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Tech Info ReportCity of Yelm Public Safety Building Yelm, Washington TECHNICAL INFORMATION REPORT (Preliminary). October 25, 2006 Prepared By: Exeltech Consulting, Inc. 615 2°d Avenue, Suite 660 Seattle, WA 98104 PH: (206) 623-9646 Contact: Choomeng Chin 06 EXPIRES: OB-24-2008 Prepared For: Arai Jackson Ellison Murakami LLP 2300 Seventh Avenue, Seattle., WA 98121 PH: (206) 323-8800 Contact: Ben Pongprot City of Yelm -Public Safety Building TIR 0634 TABLE OF CONTENTS I. Project Overview 4 Existing Drainage System 4 Proposed Drainage System 4 II. Conditions & Requirements 10 III. Offsite Analysis 12 IV. Flow Control and Water Quality Facility Analysis and Design 19 V. Conveyance System Analysis and Design 24 VI. Special Report and Studies 26 VII. Basin and Community Planning Areas 28 VIII. Other Permits 30 IX. Erosion & Sediment Control (ESC) Analysis and Design 32 X. Bond Quantities Worksheet, Retention/Detention Facility Summary Sheet and Sketch, and Declaration of Covenant ~ 35 XI. Maintenance and Operation Manual 37 2 P:\2006\0634-Yelm\02-CARD\Civil\0634tir.doc . ~}y. City of Yelm -Public Safety Building TIR~;:,ya, ~ 0634 SECTION I PROJECT OVERVIEW P:\2006\0634-Yelm\02-CARD\C ivil\0634tir. doc City of Yelm -Public Safety Building TIR 0634 I. Project Overview This Technical Information Report (TIR) provides the technical information and design analysis required for preparing the Temporary Erosion and Sediment Control Plan (TESC) and Drainage Plan for the proposed City of Yelm, Public Safety Building. The City of Yelm adopts the 1992 Stormwater Management Manual for the Puget Sound Basin (SWMM) for all development within the city. This project will follow the SWMM requirements. The proposed Public Safety Building site is located within Yelm city limits on the east side of Second Street SE. between McKenzie Avenue SE and Washington Avenue SE (see Figure 1 -Vicinity Map). The total lot area for the site is approximately 1.67 acres including portion of the portion of the lot occupied by the city water tower and pump station with paved parking, the area within the lot that will be developed is approximately 34110 s.f. (0.78 acres). Total area of the roadway improvement for this project is approximately 35,352 s.f. (0.81 acres). Existing Drainage System Presently, the project site consists of open space, fenced city water tower and pump station and paved parking on the south side of Washington Avenue SE. The existing ground slopes 2% to 4% southwesterly towards the city park. The drainage from the site sheets flow towards existing roadway drainage inlets along the eastside of Second Street SE and along the north edge of McKenzie Avenue SE. The runoff drain to the existing drainage infiltration system within the city park (see downstream analysis in Section III). Proposed Drainage System The development of the site will maintain the existing drainage patterns. The runoff from the site will continue to be infiltrated underground. The roadway and onsite drainage will be combines and drain to the proposed infiltration system within the lot located under the parking and landscaping area near the east property line. All developed impervious area will be treated by installing runoff treatmerit system by Aquaswirl or equal before being discharged to infiltration drainage system. The site slope southwesterly from 2%-4%, see topographic survey map. The proposed safety building is located on the