� BMP C103: High Visibility Plastic or Metal Fence Purpose Fencing is intended to: (1)restrict clearing to approved limits; (2)prevent disturbance of sensitive areas, their buffers, and other areas required to be left undisturbed; (3) limit construction traffic to designated construction entrances or roads; and, (4)protect areas where marking with survey tape may not provide adequate protection. Conditions of Use To establish clearing limits, plastic or metal fence may be used: • At the boundary of sensitive areas, their buffers, and other areas required to be left uncleared. • As necessary to control vehicle access to and on the site. Design and • High visibility plastic fence shall be composed of a high-density Installation polyethylene material and shall be at least four feet in height. Posts Specifications for the fencing shall be steel or wood and placed every 6 feet on center(maximum) or as needed to ensure rigidity. The fencing shall be fastened to the post every six inches with a polyethylene tie. On long continuous lengths of fencing, a tension wire or rope shall be used as a top stringer to prevent sagging between posts. The fence color shall be high visibility orange. The fence tensile strength shall be 3601bs./ft. using the ASTM D4595 testing method. • Metal fences shall be designed and installed according to the manufacturer's specifications. • Metal fences shall be at least 3 feet high and must be highly visible. • Fences shall not be wired or stapled to trees. Maintenance • If the fence has been damaged or visibility reduced, it shall be Standards repaired or replaced immediately and visibility restored. 4-6 Volume ll— Construction Stormwater Pollufion Prevention February 2005 A3 BMP C104: Stake and Wire Fence Purpose Fencing is intended to: (1)restrict clearing to approved limits; (2)prevent disturbance of sensitive areas, their buffers, and other areas required to be left undisturbed; (3) limit construction traffic to designated construction entrances or roads; and, (4)protect any areas where marking with survey tape may not provide adequate protection. Conditions of Use To establish clearing limits, stake or wire fence may be used: • At the boundary of sensitive areas, their buffers, and other areas required to be left uncleared. • As necessary, to control vehicle access to and on the site. Design and • See Figure 4.1 for details. Installation More substantial fencing shall be used if the fence does not prevent Specifications � encroachment into those areas that are not to be disturbed. Maintenance • If the fence has been damaged or visibility reduced, it shall be Standards repaired or replaced immediately and visibility restored. Survey Flagging Baling Wire Do Not Nail or Staple Wire to Trees 3' AIIN. 10'-20' Metal Fence Post —1 1 I I I I—I I I—I I I—I i I—I I I I I—I I I—I I I—I I I— I I—I I � 12" MIN. � Figure 4.1 –Stake and Wire Fence February 2005 Volume 11– Construction Stormwater Pollution Prevention 4-7 A� BMP C105: Stabilized Construction Entrance Purpose Construction entrances are stabilized to reduce the amount of sediment transported onto paved roads by vehicles or equipment by constructing a stabilized pad of quarry spalls at entrances to construction sites. Conditions of Use Construction entrances shall be stabilized wherever traffic will be leaving a construction site and traveling on paved roads or other paved areas within 1,000 feet of the site. On large commercial,highway, and road projects, the designer should include enough extra materials in the contract to allow for additional stabilized entrances not shown in the initial Construction SWPPP. It is difficult to determine exactly where access to these projects will take place; additional materials will enable the contractor to install them where needed. Design and • See Figure 4.2 for details. Note: the 100' minimum length of the Installation entrance shall be reduced to the maximum practicable size when the Specifications size or configuration of the site does not allow the full length(100'). • A separation geotextile shall be placed under the spalls to prevent fine sediment from pumping up into the rock pad. The geotextile shall meet the following standards: Grab Tensile Strength (ASTM D4751) 200 psi min. Grab Tensile Elongation(ASTM D4632) 30% max. Mullen Burst Strength (ASTM D3786-80a) 400 psi min. AOS (ASTM D4751) 20-45(U.S. standard sieve size) • Consider early installation of the first lift of asphalt in areas that will paved; this can be used as a stabilized entrance. Also consider the installation of excess concrete as a stabilized entrance. During large concrete pours, excess concrete is often available for this purpose. • Hog fuel (wood-based mulch)may be substituted for or combined with quarry spalls in areas that will not be used for permanent roads. Hog fuel is generally less effective at stabilizing construction entrances and should be used only at sites where the amount of traffic is very limited. Hog fuel is not recommended for entrance stabilization in urban areas. The effectiveness of hog fuel is highly variable and it generally requires more maintenance than quarry spalls. The inspector may at any time require the use of quarry spalls if the hog fuel is not preventing sediment from being tracked onto pavement or if the hog fuel is being carried onto pavement. Hog fuel is prohibited in permanent roadbeds because organics in the subgrade soils cause degradation of the subgrade support over time. • Fencing(see BMPs C103 and C104) shall be installed as necessary to restrict traffic to the construction entrance. 4-8 Volume ll— Construction Sformwater Pollution Prevention February 2005 �� • Whenever possible, the entrance shall be constructed on a firm, compacted subgrade. This can substantially increase the effectiveness of the pad and reduce the need for maintenance. Maintenance • Quarry spalls (or hog fuel) shall be added if the pad is no longer in Standards accordance with the specifications. • If the entrance is not preventing sediment from being tracked onto pavement, then alternative measures to keep the streets free of sediment shall be used. This may include street sweeping, an increase in the dimensions of the entrance, or the installation of a wheel wash. • Any sediment that is tracked onto pavement shall be removed by shoveling or street sweeping. The sediment collected by sweeping shall be removed or stabilized on site. The pavement shall not be cleaned by washing down the street, except when sweeping is ineffective and there is a threat to public safety. If it is necessary to wash the streets, the construction of a small sump shall be considered. The sediment would then be washed into the sump where it can be controlled. • Any quarry spalls that are loosened from the pad, which end up on the roadway shall be removed immediately. • If vehicles are entering or exiting the site at points other than the construction entrance(s), fencing(see BMPs C103 and C104) shall be installed to control traffic. • Upon project completion and site stabilization; all construction accesses intended as permanent access for maintenance shall be ermanently stabilized. Driveway shall meet the requirements of the . permitting agency it is recommended that tha en[rance be . crowned so that runoff Poyd drains off the pad E�,i�s��r9 i r 'OO. i � ! Install driveway culvert � If there is a roadside ditch presenl . 4"-8"quarry spalls Geotezti�e �5�\c !�`,�• 72"min.lhickness_� �J Provide full width ot � ingress/egress area Figure 4.2—Stabilized Construction Entrance February 2005 Volume 11— Construction Stormwater Pollution Prevention 4-9 Al� BMP C106: Wheel Wash Purpose Wheel washes reduce the amount of sediment transported onto paved roads by motor vehicles. Conditions of Use When a stabilized construction entrance (see BMP C105) is not preventing sediment from being tracked onto pavement. • Wheel washing is generally an effective BMP when installed with careful attention to topography. For example, a wheel wash can be detrimental if installed at the top of a slope abutting a right-of-way where the water from the dripping truck can run unimpeded into the street. • Pressure washing combined with an adequately sized and surfaced pad with direct drainage to a large 10-foot x 10-foot sump can be very effective. Design and Suggested details are shown in Figure 4.3. The Local Permitting Installation Authority may allow other designs. A minimum of 6 inches of asphalt Specifications treated base (ATB) over crushed base material or 8 inches over a good subgrade is recommended to pave the wheel wash. Use a low clearance truck to test the wheel wash before paving. Either a belly dump or lowboy will work well to test clearance. Keep the water level from 12 to 14 inches deep to avoid damage to truck hubs and filling the truck tongues with water. Midpoint spray nozzles are only needed in extremely muddy conditions. Wheel wash systems should be designed with a small grade change, 6 to 12 inches for a 10-foot-wide pond, to allow sediment to flow to the low side of pond to help prevent re-suspension of sediment. A drainpipe with a 2-to 3-foot riser should be installed on the low side of the pond to allow for easy cleaning and refilling. Polymers may be used to promote coagulation and flocculation in a closed-loop system. Polyacrylamide (PAM) added to the wheel wash water at a rate of 0.25 - 0.5 pounds per 1,000 gallons of water increases effectiveness and reduces cleanup time. If PAM is already being used for dust or erosion control and is being applied by a water truck, the same truck can be used to change the wash water. Maintenance The wheel wash should start out the day with fresh water. Standards The wash water should be changed a minimum of once per day. On large earthwork jobs where more than 10-20 hucks per hour are expected, the wash water will need to be changed more often. Wheel wash or tire bath wastewater shall be discharged to a separate on- site treatment system, such as closed-loop recirculation or land application, or to the sanitary sewer with proper local sewer district approval. 4-10 Volume ll—Construction Stormwater Pollution Prevention February 2005 ��I 2"Schedule 40 1 %"schedule 40 for sprayers � �.. � 11 2% 5:1 5:1 I f 2% SIoPe ' SIoPe Slope ' k � Slope _ 1�1 �� • Slo�pe Wheei Wash Plan �15'�15' 2Q' 15` � �� Elevation View :Water level �� 1:1 Slope ,._,_..,..w..,.. T.___._ � �� Section A-A � N.T.S. Figure 4.3 Wheel Wash Notes: 1. Asphalt construction entrance 6 in. asphalt treated base(ATB). 2. 3-inch trash pump with floats on the suction hose. 3. Midpoint spray nozzles, if needed. 4. 6-inch sewer pipe with bu#terfly valves. Bottom one is a drain. Locate top pipe's invert 1 foot above bottom of wheel wash. 5. 8 foot x 8 foot sump with 5 feet of catch. Build so can be cleaned with trackhoe. 6. Asphalt curb on the low road side to direct water back to poFld. 7. 6-inch sleeve under road. 8. Ball valves. 9. 15 foot.ATB apron to protect ground from splashing water. February 2005 Volume ll— Construction Stormwater Pollution Prevention 4-�� a$ BMP C107: Construction Road/Parking Area Stabilization Purpose Stabilizing subdivision roads,parking areas, and other onsite vehicle transportation routes immediately after grading reduces erosion caused by construction traffic or runoff. Conditions of Use ' Roads or parking areas shall be stabilized wherever they are constructed, whether permanent or temporary, for use by construction traffic. • Fencing(see BMPs C103 and C104) shall be installed, if necessary, to limit the access of vehicles to only those roads and parking areas that are stabilized. Design and • On areas that will receive asphalt as part of the project, install the first Installation lift as soon as possible. Specifications A 6-inch de th of 2-to 4-inch crushed rock • p , gravel base, or crushed surfacing base course shall be applied immediately after grading or utility installation. A 4-inch course of asphalt treated base(ATB)may also be used, or the road/parking area may be paved. It may also be possible to use cement or calcium chloride for soil stabilization. If cement or cement kiln dust is used for roadbase stabilization,pH monitoring and BMPs are necessary to evaluate and minimize the effects on stormwater. If the area will not be used for permanent roads, parking areas, or structures, a 6-inch depth of hog fuel may also be used,but this is likely to require more maintenance. Whenever possible, construction roads and parking areas shall be placed on a firm, compacted subgrade. • Temporary road gradients shall not exceed 15 percent. Roadways shall be carefully graded to drain. Drainage ditches shall be provided on each side of the roadway in the case of a crowned section, or on one side in the case of a super-elevated section. Drainage ditches shall be directed to a sediment control BMP. • Rather than relying on ditches, it may also be possible to grade the road so that runoff sheet-flows into a heavily vegetated area with a well- developed topsoil. Landscaped areas are not adequate. If this area has at least 50 feet of vegetation,then it is generally preferable to use the vegetation to treat runoff,rather than a sediment pond or trap. The 50 feet shall not include wetlands. If runoff is allowed to sheetflow through adjacent vegetated areas, it is vital to design the roadways and parking areas so that no concentrated runoff is created. • Storm drain inlets shall be protected to prevent sediment-laden water entering the storm drain system(see BMP C220). Maintenance • Inspect stabilized areas regularly, especially after large storm events. Standards . Crushed rock, gravel base,hog fuel, etc. shall be added as required to maintain a stable driving surface and to stabilize any areas that have eroded. • Following construction,these areas shall be restored to pre-construction condition or better to prevent future erosion. 4-12 Volume II— Construction Stormwater Pollution Prevenfion February 2005 A9 BMP C120: Temporary and Permanent Seeding Purpose Seeding is intended to reduce erosion by stabilizing exposed soils. A well-established vegetative cover is one of the most effective methods of reducing erosion. Conditions of Use ' Seeding may be used throughout the project on disturbed areas that have reached final grade or that will remain unworked for more than 30 days. • Channels that will be vegetated should be installed before majar earthwork and hydroseeded with a Bonded Fiber Matrix. The vegetation should be well established(i.e., 75 percent cover)before water is allowed to flow in the ditch. With channels that will have high flows, erosion control blankets should be installed over the hydroseed. If vegetation cannot be established from seed before water is allowed in the ditch, sod should be installed in the bottom of the ditch over hydromulch and blankets. • Retention/detention ponds should be seeded as required. • Mulch is required at all times because it protects seeds from heat, moisture loss, and transport due to runoff. • All disturbed areas shall be reviewed in late August to early September and all seeding should be completed by the end of September. Otherwise, vegetation will not establish itself enough to provide more than average protection. • At final site stabilization, all disturbed areas not otherwise vegetated or stabilized shall be seeded arid mulched. Final stabilization means the completion of all soil disturbing activities at the site and the establishment of a permanent vegetative cover, or equivalent permanent stabilization measures (such as pavement, riprap, gabions or geotextiles) which will prevent erosion. Design and • Seeding should be done during those seasons most conducive to Installation �'owth and will vary with the climate conditions of the region. Specifications Local experience should be used to determine the appropriate seeding periods. • The optimum seeding windows for western Washington are April 1 through June 30 and September 1 through October 1. Seeding that occurs between July 1 and August 30 will require irrigation unti175 percent grass cover is established. Seeding that occurs between October 1 and March 30 will require a mulch or plastic cover until 75 percent grass cover is established. • To prevent seed from being washed away, confirm that all required surface water control measures have been installed. February 2005 Volume ll— Construction Stormwater Pollution Prevention 4-13 Atb • The seedbed should be firm and rough. All soil should be roughened no matter what the slope. If compaction is required for engineering purposes, slopes must be track walked before seeding. Backblading or smoothing of slopes greater than 4:1 is not allowed if they are to be seeded. • New and more effective restoration-based landscape practices rely on deeper incorporation than that provided by a simple single-pass rototilling treatment. Wherever practical the subgrade should be initially ripped to improve long-termpermeability, infiltration, and water inflow qualities. At a minimum,permanent areas shall use soil amendments to achieve organic matter and permeability performance defined in engineered soil/landscape systems. For systems that are deeper than 8 inches the rototilling process should be done in multiple lifts, or the prepared soil system shall be prepared properly and then placed to achieve the specified depth. • Organic matter is the most appropriate form of"fertilizer"because it provides nutrients (including nitrogen, phosphorus, and potassium)in the least water-soluble form. A natural system typically releases 2-10 percent of its nutrients annually. Chemical fertilizers have since been formulated to simulate what organic matter does naturally. • In general, 10-4-6 N-P-K(nitrogen-phosphorus-potassium) fertilizer can be used at a rate of 90 pounds per acre. Slow-release fertilizers should always be used because they are more efficient and have fewer environmental impacts. It is recommended that areas being seeded for final landscaping conduct soil tests to determine the exact type and quantity of fertilizer needed. This will prevent the over-application of fertilizer. Fertilizer should not be added to the hydromulch machine and agitated more than 20 minutes before it is to be used. If agitated too much, the slow-release coating is destroyed. • 'There are numerous products available on the market that take the place of chemical fertilizers. 'These include several with seaweed extracts that are beneficial to soil microbes and organisms: If 100 percent cottonseed meal is used as the mulch in hydroseed, chemical fertilizer may not be necessary. Cottonseed meal is a good source of long-term, slow-release, available nitrogen. • Hydroseed applications shall include a minimum of 1,500 pounds per acre of mulch with 3 percent tackifier. Mulch may be made up of 100 percent: cottonseed meal; fibers made of wood,recycled cellulose, hemp, and kenaf; compost; or blends of these. Tackifier shall be plant- based, such as guar or alpha plantago, or chemical-based such as polyacrylamide or polymers. Any mulch or tackifier product used shall be installed per manufacturer's instructions. Generally,mulches come in 40-50 pound bags. Seed and fertilizer are added at time of application. 