HomeMy WebLinkAbout1997.04.23 - Design Report San Juan Infiltration System Blue Heron Schoolr'IIDESIGN REPORTSan Juan Avenue Infiltration Systemat Blue Heron Middle SchoolCity Drainage Basin No. 5In the City of Port Townsend, WashingtonPrepared for: Department of Public WorksCity of Port Townsend5210 Kuhn StreetPort Townsend, WA 98368(360) 38s-7212Prepared by:Polaris Engineering & Surveying Inc.206 S. Lincoln StreetPort Angeles, WA 98362(360) 452-5393April23,1997,G"L#; i*;$ts r-r : ;;:'*'P00p"83i;96€JobNo. 97037
Ii.t1. BackgroundCity Drainage Basin 5 drains to Townsend Meadows, a closed depression wetland ofapproximately 5 acres located west of San Juan Avenue on the Blue Heron MiddleSchool property. A portion of the drainage basin (11.0 acre sub-basin) is prevented fromdraining to the wetland due to the construction of San Juan Avenue artd the Blue HeronMiddle School. The sub.basin has been subdivided into 10,000 acre lots of which 50%are currently developed. Soils in the sub-basin are glacial outwash (San Juan Series)which are characterized as having a high capacrty for infiltration. The low point atLoganand San Juan has been fitted with two drainage inlets which collect and dispose ofsmall flows in dry wells. While there are no drainage related complaints of record at theintersection (See Port Townsend Stormwater Master Plan), localized flooding inanticipated as the sub-basin develops and the percentage of impervious area increases.A new collection system for the sub-basin is planned in association with the San JuanAvenue reconstruction project which will commence in June,1997. The plan, designedby Perteet Engineering, Inc., shows the collection of San Juan Avenue and Lopez runoffat inlet structwes, and the routing of the runoff tlrrough conduits to Drainage Basin 6(Froggy Bottoms). The routing of storm drainage from one drainage basin to another isnot acceptable practice. This project attempts to provide an alternate meaRs of disposingof the runoffwithin Drainage Basin 5.Increases in post development runofffor the Blue Heron Middle School are disposed ofby a combination of biofiltration pretreatment and direct infiltration. The infiltrationfacility is located in the a wedge of glacial outwash soil that lies in the parking lot at thefront of the school. This wedge extends to the east across San Juan Avenue for aconsiderable distance. The same outwash wedge can be used to dispose of the runoffcollected at San Juan and Lopez.This design collects runoff in the irrlets engineered by Perteet. The runoff is then routedto a sediment trap in the roadway median strip. From there, the treated runoff is pipedsouth for approximately 130 feet to an infiltration trench located in the wedge of outwashsoil. The infiltration system is designed to treat and infiltrate a lO-year storm. Thesystem will drain a 100-year storm within the 48 hour period established by the DOETechnical Manual, however, the system may not prevent street flooding during the 100-year event.2. Hydrologic CalculationsHydrologic caloulations were performed using Waterworks, an evcnt simulatordeveloped by Egenious Systems of Seattle, Washington. The I 1.0 acre sub-basin wasPage2
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r!('Ibfirst modeled in the fully developed condition and iterations were nrn for the 6-month,2-,1.A-,25-, an6100-year storms. The model was then modified to add the infrltrationtrench as a means of release.The junction box/sediment trap was modeled as a rectangular vault (Storage Structure A)which has an orifice drscharge device (Discharge Structure A) to control outflow to theinfiltration trench. The infiltration trench was modeled as a trapezoidal basin (StorageStructure B) 3 feet deep with a broad crested weir (Discharge Structure B) and a surfaceinfiltration rate as the means of discharge. The broad crested weir was added to themodel to insure the vertical limits of operation ofthe ffench at 3 feet. Control oftheinfiltration trenchwas achieved by limiting an orifice diameter (Discharge Structure A)so that the weir (Discharge Structure B) would not operate and, therefore, insure that thedischarge from the infiltration trench was only by diroct infiltration. The infiltration ratewas set at 50% of the observed rate as a factor of safety. The calculation sets are showninAppendixA.3. Infiltration System DesignThe design of infiltration systems is controlled by the DOE Technical Manual. TheManual has specific requirements for site planning soils screening, protection of existinginfrastructure and ground water quality, and infiltration trench design. Of primaryconcern is the protection of "waters of the state", insuring the infiltration system will notcontaminate the ground water aquifer. Of second greatest concern is that the trench willbe suitable placed and have a good change of successful operation. The DOE Technicalmanual worksheets for Feasibility Anatysis and general Limitations for InfiltrationBMP's are included in Appendix B.The discharge site is composed of glacial outwash material with minimal silt and claycontent whose infiltration rate (4 inch/min) is higher than recommended (2 inctr/min),and cation exchange capacity is expected to be lower than advisable. Without theaddition of pretreatment, contaminants could be inhoduced to the gtroundwater aquiferthrough the infiltration system. There will be pretreatment in the form of biofiltrationswales constructed on Lopez Street and off line biofiltration on the east side of San JuanAvenue. This will treat over 90% of the influent. All influent will be treated forsediment removal prior to entering the infiltration trench.The TM utilizes Darcy's Law methodology to determine ground water movement. Thesame approach is used by Waterworks. The infiltration ffench was modeled as atrapezoidalbasin with steep side slopes. The progam applies the infilfiation factortoboth trench bottom and sides to determine the release rate through a range of ponddepths. An overflow weir was added to the model. This does not reflect an actualItl_t"Page 3
rrIt;I'r--tJFItltrtItIcondition, but a limit on the operation of the model, To be successful, the model of theinfiltration trench must release the intended flow without overtopping the basin andcausing flow over the weir. If the weir is activated, the orifice must be reduced, or thearea of the infiltration trench increased to allow the trench to operate within the heightlimitations.In the model, time series outflow front the surface basin is metered through an orificedevice and routed to the infiltration trench. The infiltration rate varies with the depth ofwater in the infiltration trench. The summary printout provided reports the maximumdepth in the trench. Details of the variation of pond depth with time are reported indetailed printouts which are included in Appendix A of this report.The final design reflects a system that operates within the design parameters for theinfiltration trench system. Results of the simulations are reported below:Yes26.8r'r3.051.5I1O0-YearYes26.2Hr3.000.8125-YearYes25.8 Hr2.250.5210-YearYes2s.2Hr0.100.082-YearYesl5 I{r0.100.026-MonthAcceptableLimitsTime to InfiltrateMaximum DepthMaximumDischargeReturnPeriodInfiltration Trench4. Landscape PlantingConstruction of the sediment trap, transfer pipe, and infiltration trench will occur in themedian strip at the Blue Heron Middle School. The median strip was landscaped inconjunction with the school construction. It is grass planted with a number of 3"specimen trees. The sod and trees will be removed during construction of the projeot andwill be replaced in a similar condition once the trench facilities are installed. No otherintemrption of the school is anticipated.5. SummaryThe final project is the result of a number of engineering studies (hydrologic and soils),it_Page 4
r!ItrtTechnical Manual control, and engineering design. The constructed system will providea suitable means of draining the 10.0 acre sub-basin while maintaining the traditionaldrainage basin boundaries.l'-ItIr-IlIItI[-t_ILPage 5
ReferonqeisFleming, John S, Soils Logs, March 19, t997.HongWest & Associates, Infiltration Test Results - Proposed Infiltration PondSan Juan Avenue dnd Cedar Street Port Townsend, Washington, Project 94148-300, June19, 1995.Myers-Biodynamics, Inc-, Geotechnical Design Report-Port Townsend SchoolDistrict Proposed Middle School site (Site B), May 21,1993.Page 6
