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2021.0263.SP0004 20210421 Rpt (Storm - Vista) 2210152.10
Civil Engineers ● Structural Engineers ● Landscape Architects ● Community Planners ● Land Surveyors Preliminary Stormwater Report PREPARED FOR: Mill Pond Development, LLC. Fircrest, WA 98466 PROJECT: The Vista at Mill Pond Yelm, Washington 2210152.10 PREPARED BY: J. Matthew Weber, PE Principal DATE: May 2021 Preliminary Stormwater Report PREPARED FOR: Mill Pond Development, LLC. Fircrest, WA 98466 PROJECT: The Vista at Mill Pond Yelm, Washington 2210152.10 PREPARED BY: J. Matthew Weber, PE Principal DATE: May 2021 I hereby state that this Preliminary Stormwater Report for The Vista at Mill Pond has been prepared by me or under my supervision, and meets the standard of care and expertise that is usual and customary in this community for professional engineers. I understand that City of Yelm does not and will not assume liability for the sufficiency, suitability, or performance of drainage facilities prepared by me. 05/05/2021 Preliminary Stormwater Report The Vista at Mill Pond 2210152.10 Table of Contents Section Page 1.0 Project Overview ............................................................................................................................ 0 2.0 Summary of Minimum Requirements .......................................................................................... 0 2.1 MR 1 – Preparation of Stormwater Site Plans .................................................................... 0 2.2 MR 2 - Construction Stormwater Pollution Prevention ....................................................... 0 2.3 MR 3 – Source Control of Pollution ..................................................................................... 0 2.4 MR 4 – Preservation of Natural Drainage Systems and Outfalls ........................................ 1 2.5 MR 5 – Onsite Stormwater Control ..................................................................................... 1 2.6 MR 6 – Runoff Treatment ................................................................................................... 1 2.7 MR 7 – Flow Control ........................................................................................................... 1 2.8 MR 8 – Wetlands Protection ............................................................................................... 1 2.9 MR 9 – Basin/Watershed Planning ..................................................................................... 1 2.10 MR 10 – Operation and Maintenance ................................................................................. 1 3.0 Existing Conditions ....................................................................................................................... 1 4.0 Soils Reports .................................................................................................................................. 1 5.0 Wells ................................................................................................................................................ 2 6.0 Fuel Tanks ...................................................................................................................................... 2 7.0 Sub-Basin Description................................................................................................................... 2 8.0 Analysis of the 100-Year Flood ..................................................................................................... 2 9.0 Aesthetic Considerations for Facilities ....................................................................................... 2 10.0 Facility Sizing and Downstream Analysis ................................................................................... 3 10.1 Conveyance ........................................................................................................................ 3 10.2 Treatment ............................................................................................................................ 3 10.3 Flow Control ........................................................................................................................ 4 10.4 Roof Runoff ......................................................................................................................... 4 11.0 Covenants Dedications, Easements ............................................................................................ 4 12.0 Property Owners Association Articles of Incorporation ............................................................ 4 13.0 Conclusion ...................................................................................................................................... 4 Preliminary Stormwater Report The Vista at Mill Pond 2210152.10 Appendices Appendix A Exhibits A-1 ............. Vicinity Map A-2 ............. NRCS Soil Map A-3 ............. Developed Basin Map A-4 ............. FEMA 100-Year Flood Plain Map Appendix B Conveyance Calculations B-1 ............. Downspout Drywell BMP B-2 ............. WWHM Report Appendix C Geotechnical Report South Sound Geotechnical Consulting, April 20, 2021 Preliminary Stormwater Report The Vista at Mill Pond 2210152.10 1.0 Project Overview The following hydrology report summarizes the storm drainage analysis and design for a 29-lot development located at the southwest corner of 104th Avenue SE and Mill Road SE, in Yelm, Washington. The land is currently developed as a single-family residence. The project includes the addition of 29 residential lots for single-family homes, new roadways and sidewalks, sewer, water services, and stormwater facilities to treat and dispose of the project's stormwater. The proposed roadway features and utilities will be extended from both 104th Avenue SE and Mill Road SE. The individual homes will also have onsite infiltration trenches and/or drywells to infiltrate roof runoff. Frontage improvements along 104th Avenue SE will be required and will include an 11-foot travel lane, 7.5 foot parking lane, 6 foot planter strip and 5 foot sidewa lk. Right of way dedication will be required. The frontage along Mill Road SE was recently improved with new sidewalks as part of a grant awarded to the city. The 6.81-acre site (7.22 acres to centerlines) is located in Section 25, Township 17 North, Range 1 East, W.M. The Thurston County tax parcel numbers associated with the project are 21725111100 and 21725111200. The increased stormwater runoff resulting from the addition of impervious area will be treated and retained in accordance with the most recent Washington State Department of Ecology (DOE) Stormwater Management Manual for Western Washington (SMMWW). 2.0 Summary of Minimum Requirements This project is subject to the SMMWW and is a new development that will add more than 10,000 square feet of impervious surfaces; therefore, all Minimum Requirements (MR) apply to this project. 2.1 MR 1 – Preparation of Stormwater Site Plans This report and the project plans represent the Stormwater Site Plan for this project and satisfy MR 1. 2.2 MR 2 - Construction Stormwater Pollution Prevention A Construction Stormwater Pollution Prevention Plan will be prepared for the site development permit application. 2.3 MR 3 – Source Control of Pollution Pollution source control will be provided for the site by separating roof runoff from pollution generating surfaces. The residential roads should be maintained and cleaned of debris, garbage, and sediment, as required. The Construction SWPPP, to be prepared for the site development application, will provide details on the control of pollution during construction. Preliminary Stormwater Report The Vista at Mill Pond 2210152.10 2.4 MR 4 – Preservation of Natural Drainage Systems and Outfalls The project proposes to infiltrate all stormwater runoff, so all runoff will be retained in the developed condition. There are no natural drainage systems or outfalls to preserve. 2.5 MR 5 – Onsite Stormwater Control This project will meet the LID performance standard. The onsite soils have a high infiltration capacity, and all runoff will be retained onsite through treatment systems and infiltration trenches. The LID Performance Standard will be met by infiltrating all stormwater runoff from the site. Refer to Section 10.0 for facility sizing. 2.6 MR 6 – Runoff Treatment Over 5,000 square feet of pollution generating impervious surface (PGIS) will be added as part of these improvements; therefore, runoff treatment is required for this site. Stormwater runoff from pollution generating surfaces will be conveyed to a combination bio-retention swale and infiltration pond for treatment and disposal through infiltration. The bio-retention portion of the facility is sized to treat at least 91 percent of the total runoff volume as calculated using the Western Washington Hydrology Model (WWHM 2012) meeting the SMMWW treatment requirement. Refer to Section 10.0 for facility sizing. 2.7 MR 7 – Flow Control The project exceeds the thresholds for new development projects and must provide flow control. Proposed flow control is achieved with the use of an infiltration pond that will infiltrate 100 percent of runoff. Refer to Section 10.0 for facility sizing. 2.8 MR 8 – Wetlands Protection To our knowledge, there are no wetlands on or adjacent to the site. 2.9 MR 9 – Basin/Watershed Planning To our knowledge, there are no existing basin plans. 2.10 MR 10 – Operation and Maintenance The stormwater system will be publicly owned and maintained. The City of Yelm shall be responsible for the operation and maintenance of the stormwater facilities. An Operation and Maintenance Plan consisting of maintenance checklists for stormwater management. Will be prepared during the site development application process 3.0 Existing Conditions The site is presently covered with grass and evergreen trees, with slopes generally ranging from 0 to 5 percent with a steeper incline towards the south side of the property. The existing residence and outbuildings will be demolished. Presently, the site infiltrates directly into the ground with no offsite runoff. 4.0 Soils Reports Site soils are identified by the NRCS Web Soil Survey as Spanaway gravelly sandy loam and Spanaway stony sandy loam, a Type A soil. This soil is characterized as very deep, somewhat excessively drained. Preliminary Stormwater Report The Vista at Mill Pond 2210152.10 Soil test holes were dug in the vicinity of the proposed project stormwater facility and observations confirm that the soil types match the SCS soil description. A soil log map showing the location of the test holes is included in the geotechnical report. Geotechnical Testing Laboratory observed an infiltration rate of greater than 100 in/hr. Design rate of 45 in/hr is recommended by Geotechnical Testing Laboratory. A design rate of 20 in/hr was utilized for preliminary stormwater calculations. Please see Appendix C for the complete South Sound Geotechnical Consulting report 5.0 Wells There is a private well located on the property This well is planned to be abandoned prior to final plat. Each lot will be served by the City of Yelm STEP collection system. The holding tank will be maintained by the City and pumped on a regular basis. Domestic water will be provided by the City of Yelm water distribution system. 