4-14 Volume !I— Construction Stormwater Pollufion Prevention February 2005 A1e • Mulch is always required for seeding. Mulch can be applied on top of the seed or simultaneously by hydroseeding. • On steep slopes, Bonded Fiber Matrix(BFM) or Mechanically Bonded Fiber Matrix (MBFM)products should be used. BFM/MBFM products are applied at a minimum rate of 3,000 pounds per acre of mulch with approximately 10 percent tackifier. Application is made so that a minimum of 95 percent soil coverage is achieved. Numerous products axe available commercially and should be installed per manufacturer's instructions. Most products require 24-36 hours to cure before a rainfall and cannot be installed on wet or saturated soils. Generally, these products come in 40-50 pound bags and include all necessary ingredients except for seed and fertilizer. BFMs and MBFMs have some advantages over blankets: • No surface preparation required; • Can be installed via helicopter in remote areas; • On slopes steeper than 2.5:1,blanket installers may need to be roped and harnessed for safety; • They are at least$1,000 per acre cheaper installed. In most cases, the shear strength of blankets is not a factor when used on slopes, only when used in channels. BFMs and MBFMs are good alternatives to blankets in most situations where vegetation establishment is the goal. • When installing seed via hydroseeding operations, only about 1/3 of the seed actually ends up in contact with the soil surface. This reduces the ability to establish a good stand of grass quickly. One way to overcome this is to increase seed quantities by up to 50 percent. • Vegetation establishment can also be enhanced by dividing the hydromulch operation into two phases: 1. Phase 1- Install all seed and fertilizer with 25-30 percent mulch and tackifier onto soil in the first lift; 2. Phase 2- Install the rest of the mulch and tackifier over the first lift. An alternative is to install the mulch, seed, fertilizer, and tackifier in one lift. Then, spread or blow straw over the top of the hydromulch at a rate of about 800-1000 pounds per acre. Hold straw in place with a standard tackifier. Both of these approaches will increase cost moderately but will greatly improve and enhance vegetative establishment. The increased cost may be offset by the reduced need for: 1. Irrigation 2. Reapplication of mulch 3. Repair of failed slope surfaces February 2005 Volume ll— Construction Stormwater Pollution Prevention 4-15 A�Z This technique works with standard hydromulch(1,500 pounds per acre minimum) and BFM/MBFMs (3,000 pounds per acre minimum). • Areas to be permanently landscaped shall provide a healthy topsoil that reduces the need for fertilizers, improves overall topsoil quality, provides for better vegetal health and vitality, improves hydrolo�gic characteristics, and reduces the need for irrigation. This can be accomplished in a number of ways: Recent research has shown that the best method to improve till soils is to amend these soils with compost. The optimum mixture is approximately two parts soil to one part compost. This equates to 4 inches of compost mixed to a depth of 12 inches in till soils. Increasing the concentration of compost beyond this level can have negative effects on vegetal health, while decreasing the concentrations can reduce the benefits of amended soils. Please note: The compost should meet specifications for Grade A quality compost in Ecology Publication 94-038. Other soils, such as gravel or cobble outwash soils,may require different approaches. Organics and fines easily migrate through the loose structure of these soils. Therefore,the importation of at least 6 inches of quality topsoil, underlain by some type of filter fabric to prevent the migration of fines,may be more appropriate for these soils. Areas that already have good topsoil, such as undisturbed areas, do not require soil amendments. • Areas that will be seeded only and not landscaped may need compost or meal-based mulch included in the hydroseed in order to establish vegetation. Native topsoil should be re-installed on the disturbed soil surface before application. • Seed that is installed as a temporary measure may be installed by hand if it will be covered by straw,mulch, or topsoil. Seed that is installed as a permanent measure may be installed by hand on small areas (usually less than 1 acre) that will be covered with mulch, topsoil, or erosion blankets. The seed mixes listed below include recommended mixes for both temporary and permanent seeding. These mixes, with the exception of the wetland mix, shall be applied at a rate of 120 pounds per acre. This rate can be reduced if soil amendments or slow- release fertilizers are used. Local suppliers or the local conservation district should be consulted for their recommendations because the appropriate mix depends on a variety of factors, including location, exposure, soil type, slope, and expected foot traffic. Alternative seed mixes approved by the local authority may be used. 4-16 Volume II—Construction Stormwater Pollution Prevention February 2005 A�3 Table 4.1 represents the standard mix for those areas where just a temporary vegetative cover is required. Table 4.1 Tem ora Erosion Control Seed Mix %Wei ht %Puri %Germination Chewings or annual blue grass 40 98 90 Festuca rubra var. commutata or Poa anna Perennial rye- 50 98 90 Lolium erenne Redtop or colonial bentgrass 5 92 85 A rostis alba or A rostis tenuis White dutch clover 5 98 90 Tri olium re ens Table 4.2 provides just one recommended possibility for landscaping seed. Table 4.2 Landsca in Seed Mix %Wei ht %Puri %Germination Perennial rye blend 70 98 90 Lolium erenne Chewings and red fescue blend 30 98 90 Festuca rubra var. commutata or Festuca rubra This turf seed mix in Table 4.3 is for dry situations where there is no need for much water. The advantage is that this mix requires very little maintenance. Table 4.3 Low-Growin Turf Seed Mix % Wei ht %Purit %Germination Dwarf tall fescue(several varieties) 45 98 90 Festuca arundinacea var. Dwarf perennial rye(Barclay) 30 98 90 Lolium erenne var. barcla Red fescue 20 98 90 Festuca rubra Colonial bentgrass 5 98 90 A rostis tenuis Table 4.4 presents a mix recommended for bioswales and other internuttently wet areas. Table 4.4 Bioswale Seed Mix'` %Wei ht %Purit %Germination Tall or meadow fescue 75-80 98 90 Festuca arundinacea or Festuca elatior Seaside/Creeping bentgrass 10-15 92 85 A rostis alustris Redtop bentgrass 5-10 90 80 A rostis alba or A rostis i antea *Modified Briargreen,Inc. Hydroseeding Guide Wetlands Seed Ma.x February 2005 Volume 11—Construction Stormwater Pollution Prevention 4-17 a�� The seed mix shown in Table 4.5 is a recommended low-growing, relatively non-invasive seed mix appropriate for very wet areas that are not regulated wetlands. Other mixes may be appropriate, depending on the soil type and hydrology of the area. Recent research suggests that bentgrass (agrostis sp.) should be emphasized in wet-area seed mixes. Apply this mixture at a rate of 60 pounds per acre. Tabie 4.5 Wet Area Seed Mix* %Wei ht %Purit %Germination Tall or meadow fescue 60-70 98 90 Festuca arundinacea or Festuca elatior Seaside/Creeping bentgrass 10-15 98 85 A rostis alustris Meadow foxtail 10-15 90 80 Ale ocurus ratensis Alsike clover 1-6 98 90 Tri olium h bridum Redtop bentgrass 1-6 92 85 A rostis alba *Modified Briargreen,Inc.Hydroseeding Guide Wetlands Seed Mix The meadow seed mix in Table 4.6 is recommended for areas that will be maintained infrequently or not at all and where colonization by native plants is desirable. Likely applications include rural road and utility right- of-way. Seeding should take place in September or very early October in order to obtain adequate establishment prior to the winter months. The appropriateness of clover in the mix may need to be considered, as this can be a fairly invasive species. If the soil is amended,the addition of clover may not be necessary. Table 4.6 Meadow Seed Mix %Wei ht %Puri %Germination Redtop or Oregon bentgrass 20 92 85 A rostis alba or A rostis ore onensis Red fescue 70 98 90 Festuca rubra White dutch clover 10 98 90 Tri olium re ens Maintenance . Any seeded areas that fail to establish at least 80 percent cover(100 Standards percent cover for areas that receive sheet or concentrated flows) shall be reseeded. If reseeding is ineffective, an alternate method, such as sodding,mulching, or nets/blankets, shall be used. If winter weather prevents adequate grass growth, this time limit may be relaxed at the discretion of the local authority when sensitive areas would otherwise be protected. 4-18 Volume ll— Construction Sformwater Pollution Prevention February 2005 A�5 • After adequate cover is achieved, any areas that experience erosion shall be reseeded and protected by mulch. If the erosion problem is drainage related, the problem shall be fixed and the eroded area reseeded and protected by mulch. • Seeded areas shall be supplied with adequate moisture,but not watered to the extent that it causes runoff. February 2005 Volume 11— Construction Stormwater Pollution Prevention 4-19 sQ��O BMP C121: Mulching Purpose The purpose of mulching soils is to provide immediate temporary protection from erosion. Mulch also enhances plant establishment by conserving moisture, holding fertilizer, seed, and topsoil in place, and moderating soil temperatures. There is an enormous variety of mulches that can be used. Only the most common types are discussed in this section. Conditions of Use As a temporary cover measure, mulch should be used: • On disturbed areas that require cover measures for less than 30 days. • As a cover for seed during the wet season and during the hot summer months. • During the wet season on slopes steeper than 3H:1 V with more than 10 feet of vertical relief. • Mulch may be applied at any time of the year and must be refreshed periodically. Design and For mulch materials, application rates, and specifications, see Table 4.7. Installation Note: Thicknesses may be increased for disturbed areas in or near Specifications sensitive areas or other areas highly susceptible to erosion. Mulch used within the ordinary high-water mark of surface waters should be selected to minimize potential flotation of organic matter. Composted organic materials have higher specific gravities (densities)than straw, wood, or chipped material. Maintenance • The thickness of the cover must be maintained. Standards �y areas that experience erosion shall be remulched and/or protected . with a net or blanket. If the erosion problem is drainage related, then the problem shall be fixed and the eroded area remulched. 4-20 Volume II— Construction Stormwater Pollution Prevention February 2005 a�� Table 4.7 Mulch Standards and Guidelines Mulch Application Material uali Standards Rates Remarks Straw Air-dried;free from 2"-3"thick;5 Cost-effective protection when applied with adequate undesirable seed and bales per 1000 sf thickness. Hand-application generally requires greater coarse material. or 2-3 tons per thickness than blown straw.T'he thickness of straw may be acre reduced by half when used in conjunction with seeding. In windy areas straw must be held in place by crimping,using a tackifier,or covering with netting. Blown straw always has to be held in place with a tackifier as even light winds will blow it away.Straw,however,has several deficiencies that should be considered when selecting mulch materials.It often introduces and/or encourages the propagation of weed species and it has no significant long-term benefits. Straw should be used only if mulches with long-term benefits are unavailable locally. .It should also not be used within the ordinary high-water elevation of surface waters(due to flotation). Hydromulch No growth Approx.25-30 Shall be applied with hydromulcher. Shall not be used inhibiting factors. lbs per 1000 sf without seed and tackifier unless the application rate is at or 1500 -2000 least doubled. Fibers longer than about 3/<-1 inch clog lbs per acre hydromulch equipment. Fibers should be kept to less than'/ inch. Composted No visible water or 2"thick min.; More effective control can be obtained by increasing Mulch and dust during approx. 100 tons thickness to 3". Excellent mulch for protecting final grades Compost handling. Must be per acre(approx. until landscaping because it can be directly seeded or tilled purchased from 8001bs per yard) into soil as an amendment. Composted mulch has a coarser supplier with Solid size gradation than compost.It is more stable and practical Waste Handling to use in wet areas and during rainy weather conditions. Permit(unless exempt). Chipped Site Average size shall 2"minimum This is a cost-effective way to dispose of debris from Vegetation be several inches. thickness clearing and grubbing,and it eliminates the problems Gradations from associated with burning. Generally,it should not be used on fines to 6 inches in slopes above approx. 10%because of its tendency to be length for texture, transported by runoff. It is not recommended within 200 variation,and feet of surface waters. If seeding is expected shortly after interlocking mulch,the decomposition of the chipped vegetation may tie properties. up nutrients important to grass establishment. Wood-based No visible water or 2"thick;approx. This material is often called"hog or hogged fuel." It is Mulch dust during 100 tons per acre usable as a material for Stabilized Construction Entrances handling. Must be (approx.8001bs. (BMP C105)and as a mulch. The use of mulch ultimately purchased from a per cubic yard) improves the organic matter in the soil. Special caution is supplier with a Solid advised regarding the source and composition of wood- Waste Handling based mulches. Its preparation typically does not provide Permit or one any weed seed control,so evidence of residual vegetation in exempt from solid its composition or known inclusion of weed plants or seeds waste regulations. should be monitored and prevented(or minimized). February 2005 Volume ll— Construction Stormwater Pollution Prevention 4-21 �►1� BMP C123: Plastic Covering Purpose Plastic covering provides immediate, short-term erosion protection to slopes and disturbed areas. Conditions of • Plastic covering may be used on disturbed areas that require cover Use measures for less than 30 days, except as stated below. • Plastic is particularly useful for protecting cut and fill slopes and stockpiles. Note: The relatively rapid breakdown of most polyethylene sheeting makes it unsuitable for long-term(greater than six months) applications. • Clear plastic sheeting can be used over newly-seeded areas to create a greenhouse effect and encourage grass growth if the hydroseed was installed too late in the season to establish 75 percent grass cover, or if the wet season started earlier than normal. Clear plastic should not be used for this purpose during the summer months because the resulting high temperatures can kill the grass. • Due to rapid runoff caused by plastic sheeting,this method shall not be used upslope of areas that might be adversely impacted by concentrated runoff. Such areas include steep and/or unstable slopes. • While plastic is inexpensive to purchase, the added cost of installation, maintenance,removal, and disposal make this an expensive material, up to $1.50-2.00 per square yard. � • Whenever plastic is used to protect slopes, water collection measures must be installed at the base of the slope. These measures include plastic-covered berms, channels, and pipes used to covey clean rainwater away from bare soil and disturbed areas. At no time is clean runoff from a plastic covered slope to be mixed with dirty runoff from a project. • Other uses for plastic include: 1. Temporary ditch liner; 2. Pond liner in temporary sediment pond; 3. Liner for bermed temporary fuel storage area if plastic is not reactive to the type of fuel being stored; 4. Emergency slope protection during heavy rains; and, 5. Temporary drainpipe ("elephant trunk")used to direct water. 4-26 Volume ll— Construction Stormwater Pollution Prevention February 2005 p�� Design and • Plastic slope cover must be installed as follows: Installation 1. Run plastic up and down slope, not across slope; Specifications 2. Plastic may be installed perpendicular to a slope if the slope length is less than 10 feet; 3. Minimum of 8-inch overlap at seams; 4. On long or wide slopes, or slopes subject to wind, all seams should be taped; 5. Place plastic into a small (12-inch wide by 6-inch deep) slot trench at the top of the slope and backfill with soil to keep water from flowing underneath; 6. Place sand filled burlap or geotextile bags every 3 to 6 feet along seams and pound a wooden stake through each to hold them in place; 7. Inspect plastic for rips, tears, and open seams regularly and repair immediately. This prevents high velocity runoff from contacting bare soil which causes extreme erosion; 8. Sandbags may be lowered into place tied to ropes. However, all sandbags must be staked in place. • Plastic sheeting shall have a minimum thickness of 0.06 millimeters. • If erosion at the toe of a slope is likely, a gravel berm, riprap, or other suitable protection shall be installed at the toe of the slope in order to reduce the velocity of runoff. Maintercance • Torn sheets must be replaced and open seams repaired. Standards • If the plastic begins to deteriorate due to ultraviolet radiation, it must be completely removed and replaced. • When the plastic is no longer needed, it shall be completely removed. • Dispose of old tires appropriately. February 2005 Volume ll— Construction Stormwater Pollution Prevention 4-27 AZa BMP C124: Sodding Purpose The purpose of sodding is to establish permanent turf for immediate erosion protection and to stabilize drainage ways where concentrated overland flow will occur. Conditions of Use Sodding may be used in the following areas: • Disturbed areas that require short-term or long-term cover. • Disturbed areas that require immediate vegetative cover. • All waterways that require vegetative lining. Waterways may also be seeded rather than sodded, and protected with a net or blanket. Design and Sod shall be free of weeds, of uniform thickness (approximately 1-inch Installation thick), and shall have a dense root mat for mechanical strength. Specifications The following steps are recommended for sod installation: • Shape and smooth the surface to final grade in accordance with the approved grading plan. The swale needs to be overexcavated 4 to 6 inches below design elevation to allow room for placing soil amendment and sod. • Amend 4 inches (minimum) of compost into the top 8 inches of the soil if the organic content of the soil is less than ten percent or the permeabiliry is less than 0.6 inches per hour. Compost used should meet Ecology publication 94-038 specifications for Grade A quality compost. • Fertilize according to the supplier's recommendations. • Work lime and fertilizer 1 to 2 inches into the soil, and smooth the surface. • Lay strips of sod beginning at the lowest area to be sodded and perpendicular to the direction of water flow. Wedge strips securely into place. Square the ends of each strip to provide for a close, tight fit. Stagger joints at least 12 inches. Staple on slopes steeper than 3H:1 V. Staple the upstream edge of each sod strip. • Roll the sodded area and irrigate. • When sodding is carried out in alternating strips or other patterns, seed the areas between the sod immediately after sodding. Maintenance If the grass is unhealthy, the cause shall be determined and appropriate Standards action taken to reestablish a healthy groundcover. If it is impossible to establish a healthy groundcover due to frequent saturation, instability; or some other cause, the sod shall be removed, the area seeded with an appropriate mix, and protected with a net or blanket. . 