Appendix A: Hydrologic Calculations
4lZ2/97 Polaris Engineering & Survey97037 SAN JUAN RECONSTRUCTION PROJECTLOPEZ AREA INFILTRATION SYSTEMPOST DEVELOPMENT STORM SPREAD IN TRENCHESpage 1BASIN SUMMARYBASIN ID: A NAME: SJ 6-MONTHTOTAL AREA.......: 1l-.00 Acres BASEFLOhIS: 0.00 cfsRAINFALL TYPE....: TYPEI.A PERVIOUS AREAPRECIPITATION....: O.64 inches AREA..: 5.66 AcresTIME INTERVAL....: 10.00 min CN....: 65.00TIME OF CONC : 42.30 MiN IMPERVIOUS AREAABSTRACTION COEFF: O.2O AREA..: 5.34 ACTESCN....: 98.00TcReach - Sheet L: 200.00 ns:0.1500 p2yr: 1.00 s:0.O2OOTcReach - Shallow L:1350.00 ks:27.00 s:0.0050PEAK RATE: Q.O2 cfs VOt: 0.01 Ac-ft TIME: 1440 minBASIN ID: B NAME: SJ 2-YEARTOTAL AREA.......: 11-.00 Acres BASEFLOWS: 0.00 cfsRAINFALL TYPE....: TYPE1A PERVIOUS AREAPRECIPITATION....: 1.00 inches AREA..: 5.66 AcresTIME INTERVAI....: 10.00 min CN....: 65.00TIME OF CONC = 42.30 min IMPERVIOUS AREAABSTRACTION COEFF: O.2O AREA..: 5.34 ACrESCN....: 98.00TcReach - Sheet L: 2OO .00 ns:O. 1500 p2yr: 1 .00 s: 0.0200TcReach - ShaIlow L:L350.00 ks:27.00 s:0.0050PEAK RATE: 0.08 cfs VOL: 0.09 Ac-ft TIME: 1350 minBASIN ID: C NAME: SJ IO-YEARTOTAT AREA.......: 11.00 Acres BASEFLOWS: 0.00 cfsRAINFALL TYPE....: TYPE1A PERVIOUS AREAPRECIPITATION....: 1.75 inches AREA..: 5.66 AcresTIME INTERVAL....: 1-0.00 min CN....: 65.00TIME OF CONC : 42.30 NiN IMPERVIOUS AREAABSTRACTION COEFF: O.20 AREA..: 5.34 AcresCN....: 98.00TcReach - Sheet L: 200.00 ns:0.1500 p?yr: 1.00 s:0.0200TcReach - Shallow L:1-350.00 ks:27.00 s:0.0050PEAK RATEz O.52 cfs VOL: 0.41 Ac-ft TIME: 540 min
4/22/97 Polaris Engineering & Survey97037 SAN JUAN RECONSTRUCTION PROJECTLOPEZ AREA INFILTRATION SYSTEMPOST DEVELOPMENT STOR},I SPREAD IN TRENCHESpaele 2BASIN SUMMARYBASIN ID: D NAME: SJ 25-YEARTOTAL AREA.......: 11.00 Acres BASEFLOWS: 0.00 cfsRAINFALL TYPE....: TYPE1A PERVIOUS AREAPRECIPITATION.. ".: 2"OO inches AREA..: 5.66 AcresTIME INTERVAL..;. I 10.00 nin CN....: 65.00TIME OF CONCABSTRACTION COEFF: O.2O AREA..: 5.34 AcresCN....: 98.00TcReach - Sheet L: 2O0.00 ns:O.1500 p?yr: 1.00 s:0.0200TcReach - Shallow L:L350.00 ks:27.00 s:0.0050PEAK RATE: 0.8L cfs' VOL: 0.54 Ac-ft TIME: 530 minBASIN ID: E NAI\'E: SJ.I.OO YEARTOTAT AREA.......: 11.00 Acres BASEFLOWS: 0.00 cfsRAINFALL TYPE....: TYPE1A PERVIOUS AREAPRECIPITATION....: 2.50 inches AREA..: 5.66 AcresTIME INTERVAL....: L0.00 min CN....: 65.00TIME OF CONC : 42.30 min IMPERVIOUS AREAABSTRACTION COEFF: O.2O AREA..: 5.34 Acres. CN....: 98.00TcReach - Sheet L: 2O0.OO ns:0.1500 pzyr: 1.00 s:0.O2OOTcReach ShaIlow L:1350.00 ks:27.00 sJOIOO5OPEAK RATE: 1- .51- cf s VOL: 0.85 Ac-ft TIME: 530 min
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/-r'ErIi4/22/97 Polaris Engineering & Survey97037 SAN JUAN RECONSTRUCTION PROJECTLOPEZ AREA INFILTRATION SYSTEMPOST DEVELOPMENT STORM SPREAD IN TRENCHESpage 3HYDROGRAPH SIJMMARYPEAK TIME VOIT'MEHYD RUNOFF OF OF CoNtribNt M RATE PEAK HYDRO Areacfs min. cf\AcFt Acres=============================================1L -0011.001L.0011,.001L.00tO s Llt-cfcfcfcfcfL23450.0190.0820.5180.8L2L.5L2L44013s0s405305304333781L76422360836869(*Wcat< t-lrh 4trr-\ at{too . 70.019 L460430 cfLL.00 tpf .u,L\UI90. o82o.o82136013803781378Lcfcf11. OO11..00 rusrtPttu il0.519 5500,342 660 'Lrc42 CfL7644 cfL1:-OrL100vvtv!tL( L3 0794600236L2 cf11-00' ,pauluo'lP1,4L51".5L2L .5L254055036869 cf36688 c.fII:1)O-11 .00 1pr''!It_fL
r-4/22/97 Polaris Engineering & Survey97037 SAN JUAN RECONSTRUCTION PROJECTLOPEZ AREA INFITTRATION SYSTEMPOST DEVETOPMENT STORI\4 SPREAD IN TRENCHESpage 4STORAGE STRUCTURE LISTSTORAGE LIST ID NO. ADescription: SEDIMENT TRAPr-IITRAPEZOIDAT BASIN ID NO. BDescription: INFILTRATION TRENCHLength: 100 . 00 ft. hridth: 3 . 00Side Slope 1: L Side Slope 3:Side Slope 2: 1 Side Slope 4zInfiltration Rate: 4.00 min/inchft.LLIt-L
rt'.7-4/22/97 Polaris Engineering & Survey97037 SAN JUAN RECONSTRUCTION PROJECTLOPEZ AREA INFILTRATION SYSTEMPOST DEVELOPMENT STORII,I SPREAD IN TRENCHESpage 5DISCHARGE STRUCTURE LISTMULTIPTE ORIFICE ID NO. ADescription: SEDIMENT TRAP DRAINOutlet Elev: 23.33Elevz 23.33 ft Orifice Diameter:8.0000 in.BROAD CRESTED WEIR ID NO. BDescTiptioN: DTIMMY INFILTRATION TRENCH DRAIcd: 3.0300 Weir length: L00.0000 ft.El: 22.AO ft. Weir Increm: 0.L0IiBROAD CRESTED WEIRDescription:cd: 3.0300EI: 2L9 .7O ft.BROAD CRESTED WEIRDescription:cd: 3.0300EI: 18.00 ft.ID No. bWeir length:Weir Increm:ID No. pLzWeir length:Weir Increm:50.0000 fr.0. 1010.0000 ft.0.10tIIt-L
n4/22/97 Polaris Engineering & Survey97037 SAN JUAN RECONSTRUCTION PROJECTLOPEZ AREA INFILTRATION SYSTEMPOST DEVETOPMENT STORI{ SPREAD IN TRENCHESpage 6:=:::=:=:===:=::::=:=:::==:=:::=====:::::=:=:0.02 0.02 A A 23.40 6 l.l2 ct6-[0ilTH2-YEAN .LEVET POOL TABLE ST'MMARYl,tATCH II{FI,OI{ -STO. -DIS. <-PEAI(.> STORAGE<--------DESCRIPII0il---------) (cfs) (cfs) --id- --id- <-STAGD id V0l, (cf)IO-YEAR25.YEARIOO.YEARr-tIIrI0.02 0.02 B B 19.10 7 31.03 cf;up.,-0.08 0.08 A A 23.40 8 1.12 cf0.08 0.08 B B 19.10 9 31.03 cf tup..0.52 0.52 [ A 23.42 l0 l.4l cf0.52 0.52 B B 21,25 tl 1212,38 cf ru'..0.81 0.81 A A 23,55 LZ 3.53 cf0.81 0.81 B B 22,0A n 1866.?1 gf q,.,v-u1.51 1.51 A A 24.09 14 12.13 cf1.51 1.51 B B 22.05 15 1911.58 cf r*,p,-LL
nl'-i;4/22/97 Polaris Engineering & Survey97037 SAN JUAN RECONSTRUCTION PROJECTTOPEZ AREA INFILTRATION SYSTEMPOST DEVELOPMENT STORI.,I SPREAD IN TRENCHESpage LROUTING REPORTSTORAGE LIST ID NO. ADescription: SEDIMENT TRAPMUTTIPLE ORIFICE ID NO. ADescription: SEDIMENT TRAP DRAINOutlet EIev: 23.33Elev: 23.33 ft Orifice Diameter: 8.0000 in.ROUTING CURVESTAGE $TORAGE OUTT.TOH O+28(ft) (ct) (cfs) cfs-ninSTAGE(ft)24.40STORAGE(cf)0uTF[0t{(cfs)1. 79651.8786t,95722 .03282.t0572.fi622.24442.31062.37502.43772.49880+2Scfs-ninSTAGE( ft)STONAGE(cf )t36212t6232962037617456145361 I61607696047760tOUTFI,O}J(cfs)0+2Scfs-nin23.3323.4023.5023. 60n,7a23. 8023,902{.0024.t024,2024,300.00001.12002.72004. 32005.92007. 52009. 1200t0.72012.32013.92015.5200. 00000. 45950.71610.9025I .0564l. 19071.3112t.42161.52401 .62001.71050. 00000.46320.72520.91691,07621.215?1.34161. 45?31. s6511. 6664t.76232.55842.61672.67372.72952,78432.83792 .89062.94232. 993147.98074.695101.41128.t2154 .83181 .54208.25234.96261.6625.5025.6025.7025.8025.902 6.0026.n26.2026.3024 .5024,6024.7024 .8024.9025. 0025.1025.2025 .3025.4017.12018.72020.3202t.92023.5202s. 12026.72028.32029.92031 .5205630I .85361 .94102,42542 .10592.18412.25992.33352.40s02.47472.54272t,265tI'LIt-
4/22/97 Polaris Engineering & Survey97037 SAN JUAN RECONSTRUCTION PROJECTLOPEZ AREA INFILTRATION SYSTEMPOST DEVELOPMENT STORM SPREAD IN TRENCHESpage 4TRAPEZOIDAL BASIN ID NO. BDescription: INFILTRATION TRENCHROUTING REPORTWidth: 3.00 ft.Side Slope 3: 1Side Slope 4: LInfiltration Rate: 4.00 min/inchBROAD CRESTED WEIR ID NO. BDescription: DUMMY INFILTRATION TRENCH DRAIcd: 3.0300 Weir length: 100.0000 ft.El: 22.00 ft. Weir Increm: 0.10Length:Side SSide Sr.00.00 f t.lope 1: 1-lope 2: L0+2Scfs-minROUTING CURVESTAGE STORACE OUTF'IOII(ft) (cr1 (cfs)STAGE(ft)STORAGE(cr;0UTFL0I{ 0+2S(cfs) cfs-ninSTAGE STORAGE OUTFTOI{(ft) (cf) (cfs)0+2Scfs-min0.4028 5.99210.4140 6.30990.4253 6.63530. 00003r.03164.13199.306t677I 769186319602058216022632369247721 .802l .9022.0022.fi22.2022,3A22.4022.5022.6022.7022.80.3348.5478.7682.9959.2309.4734.7232.980s.2453.51 75.7973.0846.3795.682022223J3444555.2496.2603.27n.2818.2926.303s.3143.3253.3362.34t2.3583.3693.380{.391600000000000000625.54686 .25749.14814.22881.50950.9820.4020.5020.6020.7020.8020.9021.0021.1021.202i.3021.4021.5021.60n.7a0.0000 0.00000.1143 0.2n70.r24s 0.33820.1347 0.46s7136.57t7_5.922t1.37260. 93306. 60354.40404 .33456.40510.62567.0019.0019.1019.20r9 .3019.4019.5019. 6019. 7019. 8019. 9020. 0020. 1020.2020. 3010.018 16.55027.549 34.41050,247 57.44677,t24 84.668107.61 115.51141.32 t49.57177.96 186.5921t.33 226.332s88270010231097n73t25t13321415150015870.1449 0.60020.1552 0.74160.1656 0.89010.1759 1.04570.1863 1.20840.r968 1.37810.2073 1.sssr0.2178 t.73920.2284 1.93050.2390 2.ngl