6.0 Fuel Tanks No fuel tanks were observed at the project site. 7.0 Sub-Basin Description Review of available GIS topographic information indicates that there is minimal potential of runoff from pervious surfaces of adjacent properties. Runoff from a portion of the existing Mill Road SE and 104th Ave. SE will be collected and managed in the proposed stormwater facilities The entire proposed project runoff will be infiltrated on-site. To our knowledge there are no existing or anticipated impacts to the downstream basin area. 8.0 Analysis of the 100-Year Flood Federal Emergency Management Agency (FEMA) mapping does not indicate flooding in the immediate area. Please see the exhibit in Appendix A-4. 9.0 Aesthetic Considerations for Facilities The proposed bio-retention/infiltration facility will be located within the propose open space tract. The facility is designed with a maximum storage depth of 3 feet and side slopes will not exceed 3:1. The south side of the facility is shown with 5:1 slopes to blend in with the surround landscaped area and provide easier maintenance access. Preliminary Stormwater Report The Vista at Mill Pond 2210152.10 10.0 Facility Sizing and Downstream Analysis The project site is modelled as a single basin for stormwater facility sizing. Proposed impervious surfaces associated with the existing and proposed roads were calculated based on the concept site plan layout. An additional 500 square feet of impervious surfaces per lot was assumed for driveways (1,500 sf for flag lots). Roof area is assumed to be 2,500 square feet per lot. The roof runoff will be infiltrated on each lot; therefore, this area is removed from the basin area tributary to the proposed bio- retention/infiltration facility. The stormwater system was sized and analyzed using WWHM. The following table summarizes the existing and proposed areas tributary to the proposed stormwater facility. Area (sf) Area (ac) Total Basin Area 303,026 6.957 Roof Area 72,500 1.664 Total Area to Facility (Total – roof) 230,526 5.292 Offsite Pavement & Sidewalk 12,234 0.281 Onsite Pavement 38,411 0.882 Onsite Sidewalk 4,430 0.102 Onsite Driveway 17,500 0.402 Lawn/Landscape 157,951 3.626 9.1 Conveyance The conceptual conveyance system consists of catch basins and under-ground pipe. Conveyance calculations will be provided during the site development application process. 9.2 Treatment Runoff quality control is provided by a bio-retention swale with a minimum of 18 inches of treatment soil mix that extends along the side slopes 1 foot above the bottom of the cell. The bottom width is 4 feet with a length of 120 feet, side slopes are 3:1, and the maximum design water depth is 6 inches. Runoff is introduced to the swale from the conveyance pipe s provided with a rock pad protection. The standard bio-retention soil mix will be utilized, which has a soil infiltration rate of 12 inches per hour. Based on the size of the tributary area, a Ksat Safety Factor of 4 is applied to the treatment soil infiltration, resulting in a design rate of 3 inches per hour. As discussed in Section 4.0, a design infiltration rate of 20 inches per hour was used for the underlying soil. Preliminary Stormwater Report The Vista at Mill Pond 2210152.10 The bio-retention facility will receive runoff for basins with greater than 5,000 square feet of PGIS and is therefore designed so that the bottom of the treatment soil mix is a minimum of 3 feet above the seasonal high groundwater elevation. The bioretention area is provided with a maximum 6 inches of ponding prior to primary overflow. Given a design infiltration rate of 3 inches per hour, the design drawdown time is 2 hours, which is less than the maximum allowed 24-hour drawdown. The WWHM models shows that the propose bio-retention swale will infiltrate 97.09 percent of the total runoff through the treatment soil mix exceeded the minimum required of 91%. Runoff volumes that exceed the bio-retention capacity overflows to the adjacent un-lined infiltration portion of the facility. 9.3 Flow Control Stormwater runoff enters the infiltration portion of the stormwater facility as overflow along the entire length of the swale. The infiltration pond provides a 4 ft by 120 ft un-lined infiltration surface with a design infiltration rate of 20 in/hr. WWHM results show that the infiltration pond can infiltrate 100 percent of the tributary runoff with a maximum storage depth of 2.5 feet. 9.4 Roof Runoff Stormwater for the roof area of the homes will be infiltrated in individual drywells. The drywells will be sized in accordance with SMMWW Volume 3, Chapter 3, Section 3.1.1 - BMP T5.10A Downspout Full Infiltration System. See Appendix B-1 for the roof downspout system detail. 10.0 Covenants Dedications, Easements The storm management facility for this site will remain privately owned and maintained. A maintenance agreement should be executed to ensure future maintenance of the facilities. 11.0 Property Owners Association Articles of Incorporation Not applicable. 12.0 Conclusion The proposed project involves site improvements associated with a 29-lot development. The project includes clearing, grading, erosion control, utility improvements, and stormwater management facilities. The site, as proposed, will meet the requirements of the most recent Department of Ecology Stormwater Management Manual for Western Washington (SMMWW). Preliminary Stormwater Report The Vista at Mill Pond 2210152.10 This report and associated plans have been prepared within the guidelines established by the City of Yelm for stormwater management. This analysis is based on data and records either supplied to or obtained by AHBL. These documents are referenced within the text of the analysis. The analysis has been prepared using procedures and practices within the standard accepted practices of the industry. AHBL, Inc. Matt Weber, PE Principal May 2021 Preliminary Stormwater Report The Vista at Mill Pond 2210152.10 Appendix A Exhibits A-1 .................... Vicinity Map A-2 .................... NRCS Soil Map A-3 .................... Developed Basin Map A-4 .................... FEMA 100-Year Flood Plain Map 2215 N. 30th Street, #300 Tacoma, WA 98403 253.383.2422 TEL 253.383.2572 FAX www.ahbl.com THE VISTA AT MILL POND VICINITY MAP A-1 N VICINITY MAP NOT TO SCALE SITE 104TH AVE SE MILL RD SEN VICINITY MAP NOT TO SCALE SITE 104TH AVE SE MILL RD SE Soil Map—Thurston County Area, Washington (The Vista at Mill Pond) Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 4/21/2021 Page 1 of 351979505197980519801051980405198070519810051981305197950519798051980105198040519807051981005198130529320529350529380529410529440529470529500529530529560529590 529320 529350 529380 529410 529440 529470 529500 529530 529560 529590 46° 56' 9'' N 122° 36' 53'' W46° 56' 9'' N122° 36' 39'' W46° 56' 3'' N 122° 36' 53'' W46° 56' 3'' N 122° 36' 39'' WN Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 10N WGS84 0 50 100 200 300 Feet 0 20 40 80 120 Meters Map Scale: 1:1,360 if printed on A landscape (11" x 8.5") sheet. Soil Map may not be valid at this scale. A-2 MAP LEGEND MAP INFORMATION Area of Interest (AOI) Area of Interest (AOI) Soils Soil Map Unit Polygons Soil Map Unit Lines Soil Map Unit Points Special Point Features Blowout Borrow Pit Clay Spot Closed Depression Gravel Pit Gravelly Spot Landfill Lava Flow Marsh or swamp Mine or Quarry Miscellaneous Water Perennial Water Rock Outcrop Saline Spot Sandy Spot Severely Eroded Spot Sinkhole Slide or Slip Sodic Spot Spoil Area Stony Spot Very Stony Spot Wet Spot Other Special Line Features Water Features Streams and Canals Transportation Rails Interstate Highways US Routes Major Roads Local Roads Background Aerial Photography The soil surveys that comprise your AOI were mapped at 1:24,000. Warning: Soil Map may not be valid at this scale. Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed scale. Please rely on the bar scale on each map sheet for map measurements. Source of Map: Natural Resources Conservation Service Web Soil Survey URL: Coordinate System: Web Mercator (EPSG:3857) Maps from the Web Soil Survey are based on the Web Mercator projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required. This product is generated from the USDA-NRCS certified data as of the version date(s) listed below. Soil Survey Area: Thurston County Area, Washington Survey Area Data: Version 14, Jun 4, 2020 Soil map units are labeled (as space allows) for map scales 1:50,000 or larger. Date(s) aerial images were photographed: Jul 18, 2020—Jul 20, 2020 The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident. Soil Map—Thurston County Area, Washington (The Vista at Mill Pond) Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 4/21/2021 Page 2 of 3 Map Unit Legend Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI 74 Nisqually loamy fine sand, 3 to 15 percent slopes 0.1 1.1% 110 Spanaway gravelly sandy loam, 0 to 3 percent slopes 4.3 65.1% 113 Spanaway stony sandy loam, 3 to 15 percent slopes 2.2 33.7% Totals for Area of Interest 6.6 100.0% Soil Map—Thurston County Area, Washington The Vista at Mill Pond Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 4/21/2021 Page 3 of 3 DEVELOPED BASIN MAP A-3 Vista Developed Basin Boundary SITE SITE A-4 Preliminary Stormwater Report The Vista at Mill Pond 2210152.10 Appendix B Conveyance Calculations B-1 .................... Downspout Drywell BMP B-2 .................... WWHM Report Volume III – Hydrologic Analysis and Flow Control BMPs – December 2014 3-9 Source: King County Figure 3.1.4 - Typical Downspout Infiltration Drywell B-1 WWHM2012 PROJECT REPORT B-2 2210152_Vista 5/4/2021 5:52:24 PM Page 2 General Model Information Project Name:2210152_Vista Site Name:Vista Site Address:104th City:Yelm Report Date:5/4/2021 Gage:Lake Lawrence Data Start:1955/10/01 Data End:2008/09/30 Timestep:15 Minute Precip Scale:0.857 Version Date:2019/09/13 Version:4.2.17 POC Thresholds Low Flow Threshold for POC1:50 Percent of the 2 Year High Flow Threshold for POC1:50 Year 2210152_Vista 5/4/2021 5:52:24 PM Page 3 Landuse Basin Data Predeveloped Land Use 2210152_Vista 5/4/2021 5:52:24 PM Page 4 Mitigated Land Use Basin 1 Bypass:No GroundWater:No Pervious Land Use acre A B, Lawn, Flat 3.626 Pervious Total 3.626 Impervious Land Use acre ROADS FLAT 0.281 ROADS MOD 0.882 DRIVEWAYS MOD 0.402 SIDEWALKS MOD 0.102 Impervious Total 1.667 Basin Total 5.293 Element Flows To: Surface Interflow Groundwater Surface retention 1 Surface retention 1 2210152_Vista 5/4/2021 5:52:24 PM Page 5 Routing Elements Predeveloped Routing 2210152_Vista 5/4/2021 5:52:24 PM Page 6 Mitigated Routing Bioretention 1 Bottom Length: 120.00 ft. Bottom Width: 4.00 ft. Material thickness of first layer: 1.5 Material type for first layer: SMMWW 12 in/hr Material thickness of second layer: 0 Material type for second layer: Sand Material thickness of third layer: 0 Material type for third layer: GRAVEL Infiltration On Infiltration rate:20 Infiltration safety factor:1 Wetted surface area On Total Volume Infiltrated (ac-ft.):294.797 Total Volume Through Riser (ac-ft.):8.849 Total Volume Through Facility (ac-ft.):303.646 Percent Infiltrated:97.09 Total Precip Applied to Facility:6.259 Total Evap From Facility:1.556 Underdrain not used Discharge Structure Riser Height:0.5 ft. Riser Diameter:24 in. Element Flows To: Outlet 1 Outlet 2 Trapezoidal Pond 1 Bioretention Hydraulic Table Stage(feet)Area(ac.)Volume(ac-ft.)Discharge(cfs)Infilt(cfs) 0.0000 0.0385 0.0000 0.0000 0.0000 0.0330 0.0382 0.0002 0.0000 0.0000 0.0659 0.0375 0.0003 0.0000 0.0000 0.0989 0.0369 0.0005 0.0000 0.0000 0.1319 0.0363 