4-28 Volume lI— Construction Stormwater Pollution Prevention February 2005 A2t BMP C125: Topsoiling Purpose To provide a suitable growth medium for final site stabilization with vegetation. While not a permanent cover practice in itself, topsoiling is an integral component of providing permanent cover in those areas where there is an unsuitable soil surface for plant growth. Native soils and disturbed soils that have been organically amended not only retain much more stormwater,but they also serve as effective biofilters for urban pollutants and,by supporting more vigorous plant growth, reduce the water, fertilizer and pesticides needed to support installed landscapes. Topsoil does not include any subsoils but only the material from the top several inches including organic debris. Conditions of • Native soils should be left undisturbed to the maximum extent Use practicable. Native soils disturbed during clearing and grading should be restored,to the maximum extent practicable, to a condition where moisture-holding capacity is equal to or better than the original site conditions. This criterion can be met by using on-site native topsoil, incorporating amendments into on-site soil, or importing blended topsoil. • Topsoiling is a required procedure when establishing vegetation on shallow soils, and soils of critically low pH (high acid) levels. • Stripping of existing, properly functioning soil system and vegetation for the purpose of topsoiling during construction is not acceptable. If an existing soil system is functioning properly it shall be preserved in its undisturbed and uncompacted condition. • Depending on where the topsoil comes from, or what vegetation was on site before disturbance, invasive plant seeds may be included and could cause problems for establishing native plants, landscaped areas, or grasses. • Topsoil from the site will contain mycorrhizal bacteria that are necessary for healthy root growth and nutrient transfer. These native mycorrhiza are acclimated to the site and will provide optimum conditions for establishing grasses. Commercially available mycorrhiza products should be used when topsoil is brought in from off-site. Design and if topsoiling is to be done, the following items should be considered: Installation Maximize the depth of the topsoil wherever possible to provide the Specifications � maximum possible infiltration capacity and beneficial growth medium. Topsoil depth shall be at least 8 inches with a minimum organic content of 10 percent dry weight and pH between 6.0 and 8.0 or matching the pH of the undisturbed soil. This can be accomplished either by returning native topsoil to the site and/or incorporating organic amendments. Organic amendments should be incorporated to a minimum 8-inch depth except where tree roots or other natural February 2005 Volume ll-Construction Stormwater Pollufion Prevention 4-29 �22 features limit the depth of incorporation. Subsoils below the 12-inch depth should be scarified at least 2 inches to avoid stratified layers, where feasible. The decision to either layer topsoil over a subgrade or incorporate topsoil into the underlying layer may vary depending on the planting specified. • If blended topsoil is imported, then fines should be limited to 25 percent passing through a 200 sieve. • The final composition and construction of the soil system will result in a natural selection or favoring of certain plant species over time. For example, recent practices have shown that incorporation of topsoil may favor grasses, while layering with mildly acidic,high-carbon amendments may favor more woody vegetation. • Locate the topsoil stockpile so that it meets specifications and does not interfere with work on the site. It may be possible to locate more than one pile in proximity to areas where topsoil will be used. • Allow sufficient time in scheduling for topsoil to be spread prior to seeding, sodding, or planting. • Care must be taken not to apply to subsoil if the two soils have contrasting textures. Sandy topsoil over clayey subsoil is a particularly poor combination, as water creeps along the junction between the soil layers and causes the topsoil to slough. • If topsoil and subsoil are not properly bonded, water will not infiltrate the soil profile evenly and it will be difficult to establish vegetation. The best method to prevent a lack of bonding is to actually work the topsoil into the layer below for a depth of at least 6 inches. • Ripping or re-structuring the subgrade may also provide additional benefits regarding the overall infiltration and interflow dynamics of the soil system. • Field exploration of the site shall be made to determine if there is surface soil of sufficient quantity and quality to justify stripping. Topsoil shall be friable and loamy(loam, sandy loam, silt loam, sandy clay loam, clay loam). Areas of natural ground water recharge should be avoided. • Stripping shall be confined to the immediate construction area. A 4- to 6- inch stripping depth is common,but depth may vary depending on the particular soil. All surface runoff control structures shall be in place prior to stripping. Stockpiling of topsoil shall occur in the following manner: • Side slopes of the stockpile shall not exceed 2:1. • An interceptor dike with gravel outlet and silt fence shall surround all topsoil stockpiles between October 1 and Apri130. Between May 1 4-30 Volume ll— Construction Stormwater Pollution Prevention February 2005 AZ� and September 30, an interceptar dike with gravel outlet and silt fence shall be installed if the stockpile will remain in place for a longer period of time than active construction grading. • Erosion control seeding or covering with clear plastic or other mulching materials of stockpiles shall be completed within 2 days (October 1 through Apri130) or 7 days (May 1 through September 30) of the formation of the stockpile. Native topsoil stockpiles shall not be covered with plastic. • Topsoil shall not be placed while in a frozen or muddy condition, when the subgrade is excessively wet, or when conditions exist that may otherwise be detrimental to proper grading or proposed sodding or seeding. • Previously established grades on the areas to be topsoiled shall be maintained according to the approved plan. • When native topsoil is to be stockpiled and reused the following should apply to ensure that the mycorrhizal bacterial, earthworms, and other beneficial organisms will not be destroyed: 1. Topsoil is to be re-installed within 4 to 6 weeks; 2. Topsoil is not to become saturated with water; 3. Plastic cover is not allowed. Maintenance . • Inspect stockpiles regularly, especially after large storm events. Standards Stabilize any areas that have eroded. February 2005 Volume ll—Construction Stormwater Pollution Prevention 4-31 �2� BMP C140: Dust Control Purpose Dust control prevents wind transport of dust from disturbed soil surfaces onto roadways, drainage ways, and surface waters. Conditions of�Ise • In areas (including roadways) subject to surface and air movement of dust where on-site and off-site impacts to roadways, drainage ways, or surface waters are likely. Design and • Vegetate or mulch areas that will not receive vehicle traffic. In areas Installation where planting, mulching, or paving is impractical, apply gravel or Specifications landscaping rock. • Limit dust generation by clearing only those areas where immediate activity will take place, leaving the remaining area(s)in the original condition, if stable. Maintain the original ground cover as long as practical. • Construct natural or artificial windbreaks or windscreens. These may be designed as enclosures for small dust sources. • Sprinkle the site with water until surface is wet. Repeat as needed. To prevent carryout of mud onto street, refer to Stabilized Construction Entrance (BMP C105). • Irrigation water can be used for dust control. Irrigation systems should be installed as a first step on sites where dust control is a concern. • Spray exposed soil areas with a dust palliative, following the manufacturer's instructions and cautions regarding handling and application. Used oil is prohibited from use as a dust suppressant. Local governments may approve other dust palliatives such as calcium chloride or PAM. • PAM (BMP C126) added to water at a rate of O.S lbs. per 1,000 gallons of water per acre and applied from a water truck is more effective than water alone. This is due to the increased infiltration of water into the soil and reduced evaporation. In addition, small soil particles are bonded together and are not as easily transported by wind. Adding PAM may actually reduce the quantity of water needed for dust control, especially in eastern Washington. Since the wholesale cost of PAM is about$ 4.00 per pound, this is an extremely cost- effective dust control method. Techniques that can be used for unpaved roads and lots include: • Lower speed limits. High vehicle speed increases the amount of dust stirred up from unpaved roads and lots. • Upgrade the road surface strength by improving particle size, shape, and mineral types that make up the surface and base materials. 4-40 Volume ll- Construction Stormwater Pollution Prevention February 2005 �� • Add surface gravel to reduce the source of dust emission. Limit the amount of fine particles (those smaller than .075 mm)to 10 to 20 percent. • Use geotextile fabrics to increase the strength of new roads or roads undergoing reconstruction. • Encourage the use of alternate, paved routes, if available. • Restrict use by tracked vehicles and heavy trucks to prevent damage to road surface and base. • Apply chemical dust suppressants using the admix method,blending the product with the top few inches of surface material. Suppressants may also be applied as surface treatments. • Pave unpaved permanent roads and other trafficked areas. • Use vacuum street sweepers. • Remove mud and other dirt promptly so it does not dry and then turn into dust. • Limit dust-causing work on windy days. • Contact your local Air Pollution Control Authority for guidance and training on other dust control measures. Compliance with the local Air Pollution Control Authority constitutes compliance with this BMP. Maintenance Respray area as necessary to keep dust to a minimum. Standards February 2005 Volume ll—Construction Stormwafer Pollution Prevention 4-41 A�� BMP C150: Materials On Hand Purpose Quantities of erosion prevention and sediment control materials can be kept on the project site at all times to be used for emergency situations such as unexpected heavy sun�uner rains. Having these materials on-site reduces the time needed to implement BMPs when inspections indicate . that existing BMPs are not meeting the Construction SWPPP requirements. In addition, contractors can save money by buying some materials in bulk and storing them at their office or yard. Conditions of Use • Construction projects of any size or type can benefit from having materials on hand. A small commercial development project could have a roll of plastic and some gravel available far immediate protection of bare soil and temporary berm construction. A large earthwork project, such as highway construction,might have several tons of straw, several rolls of plastic, flexible pipe, sandbags, geotextile fabric and steel "T"posts. • Materials are stockpiled and readily available before any site clearing, grubbing, or earthwork begins. A large contractor or developer could keep a stockpile of materials that are available to be used on several proj ects. • If storage space at the project site is at a premium,the contractor could maintain the materials at their office or yard. The office or yard must be less than an hour from the project site. Design and Depending on project type, size, complexity, and length,materials and Installation quantities will vary. A good minimum that will cover numerous situations Specifications includes: Material Measure Quantit Clear Plastic, 6 mil 100 foot roll 1-2 Drain i e, 6 or 8 inch diameter 25 foot section 4-6 Sandba s, filled each 25-50 Straw Bales for mulchin , a rox. 50#each 10-20 u S alls ton 2-4 Washed Gravel cubic ard 2-4 Geotextile Fabric 100 foot roll 1-2 Catch Basin Inserts each 2-4 Steel "T"Posts each 12-24 Maintenance • All materials with the exception of the quarry spalls, steel"T"posts, Standards and gravel should be kept covered and out of both sun and rain. • Re-stock materials used as needed. 4-42 Volume ll—Construction Stormwater Pollution Prevention February 2005 �iZ'1 BMP C151: Concrete Handling Purpose Concrete work can generate process water and slurry that contain fine particles and high pH,both of which can violate water quality standards in the receiving water. This BMP is intended to minimize and eliminate concrete process water and slurry from entering waters of the state. Conditions of Use Any time concrete is used, these management practices shall be utilized. Concrete construction projects include,but are not limited to,the following: • Curbs • Sidewalks • Roads • Bridges • Foundations • Floors • Runways Design and • Concrete truck chutes, pumps, and internals shall be washed out only Installation into formed areas awaiting installation of concrete or asphalt. Specifications Unused concrete remaining in the truck and pump shall be returned to • the originating batch plant for recycling. • Hand tools including,but not limited to, screeds, shovels,rakes, floats, and trowels shall be washed off only into formed areas awaiting installation of concrete or asphalt. • Equipment that cannot be easily moved, such as concrete pavers, shall only be washed in areas that do not directly drain to natural or constructed stormwater conveyances. • Washdown from areas such as concrete aggregate driveways shall not drain directly to natural or constructed stormwater conveyances. • When no formed areas are available, washwater and leftover product shall be contained in a lined container. Containecl conerete shall be disposed of in a manner that does not violate groundwater or surface water quality standards. Maintenance Containers shall be checked for holes in the liner daily during concrete Standards pours and repaired the same day. February 2005 Volume ll— Construction Stormwater Pollution Prevention 4-43 AZ� BMP C153: Material Delivery, Storage and Containment Purpose Prevent, reduce, or eliminate the discharge of pollutants from material delivery and storage to the stormwater system or watercourses by minimizing the storage of hazardous materials onsite, storing materials in a designated area, and installing secondary containment. Conditions of Use These procedures are suitable for use at all construction sites with delivery and storage of the following materials: • Petroleum products such as fuel, oil and grease • Soil stabilizers and binders (e.g. Polyacrylamide) • Fertilizers,pesticides and herbicides • Detergents • Asphalt and concrete compounds • Hazardous chemicals such as acids, lime, adhesives, paints, solvents and curing compounds • Any other material that may be detrimental if released to the environment Design and The following steps should be taken to minimize risk: Installation Temporary storage area should be located away from vehicular traffic, Specifications � near the construction entrance(s), and away from waterways or storm drains. • Material Safety Data Sheets (MSDS) should be supplied for all materials stored. Chemicals should be kept in their original labeled containers. • Hazardous material storage on-site should be minimized. • Hazardous materials should be handled as infrequently as possible. • During the wet weather season(Oct 1 —April 30), consider storing materials in a covered area. • Materials should be stored in secondary containments, such as earthen dike, horse trough, or even a children's wading pool for non-reactive materials such as detergents, oil, grease, and paints. Small amounts of material may be secondarily contained in"bus boy"trays or concrete mixing trays. • Do not store chemicals, drums, or bagged materials directly on the ground. Place these items on a pallet and,when possible, in secondary containment. February 2005 Volume Il—Construction Stormwater Pollution Prevention 4-45 A2� • If drums must be kept uncovered, store them at a slight angle to reduce ponding of rainwater on the lids to reduce corrosion. Domed plastic covers are inexpensive and snap to the top of drums, preventing water from collecting. Material Storage Areas and Secondary Containment Practices: • Liquids, petroleum products, and substances listed in 40 CFR Parts 110, 117, or 302 shall be stored in approved containers and drums and shall not be overfilled. Containers and drums shall be stored in temporary secondary containment facilities. • Temporary secondary containment facilities shall provide for a spill containment volume able to contain precipitation from a 25 year, 24 hour storm event, lus 10%of the total enclosed container volume of all containers, or 110%of the capacity of the largest container within its boundary,whichever is greater. • Secondary containment facilities shall be impervious to the materials stored therein for a minimum contact time of 72 hours. • Secondary containment facilities shall be maintained free of accumulated rainwater and spills. In the event of spills or leaks, accumulated rainwater and spills shall be collected and placed into drums. These liquids shall be handled as hazardous waste unless testing determines them to be non-hazardous. � • Sufficient separation should be provided between stored containers to allow for spill eleanup and emergency response access. • During the wet weather season(Oct 1 -Apri130), each secondary containment facility shall be covered during non-working days,prior to and during rain events. • Keep material storage areas clean, organized and equipped with an ample supply of appropriate spill clean-up material(spill kit). • The spill kit should include, at a minimum: • 1-Water Resistant Nylon Bag • 3-Oil Absorbent Socks 3"x 4' • 2-Oil Absorbent Socks 3"x 10' • 12-Oil Absorbent Pads 17"x19" • 1-Pair Splash Resistant Goggles • 3-Pair Nitrile Gloves • 10-Disposable Bags with Ties • Instructions 4-46 Volume ll—Construction Stormwater Pollution Prevention February 2005 �� BMP C220: Storm Drain Inlet Protection Purpose To prevent coarse sediment from entering drainage systems prior to permanent stabilization of the disturbed area. Conditions of Use Where storm drain inlets are to be made operational before permanent stabilization of the disturbed drainage area. Protection should be provided for all storm drain inlets downslope and within 500 