n4/22/97 Polaris Engineering & Survey97037 SAN JUAN RECONSTRUCTION PROJECTTOPEZ AREA INFILTRATION SYSTEMPOST DEVELOPMENT STOR},I SPREAD IN TRENCHESpage 5LEVET POOL ROUTING TABLEIr-ttMATCH 0 (cfs) :PEAK STAGE (ft):PEAK TIME: 1.460.00INFLOW HYD NO. : 6INFtOw Q (cfs):PEAK OUTFTOW :o.o219. 10min.0.02o.02OUTFIOW t{YD No.: 7LEVET POOI ROUTING TABLE11 12 25L SUM 0L 02+2520.00000.00000.00000.00000.00010.00030.00060.001_00.001s0.002L0.00280.00340.0040o.oo470.00520.00580.00630.00680.00730.00780,00830.00890.00940.00990.01020.01060.0109,0.0LL30.01L70.0120o.oL230.0125o.oL270.01300.0r.330.01350.01370.0r.380.01390.014Lo.oL44o.oL470.00000.00000.00000.000L0.00030.00060.00100.00150.002L0.00280.00340.0040o.oo470.00s20.00s80.00630.00680.00730.00780.00830.00890.00940.00990.0L020.01060.01090.01_L30.011-70.01200.0L230.0L25o.oL270.01300.01330 . 0L-350.01370.01380.0139O;0141"o.oL440.0L470.01_500.00000.00000.00000.00000.00000.00020.00040.00070.00120.00L7o.00220.00280.00340 - 00400.00450.00500.00550.00590.00640.00690.00730.00780.00830.00880.0091.0.00940.00970.010L0.01040.01080.01.r_0o.oLtz0.01L40.01L60.0L19o.ot220.01230.0]240.0125o.oL270.01290.01310.00000.00000. 00000.00010.00040.00100.00200.00330.00490.00660.00840.01020.01210.0L390.01550.0L700.01850.02000.02150.0230o.02460.02620.02760.0289o.02990.03090.03200.033L0.03420.035L0. o3s80.03640.03710.03800.03880.03940.03980.04010.0405o.o4L20.0419o.04280.00000.00000.00000.00000.00000.00020.00040.00080.00130.00190.002s0.00310.00370.00440.00500.005s0.00600.00650.00700.00760.00810.00870.00920.00970.01010.01040.01080.011_L0.01_150.01190.0L220.01,240.0L26o.oL290.0L320.01340.01360.01370.01380.0140o.0L420.01450.00000.00000 - 00000.000L0.00030.00080.00L60.00250.0036o.oo470.00590.007L0.00830.00950.010s0.01150.01250.0134o.oL440.01_s50. o16s0.0L750.01840.01920.01_990.020so - o2L20.02200.02260.02320.02360.0240o.02450.0251_0.02560.02600.02620.0264o.0267o.o2vLo -02770.0283STAGE( ft)1,9.00L9.00L9. L019.1019. L019. 1_01_9.1.019.1019. L019. L019.1019.1019.1019.10L9. L019.10L9.l_0L9.10L9.10L9. 1019.1019. L019.1019. L019. r.019. L019. 10r.9.1019.10L9.101_9. 1_OL9. L0L9.l_0L9. r.0L9.1019.10L9.1019.1019. 1019. L019.1019.10TIME(min)850.00860.00870.00880. O0890.00900.009L0.00920.00930.00940.00950.00960.00970.00980.00990.001000.0010L0.001020.001030.001040.001050.001060.001070.00L080.00L090.0011_00 . 001L1"0.001120.001130.001L40.001L50.00l_160.00L170.001L80.00L190.001200.00L21.0.00t220.oo1_230.001240.oo1_2s0.001260.00tIIt(A- Mo *'re \ |'J F t t-'t7 Par o tJ;It-it-rY'p-
4/22/97 Polaris Engineering & Survey97037 SAN JUAN RECONSTRUCTION PROJECTTOPEZ AREA INFILTRATION SYSTEMPOST DEVELOPMENT STORM SPREAD IN TRENCHESpage 6TEVEL POOL ROUTING TABLELEVEL POOL ROUTING TABLEI1- 12 zSL SUM 0L 02+2520.01s00.01530.01560.01600.01630.01660.01690.oL720.0L750.0L790.01-8L0.01830.0L820.01-810.01810.0L820.0L830.01850.01880.01890.0LL90.01_890.00000.0r.2s0.00000.0r.530.01560.0L600.01630.0L660.0r_690.oL720.0175o.oL790.01810.01830.01820.01810.01810.0L820.0L830.0L850.01880.01890.01190.0r.890.0000o.oL250.00000.00000.01340.0L370.0L400.0r_43o.oL460.0r.490.0L520.01550.0L570.01600.01-630.01650.01650.016s0.01640.01640.01650.01670.01_690.01710.01380.01390.00830.005so. 00560.04370.04470.04560.0465a.o47s0.04840.04930.05020.05120.05200.0s270.05300.05290.05270.05270.05290.05340.05400.05460.o478o.04450.03280.02080.01800.00560.01480.01_520.01550.01580.01-610. 01650.0L680.0171-o.0L740.0L770.0L800.oL820.0182a.0L820.01810.01-810.01_830.01840.01870.0L890.01520.01540.00920.0061o -00620.02890.02950.03010.03070.03130.03190.03260.03320.03370.0343o.03470.03480.03460.03450.03450.03480.03510.03s60.03590.02900.0293o.o1740.01160.01-1_9-0.0006STAGE(ft)t-9.1_019. 1019.1019.10r.9. 1019.1019. L019.10L9.10L9. L01_9. l_0L9.10L9. L01_9. 101_9.10L9. L019.l-019. L0l_9.1019. 10l_9 .1019. t_01_9 .101_9.101-9. L0TIME(min)L270 -OO1280.00L290.00r_300.0013L0.00L320.001_330.001340.00L350.001360.001-370.00L380.001390.001400.001410.00L420.00L430.001440.001450.001460.00L470.OO1480.001490.001500.00151_0.00
t.80f'-t--t4/22/97 Polaris Engineering & Survey97037 SAN JUAN RECONSTRUCTION PROJECTLOPEZ AREA INFITTRATION SYSTEMPOST DEVELOPMENT STORM SPREAD IN TRENCHESpage LzLEVEL POOL ROUTING TABLEMATCH Q (cfs)PEAK STAGE (ftPEAK TIME: 13INFLOW HYD NO.0.08L9.1-O.00 min.I0.00000.00000.00010.00030.00080.00240.00590.01070.01s90.02100.02570;02970.033L0.03630.0390o.o4!20.0431o.04470.0461o.44740.0486o.04990.05L20.05250.05370.05480.05580.05670.05750.05820.05880.05930.06000.06090.06200.06300.06370.064L0.06460.06530.06610.0668INFLOW Q (cfs):PEAK OUTFLOW .I.i0.080.08OUTFLOW }IYD NO.: 9LEVEL POOL ROUTING TABTE1L 12 25L SUM 01 02+252 STAGE TIME-J------0.00000.00000.00020.00040.00L20.00390.00870.01_450.02010.02570.03070.03460.03820.04160.0442o. o46s0.04850.050L0.05160.05300.05430.0s580.05730.05860.05990.06LLo.o62L0.0631_0.06390.06460.06520.06s80.06670.06780.0691-0.07000.07060.07110.0716o.07250.0735o.o74L0.00000.00020.00040.00120.00390.00870.0L45o.o20Lo.02570.03070.03460.03820.04r.60.04420.046s0.048s0.0s01_0. os160. os300.0s430.0s580.05730.0s860.05990.061,Lo.o62t0.06310.06390.06460.46520.06s80.06670.06780.06910.07000.0706o.071_10.07L6o.072s0.0735o.o74Lo.07450.00000.00020.00070.00190.00580.0L500.02900.04530.06L70.o7740.09100.10250. L1300.122L0.L2970.t362o.L4t70.14640.15060.L5470. 1s870. r.630o.L67L0. 17100.L7470. 17810. 18100.18370. L8600. L8800. 18980. r9180. 19450.L9780.20100.20360.20s40.20690.20880.2LL2 ,o.2L370.2L540.00000.00000.00010.00030.00080.00260.0065o.0L'180.01760.02320.02840.03280.03660.04010.04310.045s0.44760.04940.05090.0s230.05370.05510.05660.05800.0s930.06060.06170.06260.063s0.06430.06490.06560.06630.06730.068s0.06960.07030.07090.o7L4o.o72L0.07300.0738o.00000.00020.00060.00160.00500.0123o . oz250.0335o.04.420.05420.0625o.0697o.07640.08200:08660.09070.09410.09700.09970. 10230. L0s0o. L0780. 1_1_050.1L300.1L540. 1L75o. 1193O.L2LLo . L225o.L23?0.L249o.L263o . L2820.130s0.132s0. 1340o. 13500. l_360o.t3740.1391-o.1407o. 14r.6r.9.0019.0019.1019.1019. L019.1019.101_9.1019.1019. L0L9. L0L9.1019. L019. L01_9. L019.1019. r_019.10l_9.1019 .1019.101_9.10L9. r"0L9. 1019.1019. 10L9.10L9. 101_9.10L9.10r.9.1019. L0l_9.1_019. 1019. L019.1019.10L9. 10L9.1_019. L01_9.10L9.10520.00s30.00s40.00550.00560.00s70.00580.00s90.00600.00610.00620.00630.00640.006s0.00660.00670.00680.00690.00700.007L0.00720.00730.00740.00750.00760.00770.00780.00790.00800.0081_0.00820.00830.00840.00850.00860.00870.00880.00890.00900.00910.00920.00930.00t_L '-4 cqB-t ,J F t C{Tz A'rL oL-J
Ir-!4/22/97 Polaris Engineering & Survey97037 SAN JUAN RECONSTRUCTION PROJECTTOPEZ AREA INFITTRATION SYSTEMPOST DEVETOPMENT STORI'{ SPREAD IN TRENCHESpage L3LEVET POOL ROUTING TABLELEVEL POOL ROUTING TABLE11 T.2 2S1 ; SUM 01 02+252 STAGE TIME-_-----;= =========-=- -- -r-t"0.074s0.07460.07490.07550.07620.07660.0767o.07650.07650.0769Q.O77so.07840.07930.08020.08040.0802o.07970.07950.07960.07990.07990.a7940.07870.0783o.07820.07830.0782o.07750.07660.07600.07580.07590.07630.07690.0774o.07790.07850.07900.07950.080L0.08060.08110.08170.082L0.08180.08080.07960.07460.07490.07550.0762Q.0766o.07670.07650.07650.0769o.07750.07840.07930.08020.08040.08020.07970.0795o.07960.07990.07990.07940.07870.0783o.07820.07830.07820.07750.07660.07600.07580.07590.07630.07690.07740.07790.07850.07900.07950.080r.0.08060.081L0.08170.082r.0.08180.08080.0796o.07870.06730.06750.06760.06800.06870.06920.06940.06930.06930.06940.06990.07060.07L40.0722o.07270.07270.07230.0720o.07200.072L0.07230.07200.07L50.07L00.07080.07080.07080.07040.06970.06900.06860.06860.06890.06930.06980.07030.07080.07130.0718o.07230.07270.07320.07370.074L0.074L0.073s0.o72so -2L630.2L690.21800.2L970.22L50.222so.2226o.22240.22270.22390.22584.22830.23090.23280.23330.232s0.23L50.2310o.23L40.23L90.23Ls0.2301_0.228s0.22740.22730.2273o.22640.22450.22230.22080.22030.2208o.222L0.2236o.22520.22670.22830.22990.23L40.23300.23450.23600.23740.23790.2367o.23390.2307o.07430.07450.07470.47520.07s90.07640.07670.07660.0765o.07670.07720.07800,07890.07980.08030.08030.07990.07960.0795a.07970.07990.07960.07900.0784o.07820.07830.0782o.07780.07700.07630.07590.07580:.076L0.0766o.0772o.0777o.07820.07880.07930.0798o.08040.08090.08140.08r_90.08190.08L20.080L0.1.4200.14240.1432o -14450. 14560.14600.14590. L4580.1462o.t47L0. L4860. Ls030.1_5200.1s300.15300.Ls220. L5160. L5L50. 1519o.L52L0. 15170.1505o.L4940. L4900. 14910.1490o.L4820.L4670.14530. L445o.L4440.14500. 1_4s9o.14740.1_4800. 14900.1s0L0.1_s110. 15210. Ls3L0. L54L0. 1s510. 15600. L5600. Ls48o.L5260.150619.1019.1019.1019.1019. L019.101_9.10L9. L0L9. L0L9.1019. L019.10L9.1019.1019. L019.1019.10L9.10L9.1019.101.9.1019.10L9. L0L9.10L9.10L9.1_0L9.1019. 10r.9.1019.1019. 10L9.10L9. L0l_9.1019.l_019.10L9.10L9.1019.1019.10L9. L0L9. L0L9. t_019.10L9.1_019. r.0L9.1019-10940.00950.00960.00970.00980.00990.001000.0010L0.00L020.00L030.001040.001.050.001060.001070.00L080.00L090.001100.0011r.0.001L20.001130.00L140.0011"50.00L160.001170.001180.001190.00r_200.001210.00L220.OOL230.001240.00L250.001260.00t270.001280.00l_290.00L300.00L310.001320.001330.001340.00L3s0.001360.001370.001380.001390.001400.001410.00t0.0787 0 .0782 0.0716 0 .2284 0 .0791 O.1494