0.0007 0.0000 0.0000 0.1648 0.0356 0.0009 0.0002 0.0002 0.1978 0.0350 0.0012 0.0003 0.0003 0.2308 0.0343 0.0014 0.0005 0.0005 0.2637 0.0337 0.0016 0.0007 0.0007 0.2967 0.0331 0.0018 0.0009 0.0009 0.3297 0.0325 0.0021 0.0012 0.0012 0.3626 0.0318 0.0023 0.0016 0.0016 0.3956 0.0312 0.0026 0.0020 0.0020 0.4286 0.0306 0.0029 0.0025 0.0025 0.4615 0.0300 0.0032 0.0031 0.0031 0.4945 0.0293 0.0035 0.0038 0.0038 0.5275 0.0287 0.0038 0.0046 0.0046 0.5604 0.0281 0.0041 0.0055 0.0055 0.5934 0.0275 0.0044 0.0065 0.0065 0.6264 0.0269 0.0047 0.0076 0.0076 0.6593 0.0263 0.0051 0.0089 0.0089 0.6923 0.0257 0.0054 0.0103 0.0103 0.7253 0.0251 0.0058 0.0118 0.0118 0.7582 0.0244 0.0061 0.0135 0.0135 0.7912 0.0238 0.0065 0.0154 0.0154 2210152_Vista 5/4/2021 5:52:24 PM Page 7 0.8242 0.0232 0.0069 0.0174 0.0174 0.8571 0.0226 0.0073 0.0197 0.0197 0.8901 0.0220 0.0077 0.0221 0.0221 0.9231 0.0214 0.0081 0.0247 0.0247 0.9560 0.0209 0.0085 0.0276 0.0276 0.9890 0.0203 0.0089 0.0306 0.0306 1.0220 0.0197 0.0094 0.0340 0.0340 1.0549 0.0191 0.0098 0.0375 0.0375 1.0879 0.0185 0.0103 0.0413 0.0413 1.1209 0.0179 0.0107 0.0454 0.0454 1.1538 0.0173 0.0112 0.0497 0.0497 1.1868 0.0167 0.0117 0.0544 0.0544 1.2198 0.0162 0.0122 0.0593 0.0593 1.2527 0.0156 0.0127 0.0646 0.0646 1.2857 0.0150 0.0132 0.0702 0.0702 1.3187 0.0144 0.0137 0.0761 0.0761 1.3516 0.0139 0.0143 0.0823 0.0823 1.3846 0.0133 0.0148 0.0890 0.0890 1.4176 0.0127 0.0154 0.0959 0.0959 1.4505 0.0121 0.0159 0.1033 0.1033 1.4835 0.0116 0.0165 0.1109 0.1109 1.5000 0.0110 0.0168 0.1553 0.1553 Bioretention Hydraulic Table Stage(feet)Area(ac.)Volume(ac-ft.)Discharge(cfs)To Amended(cfs)Infilt(cfs) 1.5000 0.0385 0.0168 0.0000 0.0333 0.0130 1.5330 0.0391 0.0181 0.0000 0.0333 0.0261 1.5659 0.0398 0.0194 0.0000 0.0348 0.0392 1.5989 0.0404 0.0207 0.0000 0.0355 0.0523 1.6319 0.0411 0.0220 0.0000 0.0363 0.0655 1.6648 0.0417 0.0234 0.0000 0.0370 0.0787 1.6978 0.0424 0.0248 0.0000 0.0377 0.0919 1.7308 0.0431 0.0262 0.0000 0.0385 0.1052 1.7637 0.0437 0.0276 0.0000 0.0392 0.1185 1.7967 0.0444 0.0291 0.0000 0.0399 0.1318 1.8297 0.0450 0.0305 0.0000 0.0407 0.1452 1.8626 0.0457 0.0320 0.0000 0.0414 0.1587 1.8956 0.0464 0.0335 0.0000 0.0421 0.1721 1.9286 0.0470 0.0351 0.0000 0.0429 0.1856 1.9615 0.0477 0.0366 0.0000 0.0436 0.1991 1.9945 0.0484 0.0382 0.0000 0.0443 0.2127 2.0275 0.0490 0.0398 0.0000 0.0444 0.2263 2.0604 0.0497 0.0415 0.0000 0.0444 0.2399 2.0934 0.0504 0.0431 0.0000 0.0444 0.2536 2.1264 0.0511 0.0448 0.0000 0.0444 0.2673 2.1593 0.0518 0.0465 0.0000 0.0444 0.2811 2.1923 0.0524 0.0482 0.0000 0.0444 0.2948 2.2253 0.0531 0.0499 0.0000 0.0444 0.3087 2.2582 0.0538 0.0517 0.0000 0.0444 0.3225 2.2912 0.0545 0.0535 0.0000 0.0444 0.3364 2.3242 0.0552 0.0553 0.0000 0.0444 0.3503 2.3571 0.0559 0.0571 0.0000 0.0444 0.3643 2.3901 0.0566 0.0590 0.0000 0.0444 0.3783 2.4231 0.0573 0.0609 0.0000 0.0444 0.3923 2.4560 0.0580 0.0628 0.0000 0.0444 0.4064 2.4890 0.0587 0.0647 0.0000 0.0444 0.4205 2.5220 0.0594 0.0666 0.0000 0.0444 0.4347 2.5549 0.0601 0.0686 0.0000 0.0444 0.4488 2210152_Vista 5/4/2021 5:52:24 PM Page 8 2.5879 0.0608 0.0706 0.0000 0.0444 0.4631 2.6209 0.0615 0.0726 0.0000 0.0444 0.4773 2.6538 0.0622 0.0746 0.0000 0.0444 0.4916 2.6868 0.0629 0.0767 0.0000 0.0444 0.5059 2.7198 0.0636 0.0788 0.0000 0.0444 0.5203 2.7527 0.0643 0.0809 0.0000 0.0444 0.5347 2.7857 0.0650 0.0830 0.0000 0.0444 0.5491 2.8187 0.0657 0.0852 0.0000 0.0444 0.5636 2.8516 0.0664 0.0874 0.0000 0.0444 0.5781 2.8846 0.0672 0.0896 0.0000 0.0444 0.5926 2.9176 0.0679 0.0918 0.0000 0.0444 0.6072 2.9505 0.0686 0.0940 0.0000 0.0444 0.6218 2.9835 0.0693 0.0963 0.0000 0.0444 0.6292 3.0000 0.0697 0.0975 0.0000 0.0444 0.0000 2210152_Vista 5/4/2021 5:52:24 PM Page 9 Surface retention 1 Element Flows To: Outlet 1 Outlet 2 Trapezoidal Pond 1 Bioretention 1 2210152_Vista 5/4/2021 5:52:24 PM Page 10 Trapezoidal Pond 1 Bottom Length:120.00 ft. Bottom Width:4.00 ft. Depth:4 ft. Volume at riser head:0.1064 acre-feet. Infiltration On Infiltration rate:20 Infiltration safety factor:1 Wetted surface area On Total Volume Infiltrated (ac-ft.):8.973 Total Volume Through Riser (ac-ft.):0 Total Volume Through Facility (ac-ft.):8.973 Percent Infiltrated:100 Total Precip Applied to Facility:0.128 Total Evap From Facility:0.001 Side slope 1:3 To 1 Side slope 2:3 To 1 Side slope 3:5 To 1 Side slope 4:3 To 1 Discharge Structure Riser Height:2.5 ft. Riser Diameter:24 in. Element Flows To: Outlet 1 Outlet 2 Pond Hydraulic Table Stage(feet)Area(ac.)Volume(ac-ft.)Discharge(cfs)Infilt(cfs) 0.0000 0.011 0.000 0.000 0.000 0.0444 0.012 0.000 0.000 0.242 0.0889 0.013 0.001 0.000 0.262 0.1333 0.014 0.001 0.000 0.283 0.1778 0.015 0.002 0.000 0.303 0.2222 0.016 0.003 0.000 0.324 0.2667 0.017 0.003 0.000 0.345 0.3111 0.018 0.004 0.000 0.366 0.3556 0.019 0.005 0.000 0.387 0.4000 0.020 0.006 0.000 0.408 0.4444 0.021 0.007 0.000 0.429 0.4889 0.022 0.008 0.000 0.450 0.5333 0.023 0.009 0.000 0.471 0.5778 0.024 0.010 0.000 0.492 0.6222 0.025 0.011 0.000 0.514 0.6667 0.026 0.012 0.000 0.535 0.7111 0.027 0.013 0.000 0.557 0.7556 0.028 0.014 0.000 0.579 0.8000 0.029 0.016 0.000 0.600 0.8444 0.030 0.017 0.000 0.622 0.8889 0.032 0.019 0.000 0.644 0.9333 0.033 0.020 0.000 0.666 0.9778 0.034 0.021 0.000 0.688 1.0222 0.035 0.023 0.000 0.711 1.0667 0.036 0.025 0.000 0.733 1.1111 0.037 0.026 0.000 0.755 1.1556 0.038 0.028 0.000 0.778 1.2000 0.039 0.030 0.000 0.800 2210152_Vista 5/4/2021 5:52:24 PM Page 11 1.2444 0.040 0.031 0.000 0.823 1.2889 0.042 0.033 0.000 0.846 1.3333 0.043 0.035 0.000 0.869 1.3778 0.044 0.037 0.000 0.892 1.4222 0.045 0.039 0.000 0.915 1.4667 0.046 0.041 0.000 0.938 1.5111 0.047 0.043 0.000 0.961 1.5556 0.048 0.045 0.000 0.984 1.6000 0.050 0.048 0.000 1.008 1.6444 0.051 0.050 0.000 1.031 1.6889 0.052 0.052 0.000 1.055 1.7333 0.053 0.054 0.000 1.078 1.7778 0.054 0.057 0.000 1.102 1.8222 0.055 0.059 0.000 1.126 1.8667 0.057 0.062 0.000 1.150 1.9111 0.058 0.064 0.000 1.174 1.9556 0.059 0.067 0.000 1.198 2.0000 0.060 0.070 0.000 1.222 2.0444 0.061 0.072 0.000 1.246 2.0889 0.063 0.075 0.000 1.270 2.1333 0.064 0.078 0.000 1.295 2.1778 0.065 0.081 0.000 1.319 2.2222 0.066 0.084 0.000 1.344 2.2667 0.067 0.087 0.000 1.369 2.3111 0.069 0.090 0.000 1.393 2.3556 0.070 0.093 0.000 1.418 2.4000 0.071 0.096 0.000 1.443 2.4444 0.072 0.099 0.000 1.468 2.4889 0.074 0.103 0.000 1.493 2.5333 0.075 0.106 0.129 1.518 2.5778 0.076 0.109 0.460 1.544 2.6222 0.077 0.113 0.905 1.569 2.6667 0.079 0.116 1.438 1.595 2.7111 0.080 0.120 2.044 1.620 2.7556 0.081 0.123 2.709 1.646 2.8000 0.082 0.127 3.421 1.672 2.8444 0.084 0.131 4.168 1.697 2.8889 0.085 0.135 4.939 1.723 2.9333 0.086 0.138 5.721 1.749 2.9778 0.088 0.142 6.501 1.775 3.0222 0.089 0.146 7.268 1.802 3.0667 0.090 0.150 8.008 1.828 3.1111 0.092 0.154 8.711 1.854 3.1556 0.093 0.158 9.367 1.881 3.2000 0.094 0.163 9.967 1.907 3.2444 0.095 0.167 10.50 1.934 3.2889 0.097 0.171 10.98 1.960 3.3333 0.098 0.175 11.38 1.987 3.3778 0.099 0.180 11.73 2.014 3.4222 0.101 0.184 12.02 2.041 3.4667 0.102 0.189 12.28 2.068 3.5111 0.103 0.193 12.66 2.095 3.5556 0.105 0.198 12.94 2.122 3.6000 0.106 0.203 13.21 2.150 3.6444 0.108 0.208 13.47 2.177 3.6889 0.109 0.212 13.73 2.205 3.7333 0.110 0.217 13.99 2.232 3.7778 0.112 0.222 14.24 2.260 2210152_Vista 5/4/2021 5:52:24 PM Page 12 3.8222 0.113 0.227 14.48 2.288 3.8667 0.114 0.232 14.72 2.316 3.9111 0.116 0.237 14.96 2.343 3.9556 0.117 0.243 15.20 2.371 4.0000 0.119 0.248 15.43 2.400 4.0444 0.120 0.253 15.65 2.428 2210152_Vista 5/4/2021 5:52:24 PM Page 13 Analysis Results POC 1 POC #1 was not reported because POC must exist in both scenarios and both scenarios must have been run. 2210152_Vista 5/4/2021 5:52:24 PM Page 14 Model Default Modifications Total of 0 changes have been made. PERLND Changes No PERLND changes have been made. IMPLND Changes No IMPLND changes have been made. 2210152_Vista 5/4/2021 5:52:24 PM Page 15 Appendix Predeveloped Schematic 2210152_Vista 5/4/2021 5:52:25 PM Page 16 Mitigated Schematic 2210152_Vista 5/4/2021 5:52:25 PM Page 17 Predeveloped UCI File 2210152_Vista 5/4/2021 5:52:25 PM Page 18 Mitigated UCI File RUN GLOBAL WWHM4 model simulation START 1955 10 01 END 2008 09 30 RUN INTERP OUTPUT LEVEL 3 0 RESUME 0 RUN 1 UNIT SYSTEM 1 END GLOBAL FILES <File> <Un#> <-----------File Name------------------------------>*** <-ID-> *** WDM 26 2210152_Vista.wdm MESSU 25 Mit2210152_Vista.MES 27 Mit2210152_Vista.L61 28 Mit2210152_Vista.L62 30 POC2210152_Vista1.dat END FILES OPN SEQUENCE INGRP INDELT 00:15 PERLND 7 IMPLND 1 IMPLND 2 IMPLND 6 IMPLND 9 GENER 2 RCHRES 1 RCHRES 2 RCHRES 3 COPY 1 COPY 501 DISPLY 1 END INGRP END OPN SEQUENCE DISPLY DISPLY-INFO1 # - #<----------Title----------->***TRAN PIVL DIG1 FIL1 PYR DIG2 FIL2 YRND 1 Trapezoidal Pond 1 MAX 1 2 30 9 END DISPLY-INFO1 END DISPLY COPY TIMESERIES # - # NPT NMN *** 1 1 1 501 1 1 END TIMESERIES END COPY GENER OPCODE # # OPCD *** 2 24 END OPCODE PARM # # K *** 2 0. END PARM END GENER PERLND GEN-INFO <PLS ><-------Name------->NBLKS Unit-systems Printer *** # - # User t-series Engl Metr *** in out *** 7 A/B, Lawn, Flat 1 1 1 1 27 0 END GEN-INFO *** Section PWATER*** ACTIVITY 2210152_Vista 5/4/2021 5:52:25 PM Page 19 <PLS > ************* Active Sections ***************************** # - # ATMP SNOW PWAT SED PST PWG PQAL MSTL PEST NITR PHOS TRAC *** 7 0 0 1 0 0 0 0 0 0 0 0 0 END ACTIVITY PRINT-INFO <PLS > ***************** Print-flags ***************************** PIVL PYR # - # ATMP SNOW PWAT SED PST PWG PQAL MSTL PEST NITR PHOS TRAC ********* 7 0 0 4 0 0 0 0 0 0 0 0 0 1 9 END PRINT-INFO PWAT-PARM1 <PLS > PWATER variable monthly parameter value flags *** # - # CSNO RTOP UZFG VCS VUZ VNN VIFW VIRC VLE INFC HWT *** 7 0 0 0 0 0 0 0 0 0 0 0 END PWAT-PARM1 PWAT-PARM2 <PLS > PWATER input info: Part 2 *** # - # ***FOREST LZSN INFILT LSUR SLSUR KVARY AGWRC 7 0 5 0.8 400 0.05 0.3 0.996 END PWAT-PARM2 PWAT-PARM3 <PLS > PWATER input info: Part 3 *** # - # ***PETMAX PETMIN INFEXP INFILD DEEPFR BASETP AGWETP 7 0 0 2 2 0 0 0 END PWAT-PARM3 PWAT-PARM4 <PLS > PWATER input info: Part 4 *** # - # CEPSC UZSN NSUR INTFW IRC LZETP *** 7 0.1 0.5 0.25 0 0.7 0.25 END PWAT-PARM4 PWAT-STATE1 <PLS > *** Initial conditions at start of simulation ran from 1990 to end of 1992 (pat 1-11-95) RUN 21 *** # - # *** CEPS SURS UZS IFWS LZS AGWS GWVS 7 0 0 0 0 3 1 0 END PWAT-STATE1 END PERLND IMPLND GEN-INFO <PLS ><-------Name-------> Unit-systems Printer *** # - # User t-series Engl Metr *** in out *** 1 ROADS/FLAT 1 1 1 27 0 2 ROADS/MOD 1 1 1 27 0 6 DRIVEWAYS/MOD 1 1 1 27 0 9 SIDEWALKS/MOD 1 1 1 27 0 END GEN-INFO *** Section IWATER*** ACTIVITY <PLS > ************* Active Sections ***************************** # - # ATMP SNOW IWAT SLD IWG IQAL *** 1 0 0 1 0 0 0 2 0 0 1 0 0 0 6 0 0 1 0 0 0 9 0 0 1 0 0 0 END ACTIVITY PRINT-INFO <ILS > ******** Print-flags ******** PIVL PYR # - # ATMP SNOW IWAT SLD IWG IQAL ********* 1 0 0 4 0 0 0 1 9 2 0 0 4 0 0 0 1 9 6 0 0 4 0 0 0 1 9 2210152_Vista 5/4/2021 5:52:25 PM Page 20 9 0 0 4 0 0 0 1 9 END PRINT-INFO IWAT-PARM1 <PLS > IWATER variable monthly parameter value flags *** # - # CSNO RTOP VRS VNN RTLI *** 1 0 0 0 0 0 2 0 0 0 0 0 6 0 0 0 0 0 9 0 0 0 0 0 END IWAT-PARM1 IWAT-PARM2 <PLS > IWATER input info: Part 2 *** # - # *** LSUR SLSUR NSUR RETSC 1 400 0.01 0.1 0.1 2 400 0.05 0.1 0.08 6 400 0.05 0.1 0.08 9 400 0.05 0.1 0.08 END IWAT-PARM2 IWAT-PARM3 <PLS > IWATER input info: Part 3 *** # - # ***PETMAX PETMIN 1 0 0 2 0 0 6 0 0 9 0 0 END IWAT-PARM3 IWAT-STATE1 <PLS > *** Initial conditions at start of simulation # - # *** RETS SURS 1 0 0 2 0 0 6 0 0 9 0 0 END IWAT-STATE1 END