feet of a disturbed or construction area,unless the runoff that enters the catch basin will be conveyed to a sediment pond or trap. Inlet protection may be used anywhere to protect the drainage system. It is likely that the drainage system will still require cleaning. Table 4.91ists several options for inlet protection. All of the methods for storm drain inlet protection are prone to plugging and require a high frequency of maintenance. Drainage areas should be limited to 1 acre or less. Emergency overflows may be required where stormwater ponding would cause a hazard. If an emergency overflow is provided, additional end-of-pipe treatment may be required. Table 4.9 Storm Drain Inlet Protetion Applicable for Type of Inlet Emergency Paved/Earthen Protection Overflow Surfaces Conditions of Use Dro Inlet Protection Excavated drop inlet Yes, Earthen Applicable for heavy flows. Easy protection temporary to maintain. Large area flooding will Requirement: 30'X 30'/acre occur Block and gravel drop Yes Paved or Earthen Applicable for heavy concentrated inlet protection flows. Will not pond. Gravel and wire drop No Applicable for heavy concentrated inlet protection flows. Will pond. Can withstand traffic. Catch basin filters Yes Paved or Earthen c re uent maintenance re uired. Curb Inlet Protection Curb inlet protection Small capacity Paved Used for sturdy, more compact with a wooden weir overflow installation. Block and gravel curb Yes Paved Sturdy, but limited filtration. inlet protection Culvert Inlet Protection Culvert inlet sediment 18 month expected life. tra 4-82 Volume ll- Construction Stormwater Pollution Prevenfion February 2005 �I�J� Design and Excavated Drop Inlet Protection - An excavated impoundment around the Installation storm drain. Sediment settles out of the stormwater prior to entering the Specifications storm drain. • Depth 1-2 ft as measured from the crest of the inlet structure. • Side Slopes of excavation no steeper than 2:1. • Minimum volume of excavation 35 cubic yards. • Shape basin to fit site with longest dimension oriented toward the longest inflow area. • Install provisions for draining to prevent standing water problems. • Clear the area of all debris. • Grade the approach to the inlet uniformly. • Drill weep holes into the side of the inlet. • Protect weep holes with screen wire and washed aggregate. • Seal weep holes when removing structure and stabilizing area. • It may be necessary to build a temporary dike to the down slope side of the structure to prevent bypass flow. Block and Gravel Filter- A barrier formed around the storm drain inlet with standard concrete blocks and gravel. See Figure 4.14. • Height 1 to 2 feet above inlet. � • Recess the first row 2 inches into the ground for stability. • Support subsequent courses by placing a 2x4 through the block opening. • Do not use mortar. • Lay some blocks in the bottom row on their side for dewatering the pool. • Place hardware cloth or comparable wire mesh with '/z-inch openings over all block openings. • Place gravel just below the top of blocks on slopes of 2:1 or flatter. • An alternative design is a gravel donut. • Inlet slope of 3:1. • Outlet slope of 2:1. • 1-foot wide level stone area between the structure and the inlet. • Inlet slope stones 3 inches in diameter or larger. • Outlet slope use gravel %z- to 3/-inch at a minimum thickness of 1-foot. February 2005 Volume ll— Construction Stormwater Pollufion Prevention 4-83 �132 Plan View A Drain Grate 000.,�op�o�o,�o o °°��i� °Qo� �.�� { �fJ�' ��°. ��o.. -'.'o��ooa �oo o Oa- o°oa .Qo�o°O�opv• O�p��o.��-�:O��pO /��cQ(��y� / o � �O o �° p�,O� �O° o�p _�u�� o�" o>� a•o.Q a oe Concrete 00 •o.�oo ��o. oo Block ��Qqti�4 ��0�� °o� , o° �°�s�o �0�� °.��° aa ao. o �. o �000�a � oo�o�o •Q�O�° °�O� a_��?�o� Oo. '��° Gravel °�'o�o° � Backfill o�oo,o�a�oo � a��oo �°o�o pa�°4�°Q ,00•o°O�° •�o,o�� Q1�Ck�o•O� SJ � Oo• �� d o Oo � a�, o°O °� �°° °' ° ��°' °,4 �O� �° �� 0000 .O�•�� o�� e��r °Q� A � �y�5 Section A � /1 Concrete Block Wire Screen or Filter Fabric Gravel Backfill �Overflow Water Ponding Height �e� ,o � °oo�� Water� � o�� /\��\�%\��\%��\/��\/�� _ ��\/��\��\ �\��/�j/�\/�\// Drop Inlet \\/�\/�\��\�j\� \��\/// \///\/�� Notes 1.Drop inlet sediment barriers are to be used for small,nearly level drainage areas.(less than 5%) 2.Excavate a basin of sufficient size adjacent to the drop inlet. 3.The top of the structure(ponding height)must be well below the ground elevation downslope to prevent runoff from bypassing the inlet. A temporary dike may be necessary on the dowslope side of the structure. Figure 4.14—Block and Gravel Filter Gravel and Wire Mesh Filter-A gravel barrier placed over the top of the inlet. 'This structure does not provide an overflow. • Hardware cloth or comparable wire mesh with '/z-inch openings. • Coarse aggregate. • Height 1-foot or more, 18 inches wider than inlet on all sides. • Place wire mesh over the drop inlet so that the wire extends a minimum of 1-foot beyond each side of the inlet structure. • If more than one strip of inesh is necessary, overlap the strips. • Place coarse aggregate over the wire mesh. • The depth of the gravel should be at least 12 inches over the entire inlet opening and extend at least 18 inches on all sides. 4-84 Volume 11— Construction Stormwater Pollution Prevention February 2005 A� Catchbasin Filters - Inserts should be designed by the manufacturer for use at construction sites. The limited sediment storage capacity increases the amount of inspection and maintenance required, which may be daily for heavy sediment loads. The maintenance requirements can be reduced by combining a catchbasin filter with another type of inlet protection. This type of inlet protection provides flow bypass without overflow and therefore may be a better method for inlets located along active rights-of- way. • 5 cubic feet of storage. • Dewatering provisions. • High-flow bypass that will not clog under normal use at a construction site. • The catchbasin filter is inserted in the catchbasin just below the grating. Curb Inlet Protection with Wooden WeiY-Barrier formed around a curb inlet with a wooden frame and gravel. � Wire mesh with %2-inch openings. • Extra strength filter cloth. • Construct a frame. • Attach the wire and filter fabric to the frame. • Pile coarse washed aggregate against wire/fabric. • Place weight on frame anchors. Block and Gravel Curb Inlet Protection—Barrier formed around an inlet with concrete blocks and gravel. See Figure 4.14. • Wire mesh with '/2-inch openings. • Place two concrete blocks on their sides abutting the curb at either side of the inlet opening. These are spacer blocks. • Place a 2x4 stud through the outer holes of each spacer block to align the front blocks. • Place blocks on their sides across the front of the inlet and abutting the spacer blocks. • Place wire mesh over the outside vertical face. • Pile coarse aggregate against the wire to the top of the barrier. Curb and Gutter Sediment Barrier—Sandbag or rock berm(riprap and aggregate) 3 feet high and 3 feet wide in a horseshoe shape. See Figure 4.16. • Construct a horseshoe shaped berm, faced with coarse aggregate if using riprap, 3 feet high and 3 feet wide, at least 2 feet from the inlet. • Construct a horseshoe shaped sedimentation trap on the outside of the berm sized to sediment trap standards for protecting a culvert inlet. February 2005 Volume ll- Construction Sformwater Pollution Prevention 4-85 �� Maintenance • Catch basin filters should be inspected frequently, especially after Standards storm events. If the insert becomes clogged,it should be cleaned or replaced. • For systems using stone filters: If the stone filter becomes clogged with sediment, the stones must be pulled away from the inlet and cleaned or replaced. Since cleaning of gravel at a construction site may be difficult, an alternative approach would be to use the clogged stone as fill and put fresh stone around the inlet. • Do not wash sediment into storm drains while cleaning. Spread all excavated material evenly over the surrounding land area or stockpile and stabilize as appropriate. 4-86 Volume ll— Construction Stormwater Pollution Prevention February 2005 �35 Plan View Back of Sidewalk A Catch Basin 2x4 Wood Stud Back of Curb Concrete Block Curb Inlet �°� o,�o ��O o. . "n� Oa�� a ��j,� ��o� Y��p�� ° � �.a^•�,C54 °°� �.p �� ' ��o, � s p.._._ 8 � p-� ��°,,,p� '�J j� �� 0 y� .;oo .,p o0 R .,op R 4 Q� �.Vp qo�po'�?V PfYJ.� "" ° r,� � �n �� °��' �e o 1.3��o��a°�� o��§° �oo •po'�(�'o°o�'' ('{o . �o n . � ��Q �°.°�q��o.4Sb� �°oo,n0 �� pp. R��• . 9Q��Op'Q °qD,Q�ynt O p"OQQ qOpQ..(,� 9pQ• �y O O O• ,.p�OG,p p• Y� 0. �. Q,� �. Y'Ck1°o '7��Q,�� oo$-. �°�'y�(��nn ��e Q .��(pqe�p?�o- �po 0 � • 4.°�4 0� o' ��6oU��O Wire Screen r Filter Fabric A Concrete Block Section A � A a��Drain Gravel (20mm) '/."Drain Gravel (20mm) Ponding Height Concrete Block Overfl • g' a d� � � \�/\\�/� " Curb Inlet /� \� ' ' ' . , \�� Wire Screen or \/�\�%\�/\�/\/\ �/% Filter Fabric �!��/��/i�� \�� , Catch Basin \�� 4 Wood Stud /� (100x50 Timber Stud) �\/ ��/ NOTES: 1. Use block and gravei type sediment barrier when curb inlet is located in gently sloping street segment, where water can pond and allow sediment to separate from runoff. 2.Barrier shall allow for overFlow from severe storm event. 3. Inspect barriers and remove sediment after each storm event. Sediment and gravel must be removed from the traveled way immediately. Figure 4.15—Block and Gravel Curb Inlet Protection February 2005 Volume ll—Construction Stormwater Pollution Prevention 4-87 �3� Plan View Back of Sidewalk Burlap Sacks to Catch Basin Overlap onto Curb Curb Inlet �� Back of Curb I � RUNOFF `�i l I I� �. RUNOFF SPILLWAY . / � �a/ � � \ <' ��--�%/ Gravel Filled Sandbags �.=/i Stacked Tightly \�� ._ NOTES: l.Place curb type sediment barriers on gently sloping street segments,where water can pond and allow sediment to separate from runoff. 2. Sandbags of either burlap or woven'geotextile'fabric,are filled with gravel,layered and packed tightly. 3.Leave a one sandbag gap in the top row to provide a spillway for overflow. 4.Inspect barriers and remove sediment after each storm event. Sediment and gravel must be removed from the traveled way immediately. Fi ure 4.16—Curb and Gutter Barrier 4-88 Volume ll— Construcfion Stormwater Pollution Prevention February 2005 �� BMP C233: Silt Fence Purpose Use of a silt fence reduces the transport of coarse sediment from a construction site by providing a temporary physical barrier to sediment and reducing the runoff velocities of overland flow. See Figure 4.19 for details on silt fence construction. Conditions of Use Silt fence may be used downslope of all disturbed areas. • Silt fence is not intended to treat concentrated flows, nor is it intended to treat substantial amounts of overland flow. Any concentrated flows must be conveyed through the drainage system to a sediment pond. The only circumstance in which overland flow can be treated solely by a silt fence, rather than by a sediment pond, is when the area draining to the fence is one acre or less and flow rates are less than 0.5 cfs. • Silt fences should not be constructed in streams or used in V-shaped ditches. They are not an adequate method of silt control for anything deeper than sheet or overland flow. Jbints in filter fabric shail be spliced at posts.Use staples,wire rings or 2"x2"by 14 Ga.wire or equivalent to attach fabric to posts equivalent,if standard strength fabric used I I � Filter fabric — II I � I I � �� II � N II - = - - - -- _ - _ .:_:<..: !T�,��„�=L:.�1.:.1�-L,1i1=11�iT=-Z,u iii n=�� _ _ __ _ _ui-ui_��_�� __ c �-1ii � �� 6'max—� T� Minimum 4"x4"trench �\m' � �� , � � N Backfill trench with native soil Post spacing may be increased or 3/4"-1.5"washed gravel � to 8'if wire backing is used 2"x2"wood posts,steel fence posts,or equivalent Figure 4.19—Silt Fence Design and • Drainage area of 1 acre or less or in combination with sediment basin Installation in a larger site. Specifications • Maximum slope steepness (normal (perpendicular) to fence line) l:l. • Maximum sheet or overland flow path length to the fence of 100 feet. • No flows greater than 0.5 cfs. • The geotextile used shall meet the following standards. All geotextile properties listed below are minimum average roll values (i.e.,the test result for any sampled roll in a lot shall meet or exceed the values shown in Table 4.10): 4-94 Volume ll— Construction Stormwater Pollution Prevention February 2005 ��Jg Table 4.10 Geotextile Standards Polymeric Mesh AOS 0.60 mm maximum for slit film wovens(#30 sieve). 030 (ASTM D4751) mm maximum for all other geotextile types(#50 sieve). 0.15 mm minimum for all fabric types(#100 sieve). Water Pernuttivity 0.02 sec minimum (ASTM D4491) Grab Tensile Strength 180 lbs.Minimum for extra strength fabric. (ASTM D4632) 100 lbs minunum for standard strength fabric. Grab Tensile Strength 30%m�imum (ASTM D4632) Ultraviolet Resistance 70%minimum (ASTM D4355) • Standard strength fabrics shall be supported with wire mesh, chicken wire, 2-inch x 2-inch wire, safety fence, or jute mesh to increase the strength of the fabric. Silt fence materials are available that have synthetic mesh backing attached. • Filter fabric material shall contain ultraviolet ray inhibitors and stabilizers to provide a minimum of six months of expected usable construction life at a temperature range of 0°F. to 120°F. • 100 percent biodegradable silt fence is available that is strong, long lasting, and can be left in place after the project is completed, if permitted by local regulations. • Standard Notes for construction plans and specifications follow. Refer to Figure 4.19 for standard silt fence details. The contractor shall install and maintain temporary silt fences at the locations shown in the Plans. The silt fences shall be constructed in the areas of clearing, grading, or drainage prior to starting those activities. A silt fence shall not be considered temporary if the silt fence must function beyond the life of the contract. The silt fence shall prevent soil carried by runoff water from going beneath,through, or over the top of the silt fence,but shall allow the water to pass through the fence. The minimum height of the top of silt fence shall be 2 feet and the maximum height shall be 2'/z feet above the original ground surface. The geotextile shall be sewn together at the point of manufacture, or at an approved location as determined by the Engineer,to form geotextile lengths as required. All sewn seams shall be located at a support post. Alternatively, two sections of silt fence can be overlapped,provided the Contractor can demonstrate, to the satisfaction of the Engineer, that the overlap is long enough and that the adjacent fence sections are close enough together to prevent silt laden water from escaping through the fence at the overlap. February 2005 Volume I!—Construction Stormwater Pollution Prevention 4-95 a� The geotextile shall be attached on the up-slope side of the posts and support system with staples, wire, or in accordance with the manufacturer's recommendations. The geotextile shall be attached to the posts in a manner that reduces the potential for geotextile tearing at the staples, wire, or other connection device. Silt fence back-up support for the geotextile in the form of a wire or plastic mesh is dependent on the properties of the geotextile selected for use. If wire or plastic back-up mesh is used, the mesh shall be fastened securely to the up-slope of the posts with the geotextile being up-slope of the mesh back-up support. The geotextile at the bottom of the fence shall be buried in a trench to a minimum depth of 4 inches below the ground surface. The trench shall be backfilled and the soil tamped in place over the buried portion of the geotextile, such that no flow can pass beneath the fence and scouring can not occur. When wire or polymeric back-up support mesh is used, the wire or polymeric mesh shall extend into the trench a minimum of 3 inches. The fence posts shall be placed or driven a minunum of 18 inches. A minimum depth of 12 inches is allowed if topsoil or other soft subgrade soil is not present and a minimum depth of 18 inches cannot be reached. Fence post depths shall be increased by 6 inches if the fence is located on slopes of 3:1 or steeper and the slope is perpendicular to the fence. If required post depths cannot be obtained, the posts shall be adequately secured by bracing or guying to prevent overturning of the fence due to sediment loading. Silt fences shall be located on contour as much as possible, except at the ends of the fence, where the fence shall be turned uphill such that the silt fence captures the runoff water and prevents water from flowing around the end of the fence. If the fence must cross contours, with the exception of the ends of the fence, gravel check dams placed perpendicular to the back of the fence shall be used to minimize concentrated flow and erosion along the back of the fence. The gravel check dams shall be approximately 1- foot deep at the back of the fence. It shall be continued perpendicular to the fence at the same elevation until the top of the check dam intercepts the ground surface behind the fence. The gravel check dams shall consist of crushed surfacing base course, gravel backfill for walls, or shoulder ballast. The gravel check dams shall be located every 10 feet along the fence where the fence must cross contours. The slope of the fence line where contours must be crossed shall not be steeper than 3:1. Wood, steel or equivalent posts shall be used. Wood posts shall have minimum dimensions of 2 inches by 2 inches by 3 feet minimum length, and shall be free of defects such as knots, splits, or gouges. 4-96 Volume 11— Construction Stormwater Pollution Prevenfion February 2005 � Steel posts shall consist of either size No. 6 rebar or larger, ASTM A 120 steel pipe with a minimum diameter of 1-inch,U, T, L, or C shape steel posts with a minimum weight of 1.35 lbs./ft. or other steel posts having equivalent strength and bending resistance to the post sizes listed. The spacing of the support posts shall be a maximum of 6 feet. Fence back-up support, if used, shall consist of steel wire with a maximum mesh spacing of 2 inches, or a prefabricated polymeric mesh. The strength of the wire or polyxneric mesh shall be equivalent to or greater than 1801bs. grab tensile strength. The polymeric mesh must be as resistant to ultraviolet radiation as the geotextile it supports. • Silt fence installation using the slicing method specification details follow. Refer to Figure 4.20 for slicing method details. The base of both end posts must be at least 2 to 4 inches above the top of the silt fence fabric on the middle posts for ditch checks to drain properly. Use a hand level or string level, if necessary, to mark base points before installation. Install posts 3 to 4 feet apart in critical retention areas and 6 to 7 feet � apart in standard applications. Install posts 24 inches deep on the downstream side of the silt fence, and as close as possible to the fabric, enabling posts to support the fabric from upstream water pressure. Install posts with the nipples facing away from the silt fence fabric. Attach the fabric to each post with three ties, all spaced within the top 8 inches of the fabric. Attach each tie diagonally 45 degrees through the fabric,with each puncture at least 1 inch vertically apart. In addition, each tie should be positioned to hang on a post nipple when tightening to prevent sagging. Wrap approximately 6 inches of fabric around the end posts and secure with 3 ties. No more than 24 inches of a 36-inch fabric is allowed above ground level. The rope lock system must be used in all ditch check applications. The installation should be checked and corrected for any deviation before compaction. Use a flat-bladed shovel to tuck fabric deeper into the ground if necessary. Compaction is vitally important for effective results. Compact the soil immediately next to the silt fence fabric with the front wheel of the tractor, skid steer, or roller exerting at least 60 pounds per square inch. Compact the upstream side first and then each side twice for a total of four trips. February 2005 Volume 1!