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r!1r"t4/22/97 Polaris Engineering & Survey page 2097037 SAN JUAN RECONSTRUCTION PROJECTLOPF,Z AREA INFITTRATION SYSTEMPOST DEVELOPMENT STORM SPREAD IN TRENCHESLEVEL POOL ROUTING TABLEMATCH 0 (cfs)PEAK STAGE (ftPEAK TIME: 6INFLOW IIYD NO.INFtOw Q (cfs):PEAK OUTFTOW :); 260.00 m:100.52L.25in.o -520.34OUTFLOW ITYD No.: 1.1LEVEL POOL ROUTING TABLE11 T2 2S1 SUM O1. 02+252 STAGE TIME=== ================== == ====== ==== == ==== ================ ========= === ====o. oooo o.00LL 0.0000 0.001L 0.0000 0.001-1 L9 . 10 460.000.001L 0.0067 0.0005 0.0083 0.0006 0.0077 19. 1-0 470.000.0067 0.0L72 0.0037 0 .o276 0.0041 0.0235 L9. 10 480.00o .oL72 0.04L4 0.0112 0.0698 0 .OL24 0.0575 19 . l-0 490.00a.o4L4 0. L1l_] 0.0273 0.L798 0.0302 0.L497 19.10 500.00o.1L11 0.23]5 0.0711 0.4L37 0.0786 0.3351 19.L0 510.000.23L5 0 .3649 0.2LA9 0.8073 0 .L242 0.6831 L9 .20 s20.000.3649 0 .4578 0.5321 L.3548 0. L510 1.2038 19 .46 530.00o.4s78 0.5055 L.0178 1.98L1- 0.L861 1.7950 L9.80 540.000.50s5 0.s176 L.574L 2.s972 0.2209 2.3763 20.13 550.000.5176 A.4986 2.L246 3.1408 0.25L7 2.889L 20.42 560.000.4986 0.4748 2.6L23 3.5858 0 .2768 3.3090 20 .65 570.00o.4748 0.4480 3.0L29 3.9358 0.296L 3.6397 20.83 580.000.4480 0.4295 3.3290 4.2065 0.3L07 3.8958 20.97 590.000.429s 0.4042 3.574L 4.4078 0.32L7 4.0862 2L.07 600.00o.4042 0.3851 3.7s6s 4.54s9 0.3296 4.2L62 2L.!4 610.000.3851 0.3671 3.8812 4.633s 0.3350 4.2984 2L.L9 620.000.36?1 0.3583 3.960L 4.685s 0 . 3384 4.3472 2L.22 630.000.3583 0.3479 4.0068 4.7L3L 0.3403 4.3728 2t.24 640.00o.3479 0.34s1 4.03t4 4.7244 0.34L4 4.3830 2L.25 650.000.3451 0.3373 4.04L3 4.7236 0.3418 4.3819 2L.2s 660.00o.3373 0.3339 4.0401 4.7LL3 0 .34L7 4.3696 2L.25 670.00o. 3339 0.3264 4.0284 4.6887 0 .34L2 4.3475 2L.2s 680.00o.3264 0.3236 4.OO7L 4.6572 0.3403 4.3168 2L.24 690.00o.3236 0.3L70 3.9777 4.6L83 0.3391 4.2792 2L.23 700.000.3L70 0.3165 3.94L6 4.575t 0.3376 4.237s 2L.2L 7L0.000.3165 0.3125 3.9016 4.530s 0.3359 4.1946 2t.20 720.O0o. 3125 0.3133 3.8605 4.4863 0. 3341 4.L522 21 . 18 730.000.3133 0.3104 3.8L98 4.443s O.3324 4.11l-1 2L.L6 740.00o.3104 0.311s 3.780s 4.4023 0. 3307 4.07L7 2L . L5 750.000.31ls 0.3084 3.7427 4.3626 0.3290 4.0335 2L.L3 760.000.3084 0.309L 3 .706L 4.3236 0 .3275 3.9961 2L.t2 770 .OO0.3091 0.3055 3.6702 4.2848 0.3259 3.9589 2L.LL 780.000.30s5 0.3056 3.634s 4.2457 0.3243 3.92L3 2L.09 790.000.3056 0.3018 3.5986 4.2060 0.3227 3.8833 2L.08 800.000.3018 0.3014 3.s622 4. 1653 0 .32LL 3.8442 2L.06 81-0.000.3014 0.297s 3.s247 4.1237 0.319s 3.8042 2L.05 820.00o.2975 0.2987 3.4864 4.0827 0.3178 3.7649 2L.03 830.00o.2987 0.2977 3.4488 4.04s3 0.3L61 3.7292 2L.02 840.00o .2977 0.3007 3.4L46 4.0130 0.3146 3.6984 21.00 8s0.00o.3oo7 0.2993 3.38s2 3.9852 0.3133 3.67t9 20.99 860.00o.2993 0.3000 3.3598 3.9s92 0.3L2L 3.647L 20.98 870.00tLt.\o Ye-<ru IuFruaQAl tOr''\
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4/22/97 Polaris Engineering & Survey97037 SAN JUAN RECONSTRUCTION PROJECTLOPEZ AREA INFILTRATION SYSTEMPOST DEVELOPMENT STORM SPREAD IN TRENCHESpage 22LEVEL POOI ROUTING TABLEtEVEt POOI ROUTING TABLE11 T2 2SL SUM 01 02+252STAGE(ft)TIME(min)0.25940.25900.25800.253so.2496o.24540.2439o.2424o.24340.2434o.24280.22L3o.L764O.LL4L0.0640o -o2780.007L0.00000.00000. 00000.2s900.25800.25350.24960.24s40.24390.2424o.24340.2434o.2428o.22L30.L7640.1_1_410.0640o.02780.007L0.00000.00000.00000.00002.27482.27402.27L92.26492.25052.22992.20602.L8L62.Ls902.L3972.L2L82.0848L.98851.8006L.5267L.20220.86350.5433o.26270.06362.79322.79L02.78352.76802.74552.7t932.69232 .66732 .64572.62592.58592.48242.27901.97881.6L85t.237to.87060. s4330.26270.0636o.25960.25960.25950.259L0.2s84o.2s73o.2560o.25470.25350.25250.25160.24960.2444o.2339o.2t8L0. L9810.17550.1s1_9o.L2870.07032.53362.s3142.52402. s0892 .48722.46202.43632.4t262 -39222.37342.33442.23282.0346L .7 4481_.4003L.03900.69510.39140. 1340-0.006720.4920.4920 .492A .4920.4820 .4720-4620 .4520.4420.4320.4220 .4020.3520.2520.L019.9LL9.70L9 .47L9.2419.061360.00L370.001380.00l_390.001400.001410.00L42A.OOr.430.001440.001450.001_460.001_470.001_480.00L490.00L500.001510.001520.00L530.00r_540.001550.00
r'.4/22/97 Polaris Engineering & Survey97037 SAN JUAN RECONSTRUCTION PROJECTLOPEZ AREA INFITTRATION SYSTEMPOST DEVELOPMENT STORIU SPREAD IN TRENCHESpage 28LEVEL POOI ROUTING TABLEMATCH Q (cfs) :PEAK STAGE (ft): 2PEAK TIME: 600.00 mINFLOW HYD No. : t2INFtOw Q (cfs):PEAK OUTFLOh' :0-8L2.OO0.810.79tIt-nOUTFTOW HYD No.: 13LEVEL POOL ROUTING TABTE1L 12 2S1 SUM OL 02+252STAGE(ft)TIME(min)0.00000.00090.0056o.oL440.02720.04870.07940.L2970.24430.43220.63230.76320.81050.80L90,74940.69L70.64100.60490.56650.53320. s0730.49030.47570.46790.4s76o .44930.4400o.4329o.4248o.42LL0.41660.4L49o -4L2L0.41090.4078o .40620.40240.40030.39620.39350.38940.38890.00090.00s60.01440.02720.04870.07940.L2970,24430.4322o.6323o.76320.8L050.80L90.7494o.69L70.64L00.60490.5665o.53320.50730.49030.4757o.4679o.45760.44930.44000.43290.4248o.42LL0.4166o.4L49o.4L2t0.4L090.40780.4062o.40240.4003o.39620.39350.38940.38890.38850.00000.00040.003L0.00930.01930.03510.0s910.09640.23740.6290L.32902.25963.26674.22L95.O4L7s.6941"6.L9546.22246. 1_7556.2L706.1_9856.2!446.L9876.2L276.20826.2L186,1981_6.2L046.207L6.20286.1-9096. L7386.1-5356. L3076.1-0536.07726.04586.01095.972ss.93015.88415.83700.00090.00690.02300.05090.09s20.163Lo -26820.47050.91401.693s2.72463.83344.879L5.77326.48287.02687.44L47.39387.27537.25757.r96L7.18047.L4237.L3827.LL527.LOLL7.O7LO7.068L7.05307.04057.02247.00086.976s6.94946.91936.88s86.84856.80746.76226.7L306.66256 .61440.00000.000s0.00340.0r_030.02130.03880.06530. L065o.L26s0. L5840.20610.25880.30790.34930.38210.4066o.42480.79420.424L0.6342Q.42490. s5680.42490.50470.42520 .478Lo .42490.43s80.42520.425L0.42460 .42400.4233o.42250.42L60.42050 .4t94o.4L820.41680.4r.530.4L36o.4LL90.00090.00640.0L960.04060.0739o.L2440.20290.3640o.78741.53512.51853.57454.57L25.42386. L0076.62027.0L666.59966.8sL26.62346.77L26.62376.7L746.63346.68996.62306 .646L6.63236.62786.61s56.59786.57686.55326.52696.49776.46526.42916.38936.34546.29786.24886.202sL9.00r_9.00r.9. 1019.1019.10L9.1019-1019.10L9.22L9. s319.9920 .4920.942L .322L.6L21.8322.O022.O02L.9922 -OO22.0022.O022.O022.OO22.0022.0022.OO22.0022.OO22.002L.992L.992L.982t.972L.972L.962L.952L.942L -922t.9L2L.902L. B8430.00440.00450.00460.0047A.OO480.00490.00500.00sLo.00520. O0530.00540.00550.00560.00s70.00580.00590.00600.0061_0.00620.00630.00640.006s0.00660.00670.00680.00690.00700.007L0.00720.0O730.00740.00750.00760.00770.0O780.00790.00800.0081"0.00820.00830.00840.00t,it-Z / LI ffiA-- t JtrL T{ta'Tt otw)