IMPLND SCHEMATIC <-Source-> <--Area--> <-Target-> MBLK *** <Name> # <-factor-> <Name> # Tbl# *** Basin 1*** PERLND 7 3.626 RCHRES 1 2 PERLND 7 3.626 RCHRES 1 3 IMPLND 1 0.281 RCHRES 1 5 IMPLND 2 0.882 RCHRES 1 5 IMPLND 6 0.402 RCHRES 1 5 IMPLND 9 0.102 RCHRES 1 5 ******Routing****** RCHRES 2 1 RCHRES 3 7 RCHRES 2 COPY 1 17 RCHRES 1 1 RCHRES 3 7 RCHRES 1 COPY 1 17 RCHRES 1 1 RCHRES 2 8 RCHRES 3 1 COPY 501 17 END SCHEMATIC NETWORK <-Volume-> <-Grp> <-Member-><--Mult-->Tran <-Target vols> <-Grp> <-Member-> *** <Name> # <Name> # #<-factor->strg <Name> # # <Name> # # *** COPY 501 OUTPUT MEAN 1 1 48.4 DISPLY 1 INPUT TIMSER 1 GENER 2 OUTPUT TIMSER .0011111 RCHRES 1 EXTNL OUTDGT 1 <-Volume-> <-Grp> <-Member-><--Mult-->Tran <-Target vols> <-Grp> <-Member-> *** 2210152_Vista 5/4/2021 5:52:25 PM Page 21 <Name> # <Name> # #<-factor->strg <Name> # # <Name> # # *** END NETWORK RCHRES GEN-INFO RCHRES Name Nexits Unit Systems Printer *** # - #<------------------><---> User T-series Engl Metr LKFG *** in out *** 1 Surface retentio-007 3 1 1 1 28 0 1 2 Bioretention 1 2 1 1 1 28 0 1 3 Trapezoidal Pond-008 2 1 1 1 28 0 1 END GEN-INFO *** Section RCHRES*** ACTIVITY <PLS > ************* Active Sections ***************************** # - # HYFG ADFG CNFG HTFG SDFG GQFG OXFG NUFG PKFG PHFG *** 1 1 0 0 0 0 0 0 0 0 0 2 1 0 0 0 0 0 0 0 0 0 3 1 0 0 0 0 0 0 0 0 0 END ACTIVITY PRINT-INFO <PLS > ***************** Print-flags ******************* PIVL PYR # - # HYDR ADCA CONS HEAT SED GQL OXRX NUTR PLNK PHCB PIVL PYR ********* 1 4 0 0 0 0 0 0 0 0 0 1 9 2 4 0 0 0 0 0 0 0 0 0 1 9 3 4 0 0 0 0 0 0 0 0 0 1 9 END PRINT-INFO HYDR-PARM1 RCHRES Flags for each HYDR Section *** # - # VC A1 A2 A3 ODFVFG for each *** ODGTFG for each FUNCT for each FG FG FG FG possible exit *** possible exit possible exit * * * * * * * * * * * * * * *** 1 0 1 0 0 4 5 6 0 0 0 1 0 0 0 2 1 2 2 2 2 0 1 0 0 4 5 0 0 0 0 0 0 0 0 2 2 2 2 2 3 0 1 0 0 4 5 0 0 0 0 0 0 0 0 2 2 2 2 2 END HYDR-PARM1 HYDR-PARM2 # - # FTABNO LEN DELTH STCOR KS DB50 *** <------><--------><--------><--------><--------><--------><--------> *** 1 1 0.01 0.0 0.0 0.0 0.0 2 2 0.02 0.0 0.0 0.0 0.0 3 3 0.02 0.0 0.0 0.5 0.0 END HYDR-PARM2 HYDR-INIT RCHRES Initial conditions for each HYDR section *** # - # *** VOL Initial value of COLIND Initial value of OUTDGT *** ac-ft for each possible exit for each possible exit <------><--------> <---><---><---><---><---> *** <---><---><---><---><---> 1 0 4.0 5.0 6.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 2 0 4.0 5.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 3 0 4.0 5.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 END HYDR-INIT END RCHRES SPEC-ACTIONS *** User-Defined Variable Quantity Lines *** addr *** <------> *** kwd varnam optyp opn vari s1 s2 s3 tp multiply lc ls ac as agfn *** <****> <----> <----> <-> <----><-><-><-><-><--------> <><-> <><-> <--> *** UVQUAN vol2 RCHRES 2 VOL 4 UVQUAN v2m2 GLOBAL WORKSP 1 3 UVQUAN vpo2 GLOBAL WORKSP 2 3 UVQUAN v2d2 GENER 2 K 1 3 *** User-Defined Target Variable Names *** addr or addr or 2210152_Vista 5/4/2021 5:52:25 PM Page 22 *** <------> <------> *** kwd varnam ct vari s1 s2 s3 frac oper vari s1 s2 s3 frac oper <****> <----><-> <----><-><-><-> <---> <--> <----><-><-><-> <---> <--> UVNAME v2m2 1 WORKSP 1 1.0 QUAN UVNAME vpo2 1 WORKSP 2 1.0 QUAN UVNAME v2d2 1 K 1 1.0 QUAN *** opt foplop dcdts yr mo dy hr mn d t vnam s1 s2 s3 ac quantity tc ts rp <****><-><--><><-><--> <> <> <> <><><> <----><-><-><-><-><--------> <> <-><-> GENER 2 v2m2 = 870.29 *** Compute remaining available pore space GENER 2 vpo2 = v2m2 GENER 2 vpo2 -= vol2 *** Check to see if VPORA goes negative; if so set VPORA = 0.0 IF (vpo2 < 0.0) THEN GENER 2 vpo2 = 0.0 END IF *** Infiltration volume GENER 2 v2d2 = vpo2 END SPEC-ACTIONS FTABLES FTABLE 2 47 5 Depth Area Volume Outflow1 Outflow2 Velocity Travel Time*** (ft) (acres) (acre-ft) (cfs) (cfs) (ft/sec) (Minutes)*** 0.000000 0.038499 0.000000 0.000000 0.000000 0.032967 0.038176 0.000170 0.000000 0.000000 0.065934 0.037533 0.000349 0.000000 0.000000 0.098901 0.036892 0.000537 0.000000 0.000000 0.131868 0.036253 0.000733 0.000000 0.000001 0.164835 0.035615 0.000937 0.000000 0.000188 0.197802 0.034979 0.001151 0.000000 0.000303 0.230769 0.034345 0.001372 0.000000 0.000456 0.263736 0.033713 0.001603 0.000000 0.000654 0.296703 0.033083 0.001842 0.000000 0.000901 0.329670 0.032454 0.002090 0.000000 0.001205 0.362637 0.031827 0.002347 0.000000 0.001572 0.395604 0.031202 0.002613 0.000000 0.002008 0.428571 0.030579 0.002887 0.000000 0.002521 0.461538 0.029957 0.003170 0.000000 0.003117 0.494505 0.029338 0.003462 0.000000 0.003805 0.527473 0.028720 0.003763 0.000000 0.004591 0.560440 0.028104 0.004073 0.000000 0.005483 0.593407 0.027490 0.004392 0.000000 0.006489 0.626374 0.026877 0.004720 0.000000 0.007617 0.659341 0.026266 0.005056 0.000000 0.008877 0.692308 0.025657 0.005402 0.000000 0.010276 0.725275 0.025050 0.005757 0.000000 0.011822 0.758242 0.024445 0.006121 0.000000 0.013526 0.791209 0.023842 0.006494 0.000000 0.015396 0.824176 0.023240 0.006876 0.000000 0.017442 0.857143 0.022640 0.007268 0.000000 0.019673 0.890110 0.022042 0.007668 0.000000 0.022099 0.923077 0.021446 0.008078 0.000000 0.024729 0.956044 0.020851 0.008497 0.000000 0.027575 0.989011 0.020258 0.008926 0.000000 0.030645 1.021978 0.019667 0.009363 0.000000 0.033952 1.054945 0.019078 0.009810 0.000000 0.037504 1.087912 0.018491 0.010267 0.000000 0.041313 1.120879 0.017906 0.010732 0.000000 0.045390 1.153846 0.017322 0.011207 0.000000 0.049745 1.186813 0.016740 0.011692 0.000000 0.054390 1.219780 0.016160 0.012186 0.000000 0.059336 1.252747 0.015581 0.012689 0.000000 0.064594 1.285714 0.015005 0.013202 0.000000 0.070175 1.318681 0.014430 0.013725 0.000000 0.076089 1.351648 0.013857 0.014257 0.000000 0.082348 1.384615 0.013286 0.014799 0.000000 0.088958 1.417582 0.012717 0.015350 0.000000 0.095928 1.450549 0.012149 0.015911 0.000000 0.103254 1.483516 0.011583 0.016482 0.000000 0.110897 2210152_Vista 5/4/2021 5:52:25 PM Page 23 1.500000 0.011019 0.019979 0.000000 0.155278 END FTABLE 2 FTABLE 1 47 6 Depth Area Volume Outflow1 Outflow2 Outflow3 Velocity Travel Time*** (ft) (acres) (acre-ft) (cfs) (cfs) (cfs) (ft/sec) (Minutes)*** 0.000000 0.011019 0.000000 0.000000 0.000000 0.013022 0.032967 0.039144 0.001280 0.000000 0.033333 0.013022 0.065934 0.039792 0.002581 0.000000 0.034799 0.026080 0.098901 0.040441 0.003903 0.000000 0.035531 0.039174 0.131868 0.041092 0.005247 0.000000 0.036264 0.052304 0.164835 0.041745 0.006613 0.000000 0.036996 0.065471 0.197802 0.042400 0.008000 0.000000 0.037729 0.078674 0.230769 0.043056 0.009409 0.000000 0.038462 0.091913 0.263736 0.043715 0.010839 0.000000 0.039194 0.105189 0.296703 0.044375 0.012291 0.000000 0.039927 0.118500 0.329670 0.045037 0.013765 0.000000 0.040659 0.131848 0.362637 0.045700 0.015260 0.000000 0.041392 0.145232 0.395604 0.046366 0.016778 0.000000 0.042125 0.158652 0.428571 0.047033 0.018317 0.000000 0.042857 0.172109 0.461538 0.047702 0.019879 0.000000 0.043590 0.185602 0.494505 0.048373 0.021463 0.000000 0.044322 0.199131 0.527473 0.049046 0.023068 0.096659 0.044444 0.212696 0.560440 0.049720 0.024696 0.315192 0.044444 0.226297 0.593407 0.050396 0.026347 0.605153 0.044444 0.239935 0.626374 0.051074 0.028019 0.951453 0.044444 0.253609 0.659341 0.051754 0.029714 1.345222 0.044444 0.267319 0.692308 0.052436 0.031432 1.779946 0.044444 0.281065 0.725275 0.053119 0.033172 2.250154 0.044444 0.294848 0.758242 0.053804 0.034934 2.750832 0.044444 0.308666 0.791209 0.054491 0.036719 3.277130 0.044444 0.322521 0.824176 0.055180 0.038527 3.824213 0.044444 0.336413 0.857143 0.055871 0.040357 4.387183 0.044444 0.350340 0.890110 0.056563 0.042211 4.961058 0.044444 0.364304 0.923077 0.057257 0.044087 5.540778 0.044444 0.378304 0.956044 0.057953 0.045986 6.121239 0.044444 0.392340 0.989011 0.058651 0.047908 6.697340 0.044444 0.406412 1.021978 0.059351 0.049853 7.264050 0.044444 0.420521 1.054945 0.060052 0.051821 7.816484 0.044444 0.434666 1.087912 0.060755 0.053813 8.349987 0.044444 0.448847 1.120879 0.061460 0.055827 8.860234 0.044444 0.463064 1.153846 0.062167 0.057865 9.343333 0.044444 0.477318 1.186813 0.062876 0.059926 9.795934 0.044444 0.491607 1.219780 0.063586 0.062011 10.21535 0.044444 0.505933 1.252747 0.064298 0.064119 10.59968 0.044444 0.520295 1.285714 0.065012 0.066250 10.94794 0.044444 0.534694 1.318681 0.065728 0.068405 11.26021 0.044444 0.549129 1.351648 0.066446 0.070584 11.53775 0.044444 0.563599 1.384615 0.067165 0.072786 11.78317 0.044444 0.578107 1.417582 0.067886 0.075012 12.00059 0.044444 0.592650 1.450549 0.068609 0.077262 12.19577 0.044444 0.607229 1.483516 0.069334 0.079536 12.37628 0.044444 0.621845 1.500000 0.069697 0.080682 12.70193 0.044444 0.629167 END FTABLE 1 FTABLE 3 91 5 Depth Area Volume Outflow1 Outflow2 Velocity Travel Time*** (ft) (acres) (acre-ft) (cfs) (cfs) (ft/sec) (Minutes)*** 0.000000 0.011019 0.000000 0.000000 0.000000 0.044444 0.012025 0.000512 0.000000 0.242513 0.088889 0.013036 0.001069 0.000000 0.262892 0.133333 0.014051 0.001671 0.000000 0.283358 0.177778 0.015070 0.002318 0.000000 0.303912 0.222222 0.016094 0.003011 0.000000 0.324554 0.266667 0.017122 0.003749 0.000000 0.345284 0.311111 0.018154 0.004533 0.000000 0.366102 0.355556 0.019190 0.005362 0.000000 0.387007 0.400000 0.020231 0.006239 0.000000 0.408000 2210152_Vista 5/4/2021 5:52:25 PM Page 24 0.444444 0.021277 0.007161 0.000000 0.429081 0.488889 0.022326 0.008130 0.000000 0.450250 0.533333 0.023380 0.009146 0.000000 0.471506 0.577778 0.024439 0.010208 0.000000 0.492850 0.622222 0.025502 0.011318 0.000000 0.514283 0.666667 0.026569 0.012475 0.000000 0.535802 0.711111 0.027640 0.013680 0.000000 0.557410 0.755556 0.028716 0.014932 0.000000 0.579106 0.800000 0.029796 0.016232 0.000000 0.600889 0.844444 0.030881 0.017581 0.000000 0.622760 0.888889 0.031970 0.018977 0.000000 0.644719 0.933333 0.033063 0.020423 0.000000 0.666765 0.977778 0.034160 0.021916 0.000000 0.688900 1.022222 0.035262 0.023459 0.000000 0.711122 1.066667 0.036369 0.025051 0.000000 0.733432 1.111111 0.037479 0.026692 0.000000 0.755830 1.155556 0.038594 0.028383 0.000000 0.778316 1.200000 0.039713 0.030123 0.000000 0.800889 1.244444 0.040837 0.031913 0.000000 0.823550 1.288889 0.041965 0.033753 0.000000 0.846299 1.333333 0.043098 0.035643 0.000000 0.869136 1.377778 0.044234 0.037584 0.000000 0.892060 1.422222 0.045376 0.039575 0.000000 0.915073 1.466667 0.046521 0.041617 0.000000 0.938173 1.511111 0.047671 0.043710 0.000000 0.961361 1.555556 0.048825 0.045855 0.000000 0.984636 1.600000 0.049983 0.048051 0.000000 1.008000 1.644444 0.051146 0.050298 0.000000 1.031451 1.688889 0.052314 0.052597 0.000000 1.054990 1.733333 0.053485 0.054948 0.000000 1.078617 1.777778 0.054661 0.057351 0.000000 1.102332 1.822222 0.055841 0.059807 0.000000 1.126134 1.866667 0.057026 0.062315 0.000000 1.150025 1.911111 0.058215 0.064876 0.000000 1.174003 1.955556 0.059408 0.067490 0.000000 1.198069 2.000000 0.060606 0.070157 0.000000 1.222222 2.044444 0.061808 0.072877 0.000000 1.246464 2.088889 0.063015 0.075651 0.000000 1.270793 2.133333 0.064225 0.078479 0.000000 1.295210 2.177778 0.065440 0.081360 0.000000 1.319715 2.222222 0.066660 0.084296 0.000000 1.344307 2.266667 0.067884 0.087285 0.000000 1.368988 2.311111 0.069112 0.090330 0.000000 1.393756 2.355556 0.070344 0.093429 0.000000 1.418612 2.400000 0.071581 0.096583 0.000000 1.443556 2.444444 0.072823 0.099792 0.000000 1.468587 2.488889 0.074068 0.103056 0.000000 1.493706 2.533333 0.075318 0.106376 