— Construction Stormwater Pollution Prevention 4-97 ��I • Any damage shall be repaired immediately. Maintenance If concentrated flows are evident uphill of the fence,they must be Standards � intercepted and conveyed to a sediment pond. • It is important to check the uphill side of the fence for signs of the fence clogging and acting as a barrier to flow and then causing channelization of flows parallel to the fence. If this occurs, replace the fence or remove the trapped sediment. • Sediment deposits shall either be removed when the deposit reaches approximately one-third the height of the silt fence, or a second silt fence shall be installed. • If the filter fabric (geotextile)has deteriorated due to ultraviolet breakdown it shall be re laced. •on�n�Mi�t �OST EPACINGs . mmr.s�s" T nurz.�a ep�n runs . . . ......:«..... .. ...»..�....TqQ Of FSt7dC - . � S'wwlc�n palln�u��s Attaeh tY�e{a b � . � � YVib��sl tfA��f pqst ' � . .'..��• �. �{.Q�—"' � . . ortw or.r wwp Nr.a �OS7 DBPTHs �-5 '��$�5�� As nweh Mlaw'rsund '�`. Mrh twlc�aweNn*. �� i fwbillc witow�wuad � '�, �.:' e0 O.s.i.x lnMw' 100%aM�p� f06%ea�rp+Mtlon � . �(�vlaYa[hrrwil �� :-. ..` d0lThlu111lkYj�Ih .. \��\�� \��t��\\��\ f � i`,%\i\� �i��,`��i``� �j/��i/��/� ��j�`�jf1��`/�� nw+►�r►oEx�rs: ij��jf�� f\j\�\�\� •G.u�x r.t�c a po�u,r„+�darc�. �\\�\� �� \�`�\�//��/�,/\ •Wwxsures uaro«poet er wl�l�in,lop e•wtalaic. //�%�/\j� y� �+��*\�/�� PoiNkm�aah Us diayone�y.punouring 1wNicvsrtieelry,� / / / / 3 ✓ / / / a�n o11'spp�t. ��\�\, �� ~\�\��`` •Ha�y*scf�b�an s P��P1��►111{�I+n xwduai�c � No more then 2a`ofi a 36'fabric we cew.u.a(�nr,oR,�,ars. ,. �811oweci eboYe groUnd. �r RoA ot sNt l�nce .,�.*.... OP$rehon �� P�st — �eci eit�: compacban Fat�fc �aaara ' Sik Fen�e � . .as.._. �.�.e� . .�'� '� � � `�✓,v ��'�✓�4 ��jr�r� . � � � �� T�i� : s ; , 4y� 2E�Lt-�mrn ��\,` ,�,,��t� a .�� f��'�,�l'„�`d.'�!�$','/,�w .;+,w:4?,�'i,ti.�9i� ��df��I�`'/��.,��,,1,�� ti,��.,�^Ni � r��` i,�¢.',wi ij!q VbdmdNei c7�hif pok�t S1cMg Wade (76 rtm,wkMN (1 a mm wWtl,) ,�on,p�d r�laaon ViE�tary pbw is rxx sc�e{atabie bec�t�se of t�r��mp�cUc>n Figure 4.20—Silt Fence Installation by Slicing Method 4-98 Volume 11—Construction Stormwater Pollution Prevention February 2005 A�2 APPENDIX "B" MISCELLANEOUS INFORIVIATION LARSON & ASSOCIATES, INC. 4401 S. 66TH STREET TAC4MA, WA. 98409 �� GEOTECHNICAL ENGINEERING STUDY For YELM APARTMENTS PARCEL #21724410200 304 LONGMIRE STREET, YELM, 98597 THURSTON COUNTY, WASHINGTON Prepared For MOUNTAIN TERRACE BUILDERS, LLC. 14730 STATE ROUTE 507 SE, YELM,WA 98597 Prepared By Pacific Geo Engineering Geotechnical Engineering, Consulting 8E Inspection P.O. BOX 1419, ISSAQUAH, WASHINGTON 98027 PGE PROJECT NUMBER 13-420 September 23, 2013 �Z ��#�� ir��r�� Q+�t!lIGhJ��i�lr L�it�l/t�eti/1t�t CO1�S#+1/Clfl!�$ ,�'ri�';�1�tit7l �eptetnber 23,2f313 Mcruntain Terr��Builders,LL� 147�4 State Ftc�ut�SU� SE Y�lrn,"WA� 9�597 R�: Gec�technicat Engineerir��Study Y�lz�a Apartme�tts 3t��:Lan�mire Stre�t Y�lrrt,�TV�sY�in�tor�9859? PGE prnrj�ct I�+�a. 13-42� Ref.; Site Plan uf Yelrn Apartments,prepar�by Lars�n&Assaciates. Uear�r.'Tru�ik: Paci�c Creo Er�gineering, LLC (1'G�} has cotnplste.ct tihe �eotec�nical �n�itteering study fc�r tl�� subj�cct site 1ae,ated at the ab�ve�ddress in Yelim, T'hurston County, Washin�ton. 'I"�is repc�rt inoluc�s the r�sults of aur sub�urface expic�ration �€nd engineerin� ev�luatio�i, and �rovides rec�rnm�a�datioz�s�or t�te geuie�hnical aspects of the desi�;n and d�velc►p��nt of th��ro,ject. We trust the infarmation presented in this r��rt is su�eient for yc�u�curcet�t ne.�ds. We appreciate the c�ppe�rt�nity ta provid� the ��catechnical serviees at this phase c�f th� �arc►ject anci laok fQrw�rd tc� conti�u�d participatic�n duri�a� the de�ign and cc}��s�ructian phase af this praj�ct, Shoutd ycru h�ve an� questions c�r - � ., _ , . , r . :� �it["to.�Gt`ifx�y i7if�7liG�1 Ctr�V�t' fi€t7f��.'iaax itt�t�t`E.'�'a�tls tJt` ik titi�i�Yr'A;y e3t; CiF aiitit�Yf3�� %tS51Si��'�+i:f�,�;ii�tiSi. t"�t� C1iUl�it'51��G' tu c.+ati¢ us at 4�S-218-�316 or 425-643-2�16. l�esp�ctfully s�bmitte�i, ' ' � r �: �t�.��,_ ��a�.. . '�` , �� A'' �.?+� Sarrt,�nu Mc�vvaaur�,�IS�E,P.E, � ��P�►`+��/C#�'�i`t Et�ir��'It�'X+,y "`� � �` . ��i��' ��, �7d�=�� `�' �� ed��y�� y Ki�� : ��. � ... ��t-S�� °'�5.+ . .. .. .��:Y� �:(��'r:��. e� B� p.Q, t3�x 14�.�. I�saQuah. M�lA. 98��7. (Tei� 42�-64�-2616. ��x) �2�-��3-0436. TABLE OF CONTENTS Page No. 1.0 INTRODUCTION.............................................................................................................................................. i 2.0 PROPOSED DEVELOPMENT....................................................................................................................... 1 3.0 SCOPE OF SERVICES..................................................................................................................................... 2 3.1 Field Investigation............................................................................................................................... 2 3.2 I,aboratory Testing............................................................................................................................... 3 3 3 Engineering Evaluation....................................................................................................................... 3 4.0 SURFACE AND SUBSURFACE FEATURES.............................................................................................. 4 4.1 Site Location......................................................................................................................................... 4 4.2 Site Descriptions................................................................................................................................... 4 43 Regional Geology ................................................................................................................................ 4 4.4 Visual Soil Descriptions....................................................................................................................... 4 4.5 Groundwater Conditions....................................................................................................................... 5 5.0 CONCLUSIONS AND RECOMMENDATIONS.......................................................................................... 5 5.1 General................................................................................................................................................. 5 5.2 Site Preparation.................................................................................................................................... 6 5.2.1 Clearing and Grubbing......................................................................................................... 6 5.2.2 Subgrade Preparation............................................................................................................ 6 5.23 Reuse of On-Site Soils.......................................................................................................... 7 5.2.4 Construction Season............................................................................................................. 8 5.2.5 Structural Fills...................................................................................................................... 8 5.2.6 Fill Placement&Compaction Requirements....................................................................... 9 5.2.7 Temporary Excavation Slopes ............................................................................................ 9 5.2.8 Permanent Cut and Fill Slopes ............................................................................................ 11 5.2.9 Construction Dewatering ..................................................................................................... 12 5.2.10 Construction Monitoring...................................................................................................... 12 5.3 Foundation Recommendations............................................................................................................ 12 5.4 Floor Slabs........................................................................................................................................... 14 . _ - _ _ 5.5 Site llraniage..:.:. .::.:...: _ : ...................... ......... ......... ......... ...................... ......... .......... I5 5.6 Utility Support and Bacl�'iil................................................................................................................ 16 5.7 Pavement Thickness............................................................................................................................ 17 5.8 Geologic Hazards................................................................................................................................ 18 5.8.1 Erosion Hazard..................................................................................................................... 18 5.8.2 Seismic Hazard..................................................................................................................... 18 5.8.3 Landslide Hazard.................................................................................................................. 19 5.9 Infiltration Potential Evaluation.......................................................................................................... 19 6.0 REPORT LIMITATIONS................................................................................................................................ 19 7.0 ADDITIONAL SERVICES.............................................................................................................................. 21 8.0 GEOTECHNICAL SPECIAL INSPECTIONS............................................................................................. 21 LIST OF FIGURES LIST OF APPENDICES Figure 1 Vicinity Map Appendix A Soil Test Pit Log Figure 2 Site&Exploration Pian i Pt4 PGEPaciFc Geo Enginee�ing ...e.�,��..�..�,...�. Geotechnical Engineering Study Yelm Aparhnents Project No. 13-420 September 23,2013 Page 1 1.0 INTRODUCTION This report presents the findings of our subsurface exploration and geotechnical engineering evaluation for a proposed development, to be located at 304 Longmire Street, Yelm, Washington. The general location of the site is shown on the Vicinity Map, Figure 1. The work was performed in general accordance with our proposal No. 13-06-390, dated July 09, 2013, which was authorized by the client on the same day. 2.0 PROPOSED DEVELOPMENT The development plan calls for constructing two apartment buildings, associated driveways and roadways, and shallow underground infiltration systems. Based on our experience with similar projects, we anticipate that the buildings will be single- or double-story wood-framed structures with loading carried primarily by a system of bearing walls.We expect bearing wall loads will be in the range of 2 to 3 kips per lineal foot, isolated column loads in the range of 30 to 40 kips, and slab-on-grade floor loads of 150 pounds per square foot (ps fl. We further expect that the first floor levels of the buildings will be constructed at grade or framed over a crawl space area. Final grading plan is not prepared yet for the subject development. However, we assume that minor amount of cuts and fills are likely to take place across the proposed building pad areas of the subject tracts to achieve the final grades in this site. We understand some sort of storm water management system will be built in this site to manage the stormwater runoff and the rooftop water of the proposed development. The proposed development will include several asphalt-paved driveways. We anticipate vehicle traffic will primarily consist of passenger cars and occasional waste management trucks. The current topography of the site are shown on the Site and Soil Exploration Plan,Figure 2. The conclusions and recommendations contained in this report are based upon our understanding of the above design features of the development. We recommend that PGE should be allowed to review the final grades and the actual features after the final construction plans are prepared so that the conclusions and recommendations contained in this report may be re-evaluated and modified, if necessary. �J� PGEPacitic Geo Engineering .�,.,.�..�.a.�,..�..�.. Geotechnical Engineering Study Yelm Aparhnents Project No. 13-420 September 23,2013 Page 2 3.0 SCOPE OF SERVICES The purpose of this study was to evaluate the geotechnical aspects of the proposed development, and to identify and address the geotechnical issues that may impact the proposed site development. The scope of this geotechnical study included field explorations, laboratory testing, geologic literature review, and engineering evaluation of the field and laboratory data. This study also included interpretation of this information to generate pertinent geotechnical recommendations and conclusions that may be used for the design and construction of the development. The scope of our work did not include any wetland study, or any environmental analysis or evaluation to fmd the presence of any hazardous or toxic materials in the soil, surface water, groundwater, or air in or around this site. 3.1 Field Investigation We explored the subsurface conditions in the subject site on August 06, 2013. A total of nine(9) test pits planned by Larson and Associates were excavated during our explorations to depths of about 11 feet below the existing grades, and were backfilled with loosely compacted excavated soils. Several field percolation tests were performed in test pit TP-1,TP-2, and TP-7 at 4 feet below the current grades. The test pits were completed using a backhoe provided by the client. The specific number and the locations of the test pits were selected and plotted on the site plan, referenced above in item 2, prepared by Larson and Associates. This plan is reproduced in the Site and Soil Exploration Plan by PGE iTt i'i�TLIY��. _ _ . . _ An engineering geologist from our firm observed the excavations, continually logged the subsurface conditions in each test pit, collected representative bulk samples from different soil layers, and observed pertinent site features. Samples were designated according to the test pit number and depth, stored in watertight plastic containers, and later on transported to our laboratory for further visual examination. Results of the field investigation are presented on the test pit log,which is presented on Page A-1 of Appendix A. The final log is modified based on the interpretation of our field logs and visual examination of the samples in the laboratory. Due to the similar nature of soils encountered in the test pits throughout the site, only one test pit log is prepared representing the soils encountered in all test pits. �� PaciFc Geo Engineeting .`.e.�,�.�..+�.�..�..�,..�, Geotechnical Engineering Study Yelm Apartments Project No. 13-420 September 23,2013 Page 3 3.2 Laboratory Testing The bulk samples were visually classified in the field and laboratory, and later on supplemented by grain size analyses and moisture content tests to evaluate the general physical properties and engineering characteristics of the soils encountered. Two (2) Percent Passing #200 Sieve tests were performed on two (2) selected samples in accordance with the ASTM D-1140 procedure, the results of which are presented in the test pit log in Appendix A. 3.3 Engineering Evaluation The results from the field and laboratory tests were evaluated and engineering analyses were performed to provide pertinent information and recommendations on the following geotechnical aspects of the proposed site development: • Soil and groundwater conditions of the site. • Earthwork including site preparation, clearing and grubbing, excavation, placement and compaction of structural fills, and subgrade preparation. • Structural fills and use of the on-site soils as structural fill. � Dry weather construction. • Temporary and permanent excavation slopes. • Temporary construction dewatering. • Site drainage including permanent subsurface drainage systems and temporary groundwater control measures, if necessary. • Foundation types and allowable bearing capacity for supporting the proposed residences. • Settlement due to the recommended bearing capacity and observed soil conditions. • Frictional and passive values for the resistance of lateral forces. • Subgrade preparation for slab-on-grade. • Seismic design considerations, including the site coefficient per IBC 2003. • Pavement thickness recommendations. • Geologic hazards: erosion, seismic,and landslide. • Infiltration rates of native soils in the proposed storm tract area. • Geotechnical special inspection requirements. �7 PGEPacific Geo Engineering ...�,�.�..,..�.�,..�...��„ Geotechnical Engineering Study Yelm Apartments Project No. 13-420 September 23,2013 Page 4 4.0 SURFACE AND SUBSURFACE FEATURES 4.1 Site Locations The subject site is located at 304 Longmire Street in Yelm, Thurston County, Washington,which is shown on the Vicinity Map,Figure 1. 4.2 Site Descriptions The site has an access near its southwestern corner from the intersection of Berry Valley Dr. and Longmire St. SE. In general, the site is almost a level ground with minor downward slope from its northern edge to the southern edge, with the elevations range from 342 to 348. The topography is shown on the Site&Exploration Plan,Figure 2. 4.3 Regional Geology The site is in the Puget Sound Lowland, a north-south trending structural and topographic depression lying between Olympic Mountains on the west and Cascade Mountains on the east. The lowland depression experienced successive glaciation and nonglaciation activities over the time of Pleistocene period. During the most recent Fraser glaciation, which advanced from and retreated to British Columbia between 13,000 and 20,000 years ago, the lowland depression was buried under about 3,000 feet of continental glacial ice. During the successive glacial and nonglacial intervals, the lowland depression, which is underlain by Tertiary volcanic and sedimentary bedrock; was filled up above the bedrocks to the present-day land surface with Quaternary sediments, which consisted of Pleistocene glacial and nonglacial sediments. The glacial deposits include concrete-like lodgement till, lacustrine silt, fine sand and clay, advance and recessional outwash composed of sand or sand and gravel, and some glaciomarine materials. The nonglacial deposits include largely fluvial sand and gravel,overback silt and clay deposits, and peat attesting to the sluggish stream environments that were apparently widespread during nonglacial times. 