4/22/97 Polaris Engineering & Survey97037 SAN JUAN RECONSTRUCTION PROJECTLOPEZ AREA INFITTRATION SYSTEMPOST DEVELOPMENT STORM SPREAD IN TRENCHESpage 29rr:r'ILEVEL POOI ROUTING TABTELEVET POOL ROUTING TABLE11 12 2S1 SttM 0L 02+2520.38850.39040.38960.38860.38520.38420.38330.38450.38320.381s0.37750.3759o.37450.375Lo.37340.371.00.3665o.3644o.36250.36310.36390.36620. 36690.3662o.362L0.3s8L0.35430.3s300.35160.3502o.34570.34130.3371_0.335s0.3338o.3321,o.3273o.32240.31800.31_600.3L470.31560.3L620.31_750.31800.31930.31990.321r.0.39040.38960.38860.38520.38420.38330.38450.38320.38L50.37750.37590.37450.3751o.37340.37L00.366so.3644o.36250.36310.36390.36620.36690.36620.362L0.3s810.3s430.35300.35160.3502o.34570.341_30.337L0.335s0.33380.332L0.32730.32240.31_800.3160o.3L470.3r.56o.3L620.3L750.31800.31930.31_990.32110.32L75.79225.7s2L5.71_585.68045.6432s.60455. s668s.53205 .49965 .4666s.43055.39t75.3s275.31_585.28065.24395.2033s.1s935.Lt475.07225 -03425.00194.97494.94994.922L4.88874.85034.80994.77004.73044.68814 .64064. s8844.53474.48204.43004.37584.31664.25324.L8874.t26L4.06824.OL643.97053.93023.89483.86423.83786.57LL6.53206 .49396.454L6 .4L276.372L6.33466.29976.26436.22566.18396,L4216.L0236.06436.02505.98145.93425.88625.84035.7992s.76435.73495.70795 .678L5.64235.601L5.5576s.5145s.47L85.42635.37sL5.31905.26LO5.20405.L4795.08945.02554.957L4.88734.81954.756s4.70004.65014.6061.4.567s4.534L4.50524 .4806.4LO2.4088.4074.4061.4048.4034.402A.4007.3994.3982.3969.3954.3939.3926.39L2.3898.3883.3866.3849.3833.38L8.3806.3795.3785.3774.376L.3746.3730.37L5.3699.3682.3663.3642.362L.3600.3579.3557.3532.3506.3480.3454.3429.3407.3388.337L.3356.33436.16086.L2326.08656.04806.00795.96875.93265.89905.86485.82745.787L5.74675 -70845.67185 .63375. s9165.5459s.4996s.45555.41605.38255.3s44s.32845.2996s.26485.2249s. L8305. 141s5.10035.05645.00694.95264.89684.84t94.78794.73L54.66994.60384 .53664.47L54.4tLt4 -357I4.30934.26734.23044. L9854.L7094.L475STAGE(ft)2L.8721.852L.842L.832L -8221_.8021..792L.782r.772L.762L.752L.732L.7221.7t2L.702L.682L.672L.662L.642L.632L.6L2L.6021.592L.582L.572L.s62l_.552L.532L .522L.5t2L .492L.4721.452L.432L.422l..402L.382L.352L -332t.3L2L.282L.262L -242L .222L.2L2L.L921_. L82L.L7TIME(nin)8s0.00860.00870.00880.00890.00900.009L0.00920.00930.00940.009s0.00960.00970.00980.00990.001000.0010L0.001020.001030.00L040.001_050.00L060.001_070.00L080.00L090.00L100.00L110.001120.00LL30.00LL40.0011s0.00LL60.00L170.00L1_80.00L190.001-200.001.210.00t220.oo1_230.00L240.001250.00r.260.00L270.OOL280.001290.001_300.001310.00L320 .00=00000000000000000000000000000000000000000000000IflIIt-ft"0.333L
4/22/97 Polaris Engineering & Survey97037 SAN JUAN RECONSTRUCTION PROJECTLOPEZ AREA INFILTRATION SYSTEMPOST DEVELOPMENT STORM SPREAD IN TRENCHESpage 30tEVEt POOL ROUTING TABLELEVEL POOL ROUTING TABLEIL T2 zst SUM 01 02+2520.32L70.32300.3235o.32470.3247o.32280. 31750.3120o -30720.30460.30310.30370.30410.30280.27640.2t98o.L426o.07960.03490.00870.00000.00000.00000.00000.00000.32300.3235o.32470.32470.32280.31750.3L200.30720. 30460.303L0.30370. 30410.30280.2764o.2L980.L4260.07960.03490.00870.00000.00000.00000.00000.00000.00003.8L533.79643. 78083.76823.75783.74643.729L3.70283.66873.63053.59L63.5551_3.52273.492L3.43773.30853.06262.705L2.27831.8266L.39000.99560.651_00.35430. r.0344 .45994.44284.42904.4L764 .40534.38674.358s4.32L94.28054.23824 -19844.L6294.L2954.07L33.93383.67083.28482.8L952.32L81.83s31.39000.99560.65100.3s430. L0340.33220.33'140.33070. 33010.32970.32920.3284o.32730.32580.32420.32240.32080.31940.31800.31s60.30980.29840.28L40.25980.23540.20980. 18450. 16010. r.3660. LL434.L2784'.111_54.09834.08754.07564.O5754.0301_3.99463 -95473.974L3.87603.842L3.81023.75333.6t823.3611_2.98642.53822.0620l_. s998L.LBOZ0.8L11-o .49090.2L77-0.0109STAGE(fr)2L.L62L.T62L.1,52L.L42L.L42L.L42L.L32I -1"22L.LL2L -092L.072t.0621_.052L.032L.0L20.9620. B520.7020.5020.2720.0219.781_9.55L9.3219. L0TIME(min)1330. 00r_340.0013s0.001360.001370.001380.001390.00L400.00r.41_0.00r-420.001430. 00L440.001450.00L460.00L470.001480.001_490.001500.001510.00r.520.001s30.001540.0015s0.00L560.001570.00
r-4/22/97 Polaris Engineering & Survey97037 SAN JUAN RECONSTRUCTION PROJECTLOPEZ AREA INFILTRATION SYSTEMPOST DEVELOPMENT STORI4 SPREAD IN TRENCHESpage 36tEVEt POOL ROUTING TABLEMATCH 0 (cfs) :PEAK STAGE (ft):PEAK TIME: 55O.OOINFLOW HYD No. : L4INFLOW Q (cfs):PEAK OUTFLOW :1.5L22.05min.L.51_1.5LOUTFTOW HYD No.: L5TEVEL POOL ROUTING TABLE11 12 zSL SUM 0L 02+252STAGE(ft)TIME(min)1Tt0.00000.00030.00210.00550.01120.02380.04380.06870. r.0040.14000. L834a.232s0.29L40.38070.579s0.9064L.25591.46551.5LL7L -4467L.3L49r..1788L.06920.99330.923L0.85880.8L320.77900.75300.73550.7L78o.70020.68470.66960,65630.647l.0.63970.63380 .62920 .62444.6L940.61-430.00030.002L0.00s50.01120.02380.04380.06870.10040.l-4000. r.8340.2325o.29L40.38070.579s0.9064L.2559L.46551.51L7L .4467t.3L49L. L788L.06920.9933o.923t0.85880.8L32o.77900.75300.73550.7L78o.7002o - 68470.66960.65630.6471o .63970.6338o.6292o.6244o.6L940.61430.60860.00000.00010.00110.0036o.oo77o.ot620.03130.0519o -07780. LL68o.20L40.35710.58880.9258L.49422.48954.03956.00146.37L96.37796.24206.23346 -23356.22746.22836.223t6 -22446.22066.22226.2t936.22096.2L826.2L966.2L736.2L866.2L676.2L796.2L636.2L756.2L6L6.2L7L6.2L580.00030.00260.00880.02020.04270.08390. 1439o.zzLL0.31820.44020.6L730.8811L.26091.88s92.976L4.6s186.76LO8.97879.33039. r.3368.73578.48138.29608.14388.01037.89507.8L667.75267.7L077.67257.63887.60307.57397.54337.52207. s03s7.49L57.47947.47LL7.46007 .45087.43870.00000.00020.00130.00390.0085o.oL790.03460.05740.08590. r.1550.L2330.13680. 15540. 17980.2L590.2707o.34L7o.4L7BL.5LL71.5LL71.3799t.L225L.t253o.94330.97220.81_490.8ss60.74040.78990.70150.75010. 6705o.7L29o .64370.6810o .62440. 661-30. 61390.64800.60700.63590. s9910.0003o.oo240.00750.0L63o.03420.06600.10930.16370.2323o.3247o .4940o.7443L.1-0551.706r_2.760L4 -38]-26.4L927.88367.88367.62L97.35597.3s887.L7067,20067.03807.080L6.96107.Ot226.92076.97LO6.88876.932s6.86106.89956.84106.87926.83026.86556.823L6.85306.81s06.8396L9.0019.0019.10L9.1019. L019. L019. 10L9. L019. 1019. L1L9.1919.32r_9.50L9.7420.0820 .602L.252L.9322.0522.0522.0L22.0122.4L22.Ot22.0t22.0022.0022.OO22.OO22.OO22.0022.0O22 -OO22.OO22.0022.OO22.O022.0022.O022.O022.OO370.00380.00390.00400. 0041 0.00420.00430.00440.00450.00460.00470.00480.00490.00500.005L0.00520.00530.00540.00550.00s60.00s70.00580.00590.00600.006L0.00620.00630.00640.006s0.00660.00670.00680.00690.00700.0071_0.00720.OO730.00740.00750.00760.00770.0O780.0022.0OLloo vrx<z- lu Ftornrqrrro'J/><) l|vl{>
r!4/22/97 Polaris Engineering & Survey97037 SAN JUAN RECONSTRUCTION PROJECTLOPEZ AREA INFILTRATION SYSTEMPOST DEVETOPMENT STORM SPREAD IN TRENCHESpage 37LEVEL POOL ROUTING TABTErILIILhLEVET POOL ROUTING TABLE11 LZ 2s1 SUM 01 Q2+2520.6086o.60270.59670.59010.58400.58L00.580s0.58L00.58010. s7650.57L70.56830.567L0. s6690. s6530.56090.55530.55130.54940.s4870.54640.54L40.5351_0.53050.5280o.52750.52880. s3080.53200.52970.s24L0.51700.51r.80. s0870.50700.50380.4976o ,49A2o .48450.481L0.4789o .47540.46880.46100.45480.45L2o .449s0.4500o.60270. s9670.590L0.58400.58100.58050.58100.5801_0.57650.5717o.56830.567r.0.56690. s6s30. s6090.55530.5s130.54940.5487Q.5464o.54L40. s3510. s3050.52800.52750.52880. s3080.5320o.5297o.524L0.51700.51r_80. s0870.50700. s0380 .497 60.49020.48450.481L0.4789o .47540.46880.46100.4s48o.4st2o.44950.45000.45L06.2L666.2ts56.2L626.2L5L6.2t576.2L496.21556.21496.2L556.2L486.2L526.2L466.21506.2L466.2L496.2L446.2L456.2L4L6.2L436.2L406.2L426.2L386.2L386.2L346.213s6.2L336.2L366.21356.2L376.2L346.2L346.2L306.2L306.2L276.2L286.2L266.21"256.2L2L6.2L2A6.2LL86.2LL86.21t76.2LL56.2L126.2Lt06.2L086.21086.21087.42797 .4L497 .40307.38937,38077.37637.37707.37607.372L7.36307.35527.34997.34907.34687.34LL7.33067,32LL7.3L477.3L247.309L7.302L7.29037.27937.27L97.26947.26967.27327.27637.27547.26737.25457.24L97.23357.22847.22367.2L407.20037.18687.L7757.L7L87.L6627. L5597.L4L37.L2747.LL707.LLL57.11037.LLL70.62300. s8940.60930.57850.595L0.57080.59000.572L0.58850.5687o.s79L0. s6150.57350.56090.5710o. 55580.56030.54670.5537o.54470.55030.53800.5385o.52740.53090.52480. s3130.52840.5342o.52780. s2610.51s40. s13s0.50720.50850. s0250.49900.489L0.48560.4801o.4799o .47460.46980.46030.45560.450so.45020.44936.80496.82s56.79366.81086.78566.80566.78706.80406.78366.79436.776L6.78856.77556.78s86.77026.77486.76086.76806.75876.76456.75186.75236.74096.74446.73816.74496.74L96.74786.74L26.73956.72846.72656.7L996.72!36.7L5L6.71L56.70L36 .69776.69L96.69186.68636.68136.671s6.66676.66146.661_06.66016.6624STAGE( ft)22.0022.0022.0022.0022.0022.0422.0022.0022.OA22.0022.0022.0022.0Q22.0022.0022.0022.O022.0022.0022.O022.0022.0022.O022.0022.O022.0022.0022.0022.O022.Q022.0022.O022.0022.OO22.0422.O022.0022.0022.0022.0022.O022.0022.O022.0022.0022.0022.0022.O0TIME(min)790.00800.008L0.00820.00830.00840.00850.00860.00870.00880.00890.00900.00910.00920.00930.00940.009so.00960.00970.00980.00990.00L000.00L0L0.001020.001030.00L040.001050.001_060.00L070.00L080.001090.001100.00L1_10.001120.001130.00LL40.0011s0.001160.00LL70.001L80.00LL90.00L200.001210.00t220.ooL230.00L240.OO1250.00L260.00t-IIIIl_