0.129168 1.518914 2.577778 0.076572 0.109751 0.459969 1.544209 2.622222 0.077831 0.113182 0.905080 1.569591 2.666667 0.079094 0.116669 1.438492 1.595062 2.711111 0.080361 0.120213 2.044119 1.620620 2.755556 0.081633 0.123813 2.709012 1.646266 2.800000 0.082909 0.127469 3.421187 1.672000 2.844444 0.084190 0.131182 4.168770 1.697822 2.888889 0.085474 0.134953 4.939668 1.723731 2.933333 0.086763 0.138780 5.721526 1.749728 2.977778 0.088057 0.142665 6.501843 1.775813 3.022222 0.089355 0.146608 7.268201 1.801986 3.066667 0.090657 0.150608 8.008574 1.828247 3.111111 0.091963 0.154666 8.711714 1.854595 3.155556 0.093274 0.158783 9.367577 1.881032 3.200000 0.094590 0.162957 9.967808 1.907556 3.244444 0.095909 0.167191 10.50626 1.934167 3.288889 0.097233 0.171483 10.97957 1.960867 3.333333 0.098561 0.175834 11.38772 1.987654 3.377778 0.099894 0.180244 11.73473 2.014529 3.422222 0.101231 0.184713 12.02925 2.041492 3.466667 0.102572 0.189242 12.28531 2.068543 3.511111 0.103918 0.193831 12.66832 2.095682 2210152_Vista 5/4/2021 5:52:25 PM Page 25 3.555556 0.105268 0.198479 12.94375 2.122908 3.600000 0.106623 0.203188 13.21344 2.150222 3.644444 0.107981 0.207957 13.47773 2.177624 3.688889 0.109344 0.212787 13.73695 2.205114 3.733333 0.110712 0.217677 13.99135 2.232691 3.777778 0.112084 0.222628 14.24122 2.260357 3.822222 0.113460 0.227640 14.48678 2.288110 3.866667 0.114841 0.232713 14.72824 2.315951 3.911111 0.116225 0.237848 14.96581 2.343879 3.955556 0.117615 0.243044 15.19966 2.371896 4.000000 0.119008 0.248303 15.42997 2.400000 END FTABLE 3 END FTABLES EXT SOURCES <-Volume-> <Member> SsysSgap<--Mult-->Tran <-Target vols> <-Grp> <-Member-> *** <Name> # <Name> # tem strg<-factor->strg <Name> # # <Name> # # *** WDM 2 PREC ENGL 0.857 PERLND 1 999 EXTNL PREC WDM 2 PREC ENGL 0.857 IMPLND 1 999 EXTNL PREC WDM 1 EVAP ENGL 0.76 PERLND 1 999 EXTNL PETINP WDM 1 EVAP ENGL 0.76 IMPLND 1 999 EXTNL PETINP WDM 2 PREC ENGL 0.857 RCHRES 1 EXTNL PREC WDM 2 PREC ENGL 0.857 RCHRES 3 EXTNL PREC WDM 1 EVAP ENGL 0.5 RCHRES 1 EXTNL POTEV WDM 1 EVAP ENGL 0.76 RCHRES 2 EXTNL POTEV WDM 1 EVAP ENGL 0.76 RCHRES 3 EXTNL POTEV END EXT SOURCES EXT TARGETS <-Volume-> <-Grp> <-Member-><--Mult-->Tran <-Volume-> <Member> Tsys Tgap Amd *** <Name> # <Name> # #<-factor->strg <Name> # <Name> tem strg strg*** RCHRES 3 HYDR RO 1 1 1 WDM 1000 FLOW ENGL REPL RCHRES 3 HYDR O 1 1 1 WDM 1001 FLOW ENGL REPL RCHRES 3 HYDR O 2 1 1 WDM 1002 FLOW ENGL REPL RCHRES 3 HYDR STAGE 1 1 1 WDM 1003 STAG ENGL REPL COPY 1 OUTPUT MEAN 1 1 48.4 WDM 701 FLOW ENGL REPL COPY 501 OUTPUT MEAN 1 1 48.4 WDM 801 FLOW ENGL REPL END EXT TARGETS MASS-LINK <Volume> <-Grp> <-Member-><--Mult--> <Target> <-Grp> <-Member->*** <Name> <Name> # #<-factor-> <Name> <Name> # #*** MASS-LINK 2 PERLND PWATER SURO 0.083333 RCHRES INFLOW IVOL END MASS-LINK 2 MASS-LINK 3 PERLND PWATER IFWO 0.083333 RCHRES INFLOW IVOL END MASS-LINK 3 MASS-LINK 5 IMPLND IWATER SURO 0.083333 RCHRES INFLOW IVOL END MASS-LINK 5 MASS-LINK 7 RCHRES OFLOW OVOL 1 RCHRES INFLOW IVOL END MASS-LINK 7 MASS-LINK 8 RCHRES OFLOW OVOL 2 RCHRES INFLOW IVOL END MASS-LINK 8 MASS-LINK 17 RCHRES OFLOW OVOL 1 COPY INPUT MEAN END MASS-LINK 17 END MASS-LINK 2210152_Vista 5/4/2021 5:52:25 PM Page 26 END RUN 2210152_Vista 5/4/2021 5:52:25 PM Page 27 Predeveloped HSPF Message File 2210152_Vista 5/4/2021 5:52:25 PM Page 28 Mitigated HSPF Message File 2210152_Vista 5/4/2021 5:52:25 PM Page 29 Disclaimer Legal Notice This program and accompanying documentation are provided 'as-is' without warranty of any kind. The entire risk regarding the performance and results of this program is assumed by End User. Clear Creek Solutions Inc. and the governmental licensee or sublicensees disclaim all warranties, either expressed or implied, including but not limited to implied warranties of program and accompanying documentation. In no event shall Clear Creek Solutions Inc. be liable for any damages whatsoever (including without limitation to damages for loss of business profits, loss of business information, business interruption, and the like) arising out of the use of, or inability to use this program even if Clear Creek Solutions Inc. or their authorized representatives have been advised of the possibility of such damages. Software Copyright © by : Clear Creek Solutions, Inc. 2005-2021; All Rights Reserved. Clear Creek Solutions, Inc. 6200 Capitol Blvd. Ste F Olympia, WA. 98501 Toll Free 1(866)943-0304 Local (360)943-0304 www.clearcreeksolutions.com Preliminary Stormwater Report The Vista at Mill Pond 2210152.10 Appendix C Geotechnical Report South Sound Geotechnical Consulting, Inc. dated April 20, 2021 South Sound Geotechnical Consulting P.O. Box 39500, Lakewood, WA 98496 (253) 973-0515 April 20, 2021 Mr. Matt Weber c/o AHBL 2215 North 30th Street, Suite 200 Tacoma, Washington 98403-3350 Subject: Geotechnical Engineering Report The Meadows at Mill Pond & The Vista at Mill Pond Mill Road SE Yelm, Washington SSGC Project No. 21019 Mr. Weber, South Sound Geotechnical Consulting (SSGC) has completed a geotechnical assessment for the two above named developments in Yelm, Washington. Our services have been completed in general conformance with our proposal P21031 (dated March 5, 2021) and authorized per signature of our agreement for services. Our scope of services included completion of ten test pits and two infiltration tests on the sites, laboratory testing, engineering analyses, and preparation of this report. PROJECT INFORMATION The Meadows at Mill Pond development (Meadows) is northeast of the intersection of Mill Road SE and 104th Place SE and encompasses about 5 acres. The Vista at Mill Pond development (Vista) is southwest of the intersection of Mill Pond SE and 104th Avenue SE, southwest of the Meadows development, and encompasses slightly under 7 acres. Development plans include up to twenty single-family lots on the Meadows site and twenty-seven lots on the Vista site. Access to individual lots within the developments will be provided by new cul-de-sac drives. Conventional spread footings are anticipated for support of the new buildings. Designated open space/storm-tract areas are planned to support stormwater control in both developments. SITE CONDITIONS The Meadows site is currently undeveloped and lightly forested, with an understory of principally grass. It is generally level with an estimated elevation change of around 4 (+/-) feet. The Vista site has an existing single-family residence and several out-buildings. This site is characterized by generally level ground in the central and northern portions that are covered in field grass and lawn, and a north-facing slope in the southern portion of the site, leading to a level benched area along the southern property boundary. Elevation change between the upper southern portion and the lower northern/central portions is on the order of an estimated 15 (+/-) feet. Geotechnical Engineering Report SSGC The Meadows and Vista at Mill Pond Developments Mill Road SE Yelm, Washington SSGC Project No. 21019 April 20, 2021 2 SUBSURFACE CONDITIONS Subsurface conditions were characterized by completing six test pits and one infiltration test on the Meadows site, and four test pits and one infiltration test on the Vista site on March 18, 2021. Explorations were advanced to depths between 6 and 10 feet below existing ground surface. Approximate locations of the test holes are shown on Figure 1, Exploration Plan. A summary description of observed subgrade conditions is provided below. Logs of the test holes are provided in Appendix A. Soil Conditions Topsoil was observed below the surface in the test pits and extended to depths between about 1 to 2 feet. Native soil below the topsoil consisted of gravelly sand to sandy gravel with trace silt. These soils extended to the termination depth of the test holes. Caving of sidewall soils limited depth of excavation in several of the test pits. Groundwater Conditions Groundwater was not observed in the test holes at the time of excavation. Evidence of mottling or other indicators of seasonally perched groundwater was not observed. Seasonal high groundwater levels are not anticipated to affect these lots. Groundwater levels will vary throughout the year based on seasonal precipitation and on- and off-site drainage patterns. Geologic Setting Soils on the sites consist of “Spanaway gravelly sandy loam” per the USDA Soil Conservation Service map of Thurston County. Spanaway soils reportedly formed in glacial outwash. Native soils observed in the test holes appear to conform to the mapped soil type. GEOTECHNICAL DESIGN CONSIDERATIONS Planned development of the site is considered feasible based on observed soil conditions in the test holes. Native soils can be used for support of conventional spread footing foundations, slab-on-grade floors, and pavements. Existing topsoil and any fill should be removed from planned building or pavement areas. Native outwash soils have good infiltration potential based on the tests completed and are considered suitable to support infiltration systems. Recommendations presented in the following sections should be considered general and may require modifications when earthwork and grading occur. They are based upon the subsurface conditions observed in the test holes and the assumption that finish site grades will be similar to existing grades. It should be noted that subsurface conditions across the site may vary from those depicted on the exploration logs and can change with time. Therefore, proper site preparation will depend upon the weather and soil conditions encountered at the time of construction. We recommend that SSGC review final plans and further assess subgrade conditions at the time of construction, as warranted. Geotechnical Engineering Report SSGC The Meadows and Vista at Mill Pond Developments Mill Road SE Yelm, Washington SSGC Project No. 21019 April 20, 2021 3 General Site Preparation Site grading and earthwork should include procedures to control surface water runoff. Grading the site without adequate drainage control measures may negatively impact site soils, resulting in increased export of impacted soil and import of fill materials, potentially increasing the cost of the earthwork and subgrade preparation phases of the project. Site grading should include removal (stripping) of fill and topsoil in building and pavement areas. Subgrades should consist of firm native (outwash) soils following stripping. Stripping depth will be on the order of 1 to 2 feet based on observed soil conditions in the test holes, but may vary across the site. Final stripping depths can only be determined at the time of construction. General Subgrade Preparation Subgrades in building and pavement areas should consist of firm native soil. We recommend exposed subgrades in building and conventional pavement areas are proofrolled using a large roller, loaded dump truck, or other mechanical equipment to assess subgrade conditions following stripping. Proofrolling efforts should result in the upper 1 foot of subgrade soils achieving a firm and unyielding condition and a compaction level of at least 92 percent of the maximum dry density (MDD) per the ASTM D1557 test method. Wet, loose, or soft subgrades that cannot achieve a firm and unyielding condition should be removed (over-excavated) and replaced with structural fill. The depth of over-excavation should be based on soil conditions at the time of construction. A representative of SSGC should be present to assess subgrade