south side of the lot. According to the Soil Survey of Thurston County, the soil on site is classified as Spanaway gravelly sandy loam consists of gravelly sand. Hydrologic Soil Group A. The proposed safety building area is approximately 11,838 s.f. The total impervious area including parking and sidewalk for the improvement within the lot is approximately 34,110 s.f. and the street improvement area is approximately 35,352 s.f. P:\2006\0634-Yelm\02-CARD\Civil\0634tir.doc City of Yelm -Public Safety Building TIR 0634 fir;, 27 .~ ~ °" ~ ": o ~4 T h" ~, :7' o is - , lti - ~!, fy„ ~ cy ~ ;L ] ' 2 ~2~. Y Qa ~ ~`7 'v,'t_.. ~3 ~~ r; ' ~. Berryvalln•a~.S_ ~~.`~ F10 ~~~, ~~ ~r~• Railuaayf~d~~~ ~. ~. c 4 B'~,r.~,F ~ti y ----- .r' b,. ~ ~~ 3 a :. Y , ~ y i rV~'r ~~ p ~'~y 9 ~~~ ~~ tom'' ~. `,~ Longmire St S~ ~~' ~~E ~~F ~~''~ ~~r~ - ~ 7~, ~ Y e I m `a,.. ~ , ` " .,~ .-, ~~~ ~,~ ~~ ~~%. ~ a ~c. ~ _ . ~', ~ r,~+ F. !~ '~' w z-~ .c fi` ~ ~• 105th lave Sc ~ ~ ,::,~ ~ f~ ., ~E 1a3rd Rue . ,~ . . Ffa~jfernCt~c: ~ i1 ~~'~~~ `L`~. Q`~~ 10-Fth rive st '',q °, _,...,,..,,_, ~, up ., ,^.,.. .ti o° ~._.. - 1 Oft ~.. aw `, 3r. Rte` 'x ~ ~rterG`ts~ ~~''~ v Prairie Heights c;,' S~ ~,,, ._. .~ ,r _ ~,~ n 1~ _. ~~ 4 FIGURE 1: VICINITY MAP SCALE: NTS 5 P:\2006\0634-Yelm\02-CADD\Civil\0634tir.doc City of Yelm -Public Safety Building TIR 0634 ~;~ ~~ ~, _ ~, ,o~ . 4 ~.. <- ~- -- _- u.« _ _ _ _ _ ~ _ 1 ' -~ ~. ,, WASHINGTON AVENUE SE ~, ~,. - - -.F, ------ ----1 l ~ I ;~ IT ~ , Q ~ ~ a~.~ ' ~ - _ ~ _! ~ : ~k~ .I 1 1 ~, ~I ~ _ ~~ I~~_ ~ ~- ~ ~ I I - ~ ~ ~ ~ ~ ~ ~ , ®~ P soewwn -_ I I ,~,~ay0,~ "f' . ,~~. o, ~ ,_ __ .. ~~ o _. I ~ L ~ ~~~ ~~ I .~,'~ ~_ oo I -1 0~ ~ "I~ ~ I n <, ,. ~ ~~ ~._ a ~ _~____- ~_. ,, -~;I ~ . i Ii .. -. _ _ __._ ~ _ ,, __ ~ _ ~ ,~,,i . - _ _,. I -_. ~° I ~i I ~ r_ I w I _ f ff , ,_.._..... .,.:.: OT11 I z I _._ ._.._. I -.,. - -- I ~° ~.~ I o i ~ ~ ~ i '~ %~ I, , ~.~ - -- I ' ''V ~----- I ~ !~ o- __` McKENZIE AVENUE SE -----------1--1 •.~- ~ - ~.~ ~® ------ ---------- ------- - sr b~.ss--- ,{ ' ,, -- } ,. ~ x .-.. __~ _ - ~ -~J - - -- i ~ --- --- ~- --= -- - ~ -- -- -- - --- w- > ~ i ,~, I ~ ~ _ . _ ~ _ ~ w 1 I I ~ ~ ' ;'~:~ ', ;II FIGURE 2: EXISTING SITE CONDITIONS MAP (NTS) P:\2006\0634-Yelm\02-CADD\Civil\0634tir. doc City of Yelm -Public Safety Building TIR 0634 FIGURE 3: PROPOSED SITE DEVELOPMENT MAP (NTS) 7 P:~2006v0634-Yelmv02-CADDvCivilv0634ticdoc City of Yelm -Public Safety Building TIR 0634 ~-. \` ~~~t G i Siay o~~.,t tt`.: ' ~r +~~ { ~j ~ ,~a t , y-i i tt ti ti~ ~ '< ~~ ~; ~ 4 h 4 ~~ ~ i'1 ' `r ~~~ ti ' - '' ~ ~`~ ' ~ \ ~ ~ 4 ~' ~ dry` °~ a, ~, ~'~ `~, E ~ ~ ~ ~~ ti ~ t :~ ~~. ~ `` '' °~'- r ~'i~ ~ e~ ~ ~ ', ~\ . 1 w~ ~ - ~~°. ~ ~ ~' `~ ~ ~~i,~ `' , may. 7 L ~' r'~.~ •, '` "~ T~1 ~~\ ~`'` i ~ ~~~~f~ 3, ;. ~ ~~ ti ~,'~,3 ~-. ~.-_ _ r~5 ~~'s .~o~ ° ~a~. ~,, a., ~ ~, ~~ ~~ ~ __ - ~'~~ FIGURE 4: SOIL SURVEY MAP (NTS) `, ~1,t7 ~~ ~ ~. g P:\2006\0634-Yelm\02-CADD\Civil\0634tir.doc City of Yelm -Public Safety Building TIR 0634 SECTION II PRELIMINARY CONDITIONS SUMMARY P:~2006\0634-Yel m\02-CADD\C ivil\0634tir. doc City of Yelm -,Public Safety Building TIR 0634 II. Conditions & Requirements This site is located within City of Yelm and proposed development is over 5000 sf. The development is required to comply with temporary erosion and sediment control, and drainage requirement per 1992 S WMM. Core Requirements: • Temporary Erosion and Sediment Control: See Temporary Erosion and Sediment Control Plan design per SWMM requirements. • Discharge