4.4 Visual Soil Descriptions In general, the site is underlain by approximately 24 inches thick brown silty sandy soils containing abundant gravels and cobbles, and roots and organics. This soils are underlain by a soil deposit consisted of primarily gravels, cobbles, and boulders with some sands and trace silts upto the bottom of the exploration depths. In general,the soils are in loose consistencies in the upper 4 feet depth, and in medium dense consistencies below that depth.The soils have good permeability characteristics. 88 j'�/^r�Pacifc Geo Engineering s—V ...�„d„�.�.,.,�.�.�,..�..�, Geotechnical Engineering Study Yelm Apartments Project No. 13-420 September 23,2013 Page 5 4.5 Groundwater Conditions No groundwater or seepage, or any sign of mottling was noticed in the test pits within their exploration depths. It is to be noted that seasonal fluctuations in the groundwater elevations and the presence of perched water in the upper permeable loams may be expected in the amount of rainfall, surface runoff, and other factors not apparent at the time of our exploration. Typically, the groundwater levels rise higher and the seepage flow rates increase during the wet winter months in the Puget Sound area. The possibility of groundwater level fluctuations and the presence of perched water and seepage through excavations must be considered when designing and developing the proposed development in this site. The preceding discussion on the subsurface conditions of the site is intended as a general review to highlight the major subsurface stratification features and material characteristics. For more complete and specific information at individual test pit locations, please review the Test Pit Log (Page A-1) included in Appendix A. This log include soil descriptions, stratification, and location of the samples and laboratory test data. It should be noted that the stratification lines shown on the log represent the approximate boundaries between various soil strata; actual transitions may be more gradual or more severe. The subsurface conditions depicted in the log are for the test pit locations indicated only, and it should not necessarily be expected that these conditions are representative at other locations of the site. 5.0 CONCLUSIONS AND RECOMMENDATIONS 5.1 General Based on this study, there are no geotechnical considerations that would preclude the proposed development as planned,therefore,the subject site is considered suitable for the proposed development. The proposed structures, e.g., buildings, slab-on-grades, driveways, pavements, and any other structures may be supported on the native soils, provided the final subgrades for such structures are to be prepared as per the recommendations provided in this section and in its following sections. We recommend that the building footings, floor slabs if slab-on-grade type is chosen, the driveways and the pavements, and any other structures must be placed on the firm, unyielding soils, either consisted of native soils, existing fills, or newly placed structural fills. The final grade preparation and the final grades to support any structures must be monitored and approved, respectively, by the geotechnical special inspector during the construction phases of the project. Based on the findings of our subsurface explorations the native soils encountered in this site within the shallow depths of approximately 4 feet below the existing grades are found in general, in loose B� P��Pacltic Geo Engineering .�,......�,...�,..�..�..�.. Geotechnical Engineering Study Yelm Aparhnents Project No. 13-420 September 23,2013 Page 6 consistencies. If these soils have to support new structures, e.g., foundations, floor slabs, retaining walls, driveways, pavements, new structural fills, and any other structures then these soils must be adequately proofrolled with a big vibratory roller to increase these sand deposits' compactions and their bearing capacity values. In addition to the regular proofrolling effort we believe that extra compaction effort will be needed to compact the upper loose soil deposits and to transmit the compaction effort to greater depths. It should be noted that the proofrolling and the resulting compactions of the soil deposits should be achieved to its firm and unyielding conditions, and to a minimum of 95% compaction of the native sand's Modified Proctor dry density value to develop a stable and firm final subgrades. The soil deposits encountered in the test pits are found of good permeability characteristics, therefore,are considered to be conducive for installing infiltration system. The remainder of this section (5.0) presents specific engineering recommendations on the pertinent geotechnical aspects that are anticipated for the design and construction of the proposed development. These recommendations should be incorporated into the final design and drawings, and construction specifications. 5.2 Site Preparation Preparation of the site should involve clearing, stripping, subgrade proofrolling, cutting, filling, excavations, dewatering, and drainage installations. The following paragraphs provide specific recommendations on these issues. S.Z.i CY��ai��i�d«��u��f�g . _ __ Initial site preparation for construction of new buildings, driveways, pavements, and any other structures should include stripping of vegetation and topsoil from the site. Based on the topsoil thickness encountered at our test pit locations, we anticipate topsoil stripping depths of about 12 to 18 inches, however, thicker layers of topsoil may be present in unexplored portions of the site. It should be realized that if the stripping operation takes place during wet winter months, it is typical a greater stripping depth might be necessary; therefore, stripping is best performed during dry weather period. Stripped vegetation debris should be removed from the site. Stripped organic topsoils will not be suitable for use as structural fill but may be used for future landscaping purposes. 5.2.2 Subgrade Preparation After the site clearing and site stripping, cut and fill operations can be initiated to establish desired driveways and building grades. Any exposed subgrades that are intended to provide direct j�a P/'��PaciFc Geo Engineering V ....�.e,w�...,ti,�w..s...m..,, Geotechnical Engineering Study Yelm Apariments Project No. 13-420 September 23,2013 Page 7 support for new construction and/or require new fills should be adequately proofrolled to evaluate their condition. Proofrolling should be done with a loaded dump truck or front-end loader under the supervision of a geotechnical engineer, and/or must be probed with a T-probe by the geotechnical engineer to identify the presence of any isolated soft and yielding areas and to verify that stable subgrades are achieved to support the buildings, driveways, and the new fills. As mentioned earlier in Section 5.1, in addition to the regular proofrolling an extra compaction effort will be required during the proofrolling of the native sand deposit to enhance their bearing capacity values. It should be noted that the proofrolling and the resulting compactions of the sand deposits should be achieved to its firm and unyielding conditions, and to a minimum of 95% compaction of the native sand's Modified Proctor dry density value to develop a stable and firm final subgrades. The loosely backfilled soils in the areas of exploratory test pits should be overexcavated completely to the firm native soils and backfilled with adequately compacted new structural fills to the final grades. Tree stumps and large root balls should be removed completely and backfilled with new structural fills to the desired subgrade levels. 5.2.3 Reuse of On-Site Soils The ability to use on-site soils obtained from the site excavations as structural fills depends on the gradation, moisture content of the soils, and the prevailing weather conditions exist during the grading activities. As the fines content (that portion passing the U.S.No. 200 sieve)of a soil increases, it becomes increasingly sensitive to small changes in moisture content, and adequate compaction becomes more difficult or impossible to achieve. Soils containing more than about 5 percent fines by weight C�ttYlit•Ji'UC GOri�1SLC;ittly Ci�IYI'Ydt�tCti it�ihf'>PC;C('ritllii�;ilCi t'iB�iC;�Wiletl iI1C TYlO1�CUI"�;-CGlii�iii IS itiUic; i:i'lail a�r�7iii ' 2 percent above or below the optimum. The native sand encountered in the test pit locations has percentages passing #200 sieve ranges from 0.7% to 1.3%. Based on these very low fines content the native soils are considered suitable for reusing them as new structural fills during the any weather period, dry or wet. However, it should be noted that the native soils are primarily consisted of gravels, cobbles, and boulders, which may pose some problem during their compaction to achieve 95%of the soils'dry density value determined from the laboratory testing method. Care should be taken during the laying of the native soils to avoid clustering of excessive gravels, cobbles, and builders in any one location, which otherwise would pose problem during the compaction. The top 12 inches of compacted structural fill layer should have a maximum 2 to 3-inch particle diameter and all underlying fill a maximum 4 to 6-inch diameter unless specifically approved by the geotechnical engineer. An experienced geotechnical inspector should be monitoring the fill placement and the compaction to avoid the above issues during the fill operations. '�l� j�/"��PaciFc Geo Engineervng r V .�,��».��.�..�. Geotechnical Engineering Study Yelm Apartments Project No. 13-420 September 23,2013 Page 8 In the event that whether the structural fill materials are to be imported to the site, or if on-site soils are to be reused as structural fill, we recommend that the potential structural fill materials be verified and approved by the project geotechnical engineer prior to their use. However, it should be noted that the native soils are primarily consisted of gravels, cobbles, and boulders, which may pose problem during the compactions of this soils to 95% of the soils' dry density value to be determined based on the laboratory testing method. 5.2.4 Construction Season Due to the low fines content in the native soils, the proposed site development activities can takes place in any weather period, dry or wet. However, construction in wet weather season may contribute some minor erosion related problems in this site. This may particularly happen, when uncontrolled surface runoff is allowed to flow over unprotected excavation areas during the wet winter months. 5.2.5 Structural Fills Structural fill is defined as non-organic soil, free of deleterious materials, and well-graded and free-draining granular material, with a maximum of 5 percent passing the No. 200 sieve by weight, and not exceeding 6 inches for any individual particle. A typical gradation for structural fill is presented in the following table. _ . ,_ . <- , ..._ a�ruci�ura�Fill. - ,, _ _. U.S. Standard Sieve Size Percent Passing by Dry Weight 3 inch 100 3/ inch 50—100 No.4 25—65 No. 10 10—50 No.40 0—20 No. 200 5 Maximum* *Based on the 3/ inch fraction. Other materials may be suitable for use as structural fill provided they are approved by the project geotechnical engineer. Such materials typically used include clean, well-graded sand and gravel (pit-run); clean sand; various mixtures of gravel; crushed rock; controlled-density-fill (CDF); and lean- mix concrete (LMC). Recycled asphalt; concrete, and glass, which are derived from pulverizing the $i2 P/"!CPacific Geo Engineering ��.tl.�,a.e..,�.a,..�..z.,..�.�. Geotechnical Engineering Study Yelm Aparhnents Project No. 13-420 September 23,2013 Page 9 parent materials are also potentially useful as structural fill in certain applications. These materials must be thoroughly crushed to a size deemed appropriate by the geotechnical engineer (usually less than 2 inches). The top 12 inches of compacted structural fill should have a maximum 2 to 3-inch particle diameter and all underlying fill a maximum 4 to 6-inch diameter unless specifically approved by the geotechnical engineer. 5.2.6 Fill Placement and Compaction Requirements Generally, quarry spalls, controlled density fills (CDF), lean mix concrete (LMC) do not require special placement and compaction procedures. In contrast, clean sand, crushed rock, soil mixtures and recycled materials should be placed under special placement and compaction procedures and specifications described here. Such structural fills under structural elements should be placed in uniform loose lifts not exceeding 12 inches in thickness for heavy compactors and 4 inches for hand held compaction equipment. Each lift should be compacted to a minimum of 95 percent of the soil's laboratory maximum dry density as determined by ASTM Test Designation D-1557 (Modified Proctor) method, or to the applicable minimum City or County standard,whichever is the more conservative. The fill should be moisture conditioned such that its final moisture content at the time of compaction should be at or near (typically within about 2 percent) of its optimum moisture content, as determined by the ASTM method. If the fill materials are on the wet side of optimum, they can be dried by periodic windrowing and aeration or by intermixing lime or cement powder to absorb excess moisture. In-place density tests should be performed to verify compaction and moisture content of the fills and base materials. Each lift of fill or base material should be tested and approved by the soils engineer • , . _,. . . . � ;_ ,a .. , �5;i3CiT` �O j3i�l�CIYiCT11 tli SYi�Sr.��t�liC '�11�5.'f�� i �UYdc;ii7�� li ilJ"'ieG(3II'.:ReTlCle(I'Lllcll, ii2tu'�t�IlStiy' i��i5 �L _ ._ performed at a frequency of not less than 1 test per 2,000 square feet of surface area per lift in the building and pavement areas. If field density tests indicate that the last lift of compacted fills has not been achieved the required percent of compaction or the surface is pumping and weaving under loading,then the fill should be scarified,moisture-conditioned to near optimum moisture content,re-compacted,and re-tested prior to placing additional lifts. 5.2.7 Temporary Excavation Slopes The owner and the contractor should be aware that in no case should the excavation slopes be greater than the limits specified in local, state, and federal safety regulations, particularly, the Occupational Safety and Health Administration (OSHA) regulations in the "Construction Standards for Excavations, 29 CFR,part 1926, Subpart P, dated October 31, 1989"of the Federal Register,Volume 54, $t3 p�cPacifc Geo Engineering L wr�.�.�n�...w.w�.w,..n...w.�. Geotechnical Engineering Study Yelm Apartments Project No. 13-420 September 23,2013 Page 10 the United States Department of Labor. As mentioned above,we also recommend that the owner and the contractor should follow the local and state regulations such as WSDOT section 2-093(3)B,Washington Industrial Safety and Health Act (WISHA), Chapter 49.17RCW, and Washington Administrative Code (WAC) Chapter 296-115,Part N. These documents are to better insure the safety of construction worker entering trenches or excavation. It is mandated by these regulations that excavations, whether they are for utility trenches or footings, be constructed in accordance with the guidelines provided in the above documents. We understand that these regulations are being strictly enforced and, if they are not closely followed,both the owner and the contractor could be liable for substantial penalties. Stability of temporary excavations is a function of many factors including the presence of and abundance of groundwater and seepage, the type and density of the various soil strata, the depth of excavation, surcharge loadings adjacent to the excavation, and the length of time and weather conditions while the excavation remains open. It is exceedingly difficult under these unknown and variable circumstances to pre-establish a safe and maintenance-free temporary excavation slope angle at this time of the study. We therefore, strongly recommend that all temporary, as well as permanent, cuts and excavations in excess of 4 feet be examined by a geotechnical engineer during the actual construction to verify that the recommended slope inclinations in this section are appropriate for the actual soil and groundwater seepage conditions exposed in the cuts. If the conditions observed during the actual construction are different than anticipated during this study then, the proper inclination of the excavation and cut slopes or requirements of temporary shoring should be determined depending on the condition of the excavations and the slopes. As a general rule, all temporary soil cuts greater than 4 feet in height associated with site - r-,' ,� �_ _ a „ ; , , . , _ L� . , . , •. _ : i'C:�i2�iixlli� �T'�.1CCdW�IIrYt�'3EiCitiirl C)i. a(i�.�uaft.�� iG�J�f1 t`�di:ii i)t`�JYti�3eT'f�_�ll(jI'@Q [Z7�JI`��Cill �1vi.t�It�Ii1� cftlfi collapse. As for the estimation purposes, in our opinion, for temporary excavations equal to the exploration depths, the side slopes should be laid back at a minimum slope inclination of 3:1 (Horizontal:Vertical)for the native loose to medium dense soil deposits. The recommended inclinations assumes that the ground surface behind the cut slopes is level, that surface loads from equipment and materials are kept a sufficient distance away from the top of the slope. If these assumptions are not valid, we should be contacted for additional recommendations. Flatter slopes may be required if soils are loose or caving and/or water, are encountered along the slope faces. If such conditions occur and the excavation cannot stand by itself, or the excavation slope cannot be flattened because of the space limitations between the excavation line and the boundary of the property,temporary shoring may be considered. The shoring will assist in preventing slopes from failure and provide protection to field personnel during excavation. Because of the diversity available of shoring stems and construction techniques, the design of temporary shoring is most appropriately left up 8� P/='►CPacifc Geo Engineering v c...�,�,,,.�.�.�.�,..