conditions during proofrolling. Grading and Drainage Positive drainage should be provided during construction and maintained throughout the life of the development. Allowing surface water into cut or fill areas, utility trenches, and building footprints should be prevented. Structural Fill Materials The suitability of soil for use as structural fill will depend on the gradation and moisture content of the soil when it is placed. Soils with higher fines content (soil fraction passing the U.S. No. 200 sieve) will become sensitive with higher moisture content. It is often difficult to achieve adequate compaction if soil moisture is outside of optimum ranges for soils that contain more than about 5 percent fines. Geotechnical Engineering Report SSGC The Meadows and Vista at Mill Pond Developments Mill Road SE Yelm, Washington SSGC Project No. 21019 April 20, 2021 4 Site Soils: Topsoil is not considered suitable for structural fill. Native outwash soils are considered suitable for use as structural fill provided they can be moisture conditioned to within optimal ranges. Optimum moisture is considered within about +/- 2 percent of the moisture content required to achieve the maximum density per the ASTM D-1557 test method. If moisture content is higher or lower than optimum, soils would need to be dried or wetted prior to placement as structural fill. Outwash contains variable cobbles and occasional boulders. Particles larger than about 4 inches should be screened from outwash soils prior to their use as structural fill. Larger particles tend to cluster during earthwork and can form voids and non-uniform compaction if not screened. Import Fill Materials: We recommend import structural fill placed during dry weather periods consist of material which meets the specifications for Gravel Borrow as described in Section 9- 03.14(1) of the 2018 Washington State Department of Transportation (WSDOT) Specifications for Road, Bridge, and Municipal Construction (Publication M 41-10). Gravel Borrow should be protected from disturbance if exposed to wet conditions after placement. During wet weather, or for backfill on wet subgrades, import soil suitable for compaction in wetter conditions should be provided. Imported fill for use in wet conditions should generally conform to specifications for Select Borrow as described in Section 9-03.14(2), or Crushed Surfacing per Section 9-03.9(3) of the 2018 WSDOT M-41 manual, with the modification that a maximum of 5 percent by weight shall pass the U.S. No. 200 sieve. It should be noted that structural fill placement and compaction is weather-dependent. Delays due to inclement weather are common, even when using select granular fill. We recommend site grading and earthwork be scheduled for the drier months of the year. Structural fill should not consist of frozen material. Structural Fill Placement We recommend structural fill is placed in lifts not exceeding about 10 inches in loose measure. It may be necessary to adjust lift thickness based on site and fill conditions during placement and compaction. Finer grained soil used as structural fill and/or lighter weight compaction equipment may require significantly thinner lifts to attain required compaction levels. Granular soil with lower fines contents could potentially be placed in thicker lifts if they can be adequately compacted. Structural fill should be compacted to attain the recommended levels presented in Table 1, Compaction Criteria. Geotechnical Engineering Report SSGC The Meadows and Vista at Mill Pond Developments Mill Road SE Yelm, Washington SSGC Project No. 21019 April 20, 2021 5 Table 1. Compaction Criteria Fill Application Compaction Criteria* Footing areas (below structures and retaining walls) 95 % Upper 2 feet in pavement areas, slabs and sidewalks, and utility trenches 95 % Below 2 feet in pavement areas, slabs and sidewalks, and utility trenches 92 % Utility trenches or general fill in non-paved or -building areas 90 % *Per the ASTM D 1557 test method. Trench backfill within about 2 feet of utility lines should not be over-compacted to reduce the risk of damage to the line. In some instances the top of the utility line may be within 2 feet of the surface. Backfill in these circumstances should be compacted to a firm and unyielding condition. We recommend fill procedures include maintaining grades that promote drainage and do not allow ponding of water within the fill area. The contractor should protect compacted fill subgrades from disturbance during wet weather. In the event of rain during structural fill placement, the exposed fill surface should be allowed to dry prior to placement of additional fill. Alternatively, the we t soil can be removed. We recommend consideration be given to protecting haul routes and other high traffic areas with free-draining granular fill material (i.e. sand and gravel containing less than 5 percent fines) or quarry spalls to reduce the potential for disturbance to the subgrade during inclement weather. Earthwork Procedures Conventional earthmoving equipment should be suitable for earthwork at this site. Earthwork may be difficult during periods of wet weather or if elevated soil moisture is present. Excavated site soils may not be suitable as structural fill depending on the soil moisture content and weather conditions at the time of earthwork. If soils are stockpiled and wet weather is anticipated, the stockpile should be protected with securely anchored plastic sheeting. If stockpiled soils become unusable, it may become necessary to import clean, granular soils to complete wet weather site work. Wet or disturbed subgrade soils should be over-excavated to expose firm, non-yielding, non-organic soils and backfilled with compacted structural fill. We recommend the earthwork portion of this project be completed during extended periods of dry weather. If earthwork is completed during the wet season (typically late October through May) it may be necessary to take extra measures to protect subgrade soils. If earthwork takes place during freezing conditions, we recommend exposed subgrades are allowed to thaw and re-compacted prior to placing subsequent lifts of structural fill. Alternatively, the frozen soil can be removed to unfrozen soil and replaced with structural fill. Geotechnical Engineering Report SSGC The Meadows and Vista at Mill Pond Developments Mill Road SE Yelm, Washington SSGC Project No. 21019 April 20, 2021 6 The contractor is responsible for designing and constructing stable, temporary excavations (including utility trenches) as required to maintain stability of excavation sides and bottoms. Excavations should be sloped or shored in the interest of safety following local and federal regulations, including current OSHA excavation and trench safety standards. Temporary excavation cuts should be sloped at inclinations of 1H:1.5V (Horizontal:Vertical) or flatter, unless the contractor can demonstrate the safety of steeper inclinations. Shoring may be required in deeper excavations (below 4 feet) as glacial outwash soils have a tendency to cave into open excavations. A geotechnical engineer and accredited testing material laboratory should be retained during the construction phase of the project to observe earthwork operations and perform necessary tests and observations during subgrade preparation, placement and compaction of structural fill, and backfilling of excavations. Foundations Foundations for the new gym should be placed on native subgrade soils prepared as described in this report. The following recommendations are for conventional spread footing foundations: Bearing Capacity (net allowable): 3,000 pounds per square foot (psf) for footings supported on firm native soils prepared as described in this report. Footing Width (Minimum): 18 inches (Strip) 24 inches (Column) Embedment Depth (Minimum): 18 inches (Exterior) 12 inches (Interior) Settlement: Total: < 1 inch Differential: < 1/2 inch (over 30 feet) Allowable Lateral Passive Resistance: 325 psf/ft* (below 18 inches) Allowable Coefficient of Friction: 0.40* *These values include a factor of safety of approximately 1.5. The net allowable bearing pressures presented above may be increased by one-third to resist transient, dynamic loads such as wind or seismic forces. Lateral resistance to footings should be ignored in the upper 12-inches from exterior finish grade. Geotechnical Engineering Report SSGC The Meadows and Vista at Mill Pond Developments Mill Road SE Yelm, Washington SSGC Project No. 21019 April 20, 2021 7 Foundation Construction Considerations All foundation subgrades should be free of water and loose soil prior to placing concrete , and should be prepared as recommended in this report. Concrete should be placed soon after excavating and compaction to reduce disturbance to bearing soils. Should soils at foundation level become excessively dry, disturbed, saturated, or frozen, the affected soil should be removed prior to placing concrete. We recommend SSGC observe all foundation subgrades prior to placement of concrete. Foundation Drainage Ground surface adjacent foundations should be sloped away from buildings. We recommend footing drains are installed around perimeter footings if footings are placed on structural fill containing more than 5 percent fines. Footing drains are not considered necessary if foundations are placed directly on native outwash soils. Footing drains should include a minimum 4-inch diameter perforated rigid plastic drain line installed at the base of the footing. The perforated drain lines should be connected to a tight line pipe that discharges to an approved storm drain receptor. The drain line should be surrounded by a zone of clean, free-draining granular material having less than 5 percent passing the No. 200 sieve or meeting the requirements of section 9-03.12(2) “Gravel Backfill for Walls” in the 2018 WSDOT Standard Specifications for Road, Bridge, and Municipal Construction manual (M41 - 10). The free-draining aggregate zone should be at least 12 inches wide and wrapped in filter fabric. The granular fill should extend to within 6 inches of final grade where it should be capped with compacted fill containing sufficient fines to reduce infiltration of surface water into the footing drains. Cleanouts are recommended for maintenance of the drain system. On-Grade Floor Slabs On-grade floor slabs should be placed on native soils or structural fill prepared as described in this report. We recommend a modulus subgrade reaction of 200 pounds per square inch per inch (psi/in) for native soil or compacted granular structural fill over native soil. We recommend a capillary break is provided between the prepared subgrade and bottom of slab. Capillary break material should be a minimum of 4 inches thick and consist of compacted clean, free- draining, well graded course sand and gravel. The capillary break material should contain less than 5 percent fines, based on that soil fraction passing the U.S. No. 4 sieve . Alternatively, a clean angular gravel such as No. 7 aggregate per Section 9-03.1(4)C of the 2018 WSDOT (M41-10) manual could be used for this purpose. Geotechnical Engineering Report SSGC The Meadows and Vista at Mill Pond Developments Mill Road SE Yelm, Washington SSGC Project No. 21019 April 20, 2021 8 Seismic Considerations Seismic parameters and values in Table 2 are recommended based on the 2018 International Building Code (IBC). Table 2. Seismic Parameters PARAMETER VALUE 2018 