at a natural location: Runoff from the site will be discharged at the natural location. • Source Control of Pollution: Proposed site does not generate commercial pollution besides vehicular traffic. • Runoff treatment BMPs: Runoff from the site will be treated before being discharged to the infiltration system. • Stream bank Erosion Control: Not applicable. Infiltration system is proposed. • Wetlands: The site does not contain any wetland. • Water Quality Sensitive Area: The site does not flow to any surface water quality sensitive area. • Offsite Analysis and Mitigation: Level 1 downstream analysis included in Section III. • Basin Planning: The site is within City of Yelm. • Operation and Maintenance: On-site storm drainage system is owned and maintained by City of Yelm. See Section XI for guidelines information. • Financial Guarantees and Liability: The City of Yelm will attain all necessary permits required by the City prior to the beginning of construction. Special Requirements: • Floodplain/Floodway Delineation: The project site is not located within a 100-year floodplain (see Figure 7). • Flood Protection Facilities: The project site does not contain a class I or 2 stream and will not be constructing or modifying an existing flood protection facility. 10 P:\2006\0634-Yelm\02-CADD\Civil\0634tir.doc .i. City of Yelm -Public Safety.Building TIR~I~w 0634 ,. SECTION III OFF-SITE ANALYSIS 1 1 p:\2006\0634-Yelm\02-CADD\Civil\0634tir.doc of Yelm -Public Safety Building TIR 0634 III. Offsite Analysis Upstream Analysis Upstream area consists of developed roadway to the north. The upstream drainage will not affect the drainage system on site as it bypasses the site drainage system through the provided pipes and catch basins and discharge to the existing infiltration system within Yelm City Park. Downstream drainage Analysis: Level 1 Runoff exist the project site at the southwest corner of the property into an existing catch basins along Second Street SE. General slope of the. site is from northeast to southwest. Task 1: Study Area Definition and Maps The upstream tributary area to this project consists of the developed Washington Avenue SE to the north where existing roadway drainage system collects runoff from the street and connect to the on site parking storm system. The existing parking drainage system runs westerly and exists to Second Street SE drainage system that flow to the infiltration system within Yelm City Park. Majority of the onsite runoff sheet flows to Second Street SE that ends at the infiltration system within the Yelm City Park. There is no likelihood that the proposed project activities could affect the upstream area with backwater conditions. The discharge point of the project is at the southwest corner of the property into the Second Street SE infiltration drainage system. A reduced copy of the existing conditions map is included as Figure 2, a site map showing the property lines. The drainage system ends at the west side of Second Street SE where the park entrance and the infiltration system is located (see Figure 5, Drainage System Map). Task 2: Resource Review In our effort to determine, if there were any existing or potential problems with this downstream portion of the city drainage system, the following resources were reviewed: a) Adopted Basin Plans. (None) b) Floodplain/floodway (FEMA) Maps. c) U.S. Department of Agriculture Soil Survey. d) Wetland Inventory Maps. (None) 12 P:~2006\0634-Yelm\02-CARD\Civil\0634tir.doc City of Yelm -Public Safety Building T[R 0634 FIGURE 5: DRAINAGE SYSTEM MAP (NTS) 13 P:~2006\0634-Yelm\02-CADD\Civil\0634ticdoc City of Yelm -Public Safety Building TIR 0634 ~,. _. ~' ~~ ~. `'~ 1 ~~ ~V - - . , i `` ~ ..,-~ t ~"~ ~ Y~ • ~ t,r ..rwrw.n...