�..m.. Geotechnical Engineering Study Yelm Apartments Project No. 13-420 September 23,2013 Page 11 to the contractor engaged to complete the installation. We can assist in designing the shoring system by providing with detailed shoring design parameters including earth-retaining parameters, if required. Where sloped embankments are used, the top of the slopes should be barricaded to prevent vehicles and storage loads within 10 feet of the top of the slopes. Greater setbacks may be necessary when considering heavy vehicles, such as concrete trucks and cranes. If the temporary construction embankments are to be maintained during the rainy season, berms are suggested along the top of the slopes to prevent runoff water from entering the excavation and eroding the slope faces. All temporary slopes should be protected from surface water runoff. The above information is provided solely for the benefit of the owner and other design consultants, and under no circumstances should not be construed to imply that PGE assumes responsibility for construction site safety or the contractor's activities; such responsibility is not being implied and should not be inferred. Therefore, the contractor is solely responsible for designing and constructing stable, temporary excavations and should shore, slope, or bench the sides of the excavations as required to maintain stability of both the excavation sides and bottom. The contractor's "responsible person", as defined in 29 CFR Part 1926, should evaluate the soil exposed in the excavations as part of the contractor's safety procedures. We expect that the excavation can be completed using conventional equipments such as bulldozers or backhoes. 5.2.8 Permanent Cut and Fill Slopes For permanent cut slopes the side slopes should be laid back at a minimum slope inclination of 3:1. Where the above slopes are not feasible, protective facings and/or retaining structures should be considered. Temporary erosion protection described later on in Section 5.8.1 of this report should be used until permanent protection is established. Cut slopes should be re-vegetated as soon as practical to reduce the surface erosion and sloughing. We recommend that any permanent fill slope be constructed no steeper than 2H:1 V. To achieve uniform compaction, we recommend that fill slopes be overbuilt slightly and subsequently cut back to expose well compacted fill. We recommend that a permanent berm, swale, or curb be constructed along the top edge of all permanent slopes to intercept surface flow. Also, a hardy vegetative groundcover should be established as soon as feasible, to further protect the slopes from runoff water erosion. Alternatively,permanent slopes could be armored with quarry spalls or a geosynthetic mat. t3i5 P/'!cPaciFc Geo Engineering �i ..aw�n.b..ma.a.,.wm,..a...� Geotechnical Engineering Study Yelm Aparhnents Project No. 13-420 September 23,2013 Page 12 5.2.9 Construction Dewatering If the regional groundwater levels rise above the planned excavation base during the winter and spring months, the contractor should be prepared to dewater the excavations especially the underground utility trenches. If localized (perched) groundwater or minor seepage is encountered, we anticipate that internal collection ditches directing water inflow to sumpholes and then removal of water by conventional filtered sump pumps will be adequate to temporarily dewater the excavations and to maintain a relatively dry working area for construction purposes. The dewatering must remain in operation to maintain a dry working condition throughout the construction period in the trenches. If severe water conditions encountered, more specialized dewatering techniques, such as vacuum wells, well points, etc., may be needed. However, these more extensive dewatering techniques can lead to settlement of the ground surface in the surrounding vicinity when the groundwater is drawn down. If such dewatering techniques are contemplated a geotechnical engineer should be consulted for specific design and construction recommendations for the excavation areas. 5.2.10 Construction Monitoring Problems associated with earthwork and construction can be avoided or corrected during the progress of the construction if proper inspection and testing services are provided. It is recommended that site preparation activities including but not limited to stripping, clearing, cut and filling, final �._ .._.• •_ n .. � .'e ._ .a�,.� �• __ . • '� 9 1 °. : ., :.: ' ._: . ..-. . . - - �uv�i�ii�i. �3i(:T9tlT'u'CiUY1 �C3I''1"vUiitlallvil, iivlSi"��iAi3; auu ��ivcii7�,Zlf"vCj'iil`villl�t�il Uy $'S�GC�IdI`��utc;�:ittlll';d't inspector. PGE can assist the owner before construction begins to develop an appropriate monitoring and testing plan to aid in accomplishing a fast and cost-effective construction process. A list of items to be inspected as a geotechnical special inspection services are recommend later on in Section 8.0 of this report. 5.3 Foundations Recommendations Spread Footing Based on the subsurface conditions encountered in our test pits, it is our opinion that the proposed buildings can be supported on conventional shallow strip and spread footings. The footings �il(o p/��PaciFc Geo Enyineering r"u .....�,.d,�.�.,..,�,..n...m.. Geotechnical Engineering Study Yelm Aparhnents Project No. 13-420 September 23,2013 Page 13 should be supported on the firm native soils or on new structural fills placed above the properly proofrolled native subgrades as described earlier in Section 5.1 and 5.2 of this report. The new structural fills may be consisted of well-graded sands and gravels, such as `Ballast' per WSDOT Standard Specifications 9-03.9(1), or uniformly graded crushed rock, such as `Crushed Surfacing Base Course' per WSDOT Standard Specifications 9-03.9(3), structural fills described earlier in Structural Fill Table of Section 5.2.5. If the construction takes place during dry summer period and if the optimum moisture content of these soils is maintained during the compaction the on-site silty soil could also be used as building pad materials. All bearing pad soils should be compacted to at least 95 percent of the Modified Proctor maximum dry density value (ASTM:D-1557). Controlled density fills (CDF) and lean mix concrete (LMC) should be used for higher bearing pressure (more than 2500 ps fl footing in order to maintain adequate bearing capacities. The footing bearing pads if constructed with new structural fills need to be extended beyond the actual outer edges of the footings. This is because footing stresses are transferred outward as well as downward into the bearing pad soils. All footing bearing pads should extend horizontally outward from the edge of the footing a distance equal to the bearing pad thickness (1H:1V). For bearing pads composed of controlled density fills(CDF)or lean mix concrete (LMC)the horizontal distance should be at least half of the fill depth. For the design of shallow footing foundation supported on the above-described native soils or properly compacted structural fill we recommend using a maximum net allowable bearing capacity of 1500 pounds per square foot (ps fl. For short-term loads, such as wind and seismic, a 1/3 increase in this . . _v ..-r5-� :,,_ • - t s :e- . • � . . . .' ' f=s- ,.. ..: .:. . ; , . t,�;.- _-..�. �� : i.. uiYJvvBi�its-i,t[�iciCiCy Cc1TI'[7C'{CS�CI.�'i�Y€. 1cC;f7YiTTii�Tii� �iI�1� �:UYfLiTiCiUiiiS ItiV'iiT1�5'YIdF�e d IIlI:ITTY1ll:ii bi%iC1C�'1�7i tL,�—' 15, and 18 inches for 1-, 2-, and 3-strory residential structures as presented in the Table 1805.4.2 of 2003 International Building Code (IBC). We recommend a minimum width of 24 inches for the individual column footings. Based on our settlement potential evaluation in this site, we anticipate that properly designed and constructed foundations supported on the recommended materials should experience total and differential settlements of less than 1 inch and 1/2 inch, respectively. Most of these settlements are expected to occur immediately following the building loads are applied. The predicted settlement values may be expected larger if soft, loose, organic soil is encountered, or if the foundation subgrade is disturbed and becomes soft during construction.The settlement evaluation was done without the aid of any laboratory consolidation test data,and on the basis of our experience with similar types of structures and subsoil conditions. Lateral foundation loads can be resisted by friction between the foundation base and the supporting soil, and by passive earth pressure acting on the face of the embedded portion of the �Ih PGEpaciFc Geo Engineering .�,.d,.�..�,d.a.,...�..�...� Geotechnical Engineering Study Yelm Aparhnents Project No. 13-420 September 23,2013 Page 14 foundation. We recommend using a coefficient of friction of 0.4 to calculate friction between the concrete, and the native soils or the structural fills. For passive earth pressure, the available resistance may be determined using an equivalent fluid pressure of 300 pcf, which includes a factor of safety of 1.5. This value assumes the foundations are cast "neat" against the undisturbed native soils or structural fills placed and compacted as recommended in Section 5.2 of this report. We recommend to disregard the upper 12 inches of soil while computing the passive resistance value because this depth can be affected by weather or disturbed by future grading activity. To achieve the adequate passive resistance from the embedded soils as well as for frost and erosion protection, we recommend that all exterior footings must be embedded at least 18 inches below the final adjacent outside grades consisted of either the undisturbed native soils or structural fills placed and compacted as recommended in Section 5.1 and 5.2 of this report. The interior footings may be embedded only 12 inches below the surrounding slab surface level. Variations in the quality and strength of these potential bearing soils can occur with depth and distance between the test pits. Therefore, careful evaluation of the appropriate bearing materials is recommended at the time of construction to verify their suitability to support the above recommended bearing pressure. We recommend that a PGE representative examine the bearing materials prior to placing forms or rebar. 5.4 Floor Slabs If slab-on-grade option is chosen for the buildings then the slab-on-grade floors should bear on the properly prepared subgrades as discussed earlier in Section 5.1 and 5.2. All soil-supported slab-on- � !` S . '� � . ._('^1S -�. . � . ..:�. _ . ... . . v. :-�-�-:.; , .-:. . . .. �:.r... '�id��`iI'�3r3iS`SiT�'u'ltl"O'�'ciI'UTl`T77'TTl�'E'XT"iyicTflTii"�f i1�lCiVG ytliiS�i vI'i"Stti�ai7it:�I�l'7jJCT�y COiI1�1dC�eCi'Dl��`T"�,iit't"ai'ilYi: After subgrade preparation is completed, the slab should be provided with a capillary break to retard the upward wicking of ground moisture beneath the floor slab. The capillary break would consist of a minimum of 6-inch thick clean, free-draining sand or pea gravel. The structural fill requirements specified in Structural Fill Table of Section 5.2.5 could be used as capillary break materials except that there should be no more than 2 percent of fines passing the no. 200 sieve. Altematively, `Gravel Backfill for Drains' per WSDOT Standard Specifications 9-03.12(4) can be used as capillary break materials. Where moisture by vapor transmission is undesirable, we recommend the use of a vapor barrier such as a layer of durable plastic sheeting (such as Crossstuff, Moistop, or Visqueen) between the capillary break and the floor slab to prevent the upward migration of ground moisture vapors through the slab. During the casting of the slab, care should be taken to avoid puncturing the vapor barrier. At owner's or architecture's discretion, the membrane may be covered with 2 inches of clean, moist sand as a `curing course' to guard against damage during construction and to facilitate uniform curing of the overlying concrete slab. The addition of 2 inches of sand over the vapor barrier is a non-structural recommendation. Based on the subgrade preparation as described in Section 5.1 and 5.2 of this report, a modulus of �g p�EPacific Geo Engineering .�.�.�,.,�,..�...,��,..,�,..�...�. Geot�hnical Engineering Study Yelm Apartments Project No. 13-420 September 23,2013 Page 15 subgrade reaction value of about 150 pounds per cubic inch(pci)can be used to estimate slab deflections, which could arise due to elastic compression of the subgrades. 5.5 Site Drainage Surface Draina�e The final site grades must be such that surface runoff will flow by gravity away from the structures, and should be directed to suitable collection points. We recommend providing a minimum drainage gradient of about 3% for a minimum distance of about 10 feet from the building perimeter. A combination of using positive site surface drainage and capping of the building surroundings by concrete, asphalt, or low permeability silty soils will help minimize or preclude surface water infiltration around the perimeter of the buildings and beneath the floor slabs. Driveways should be graded to direct runoff to catch basins and or other collection facilities. Collected water should be directed to the on-site drainage facilities by means of properly sized smooth walled PVC pipe. Interceptor ditches or trenches or low earthen berms should be installed along the upgrade perimeters of the site to prevent surface water runoff from precipitation or other sources entering the site. Surface water collection facilities should be designed by a professional civil engineer. Footin�Excavation Drain Water must not be allowed to pond in the foundation excavations or on prepared subgrades either during or after construction. If due to the seasonal fluctuations, groundwater seepage is encountered - ... -._ �... � .�, - , :. -_ . __. _ _, .: wltIilll ii7(1iTFYS'CI�:j3iiiS`�`'GV�"T'EljG1TIIT1�I17T""�iit`tZ ilit;''�19ttUTfi v'i C:A'vai�a�l�CiY75TTi/�l�l�``CJ�:'�t2pC:�LCS�VaFC�.��'ti)illGi`" ' to facilitate removal of any collected rainwater, groundwater, or surface runoff, and then direct the water to ditches, and to collect it in prepared sump pits from which the water can be pumped and discharged into an approved storm drainage system. Footing Drain Footing drains should be used where (1) crawl spaces or basements will be below a structure,(2) a slab below the outside grade, and (3)the outside grade does not slope downward from a building. The drains must be laid with a gradient sufficient to promote positive flow to a controlled point of approved discharge. The foundation drains should be tightlined separately from the roof drains to this discharge point. Footing drains should consist of at least 4-inch diameter perforated PVC pipe. The pipe should be placed in a free-draining sand and gravel backfill. Either the pipe or the pipe and free-draining backfill should be wrapped in a non-woven geotextile filter fabric to limit the ingress of fines. Cleanouts should be provided. In the flatter areas of the site the drains should be located on the outside of the spread P�19 ��PaciFc Geo Enginee�ing ��.� Geotechnical Engineering Study Yelm Aparhnents Project No. 13-420 September 23,2013 Page 16 footings. In sloped areas of the site, the footing drains should be installed at the inner base of the lower perimeter footings and at the outer base of the upper and the side perimeter footings. Downspout or Roof Drain These should be installed once the building roof is in place. They should discharge in tightlines to a positive, permanent drain system. Under no circumstances connect these tightlines to the perimeter footing drains. 5.6 Utility Support and Backfill Based on the soils encountered at the site within the exploration depths, the majority of the soils appear to be adequate for supporting utility lines; however, softer soils may be encountered at isolated locations, where, it should be removed to a depth that will provide adequate support for the utility. A major concern with utility lines is generally related to the settlement of trench backfill along utility alignments and pavements. Therefore, it is important that each section of utility be adequately supported on proper bedding material and properly backfilled. It is recommend that utility trenching, installation, and backfilling conform to all applicable Federal, State, and local regulations such as WISHA and OSHA for open excavations. Utility bedding should be placed in accordance with manufacturer's recommendations and local ordinances. Bedding material for rigid and flexible pipe should conform to Sections 9-03.15 and 9-03.16, respectively, of the 1994 WSDOT/APWA (American Public Works Association) Standard Specifications for Road, Bridge, ??�d ��n�ci�al.Cer�tni�ti�n.,-,For ssitP,utilities. ?�cat°� �.TI�«Ai��l t11P ��,P_t'�g �n,�ty_ri�ht-o��!8}�Sy,.i!�.!��?':_. .-� ,..- . :, ,. _ .. ,...�..._ , _ . . ., - . . , -,.. _ . _-. . _ . . . . . ... ._ .. . . , • ,�a._. .. . ._ .. . . , ,----.._ . . and backfill should be completed in accordance with the Pierce County specifications. As a minimum, 5/8 inch pea gravel or clean sand may be used for bedding and backfill materials. The bedding materials should be hand tamped to ensure support is provided around the pipe haunches. Trench backfill should be carefully placed and hand tamped to about 12 inches above the crown of the pipe before any heavy compaction equipment is brought into use. The remainder of the trench backfill should be placed in lifts having a loose thickness of less than 12 inches and compacted to 90 percent of the maximum dry density per ASTM Test Designation D-1557 (Modified Proctor) except for the uppermost foot of backfill which should be compacted to 95 percent of the maximum dry density per ASTM Test Designation D-1557 (Modified Proctor). The utility trenches should not be left open for extended periods to prevent water entry and softening of the subgrade. Should soft soils be encountered at the bottom of the trench, it should be overexcavated and replaced with select fills. As an alternative to undercutting, a Geotextile fabric or crushed rock may be used to stabilize the trench subgrade. Where water is encountered in the trench 82b ��CPacific Geo Engineering G...�.�,,,,a,...s....,.,o.,�...z,..�..�. Geotechnical Engineering Study Yelm Apartments Project No. 13-420 September 23,2013 Page 17 excavations, it should be removed prior to fill placement. Alternatively, quarry spalls or pea gravel could be used below the water level if allowed in the project specifications. 5.7 Pavement Thickness A properly prepared subgrade is very important for the life and performance of the driveway pavements. Therefore, we recommend that all driveway and pavement areas be prepared as described in Section 5.1 and 5.2 of this report. Subgrades should either be comprised of adequately proofrolled competent undisturbed native soils, or be comprised of a minimum of one foot of granular structural fill that is compacted adequately. The structural fill should be compacted to 95 percent of the maximum dry density as determined by Modified Proctor (ASTM Test Designation D-1557). It is possible that some localized areas of yielding and weak subgrade may still exist after this process. If such conditions occur, crushed rock or other qualified materials as addressed in Section 5.2.5 may be used to stabilize these localized areas. We assumed that the traffic would mostly consist of passenger cars and occasional waste management trucks, which is typical for a residential community. Two types of pavement sections may be considered for such traffic,the minimum thicknesses of which are as follows: • 2 inches of Asphalt Concrete (AC) over 2 inches of Crushed Surface Top Course (CSTC) over a 6 inches of Granular Subbase, or • 2 inches of Asphalt Concrete(AC) over 3 inches of Asphalt Treated Base(ATB)material. �-� ��- �.. , ., ; . _ ..._�__.