International Building Code (IBC) Site Classification1 D Ss Spectral Acceleration for a Short Period 1.286 S1 Spectral Acceleration for a 1-Second Period 0.465g SDS Seismic Design Value at 0.2s SA 0.857 SD1 Seismic Design Value at 1.0s SA 0.522 1 Note: In general accordance with the 2018 International Building Code, Section 1613.3.2 for risk categories I,II,III. IBC Site Class is based on the estimated characteristics of the upper 100 feet of the subsurface profile. Liquefaction Soil liquefaction is a condition where loose, typically granular soils located below the groundwater surface lose strength during ground shaking, and is often associated with earthquakes. Native soils below this site consist of coarse outwash over dense glacially consolidated soil. The risk of liquefaction at this site is considered low for the design level earthquake. Infiltration Characteristics Infiltration facilities are proposed to assist in stormwater control. An assessment of infiltration potential of native outwash was completed per the DOE’s 2019 Stormwater Management Manual for Western Washington (SWMMWW) in the proposed open space/storm tract areas in each development. Results of the infiltration tests are presented in Table 3. Geotechnical Engineering Report SSGC The Meadows and Vista at Mill Pond Developments Mill Road SE Yelm, Washington SSGC Project No. 21019 April 20, 2021 9 Table 3. PIT Infiltration Test Results Infiltration Test No. (Site) Depth of Test from Surface (feet) Soil Type Field Infiltration Rate (in/hr) Corrected Infiltration Rate (in/hr) Correction Factors* (CFv/CFt/CFm) PIT-1 (Meadows) 4 Native Outwash >100 >45 (1.0/0.5/0.9) PIT-1 (Vista) 4 Native Outwash >100 >45 (1.0/0.5/0.9) *Correction Factors from the 2019 DOE SWMMWW. The measured field infiltration rate is considered appropriate for the outwash soil tested. Gradation tests were also performed on three samples of outwash from the test holes. Results of those tests (presented in Appendix B) show these outwash soils would typically be classified as poorly graded sand or gravel (SP/GP) per the Unified Soil Classification System and a Type A Hydrologic soil. We recommend a design infiltration rate of 45 in/hr (or maximum allowed by the DOE manual) is used in design of infiltration facilities in these developments. Following completion of the infiltration tests, the test holes were excavated to a depth between 4 and 5 feet below the test elevation (maximum depth due to caving). Ponded or perched water introduced during the test was not observed. Groundwater was not observed in the test holes to the maximum depth of 10 feet. Mottling or other indicators of elevated groundwater were not observed in the test holes. Cation Exchange Capacity (CEC) and organic content tests were completed on a sample of native outwash from the bottom of the infiltration test elevation (4 feet below grade). Test results are summarized in the table below. Table 4. CEC and Organic Content Results Test Site, Sample Number, Depth CEC Results (milliequivalents) CEC Required* (milliequivalents) Organic Content Results (%) Organic Content Required* (%) Meadows PIT-1, S-1, 4 ft 12.6 ≥ 5.0 7.58 ≥1.0 Vista PIT-1, S-1, 4 ft 10.5 3.5 *Per the 2019 DOE SWMMWW The samples tested satisfy DOE required organic content and CEC values. Geotechnical Engineering Report SSGC The Meadows and Vista at Mill Pond Developments Mill Road SE Yelm, Washington SSGC Project No. 21019 April 20, 2021 10 Conventional Asphalt Pavement Sections Subgrades for conventional pavement areas should be prepared as described in the “Subgrade Preparation” section of this report. Subgrades below pavement sections should be graded or crowned to promote drainage and not allow for ponding of water beneath the section. If drainage is not provided and ponding occurs, subgrade soils could become saturated, lose strength, and result in premature distress or failure of the section. In addition, the pavement surfacing should also be graded to promote drainage and reduce the potential for ponding of water on the pavement surface. Minimum recommended pavement sections for conventional asphalt pavements are presented in Table 5. Table 5. Pavement Sections Traffic Area Minimum Recommended Pavement Section Thickness (inches) Asphalt Concrete Surface1 Portland Cement Concrete2 Aggregate Base Course3,4 Subbase Aggregate5 Access Cul-De-Sacs 3 6 6 12 Driveways 2 5 4 12 1 1/2 –inch nominal aggregate hot-mix asphalt (HMA) per WSDOT 9-03.8(1) 2 A 28 day minimum compressive strength of 4,000 psi and an allowable flexural strength of at least 250 psi 3 Crushed Surfacing Base Course per WSDOT 9-03.9(3) 4Although not required for structural support under concrete pavements, a minimum four-inch thick base course layer is recommended to help reduce potential for slab curl, shrinkage cracking, and subgrade “pumping” through joints 5 95% compacted native subgrade or Gravel Borrow per WSDOT 9-03.14(1) or Crushed Surfacing Base Course WSDOT 9-03.9(3) Conventional Pavement Maintenance The performance and lifespan of pavements can be significantly impacted by future maintenance. The above pavement sections represent minimum recommended thicknesses and, as such, periodic maintenance should be completed. Proper maintenance will slow the rate of pavement deterioration, and will improve pavement performance and life. Preventive maintenance consists of both localized maintenance (crack and joint sealing and patching) and global maintenance (surface sealing). Added maintenance measures should be anticipated over the lifetime of the pavement section if any fill or topsoil is left in-place beneath pavement sections. Geotechnical Engineering Report SSGC The Meadows and Vista at Mill Pond Developments Mill Road SE Yelm, Washington SSGC Project No. 21019 April 20, 2021 REPORT CONDITIONS This report has been prepared for the exclusive use of Mr. Matt Weber for specific application to the project discussed, and has been prepared in accordance with generally accepted geotechnical engineering practices in the area. No warranties, either express or implied, are intended or made. The analysis and recommendations presented in this report are based on observed soil conditions and test results at the indicated locations, and from other geologic information discussed. This report does not reflect variations that may occur across the site, or due to the modifying effects of construction or weather. The nature and extent of such variations may not become evident until during or after construction. If variations appear, we should be immediately notified so that further evaluation and supplemental recommendations can be provided. This report was prepared for the planned type of development of the sites as discussed herein. It is not valid for third party entities or alternate types of development on the sites without the express written consent of SSGC. If development plans change we should be notified to review those changes and modify our recommendations as necessary. The scope of services for this project does not include any environmental or biological assessment of the site including identification or prevention of pollutants, hazardous materials, or conditions. Other studies should be completed if the owner is concerned about the potential for contamination or pollution. We appreciate the opportunity to work with you on this project. Please contact us if additional information is required or we can be of further assistance. Respectfully, South Sound Geotechnical Consulting Timothy H. Roberts, P.E. Member/Geotechnical Engineer 'Z-0 -Zl Attachments: Figure IA — Exploration Plan, The Meadows at Mill Pond Figure 1 B — Exploration Plan, The Vista at Mill Pond Appendix A — Field Exploration Procedures and Exploration Logs Appendix B — Laboratory Testing and Results Unified Soil Classification System N South Sound Geotechnical Consulting P.O. Box 39500 Lakewood, WA 98496 (253) 973-0515 Figure 1A – Exploration Plan The Meadows at Mill Pond Yelm, WA SSGC Project #21019 Approximate Test Pit Location PIT - 1 TP - 1 PIT - 1 Approximate Infiltration Test Location Scale: NTS Legend TP-6 PIT-1 TP-5 TP-2 TP-1 TP-4 TP-3 N South Sound Geotechnical Consulting P.O. Box 39500 Lakewood, WA 98496 (253) 973-0515 Figure 1B – Exploration Plan The Vista at Mill Pond Yelm, WA SSGC Project #21019 Approximate Test Pit Location PIT - 1 TP - 1 PIT - 1 Approximate Infiltration Test Location Scale: NTS Legend PIT-1 TP-1 TP-4 TP-3 TP-2 Geotechnical Engineering Report SSGC The Meadows and Vista at Mill Pond Developments Mill Road SE Yelm, Washington SSGC Project No. 21019 April 20, 2021 12 Appendix A Field Exploration Procedures and Exploration Logs Geotechnical Engineering Report SSGC The Meadows and Vista at Mill Pond Developments Mill Road SE Yelm, Washington SSGC Project No. 21019 April 20, 2021 13 Field Exploration Procedures Our field exploration for this project included ten test pits and two infiltration tests completed on March 18, 2021. The approximate locations of the explorations are shown on Figure 1, Exploration Plan. Exploration locations were determined by pacing from site features. Ground surface elevations referenced on the logs were inferred from Google Earth satellite imagery. Test locations and elevations should be considered accurate only to the degree implied by the means and methods used. A private excavation company subcontracted to SSGC dug the test holes. Soil samples were collected and stored in moisture tight containers for further assessment and laboratory testing. Explorations were backfilled with excavated soils and tamped when completed. Please note backfill in test pits could settle with time. Backfill material located in building or pavement areas should be re-excavated and recompacted, or replaced with structural fill. The following logs indicate the observed lithology of soils and other materials observed in the test pits at the time of excavation. Where a soil contact was observed to be gradational, our log indicates the average contact depth. Our logs also indicate the approximate depth to groundwater (where observed at the time of excavation), along with sample numbers and approximate sample depths. Soil descriptions on the logs are based on the Unified Soil Classification System. Project: The Meadows at Mill Pond SSGC Job # 21019 TEST PIT LOGS PAGE 1 OF 3 Location: Mill Road SE, Yelm, WA TEST PIT LOGS FIGURE A-1 South Sound Geotechnical Consulting TP-1 TO TP-6, PIT-1 Logged by: THR Test Pit TP-1 Depth (feet) Material Description 0 – 1 1 – 9 Topsoil Cobbly gravelly SAND with trace silt: Loose to medium dense, moist, brown. (SP/GP)(Outwash)(Sample S-1@ 7 feet) Test pit completed at approximately 9 feet on 3/18/21 due to caving. Groundwater not observed at time of excavation. Piezometer set in test pit. Approximate surface elevation: 348 feet Test Pit TP-2 Depth (feet) Material Description 0 – 1.5 1.5 – 8 Topsoil Gravelly SAND/Sandy GRAVEL with cobbles and trace silt: Loose, moist, brown grading gray at 5 feet, less cobbles (SP/GP)(Outwash) Test pit completed at approximately 8 feet on 3/18/21 due to caving. Groundwater not observed at time of excavation. Approximate surface elevation: 348 feet Test Pit TP-3 Depth (feet) Material Description 0 – 1.5 1.5 – 8 Topsoil Gravelly SAND/Sandy GRAVEL with cobbles and trace silt, boulder: Loose to medium dense, moist, brown grading gray, less cobbles at 4 feet. (SP/GP)(Outwash) Test pit completed at approximately 8 feet on 3/18/21 due to