++«rwa.~~-.. ~ v ;. ~ ~ -._._ Galf Course ._~ 'y ~ .r .r., _._._ `` ~ . . . ~~ _ /; FIGURE 6: USGS TOPOGRAPHIC MAP (NTS) ~/}\~~ ~~~, r, •.. °Jf +! 14 P:\2006\0634-Yelm\02-CARD\Civil\0634tir.doc City of Yelm -Public Safety Building TIR 0634 ~. ~ . . F : ', ~ ' ~ .> I Re ` ~ I ~ ~~ APP RO%IMAfE S~A~L IN FEET 500 a 500 Z `F !~ VS ONEX T ~0 ~~ p ~ZU N ~ k gS ~ , , 1 p~ ENE. f ~' ~ ~ ' ~ A s I". NkTIONAI iL000 INSUTAMCE P19iiAM ~ i yt ~~~, P.Ec`4~ `. O ~ ~% .. ! ` - ~' h ~ ~ ,~, V ~',% y! Step ~ F~C`q's `~ ~~., ~ ~ r [ pp ~~i~~~i ~~ F~RIN ~ /~ `ru 5~ O u~i FLOOD INSURANCE RATE MAP pL~ ~i~~. P' ~l~ `2~ ~9'Ma 'C~ ~ ~ j ' ~ I ~~V' CITY F ~ ~H sr ~ ~~ s ~~ ~ ~ O YELM, q~ a~ ~ e ~' ~ ~~!' ~ WASHINGTON ~ ~ ~ ~ 9 ~ (ITWRSTON COUNTY) i~ S //~ /' Pyt ~r~Ja T9~? ~~ ~ v ~`~ ""' n ST ° S ONLY PANEL PRINTED it Kil n Fr ~ ~~ ~rFry~ ¢ gO J tip P~ '~q~~r sr~~ ¢~J~ \ ~~ \ ~' ~- ~ ~ ~ti CBMATIINITI-PANEL NUtIBEN !'~;P,i~riry s9o31oaoolA ~ Sesels r ~ EFFECTIVE DATE: ~ Lake ~ TUNE 16, 1999 ~ k ~~ FedeN Emctgncy Mmgsemmt Ay~y g L ~ _ FIGURE 7: FEMA FLOOD MAP (NTS) I $ P:\2006\0634-Yelm\O2-CADD\Civil\0634tir.doc City of Yelm -Public Safety Building TIR 0634 Task 3. Field Inspection A field observation was conducted to gather information including a level 1 Downstream Analysis and off-site conveyance system. Level 1 Field Study 1. No reported or observed problems. 2. No existing or potential constrictions or lack of capacity in the existing drainage system was apparent. 3. No reported flooding areas were discovered. 4. No existing/potential overtopping, scouring, bank sloughing, or sedimentation is apparent. 5. No known aquatic habitats in the conveyance route. 6. The downstream area consists mainly of an existing developed roadway drainage system. The topography is gentle to moderate with no significant steep slopes. The soil types described in the USGS soil survey is classified as Spanaway gravelly sandy loam, type A hydrologic soil group. 7. The pipe sizes encountered are from 6 inches up to 12 inches in diameter. 8. Off site areas tributary to the project site were consistent with the site map included. 9. No known complaints of flooding. 10. The site visit was conducted at 5 pm. on October 11, 2006. The weather was sunny and 70 °F. Task 4. Drainage System Description and Problem Descriptions Upstream . The upstream tributary area to this project consists of the area within the developed Washington Avenue SE to the north. Runoff entering the site through the catch basin and drainage pipes to the north parking lot catch basin and exists the parking to the east side of Second Street SE. All runoff will continue flowing southerly within the roadway drainage system and discharge to the infiltration system at the west side of Second Street SE within the entrance of the Yelm City Park. No anticipation of any impact to the upstream drainage system due to this development Down Stream Drainage System Description: Runoff from the proposed site is presently sheet flow across the mostly open space grass lot to the intersection of Second Street SE and McKenzie Avenue SE. All runoff discharges to the existing catch basins approximately 110 feet southerly along the east side of Second Street SE where infiltration system/dry well is located within the roadway based on the survey information that the drainage catch basin structure does not have any outlet. During the down stream drainage field visit no areas of an existing or potential drainage problems were apparent. 