4/22/97 Polaris Engineering & Survey97037 SAN JUAN RECONSTRUCTION PROJECTLOPEZ AREA INFILTRATION SYSTEMPOST DEVELOPMENT STORM SPREAD IN TRENCHESpage 38TEVEL POOL ROUTING TABLELEVEL POOL ROUTING TABTEI1" T2 2S1 SUM O1- O2+2SZSTAGE( ft)TIME(min)0.4510o .452L0.4s30a .45410.45500.4561_0.45700.4581-0.45890.4600o .4602o .45670.4494o .4409o .43430.4301-0.428Lo.4282o .4290o .42660.38960.30950.20100.11200.04930.01200.00010.00000.00000.00000.00000.00000.00000.00000.00000 .452L0.4530o .454L0.45500.4561_o .45700.4s81-0.45890.4600o .4602o.4567o .4494o - 4409o .4343o.4301o .428Lo .4282o - 4290o .42660.38960.309s0.201_0o.tL200.04930.01200.0001_0.00000.00000.00000.00000.00000.00000 - 00000.00000.00006.2L096.2L096.2L096.2L096.ztLO6.zLtO6.ZLLL6.2LLL6.zLtt6.2L126.2LL26.ztto6.2LO86.210s6-2LO36.2L026.aLOL6.ztOL6.2L0L6.ZLOO6.1,7s66.03t75. 71s85.23204.63763.99303.35352.75782.2L73L.7307L.29660.9r.360.58000.29380.o77L7.LL397. 1_1597. 11807.L20L7 -1"22J"7.L24L7.L2627.128L7.L30L7. 13L37.L28L7.LL727.L0L27 .08577.07467.06837 .06647.Q6737.06577 .02626.87476.54226.02885.39324 .69894.00513.35362.75782 -2173L.7307L.29660.91_360.58000.2938o.077L0.45150.4s150.45350.45360.45550.4556o .457 4o.45770. 45930.4s960.46050.4565o .44980.44080.4346o .42990.4283o ,4280o.429Lo .42650.424t0.41_890 .407 40.3894o.36620.33970.31180.28390.25660.23004.204L0.17890.L5470.l_31_40.08526 .66246 .66446 .66456.66656.66666.66856.66886.67046.67086 .67L76.66766.66076. 65136 .64496 .640L6.63846. 63816.63936.63666.sggt6 .45066.!2335.62L4s.00394.33273. 66533.04L72 .4739L.96071.5007L.0926o -73470.4252o.L623-0.008122.0022.0022 -OO22.0022.0022.0A22.0022.O022.0022.0022.0022.0022.0A22.0022.0022.0022.0022.0022.0022.002L.992L.942L.842L.682t .472L.2320.9820.7220 -4720.22L9.97L9.731_9.50L9.27L9 -07L270.OOL280. O01290.00L300.001_31_0.001320.00L330. 00L340.00L350.00L360.001_370.00r_380.001390.001400.00141_0.00L420 -OOL430.001_440.0014s0.00r_460.001_470.001480.001490.00L500.00l_s10.001520.001,530.001s40.001550.00L560.001570. OO1580.00L590.001600.00161_0.00
Appendix B; Technical Manual Worksheets for Infiltration TrenchesnriIr'ht-It'It"tItIItIIIt.t-LL
r!.r-Iitl"III:IM-3.3 TEASIBILITY ANALYSIS AND GENERAL LI1WITATIONS FOR INFILTRATION BMPsIII-3.3.1 QyeryiewThis section provides the basis for an assessment ofthe maximum amoult of on-site infiltration that ispractically achievable for each Hydrologic soil group. In additio4 it provides guidance in determiningimportant design Variables.For a site to be suitable it must meet or exceed all of the specifio oriteria listed under GL-l through 6.Should a site investigation reveal that any one of the General Limitations cannot be met, the implementationofthe infiltration practice should not be pursued.III-3.3.2 General LimitationSThe General Limitations (GL's) are governed by the physical suitability of the site and the need to preventpollution ofground wat€r. They include:t-IGL-IGL.zGL-3Soil SuitabiliryDepth to Bedr-och Water Tablg or ImpermeableLayer, or Dissimilar soil layerProximity to Drinking Water Wells, Septic Tanks, Drainfields, Building Foundations,Structures, Nativo Growth Protection Easements, and Property LinesLand SlopeDrainage fueaControl of SiltationGL-4GL-5GL-6GL-l Soil Suitg.bilitvThe suitability of soil for infiltration is to be based on evaluating the following:For runqfftreatmont. the soil infiltration rate, (f), shell be between 0.5 and 2.4 inches perhour;Ans. Inflltration rate used was 4 inehes/hour. Runofftreatment will be provided bybiofiltration swales and a sediment trap.o)For strear,nbank-elosiqn cofrtrol there is no limitation on soil infiltration rate but aminimum rate of 0.5 inches per hour is recommended;Ans. Not applicabla(c)Runoffmust infiltrate through at least l8 iltches of soil which has a minimum cationexchange capacity (CEC) of 5 milliequivalents per 100 grams of dry soil.Ans.Soll tests show soil to be dlscharged into is lonmy sand having s cation exchange ofless than 5 milliequivalents per 100 grams, Cation exchange will be prcvided by theadditlon of clay to the ends of the biofiItration swales during prctrertment.(d)Soils with 30 percent or greater clay content or 40 percent or greater silt/clay content shallnot be used;Ans. SllUc{ay content is ryell below 30%o(a)tLLAppendix B Page I
r-rr'(e) Infiltration $ystems shall not utilize filI material nor be placed over fill soils;Ans. Inliltration $y$tem utilizes rock fill within sandy netive material.(DAny stone subgrade installed as part of an infiltration structure must €xtend below the frostline.Ans. Stone materiel will be buried at least 5 feet deep, woll below the frost line.Aerobic conditions are to be maintained to the fullest extent possible for runofftreatmentBMPs by designing them to drain the water quality desigrr storm in 24 hours or less.(Note: If al(ater Quality InfiItration Basin or Treneh (BMP N.05 or R1.06,respectively) is preceded by a Presettling Basin (BW RD.l0) then the combinalion ofboth BMPs (i.e., the Presettling Basin qnd the Infiltration BMP) rmtst be designed todrain the 6-month, 24-hour design storm within 24 hoars. This is necessaqt to ensurethat qerobic conditions are maintained in the infltration BMP.)Ans. The infiltration trench will be infiltratcd within the 24-hour timc period forthe 6-monthr 24-hour stor:nt.In addition, it is recommended that a more detailed soils investigation be conducted if potential impacts toground water are a concern, or if the applicant is proposing to irfrltrate in areas underlain by till or otherimpermeable layers. No formal procedures have been adopted for use in this manual. For furtherinvestigations, consultation with soils and ground water specialists is recommended. One document whichmay be of use is the Soil Conservation Service's "Washington State Water Quality Guide," available (inlimited supply) from the SCS ofEce in Spokane, Washington (W. 316 Boone Avenug Spokane, WA 99201-2348).Ans.Detailed soils investigations were undertaken by Mycrt-Biodynamics for the MiddleSchool site and by Perteet Engineering nnd by Polaris Engineering & surveying'fnc., for the subject drainage facility. Soil logs rnd cross sectiorrs are included withthe engineering report. Inliltration rates for the sand layer were determlned byJohn Fleming, PE, of Polaris Engineering.GL-2 Depth to Bedrock. Water Teble. or Impqd$eable LayerThe base of all facilities shall be located at least three feet above the seasonal high water marlg bedrock (orhardpan), and/or impermeable layer, A high water table can indicate the potential for ground watercontamination. Also, infiltration may be ffibited by the water table; this could result in the BMP notfunctioning as designed,Ans.Seasonal high water table for wetlnnd arca (Townsend Meadows) ir 15.O, four feetlower than bottom of infiltration trench. No standing wetet was noted in bores intothe sand during explorntoly trenching in Mrch, 1997 , n time of year when theground water level should be at its hlghest stage.GL:3 ProfifnitI to Drin\ing Watcr Wells- Septic Tanks. Drainfel4S.Sqildi{rg FouqdationsnStru4ures" Native Grolvth Protection Easements (I'IGPEJ- and P{operty-LinesThe proximity of infiltration facilities to other structures and facilities must be taken into account. Otherwisethe potential exists to contaminate ground water, disrupt the proper functioning of septic tank systems,(e)IlAppendix B Page 2
r-r"r-tdamage foundations and other property. The site designer/engineer must conduct an investigation todetermine the most appropriate locations of infiltration facilities; this is best done on a case-by-case basis butthe following basic criteria is provided for information purposes:. Infiltration facilities on commercial and industrial sites should be placed no closer than 1o0feet from drinking water wells, septic tanks or drainfields, and springs used for publicdrinking water supPlies.Ans. Area is served by City water and sewer. There are no known wells, septicsystems, or springs in the immediate area.Infiltration facilities should be situated at least 20 feet downslope and 100 feet up slopefrom building foundations. Infiltration facilities should be situated at least 20 feet &om aNGPE. An exception is roof dourn spout systems which should be located a minimum'ofl0 feet from any structure, property line or NGPE, and 30 feet from a water supply well,septic tank or drainffeld.Ans.Infiltration facilities are situated at least 20 feet downslope from anyexisting building foundations. There are no Native Growth ProtectionEasements in the'area. There are no water supply wells in the area.GL-4 Land SlooeSlope restrictions depend on the BMP