�..... _-. .,._._... .:_ . •.s�.. _ ., . .�.�... � � . --_ �-.. ` ' :>>u �°�'�-'iY1�ia.,itl*.5.��'1b�1 I"'fiii('iii;i ivi tiF u�..r x��„� '�3�L'}�'"u:::i...�T,�-.:::�i"iiT:��fu�i1��t�vvi j� ��<�° „ .�.u�a. and American Public Works Association (APWA) should be applicable to our recommendations that aggregate for AC should meet the Class-B grading requirements as specified in 9-03.8(6). For the Crushed Surfacing Top Course(CSTC), we recommend using imported,clean, crushed rock per WSDOT Standard Specifications 9-03.9(3). For the sub base course, we recommend using imported, clean, well- graded sand and gravel, such as Ballast or Gravel Borrow per WSDOT Standard Specifications 9-03.9(1) and 9-03.14, respectively. For the asphalt treated base course (ATB) the aggregate should be consistent with WSDOT Standard Specifications 9-03.6(2). Long-term performance of the pavement will depend on its surface drainage. A poorly-drained pavement section will deteriorate faster due to the infiltration of surface water into the subgrade soils, thereby reducing their supporting capability. Therefore, we recommend using a minimum surfacing drainage gradient of about 1% to minimize this problem and to enhance the pavement performance. Also,regular maintenance of the pavement must be considered. 62� PGEPaciFc Geo Enginee�ing ��IY�M�G�..L,..a..n Geotechnical Engineering Study Yelm Apartments Project No. 13-420 September 23,2013 Page 18 5.8 Geologic Hazards 5.8.1 Erosion Hazard Uncontrolled surface water with runoff over unprotected site surfaces during construction activities is considered the single most important factor that impacts the erosion potential of a site. The erosion process may be accelerated significantly when factors such as soils with high fines, sloped surface, and wet weather combines together. Taking into consideration of the fines content(0.7 to 13%)in the near surface sands, the project site may have some minor or no impact due to erosion during the wet winter months. The erosion hazard can be mitigated if the mass grading activities and the earthwork can be completed within the dry summer period. Also, measurements such as the control of surface water must be maintained during construction, and a temporary erosion and sedimentary control (TESC) plan, as a part of the Best Management Practices (BMP) must be developed and implemented as well. The TESC plan should include the use of geotextile barriers (silt fences) along any down-slope, straw bales to de- energize downward flow, controlled surface grading, limited work areas, equipment washing, storm drain inlet protection, and sediment traps. Also, vegetation clearing must be kept very limited in this site to reduce the exposed surface areas. A permanent erosion control plan is to be implemented following the completion of the construction. Permanent erosion control measurements such as establishment of landscaping, control of downspouts and surface drains, control of sheet flow over the final slope grades, prevention of discharging water over the final slopes and at the toe of the slope are to be implemented following the completion of the construction. �. �.�� ____ , ,.� � -L,. �x 5.8Z Seismic Hazard Structural design of the buildings at the project site should follow 2003 International Building Code (IBC) standards. Based on our evaluations of the subsurface conditions and review of Table 1615.1.1 of IBC,we interpret the underlying bearing soils to correspond to `C',which refers to very dense soils. According to the IBC standards, the mapped spectral response accelerations SS= 1.5 and S� = 0.5, and corresponding site co-efficient values Fa = 1.0 and F„ = 1.3, respectively, should be used for the design of the buildings. As part of the seismic evaluation of the site, the liquefaction potential of the site was also evaluated. Liquefaction is a phenomenon, which takes place due to the reduction or complete loss of soil strength due to increased pore water pressure during a major earthquake event. Liquefaction primarily affects geologically recent deposits of fine-grained sands that are below the groundwater table. Based on the soil and groundwater conditions, it is our opinion that the on-site soils are not prone to liquefaction, �'L2 ��cPaci�c Geo Engineering L...�,�,�w�.�xg.o.,—nw..n.�..d... Geotechnical Engineering Study Yelm Apartments Project No. 13-420 September 23,2013 Page 19 therefore, potential for widespread liquefaction and its associated hazards over the site during a seismic event is none. Therefore, subsurface conditions do not warrant additional mitigation techniques relating to seismic hazards. 5.8.3 Landslide Hazard Evaluation The subject site is a relatively level ground with some minor undulations, therefore, landslide hazard is not expected in this site. 5.9 Infiltration Potential Evaluation The native soils encountered in the subject site are considered good permeable soils, therefore should be considered conducive for installing the proposed infiltration storm tract. The infiltration potential of the native sands in the proposed storm tract area was evaluated by performing several field percolation tests in test pit TP-1, TP-2, and TP-7 at 4 feet depths below the existing grades following the EPA Falling Head Permeability Test method described in Pierce County Stormwater Design Manual. The average permeability value found from these tests is 12 inches/hr. A factor of safety value of 2 must be used to determine the design infiltration rate. It should be noted that the operational verification testing of the permeability of the native soils must be done in the proposed storm tract area during the construction of the pond. _ .� � ,��. _. . .�>�,, ..�i��W� ��'o��=�g��i�T� , _ ._ The conclusions and recommendations presented in this report are based on a site reconnaissance, a subsurface exploration program, review of pertinent subsurface information, the preliminary design information provided by Larson and Associates, and our understanding of the project. The study was performed using a mutually agreed-upon scope of work. It should be noted that PGE cannot take the responsibility regarding the accuracy of the test pit locations plotted on the attached Site and Soil Exploration Plan prepared by the other consultant. If any of the information considered during this study is not correct or if there are any revisions to the plans for this project, PGE should be notified immediately of such information and the revisions so that necessary amendment of our geotecluiical recommendations can be made. If such information and revisions are not notified to PGE, no responsibility should be implied on PGE for the impact of such information and the revisions on the project. t323 ��Pacifc Geo Enginee�ing -.�.d,�....n..a..,�,..�.,..�.,. Geotechnical Engineering Study Yelm Apartments Project No. 13-420 September 23,2013 Page 20 Variations in subsurface conditions may exist between the locations of the explorations and the actual conditions underlying the site. The nature and the extent of the subsurface variations may not be evident until construction occurs. If any subsurface conditions are encountered at the site that are different from those described in this report, we should be notified immediately to review the applicability of our recommendations if there are any changes in the project scope. This report may be used only by the client and for the purposes stated, within a reasonable time from its issuance. Land use, site conditions (both off and on-site), or others factors including advances in our understanding of applied science, may change over time and could materially affect our findings. Therefore, this report should not be relied upon after 24 months from its issuance. PGE should be notified if the project is delayed by more than 24 months from the date of this report so that we may review to determine that the conclusions and recommendations of this report remain applicable to the changed conditions. The scope of our work does not include services related to construction safety precautions. Our recommendations are not intended to direct the contractors'method,techniques, sequences or procedures, except as specifically described in our report for consideration in design. Additionally, the scope of our work specifically excludes the assessment of environmental characteristics, particularly those involving hazardous substances. This report including its evaluation, conclusions, specifications, recommendations, or professional advice has been prepared for planning and design purposes for specific application to the proposed project in accordance with the generally accepted standards of local practice at the time this � _.. . _ . .. ; . , _. i�r :,- . . _._ , .: 1'i:��3fi`'w`ixa JdiiiLC�Y,: ivv ✓v`&3Tft1'xi.��e7C�T'eSS�-OT'.IlI�7IICti�iS IIi�CiC.° - ._.;: .: �; .. .�.... : , . ,, , This report is the property of our client Mountain Terrace Builders, LLC, and has been prepared for the exclusive use of our client and its authorized representatives for the specific application to the proposed development at the subject site in Yelm,Washington. It is the client's responsibility to see that all parties to this project, including the designer, contractor, subcontractors, etc., are made aware of this report in its entirety. The use of information contained in this report for bidding purposes should be done at the contractor's option and risk. Any party other than the client who wishes to use this report shall notify PGE of such intended use and for permission to copy this report. Based on the intended use of the report, PGE may require that additional work be performed and that and updated report be reissued. Noncompliance with any of these requirements will release PGE from any liability resulting from the use this report. gZ`� p�EPaciFc Geo Engineering ...a,.d,�.�..�,�.�.�..�..z...e.� Geotechnical Engineering Study Yelm Apartrnents Project No. 13-420 September 23,2013 Page 21 7.0 ADDITIONAL SERVICES As the geotechnical engineer of record for the proposed development,PGE can perform a review of the project plans and specifications to verify that the geotechnical recommendations of this report have been properly interpreted and incorporated into the project design and specifications. PGE can also provide geotechnical consultation, material testing, and construction monitoring services during the construction phase of the project. These services are important for the project to confirm that the earthwork and the general site development are in compliance with the general intent of design concepts, specifications, and the geotechnical recommendations presented in this report. Also, participation of PGE during the design and the construction phases will help PGE engineers to make on-site engineering decisions in the event that any variations in subsurface conditions are encountered or any revisions in design and plan are made. S.0 GEOTECHNICAL SPEICAL INSPECTIONS Pacific Geo Engineering (PGE) recommends that the following geotechnical special inspection services to be performed during the construction of the proposed development. According to PGE, the following items should be considered as a minimum but not limited to. • A professional geotechnical engineer should be retained to provide geotechnical consultation, material testing, and construction monitoring services during the construction of the project. � A pre-construction meeting should be held on-site to discuss the geotechnical aspects of the development and the special inspection services to be performed during the construction. ._ _ . . __ ,: , , :� __.�_� �. __._._.,� - . _ < , , _..., -- - -�" S:I:: Sil., �::"�.,,aiivIl 2Gi1V1tICS 111(:ILtC�IiTl� V:.Si�I1vC IiititCa:1Y �v u�ii��ili't�� -t;ui aii(f'�i�t2111�� 21[t`i subgrade preparation for foundation, floor slab, and pavement be monitored by a geotechnical engineer or his representative under the engineer's supervision. • A list of the possible items that require special geotechnical inspection and approval by the geotechnical engineer is as follows: 1. Stripping of topsoils. 2. Removal of unsuitable soils. 3. Proofrolling of any exposed subgrades that are intended to provide direct support for new construction and/or require new fills. 4. Any structural fills to be used in this site, and structural fills placement and its compaction. 5. The temporary or permanent excavation inclinations and excavation stability. 6. The footing bearing materials, bearing capacity value, and the embedment depth of the footings prior to placing forms and rebars. �� P��Pacific Geo Engineering .�.�,�..�..�,..�...�. Geotechnical Engineering Study Yelm Apariments Project No. 13-420 September 23,2013 Page 22 7. Subgrade preparation for soil supported slab-on-grade floors. 8. Subgrade preparation for driveways and pavements. 9. The compaction of the CSBC, CSTC, and the asphalt layers in driveways and pavements. 10. The backfilling and its compaction, and drainage behind the retaining walls. 11. The installation of drainage systems such as footing excavation drain and footing drain, and daylighting of such drains and downspout or roof drains. 12. Bedding and the backfilling materials, and backfilling of utility lines. 13. The verification of the presence of the intended infiltrative soils at the bottom of the infiltration pond and the verification tests of the design infiltration rates of the infiltrative soils, and the installation of the infiltration systems. 14. Buffer distances from the vegetation clearing limit and the vegetation clearing limit. 15. The installation and functioning of the temporary and permanent erosion and sedimentation control plan. 16. The development consideration and construction limitations mentioned in this report. 17. Any other items specified in the approved project plans prepared by other consultants relevant to the geotechnical aspect of the project. 81.tO 01 ,C � � C y �� . W O; ^+ � ' � !� 'w � 4 � V � � � E-� � ,�., � W � � � u E" � � o r�i U [-� � Ho � � � � � � � z � �� U a � ,� � "� ,.a o � W �'' i � � .� - ._ g:,--�- ,. ..-- ._:� .��{-5�-��,. � � � :'� � GQ M � � v O , � N R, ^ � N N � �t' �"' •� � � � i� a Z r..� � o �' .n � � vs p �.+ .� � � � w A A U Of 'i � � C � ,� � W � N � � � ; � ,` � b�A � � . _� � �� ,� w � 4 .� , � : , „�� , � .�y � � �� a� s;: � �: �' �. � � � � +� � � � _� � � �t ; �, � ,j�� . f . � - ��. �5 ` A ��; z � �- � � �" � " i , a w r.��",, � � ��P � a N � � o z � H � � � � � �~ b , H a q � � �:y a� � o � :c � � � � � a � a , ;�,, �: � � � � � ' � � �� a ;� � � wM � � � �E � H r� a a � � � � a � � �, � a�� ., � �� : � �. � � � � � �':� �... "� W z �� a � � s t � O � c�.�� '`' � 4 �e�y�: 3�>�� b "�� .. '�. �, ��L'"a,�`�"`i, + "' ""`�,4i.°xt4 n r"�".a",s 'S�b'", � 'c vl � * + i �":" y �, � '°�.,�"� �° . m'� '�� ,� . �3 s�„� '�,�.; '� � i ti . � >a e °: �.:y� ^� _ � �. �'!' ?� . �.ar� �.,.. �y `�..o.., ._ � � , ,k',� � � ' . ��. s �c�',"c e � � .� �„�.� '"; � . . .�...�°._ > r4^+,��a 1`��.�'t� �4�r �; a . =x �,x�, c. `R� ��4 �,�+ t�, �. s � �: ; ��. —� . �, ,�a�` v`�, w�°�`� *,.e v. ;.��i � �._ �' x�.`�.."t,�"�`�•� � �,,,``�.�`� �s :�. ��'a `�' a��., '" �,�,� p"1 C� s�a� E � '_ w' , �* ,. �'k a� � , �,�. zs� 5� �� '' �� . � � iSr t. °; k i�,�,� e ,yF � a w.L � �r *� � k'b v c '�. '� �: x ��'a '� �' E �. � e " �x '' L6�, � ��` t, �4 . w . � Q M ['� _....�. .w...... .,..__� ,.�..e. , � �._ *,� �� ,g� � � � N . ',�� .;� �� ,. ��. N � y� � s � �� ..;+�'� �' � .r.r � 't��, � L `�t ,x M "�� "*ti` �,- � � � .. ' �*g � e �S'`Y�o �..�� .. � �ti ' .� O +�+ O F�� b � � F�M � j kq. I , R. .,� , h p � � � �y � , � ` ��yk�` . V � M �1 f ' 4�xe � � rl i..'. . � �. . � I�il ��'. yt� ° , *� Y °� - � •, � � � �. � ; O ,.., �� ` � �� ` a A A U �� o � „ ' a�� `�� ,"a. ` .by e k�.�s� > � R� €", `� :� �� € '� °�;�, F ' :R�;� �" ti � � F- � � c H � o 6'� o 0 0 � � a y °' w Qa.� Qa � W � 8 a � � ��8 p�' +`. � ..a.:.� ...,� ..�,. "_ _ , _ ,. _. ____ . �, .:�,.. -�� PaciFc Geo Engineering PGE-- _�� _._.___ . ..�.�,e,�..�..o...�..a...� Yelm Apartments 304 Longmire Street Yelm,Thurston County,Washington Project No. 13-420 September 23,2013 Page A-1 SOIL TEST PIT LOGS TEST PIT — 1 to 9 Date of Excavation:08/06/13 Depth USCS Soil Description Sample No. Moisture -#200% /De th,Ft. Content% 0— 12" Top soils: Brn., Silty Sandy gravelly Soils w/ roots and organics,Sl.Moist,Loose 12"—24" GP Brn., Silty Sandy Soils w/ abundant Gravels & TP-1 13 Cobbles, some roots and organics, Sl. Moist, S-1 @ 1.5' Loose 24"—11' GP Gray Sand w/ trace Silt, & abundant Gravels, TP-1 0.7 Cobbles,Boulders,Sl.Moist,Med.Dense S-2 @ 4' Note: Test pit was terminated at approximately 11 feet below the existing gound surfaces. No groundwater or seepage was encountered within the exploration depth. No signs of mottling were noticed within the exploration depth. Slight caving was noticed within the upper 24"depth,and severe caving in the remaining depth. Field�►ercolation tests were performed(a�4'below ground surfaces in Test Pit_1,2,and 7. .. -» . _ , . _ ,.. . ._._. Percolation rates�IC�T2"'hr. ` �J� r/x lxs� I�'0 uos-0 csa au s �-.�� ,• � �•m•�•� �1M0064U�p�ti0�1 133HS 2�3/�O� �� IIYJS IMJ 1MWl AMl ' i � �W U¢ a F �� O �1� v �M.� c4 O " R o � � " � �!� �� : a µ`�j � � Q�� aW � Nk � l�il.y��e��ii�Bffi��3�Fit°. � ��^j� ��[F�E��i��e��6�� ' I �� #�� f��* ��f al:,��o�s,z g��'�� , i a ''� ' i �.`�I \ ` �' l ---- ,� , �_� �,, � � , �' ; 3 ' I `` �p Y',�,�� R � ��k � � � �4��4 � � � k � �� I � ``;�� i If Q . � I t � � � �� $�� "i`k� 1 2r ; � � -��..>-�;�� ; ,, ; :. . �. � �� ' �O $��y � il�°�� I 1 I . 1. I . 1.. I I I I I' F € E g � I � i i '�,i i � �: b .,. .�i i i i� � �� !�'�.��i �i�� i i i 'i i i � � � � �" !�19� i i � i i i i i � *� �� g'��ii1=��Q '� � i: �e €p4 �!pt ��f ---�� b6Y3��7[ � N �; ��$g ° r�� ((�, ,: Y� � �� j �';I 1 I j � I i < � 1 f I I � j �' 1 5��' � � � � '-__ }I I I I I i � ��y �:... ',;I 1 I 1 I j y �� r i � ..„ '' � � � * I `��' 'i �Cd� � . L____ __ __ _-�� „�, , I � i� `4 __-� � ' "�� i i z-kt: .a.. ' iy :.i r ... � . . .... ,��\�� ,��{�` �� i\ \�-• \ � � � � :. _. _ �bTK�3�� j � �� ee �� '� �E�> ��k�,� ��` '1� .�,�k'� , � ,�� i a� ' v++.> >.. � 1�� `�A �� A� �� AA A�' �`� �� -� � t \ x � �� .+� z'� � i� �\ a��.. � �.� �\� �Z - �� y �^c �\� .t�� a \\ �� . \�� a\,� �t ��>4�. � �i?^ 1R�� \�`i., � � CyL �'E ��A �� * �� <�� -:�x ��`- ��.4 �\ �� "� � '"'�. --.c�rt.�.«-.' +?- -.��.. �� \ ��:'` ��\4 ��yx� �� . al ,� . ��C ��'`�-y'\"`'' �rrL��«.L �.�n1-.e "��1� �-� � �� Yy; ;@ � �` ��`�� `�� ;::� ti�,� �� y�� ` � . �1 ..` ' ��R � �� 3�� .V V�� A •��`. \� .�� `� . �� \ �� \\l��'��` ��` 6p � �ga � \ � ! •�� ,�`� \\��\� \\\�\�\\�i., �\�� p � �i■ \\ � ��:�\� \ � : �� \�� e��$;� � �:��v��`�` �� s�4 a� ��\ � _}(�� ,��\` � ��k��M�� ,,•` ; �� r�� \� .�.� � � \��x`�;�� ' $� �g � �� '�1��`�� '��i� � ' , � �i�:�`,� . � y6y6yfiyg gg9g ,� � G��E�E��!!��'EE�� \�\\�`� _.._. ��R�� `�`��.'�i��t�i� ��a�� sastsatsssssasaaess ��i� � !!!!!lbbbb6lb6bbbb! p -........yeazzaacas � � �S�e:.� . 9 �� EtC�sep:6FExai9�ria � i �i � � ~ __ � � � e e gp ��Y$�� .1 � , � € € e ��pp� d �i` ,i d a ! y �9�� Y R $��\ # � �p � q $ � = a Y�� ' .� i; � Q e�. ' g� � :�,�^ � � \ ar��! '°`;,��+�...� ��'l �� ; —..-��