16 P:\2006\0634-YeVm\02-CARD\Civil\0634tir.doc . t"~, ~r 't '"1 1 ka 'rvt, ,t, r '.`Y City of Yelm -Public Safety Building T[R~~~t: 0634 Problem description: - `.,:~,:.,. ,:'`v~""'-„u=~:'~~ The down stream drainage system as described above is a not prone to stream bank erosion, siltation, slides and does not threaten destruction of aquatic habitats. Task 5. Mitigation of Existing or Potential Problems No off-site mitigation is necessary, as there are no observed problems during the analysis. However, since the development of this site and the improvement of the street will have a new separate infiltration system within the lot, the existing runoff to the existing infiltration within the entrance of the Yelm City Park will be substaritially reduced. This proposed drainage system would attenuate any concern that the city has for the near capacity of the existing infiltration system at the west side of Second Street SE within-the Yelm City Park entrance. 1 ~ P:\2006\0634-Yelm\02-CARD\Civil\0634tir.doc City of Yelm -Public Safety Building TIR 0634 SECTION IV FLOW. CONTROL AND WATER QUALITY FACILITY ANALYSIS AND DESIGN 18 P:\2006\0634-Ye1m\02-CARD\Civil\0634tir.doc of Yelm -Public Safety Building TIRa:~-t~~i~i~,', 0634 IV. Flow Control and Water Quality Facility Analysis and Design Flow control for this site will be handled by the infiltration system up to 100-year 24/hr storm event. Based on the Geotechnical Engineering Investigation Report dated October 9, 2006 prepared by Krazan and Associates, Inc., the soil infiltration rate at the location of the proposed area is in access of 20 inches per hour. A safety factor of 2 is used for sizing of the infiltration bed. "Water Works" program is used with SBUH methodology for level pool computation as presented below. The runoff will be treated by utilizing Aquaswirl system for water quality before entering the infiltration system. The following tables show the area summary and infiltration design: PROPOSED CONDITION ONSITE SF Acre Pervious Forest 0 0.00 Pasture 0 0.00 Grass/Landscaping 6115 0.14 Impervious -Parking/Driveway 12434 0.29 -Sidewalk 3682 0.08 -Building Roof 11879 0.27 Total = 34110 0.78 OFFSITE Pervious Forest 0 0.00 Pasture 0 0.00 Grass/Landscaping 0 0.00 Impervious -Roadway 26438 0.61 -Sidewalk 8913 0.20 Total = 35352 0.81 Total Site Pervious 6115 0.14 Impervious 63347 1.45 69461 1.59 Table 1-DRAINAGE AREA SUMMARY l 9 P:\2006\0634-Yelm\02-CADD\Civil\0634tir.doc City of Yelm -Public Safety Building TIR 0634 Project Precipitations. [2 yr] 2.30 in [10 yr] 3.20 in [25 yr] 3.80 in [100 yr] 4.50 in [6-mo] 1.50 in All Event Summary: BasinlD Peak Q Peak T Peak Vol Area Method Raintype Event ------- (cfs) (hrs) (ac-ft) ac /Loss All 0.74 8.00 0.2576 1.59 SBUH/SCS TYPEIA 2 yr All 1.06 8.00 0.3727 1.59 SBUH/SCS TYPE1A 10yr All 1.27 8.00 0.4502 1.59 SBUH/SC S TYPEIA 25 yr All 1.52 8.00 0.5410 1.59 SBUH/SC S TYPE1A 100 yr All 0.46 8.00 0.1571 1.59 SBUH/SC S TYPEIA 6-month Drainage Area: All Hyd Method: SBUH Hyd Loss Metho d: SCS CN Number Peak Factor: 484.00 SCS Abs: 0.20 Storm Dur: 24.00 hrs Intv: 10.00 min Area CN TC Pervious 0.1400 ac 77.00 0.32 hrs Impervious 1.4500 ac 98.00 0.13 hrs Total 1.5900 ac Supporting Data: Pervious