selected. Application of infiltration practices on a steep gradeincfeases the chance ofwater seepage from the subgrade to the lower areas ofthe site and reduces theamount ofwater which actually infiltrates.Ans. Inllltration trcnch is situated near the bottom of a sub-basin depression. The slope. is minimal. There are no anticipated losses from interflow.Infiltration facilities can be located on slopes up to 15 percent as long as the slope ofthe base ofthe faoilityis less than 3 percent. All basins should be a minimum of 50 feet from any slope greater than 15 percent.Ans Not applicsble due to flat land slopes.GL-5 Drainase AreaInfiltration BMPs are limited in their ability to accept flows from larger drainage areas. The followingdrainage area limitations will be applied:Infiltration basins - maximum of 50 acresInfiltration trenches - maximum of 15 acresPorous pavement - maximum of 15 acresConcrste grid/modular pavement - maximum of l5 acresRoof down spout system - maximum of 5000 square feetAns.Trlbutary ar€s is 11.0 acres of which soils are primarily glaciel outwash.G@Surveys show that siltation is one ofthe major reasons for failure of infiltration facilities. This often occursduring construction, thus it is most important not to excavate trenches or ponds to final grade during thisIaIaaaItt-Appendix B Page 3
phase. Even after construction it is vital to prevent as much sediment as possible from entering by firstrouting the water through a pretreatment BMP. Also there may be other construction activities upstreamthat take place and could result in surges ofsediment entering the site.The following conditions also apply:(a)Final construction of infiltration facilities shall not be done until after other siteconstruction has finished and the site has been properly stabilized with permanent erosioncontrol practices as outlined in Volume II, Erosion and Sediment Control.Ans. Infiltration trench is only construction anticipated in the immediate area.There will be no conflict with other activities.(b)Infiltration facilities are not recommended for use as temporary sediment traps during theconstruction phase. Infiltration facilities should be constructed only after upstreamdrainage areas have been stabilized. If an infiltration BMP is to be used as a sediment trapit must not be excavated to final grade until after the upstream drainage area has beenstabilized. Any accumulation of silt in the basin must be removed before putting it inservice.Ans.Infiltration facilities will not be used as t€mporary sediment traps. Suitabletemporary devices will be installed.(c)Inflow to infiltration BMPs used for runofftreatme,nt, other than roof down spoutsystems, must first pass through a pretreatment BMP in order to minimize the suspendedsolid load and prevent siltation of the infiltration facility.Ans. 907' of inflow will be treated by biofiltration. All of inflow will be treatedfor sediment removal.lll-3.3.3 Feasibilit), Analysis DiscussionCollection and analysis of soils, geologic, and Hydrologic information are a critical component oftheplanning and design process for infiltration BMPs. A subsurface investigation must be conducted under thesupervision ofan engineer or scientist ofappropriate qualifications. The investigation shall involve both areview of the available literature from the U.S. Soil Conservation Service and any other relevant sources anda field investigation as part ofthe overall geotechnical site investigation.A soils report is required for each location. A soil log should be taken at a minimum 3 foot depth below theproposed base ofthe facility and an additional soil log shall be taken for every 5,000 square feet ofinfi ltrating surface area.To effectively design an infiltration structure, the following information is required:(a) Textural character of the soil horizons atdlor strata units within the subsoil profile. Basedon this textural analysis the following variables are to be determined:soil infiltration rate, "f'soil cation exchange capacity (or CEC),percent clay contort in soil(b) Location of the seasonal high ground water table, depth to bedrock or impermeable layer,(D(ii)(iii)Appendix B Page 4
r!t-rand/or depth to dissimilar soil layers (duplex soils).The first step in determining the site capabilities should be to conduct an on-site investigation, in conjunctionwith consulting the available soil survoy data. Soil Surveys are available for all counties in Washington andmay be obtained from the Soil Conservation Service of the local Soil Conservation District. Due toglaciation, soil types fiay vary dramatically within a small area. An on-site investigation is always necessarybecause local conditions may be different than what published soil survey data indicates.For larger land developments, soil information has traditionally been collected during the geoteohnical siteinvestigation in order to determine foundation conditions for structures and to design earth structures suohas fills and cuts. The standard method of conducting subsurface investigations is to drill holes and collect al-sls inch diameter soil sample, 1.5 feet long at 3 to 5 foot intervals in the boring using a split-spoon samplerSolid augers are also used to collect large samples for oompaction tosting but do not provide an aocuratepicture ofthe soil profile.For streambank grosion control the most suitable soils will generally be in Hydrologio Group A, though it ispossible some Group B soils could also be used.The location of the seasonal high ground water table can be deterrnined by field observation of static waterelevation in bores, changos in soil moisture coiltent, and changes in soil color (mottling, for example). Itshould be noted that the ground water table elevation fluctuates not only on a seasonal basis but also on anannual basis in response to prolonged periods of wet and dry precipitation cycles. Thus, the field workshould be supplemented with consultation of the local govemment's health atrd public works departments tobeneflt from their long-term experience with local ground wster conditions.Developments which occur on sloping and rolling sites may use extensive cut and fill operations. The use ofinfiltration systems on filImaterial is not permitted because of the possibility of creating an unstablesubgrade. Fill areas can be very susceptible to slopo failure due to slippage along the interface ofthe in-situand flll material. This condition could be aggravated if the fill material is allowed to become saturated byusing infiltration practices.In summary, the foltowing procedure may be used for investigating the feasibility of using infiltration BMPs:Pre.liminary Screening - Investigate soil characteristics and General Limitations based on published soilsurveys,localstudies,andfieldinvestigationsofsite. Ifthesoilinfiltrationrateislessthan0.5inchesperhour, the site is not feasible for infiltration. If the soil infiltration rate is greater than2.4 inches per hour itmay be acceptable for streambank erosion control purposes but not runofftreatment.Soil Bore$ - Soil bores will be required for two purposes:(l) Collect soil samples so that a textural analysis can be conducted. The textrrral analysis is to be used todetermine the following variables:infiltration rate, fcation exchange capacity, CECpercent clay contentSoils iderrtified by the textural analysis as Hydrologic Soil Group B are the most appropriate ones forproviding runoff treatmen\ those which are Hydrologic Soil Group A are most appropriate for providingstre qm bank e rosi on control.Ifthis analysis indicates that any ofthe conditions in General Limitation #1 are violated, then infiltrationaaot"It_Appendix B Page 5