caving. Groundwater not observed at time of excavation. Approximate surface elevation: 350 feet Project: The Meadows at Mill Pond SSGC Job # 21019 TEST PIT LOGS PAGE 2 OF 3 Location: Mill Road SE, Yelm, WA TEST PIT LOGS FIGURE A-1 South Sound Geotechnical Consulting TP-1 TO TP-6, PIT-1 Logged by: THR Test Pit TP-4 Depth (feet) Material Description 0 – 1 1 – 10 Topsoil Gravelly SAND/Sandy GRAVEL with trace silt: Loose to medium dense, moist, brown grading gray at 4 feet, less cobbles. (SP/GP)(Outwash) Test pit completed at approximately 10 feet on 3/18/21 due to caving. Groundwater not observed at time of excavation. Approximate surface elevation: 351 feet Test Pit TP-5 Depth (feet) Material Description 0 – 1.5 1.5 – 6 Topsoil Gravelly SAND/Sandy GRAVEL with trace silt: Loose to medium dense, moist, brown grading gray at 4 feet. (SP/GP)(Outwash) Test pit completed at approximately 6 feet on 3/18/21. Groundwater not observed at time of excavation. Approximate surface elevation: 352 feet Test Pit TP-6 Depth (feet) Material Description 0 – 1.5 1.5 – 6 Topsoil Gravelly SAND/Sandy GRAVEL with trace silt: Loose to medium dense, moist, brown grading gray at 4 feet. (SP/GP)(Outwash) Test pit completed at approximately 6 feet on 3/18/21. Groundwater not observed at time of excavation. Approximate surface elevation: 351 feet Project: The Meadows at Mill Pond SSGC Job # 21019 TEST PIT LOGS PAGE 3 OF 3 Location: Mill Road SE, Yelm, WA TEST PIT LOGS FIGURE A-1 South Sound Geotechnical Consulting TP-1 TO TP-6, PIT-1 Logged by: THR Infiltration Test PIT-1 Depth (feet) Material Description 0 – 1.5 1.5 – 8 Topsoil Gravelly SAND/Sandy GRAVEL with trace silt: Loose to medium dense, moist, brown. (SP/GP)(Outwash)(Sample S- 1 @ 4 feet) Test pit completed at approximately 8 feet on 3/18/21. Infiltration test performed at 4 feet. Groundwater not observed at time of excavation. Approximate surface elevation: 348 feet Project: The Vista at Mill Pond SSGC Job # 21019 TEST PIT LOGS PAGE 1 OF 2 Location: Mill Road SE, Yelm, WA TEST PIT LOGS FIGURE A-1 South Sound Geotechnical Consulting TP-1 TO TP-4, PIT-1 Logged by: THR Test Pit TP-1 Depth (feet) Material Description 0 – 1.5 1.5 – 2.5 2.5 – 6 Topsoil Silty SAND with gravel: Loose, moist, brown. (SM) Gravelly SAND/Sandy GRAVEL with cobbles and trace silt: Loose to medium dense, moist, brown grading gray. (SP/GP)(Outwash) Test pit completed at approximately 6 feet on 3/18/21. Groundwater not observed at time of excavation. Approximate surface elevation: 350 feet Test Pit TP-2 Depth (feet) Material Description 0 – 1.5 1.5 – 6 Topsoil Gravelly SAND/Sandy GRAVEL with cobbles and trace silt: Loose, moist, brown grading gray. (SP/GP)(Outwash) Test pit completed at approximately 6 feet on 3/18/21. Groundwater not observed at time of excavation. Approximate surface elevation: 351 feet Test Pit TP-3 Depth (feet) Material Description 0 – 1.5 1.5 – 9 Topsoil Gravelly SAND/Sandy GRAVEL with cobbles and trace silt, boulder: Loose to medium dense, moist, brown grading gray. (SP/GP)(Outwash) Test pit completed at approximately 9 feet on 3/18/21 due to caving. Groundwater not observed at time of excavation. Approximate surface elevation: 366 feet Project: The Vista at Mill Pond SSGC Job # 21019 TEST PIT LOGS PAGE 2 OF 2 Location: Mill Road SE, Yelm, WA TEST PIT LOGS FIGURE A-1 South Sound Geotechnical Consulting TP-1 TO TP-4, PIT-1 Logged by: THR Test Pit TP-4 Depth (feet) Material Description 0 – 1 1 – 9 Topsoil Gravelly SAND/Sandy GRAVEL with trace silt: Loose to medium dense, moist, brown grading gray. (SP/GP)(Outwash) Test pit completed at approximately 9 feet on 3/18/21 due to caving. Groundwater not observed at time of excavation. Approximate surface elevation: 364 feet Infiltration Test PIT-1 Depth (feet) Material Description 0 – 2 2 – 9 Topsoil Gravelly SAND/Sandy GRAVEL with trace silt: Loose to medium dense, moist, brown grading gray at 5 feet. (SP/GP)(Outwash)(Sample S-1 @ 4 feet) Test pit completed at approximately 9 feet on 3/18/21. Infiltration test performed at 4 feet. Piezometer set in test pit. Groundwater not observed at time of excavation. Approximate surface elevation: 347 feet Geotechnical Engineering Report SSGC The Meadows and Vista at Mill Pond Developments Mill Road SE Yelm, Washington SSGC Project No. 21019 April 20, 2021 14 Appendix B Laboratory Testing and Results Geotechnical Engineering Report SSGC The Meadows and Vista at Mill Pond Developments Mill Road SE Yelm, Washington SSGC Project No. 21019 April 20, 2021 15 Laboratory Testing Select soil samples were tested for organic content and cation exchange capacity (CEC) by Northwest Agricultural Consultants of Kennewick, Washington. Grain size (gradation) tests were completed by Construction Testing Laboratories (CTL) of Puyallup, Washington. Results of the laboratory testing are included in this appendix. Report shall not be reproduced except in full without the written approval of the Laboratory. Report pertains only to the material tested.Tested By: R Rowden Checked By: C Pedersen Particle Size Distribution Report ASTM C117/C136 PERCENT FINER0 10 20 30 40 50 60 70 80 90 100 GRAIN SIZE - mm. 0.0010.010.1110100 % Stones % +3"Coarse Medium % Gravel Fine V. Crs.Crs.Med.Fine % Sand V. Fine Crs. % Silt Fine % Clay 0 0 4 54 16 9 6 3 3 56 in.3 in.2 in.1½ in.1 in.¾ in.½ in.3/8 in.#4#10#20#30#40#60#100#140#200SIEVE PERCENT SPEC. *PASS? SIZE FINER PERCENT (X=NO) Material Description Atterberg Limits Classification Remarks Source of Sample: Pit #1 Sample Number: 21-433 Date: Client: Project: Project No:Figure Grab Sample, S-1 Sampled at 4'1" 3/4" 1/2" 3/8" #4 #8 #16 #30 #50 #100 #200 100 96 80 68 42 28 18 12 8 6 4.3 GW Report: #03 Sampled By: Client South Sound Geotechnical Alpine (21019) 9100 PL=LL=PI= USCS=AASHTO= *(no specification provided) 03-18-21 Construction Testing Laboratories 400 Valley Ave. NE, Suite #102 Puyallup WA, 98372 Tel. (253) 383-8778 Report shall not be reproduced except in full without the written approval of the Laboratory. Report pertains only to the material tested.Tested By: R Rowden Checked By: C Pedersen Particle Size Distribution Report ASTM C117/C136 PERCENT FINER0 10 20 30 40 50 60 70 80 90 100 GRAIN SIZE - mm. 0.0010.010.1110100 % Stones % +3"Coarse Medium % Gravel Fine V. Crs.Crs.Med.Fine % Sand V. Fine Crs. % Silt Fine % Clay 0 0 16 50 10 8 7 2 2 56 in.3 in.2 in.1½ in.1 in.¾ in.½ in.3/8 in.#4#10#20#30#40#60#100#140#200SIEVE PERCENT SPEC.*PASS? SIZE FINER PERCENT (X=NO) Material Description Atterberg Limits Classification Remarks Source of Sample: TP 1 Sample Number: 21-431 Date: Client: Project: Project No:Figure Grab Sample, S-1 Sampled at 7'2" 1" 3/4" 1/2" 3/8" #4 #8 #16 #30 #50 #100 #200 100 91 84 62 53 34 25 18 11 8 6 4.7 GW Report: #01 Sampled By: Client South Sound Geotechnical Alpine (21019) 9100 PL=LL=PI= USCS=AASHTO= *(no specification provided) 03-18-21 Construction Testing Laboratories 400 Valley Ave. NE, Suite #102 Puyallup WA, 98372 Tel. (253) 383-8778 Report shall not be reproduced except in full without the written approval of the Laboratory. Report pertains only to the material tested.Tested By: R Rowden Checked By: C Pedersen Particle Size Distribution Report ASTM C117/C136 PERCENT FINER0 10 20 30 40 50 60 70 80 90 100 GRAIN SIZE - mm. 0.0010.010.1110100 % Stones % +3"Coarse Medium % Gravel Fine V. Crs.Crs.Med.Fine % Sand V. Fine Crs. % Silt Fine % Clay 35 7 8 7 7 8 116 in.3 in.2 in.1½ in.1 in.¾ in.½ in.3/8 in.#4#10#20#30#40#60#100#140#200SIEVE PERCENT SPEC.*PASS? SIZE FINER PERCENT (X=NO) Material Description Atterberg Limits Classification Remarks Source of Sample: TP 1 Sample Number: 21-432 Date: Client: Project: Project No:Figure Grab Sample, S-2 Sampled at 9'1" 3/4" 1/2" 3/8" #4 #8 #16 #30 #50 #100 #200 92 83 65 61 48 42 35 28 21 14 9.9 Report: #02 Sampled By: Client South Sound Geotechnical Alpine (21019) 9100 PL=LL=PI= USCS=AASHTO= *(no specification provided) 03-18-21 Construction Testing Laboratories 400 Valley Ave. NE, Suite #102 Puyallup WA, 98372 Tel. (253) 383-8778 2545 W Falls Avenue Kennewick, WA 99336 509.783.7450 www.nwag.com lab@nwag.com Sample ID Organic Matter Cation Exchange Capacity Pit-1, S-1 @ 4’ 7.58% 12.6 meq/100g Method ASTM D2974 EPA 9081 South Sound Geotechnical Consulting PO Box 39500 Lakewood, WA 98496 Report: 54765-1-1 Date: March 31, 2021 Project No: 21019 Project Name: Meadows 2545 W Falls Avenue Kennewick, WA 99336 509.783.7450 www.nwag.com lab@nwag.com Sample ID Organic Matter Cation Exchange Capacity Pit-1, S-1 3.50% 10.5 meq/100g Method ASTM D2974 EPA 9081 South Sound Geotechnical Consulting PO Box 39500 Lakewood, WA 98496 Report: 54766-1-1 Date: March 31, 2021 Project No: 21019 Project Name: Vista UNIFIED SOIL CLASSIFICATION SYSTEM Criteria for Assigning Group Symbols and Group Names Using Laboratory TestsA Soil Classification Group Symbol Group NameB Coarse Grained Soils More than 50% retained on No. 200 sieve Gravels More than 50% of coarse fraction retained on No. 4 sieve Clean Gravels Less than 5% finesC Cu 4 and 1 Cc 3E GW Well-graded gravelF Cu 4 and/or 1 Cc 3E GP Poorly graded gravelF Gravels with Fines More than 12% finesC Fines classify as ML or MH GM Silty gravelF,G, H Fines classify as CL or CH GC Clayey gravelF,G,H Sands 50% or more of coarse fraction passes No. 4 sieve Clean Sands Less than 5% finesD Cu 6 and 1 Cc 3E SW Well-graded sandI Cu 6 and/or 1 Cc 3E SP Poorly graded sandI Sands with Fines More than 12% finesD Fines classify as ML or MH SM Silty sandG,H,I Fines Classify as CL or CH SC Clayey sandG,H,I Fine-Grained Soils 50% or more passes the No. 200 sieve Silts and Clays Liquid limit less than 50 inorganic PI 7 and plots on or above “A” lineJ CL Lean clayK,L,M PI 4 or plots below “A” lineJ ML SiltK,L,M organic Liquid limit - oven dried 0.75 OL Organic clayK,L,M,N Liquid limit - not dried Organic siltK,L,M,O Silts and Clays Liquid limit 50 or more inorganic PI plots on or above “A” line CH Fat clayK,L,M PI plots below “A” line MH Elastic SiltK,L,M organic Liquid limit - oven dried 0.75 OH Organic clayK,L,M,P Liquid limit - not dried Organic siltK,L,M,Q Highly organic soils Primarily organic matter, dark in color, and organic odor PT Peat A Based on the material passing the 3-in. (75-mm) sieve B If field sample contained cobbles or boulders, or both, add “with cobbles or boulders, or both” to group name. C Gravels with 5 to 12% fines require dual symbols: GW -GM well-graded gravel with silt, GW -GC well-graded gravel with clay, GP-GM poorly graded gravel with silt, GP-GC poorly graded gravel with clay. D Sands with 5 to 12% fines require dual symbols: SW -SM well-graded sand with silt, SW -SC well-graded sand with clay, SP-SM poorly graded sand with silt, SP-SC poorly graded sand with clay E Cu = D60/D10 Cc = 6010 2 30 DxD )(D F If soil contains 15% sand, add “with sand” to group name. G If fines classify as CL-ML, use dual symbol GC-GM, or SC-SM. HIf fines are organic, add “with organic fines” to group name. I If soil contains 15% gravel, add “with gravel” to group name. J If Atterberg limits plot in shaded area, soil is a CL-ML, silty clay. K If soil contains 15 to 29% plus No. 200, add “with sand” or “with gravel,” whichever is predominant. L If soil contains 30% plus No. 200 predominantly sand, add “sandy” to group name. M If soil contains 30% plus No. 200, predominantly gravel, add “gravelly” to group name. N PI 4 and plots on or above “A” line. O PI 4 or plots below “A” line. P PI plots on or above “A” line. Q PI plots below “A” line.