CN Data: Landscaping 77.00 0.1400 ac Impervious CN Data: Pavement 98.00 1.4500 ac Pervious TC Data: Flow type: Description: Length: Slope: Coeff: Travel Time Sheet Grass 150.00 ft 1.25% 0.1500 20.19 min Impervious TC Data: Flow type: Description: Length: Slope: Coeff: Travel Time Sheet Pavement 199.00 ft 0.60% 0.0110 4.01 min Channel Pipes 21.00 ft 0.50% 42.0000 0.12 min Channel Pipes 205.00 ft 0.50% 42.0000 1.15 min Channel Pipes 21.00 ft 0.50% 42.0000 0.12 min Channel Pipes 43.00 ft 0.50% 42.0000 0.24 min Channel Pipes 34.00 ft 0.50% 42.0000 0.19 min Channel Pipes 81.00 ft 0.50% 42.0000 0.45 min Channel Pipes 34.00 ft 0.50% 42.0000 0.19 min Channel Pipes 146.00 ft 0.50% 42.0000 0.82 min Channel Pipes 30.00 ft 0.50% 42.0000 0.17 min Channel Pipes 40.00 ft 0.50% 42.0000 0.22 min Table 2 -DRAINAGE AREA PEAK RUNOFF 20 P:\2006\0634-Yelm\02-CADD\Civil\Ob34tir.doc City of Yelm -Public Safety Building TIR~,.,F~i,~,, ~ 0634 TRIBUTARY AREA TO THE INFILTRATION BED Onsite = 0.78 Ac. Roadway = 0.81 Ac. SBUH 100-yr Peak Flow :Total = 1.52 cfs STAGE-DISCHARGE RELATIONSHIP BED DIMENSIONS : L = 78 FT H = H FT W = 24.25 FT INFILTRATION RATE, f = 20 IN/HR FACTOR OF SAFETY, S. F. = 2 INFILTRATION RATE WITH S. F., fd = 10 IN/HR 0.83 FT/H R 0.000231 FT/S BOTTOM DEPTH OF BED TO STRATUM, L = 10 FT BOTTOM BED SURFACE AREA, As = 1891.5 S.F. SOLVING FOR Q IN DARCY'S (Infiltrated Flow EQUATION. Rate) Q,;= fd " i '' As = fd * (H+L)/L * As Where : i =hydraulic gradient STAGE-STORAGE RELATIONSHIP S=As"H*VOID RATIO WHERE VOID RATIO = 0.57 RESULT OF PRELIMINARY SIZING H i Q S (storage) ft. ft/ft cfs cf 0 1 0.44 0 1 , 1.1 0.48 1078.155 2 1.2 0.53 2156.31 2.5 1.25 0.55 2695.388 3 1.3 0.57 3234.465 3.5 1.35 0.59 3773.543 4 1.4 0.61 4312.62 5 1.5 0.66 5390.775 Table 3 -PRELIMINARY INFILTRATION BED SIZING (ASSUMED) 21 P:\2006\0634-Yelm\02-CADD\Civil\0634tir.doc City of Yelm =Public Safety Building TIR 0634 . Node ID: INF-1 Start El: 343.5000 ft Max El: 346.4000 ft Contrib Basin: Contrib Hyd: Hgl Elev: 346.4000 ft Storage Id: ST1 Discharge Id: INF Node ID: ST1 Desc: Chamber Storage Start El: 343.5000 ft Max El: 347.0000 ft Contrib Basin: Contrib Hyd: Hgl Elev: 346.6870 ft Length Width Void Ratio 78.0000 ft 24.2500 ft 57.00 Bottom area only with infiltration Control Structure ID: INF -Infiltration control structure Descrip: Storm Chamber Start El Max El Increment 343.5000 ft 347.0000 ft 0.10 Infil: 10.00 in/hr Multiplier: 1.00 Table 4 -INFILTRATION BED AND STAGE STORAGE Summary: The calculation indicates that the required area for the infiltration to handle the entire runoff up to 100-yr/24-hr storm is 1949 s.f. Using the "Storm Chamber" with overall void ration of 0.57, the stage-storage calculation indicates that the maximum HGL level for 100-yr/24-hr peak runoff is 346.69 that is below the maximum elevation for the infiltration bed of 347.00. 22 P:\2006\0634-Yelm\02-CADD\Civil\0634tir.doc City of Yelm -Public Safety Building TIR~..~;,_,, 0634 SECTION V CONVEYANCE SYSTEM ANALYSIS AND DESIGN 23 P:\2006\0634-Yelm\02-CARD\Civil\0634tir.doc City of Yelm -Public Safety Building T1R 0634 V. Conveyance System Analysis and Design Conveyance requirements for new systems: The new conveyance system mainly consists of roof drain tightline and driveway drainage. The 12" drainage pipes with a minimum design slope of 0.5% have capacity of 2.52 cfs. This is sufficient to convey the proposed entire area for 100-yr 24/hr storm with peak runoff of 1.52 cfs. 24 P:\2006\0634-Yelm\02-CADD\Civil\0634tir.doc City ofYelm -Public Safety Building TIR_,; 0634 SECTION VI SPECIAL REPORT AND STUDIES 25 P:\2006\0634-Yelm\02-CARD\Civil\0634tir.doc City of Yelm -Public Safety Building TIR 0634 VI. Special Report and Studies Not required. 26 P:\2006\0634-Yelm\02-CADD\Civil\0634tir.doc City of YeUn -Public Safety Building T[R,; , __.. 0634 SECTION VII BASIN AND COMMUNITY PLANNING ARES 27 P:\2006\0634-Yelm\02-CARD\Civil\0634tir.doc City of Yelm -Public Safety Building TIR 0634 VII. Basin and Community Planning Areas Not Applicable. 28 P:\2006\0634-Yelm\02-CADD\Civil\0634ticdoc City of Yelm -Public Safety Building TIR : ~_ 0634 SECTIOl~ VIII OTHER PERMITS 29 P:\2006\0634-Yelm\02-CADD\Civil\0634tir.doc of Yelm -Public Safety. Building T[R 0634 VIII. Other Permits SEPA Application. Land Use Permit. Building Permit. 30 P:\2006\0634-Yelm\02-CADD\Civil\0634ticdoc City of Yelm -Public Safety Building TIR ., 0634 SECTION IX EROSION AND SEDIMENT CONTROL ANALYSIS AND DESIGN 31 P:\2006\0634-Yehn\02-CADD\Civil\0634tir.doc City of Yelm -Public Safety Building TIR 0634 IX. Erosion & Sediment Control (ESC) Analysis and Design Project Description: The project will consist of a public safety building. Approximately 1.59 acres will be involved in the development activity including roadway improvement. Existing Site Conditions: The existing project site is open with grass cover. Existing drainage for the project site is from the northeast to the southwest of the site. During the proposed construction this drainage pattern will be maintained. The runoff discharge from the project will exit the site at the southwesterly direction of the property to the existing drainage system. Erosion and Sediment Control Measures: Delineate Clearing and easement limits The development drawings clearly indicate the limits of development activities. Prior to any clearing or construction on site, the clearing limits for the project stage shall be clearly marked. The stakes shall be vividly marked with surveyors flagging and located with surveying methods. Cover measures According to the standard ESC notes included, all disturbed areas to remain unworked for more than seven days during the dry season (May 1 to September 30) or two days during the wet season (October 1 to April 30), unless otherwise determined by the city. Any disturbed areas to remain unworked for more than 30 days will be seeded or sodded, unless the city determines that winter weather makes the vegetation establishment unfeasible. During the wet season any stockpiles to remain unworked for more than 12 hours will remain covered. Perimeter Protection A filter fabric silt fence shall be installed at the downstream end of the disturbed areas of the site. The fence shall be so located that any sediment laden runoff that does not directly enter the protected inlets will be filtered prior to offsite discharge. The perimeter protection will be installed prior to upstream grading. Construction Entrance Routes Prior to the start of general construction the construction vehicle entrances to the site shall be stabilized with a rock pad as detailed on the drawings, unless the proposed location of the construction entrance at the existing asphalt access is acceptable to the city. 32 P:~2006\0634-Yelm\02-CADD\Civil\0634tir.doc City of Yelm -Public Safety Building TIR„ 0634 Sedament retention ~~-~ ~~ The contributing drainage area for this development is much less than 3 acres, therefore a sediment trap is proposed at the same downstream location as the proposed outfall. Immediately following the installation of the filter fabric fence, sediment trap basin shall be installed at the northwest corner of the parcel, which is the lower end of the natural drainage basin. The sediment laden runoff from the site will be directed to the basin and treated prior to offsite discharge. ..The surface area of the sediment trapping basin is evaluated based on the SWMM ESC standards. The surface area is based on the 2 year 24 hour runoff generated by the exposed site. For the proposed development, the runoff volume Q2 for the development is approximately 0.0526 cfs. Using the value of velocity of sedimentation Vsed equal to 0.00096 foot per second in the following equation, the area of sediment basin obtained is 109 SF. SA = 2 Q2 /Vsed = 2 x 0.0526 / 0.00096 = 109 sf A minimum surface area of 109 sf will be provided at elevation 347' that is the invert of the weir. Please note that a 2 year discharge value was utilized because the development area and the impact of the development are minor. A sediment storage depth of 1.5 feet is provided below the bottom of this pond with a slope of 3: 1. A depth 2 feet is provided above this area for sediment settling pond at 3:1 slope. Total depth of the sediment basin is 3.5 feet. Dust Control Preventive measures to minimize wind transport of soil by water truck shall be implemented to prevent traffic hazard or sediment transported by wind into existing water resources. 33 P:\2006\0634-Yelm\02-CARD\Civil\0634tir.doc of Yelm -Public Safety Building TIR 0634 SECTION X BOND QUANTITIES WORKSHEET, RETENTION/DETENTION FACILITY SUMMARY SHEET AND SKETCH, AND DECLARATION OF COVENANT 34 P:\2006\0634-Yelm\02-CADD\Civil\0634tir.doc City of Yelm -Public Safety Building TIR 0634 X. Bond Quantities Worksheet, Retention/Detention Facility Summary Sheet and Sketch, and Declaration of Covenant Not Applicable. 35 P:\2006\0634-Yelm\02-CARD\Civil\0634tir.doc City of Yelm -Public Safety Building TIR 0634 SECTION XI 1VIAINTENANCE AND OPERATION MANUAL 36 P:~2006\0634-Yelm\02-CADD\Civil\0634tir.doc City of Yelm -Public Safety Building TIR 0634 XI. Maintenance and Operation Manual The project site development proposes the following drainage conveyance and water quality treatment. The following is brief description of the facilities, their purpose, and their operation. Inlet Structures The inlets structures provided at strategic locations within the development to provide bypass of the offsite flow runoff. The inlet structures receive surface runoff and convey the same to the existing roadway drainage system. These include catch basins minimum with catch bottom of 18 inches in depth that holds any sediment that enter the site during its normal operation. Water Quality Treatment Facility All surface runoff from the site is routed through the Aquaswirl water quality treatment system. Following are the maintenance tasks to be performed on the above facilities and their frequency. Facility Task Frequency Catch Basins Pipes Removal of Trash & Debris Sediment removal Structural damage repair Removal of Trash & Debris Sediment Removal Structural repair Twice a month in wet season Twice a month in wet season Yearly as needed Twice a month in wet season Yearly and as needed Yearly and as needed The infiltration bed and Aquaswirl treatment system maintenance and operation will be added in the final report. 37 P:\2006\0634-Yelm\02-CARD\Civil\0634tir.doc