/-rttItshould ilot be pursued.(2) Determine location and depth to the seasonal lugfi water tablo, bedrock, impermeable layer, and/ordissimilar soil layers.If this analysis indicates that any of the conditions in General Limitation #2 are violated, then infiltrationshould not be pursued.At this point, the feasibility of infiltration should be clearly established. If feasiblg the applicant may proceedto size and design the BMP as described in Sections III-3.4, m-3.6, and III.3.7 subject to meeting all otherGeneral Limitations.tlr€.4 GENERAL DESIGN CRITERIA TOR INFILTRATION AI\[D tr'ILTRATION BMPSA Darcy's Law approach is recoinmended for sizing both infiltration and filtration BMPs, Stage-storage andstage-discharge relationships can be developed and, through an iterative process, the final BMP size andgeometry can then be determined by routing the appropriate design storm(s) through the facility. SeeSection m-l.4.3 for guidance on developing storage-discharge relationships.Darcy's Law of ground water movement can be used to dwelop the stage-discharge relationship:Q = f+i*Ar,whereflowrate at which runoffis infiltrated/filtrated by BMPinfiltration rate of soil or filtration mediahydraulic gradientSurface area ofthe infiltration or filtration BMPConsorvative values of "f' should be used. For infiltratipn BMPs, a factor of safety of tw.q should be appliedto the infiltration rate determined from the textural analysis and, hereaften, the design infiltration rate will belabeled "fi" wl ere fu : 0.5 * f For sqnd filtrafiq.n BMPs an "f' value of about 2 inches per hour isrecommended for desigrr purposes. This appears to be a low value but reflects actual rates achieved byoperating sand filtration systems treating u6an runoff.If the approximate depth available for the BMP is known then a stage"storage relationship can also bedeveloped (see Section m-l.4). A minimum of one foot of fteeboard is recommended when establishing theBMP depth.The appropriate design storms can then be routed tlrough the BMP using a level pool analysis (Section trI-1.4.4) to finalize the BMP size a d geometry. This will be an iterative proaess. The analysis mustdemonstrate that the BMP will completely percolate the design storm within 24 hours (or 48 hours for the100-year event). Ifthis is not the oase the surface area and or depth ofthe bNdP will havo to be increased. Ifthe analysis indicates that the design stoms can only be pa'rtially infiltrated the BMP should still bo utilizedbut the additional runoffmust be conveyed to another BMP for runofftreatment and/or streambank erosioncontrol.Ans,Discharge or infiltration was calculatcd using the program Watcrworks whichutilizes the Darcy equation to calculNte inliltration. A level pool routing routine wasused in the calculations. Both the design storm and the 100-year storm percolatedwithin the required time periods.afiA"t-ItfLLAppendix B Page 6
/-r-jLlI(Ittote: If a Water Qaality Infiltration Basin or Trench (BMP RL05 or N.A6, respectively) is preceded by aPresettling Basin (BMP RD. I0) then the cqrtQination of both BMPs (i.e., the Presettling Basin &d theWltration BMP) must be designed to drain the 6-month, 24-hour design stormwithin 24 hours. This isnecessary to ensure that aerobic conditions qre maintained in the inrtltation BMP.)Ans. Not Applicable.M.3.5 CONSTRUCTION AND MAINTINANCEIII-3.5.1 OveryiqwThe failure of infiltration and filtration BMPs to function properly can often be trsced back to constructiongnd maintenance issues. By utilizing appropriate construction praotices and conducting systematic andrigorous maintenance, infiltratiorlfiltration BMPs should funotion properlyIII-3,.5.2 Cor,rstructipnRegardless of the type of infiltration/filtratiofr practice to be constructe4 careful consideration must be givenin advance of construction to the effects of the work sequence, techniques, and the equipment employedduring construction ofthe facility. Serious maintenance problems can be averted, or in large part mitigated,by the adoption of relatively simple measures during construction.Previous experience with infiltration and filtration practices in the States of Maryland and Texas has shownthat these BMPs must 4q! be put into usg or preferably even constructed, until the drainage areas thatcontribute runoffto the structure have been adequately stabilized. When this precaution is not taken,infiltration/ filtration struqtures often become clogged with sediment from upland construction and thus failto operate properly from the outset. It cannot be emphasized enough how important it is to protect thesefacilities from sediment doposition at all times.Care must also be taken to not sompaqt soils during the oonstruction phase as this can seriously affectinfiltration and filtration rates. If vehiclos must be driven over the infiltration/filtration BMP duringconstruction only those with large tracks shall be used.Specifie construction methods and specifications are provided for eaoh infiltration and filtration BMP inSections III-3.6 and III-3.7III-3.5.3 MaintenanceThe maintenance requirements of infiltration and filtration BMPs are an important aspect which is often notaddressed in the planning and design ofthese structures. Infiltration and filtration basins can be visuallyinspected and easily maintained. The surface of an infiltratior/filtration trench or roof down spout systemcan also be visually inspected and maintained, but the subsurface storage area cannot. It is therefore arequirement to install an observation well in practices such as these in order to have an observationmechanism available.Infiltration and filtration practices must be regularly inspected. Specific maintenance specifications andrecommendations are provided for each infiltration and filtration BMP in Sections IU-3.6 and III-3.?.m€.6 STANDARDS AND SPECIFICATIONS FOR INFILTRATION BMPsI[-3.6..4 FMP RI. 1 0 Water,Ou4litv (WO), I+filFation TrenqhAppendix B Page 7LNL
r-r-L[-IIPurpose and DefinitionThis BMP is a shallow o<cavated trench designed primarily to provide runofftreathent but Uet streambankerosion control. The soils underlying this 8MP must be capable of removing pollutants from runoffand willlikely have insufficient permeability to be used for streambank erosion control. Trenches are generally 2 tol0 feet in depth backfilled with a coame stone aggregat€, allowing for temporary storage of storm runoffinthe voids between the aggregate material. Stored runoffthen gradually infiltrates into the surrounding soil.The surface ofthe trench can be covered over with grating and/or consist ofstonq gabioq sand, or agrassed covered area with a surface inlet.One alternative design is to install a pipe in the trench and surround it with coarse stone; this will increase thetemporary storage capacity ofthe trench. A second alternative design is to build a vault or tank without abottom (see BMP RD.15 for details). An infiltration vault/tank is equivalent to a detention vault with thebottom acting as the outlet, instead of having a control structure.Ans. Trench will have a slotted pipe surrounded by drain rock and filter fabric. Trenchwill be installed in non-traffic anea.Design CriteriaThe procedure described in Section IU-3.4 should be used to desigrr an infiltration trench. Trenches areassurned to have rectangular cross-sectiong thus the infiltration surface area (sides and bottom) can bereadily calculated from the trenoh geometry. The storage volume of the trench must take into account thevolume ofbacldll material placed in the trench (i.e., void ratio).Ans.Volumc requirement$ are not applicable for this applicatlon. Purpose of rock is toprovide support for the roof system and porosity for water movement. Trench {illsuntil surface lnfiltration matches inflow rate, At that point' the system is inequtlibria.The same general criteria that were presented for Water Qualrty Infiltration Basins (BMP RI.05) shall applyto trenches; the following information is also provided for guidance:Soils Investigation - A minimum of one soils log shall be required for every 50 feet of trench length,and in no case less than two soils logs for each proposed trench location, Each soils log shouldexitend a minimum of 3 feet below the bottom of the trenclq describe the SCS series of the soil, thetextural class ofthe soil horizon(s) through the depth ofthe log, and note any evidence ofhighground water level, such as mottling. In addition, the location of impermeable soil layers ordissimilar soil layers shall be determined.Ans. Two deep soil logs were ttken in the Sench line. Additional soil logt werc taken inthe gencral area to provide a soil prollle showing that sulliclent permeable soil ispresent in the area ofconstruction for a successful infiltration trench.aThe design infiltration rate, fo, will be equal to one-half the infiltration rate found from the soiltextural analysis.Ans. Infiltrrtion rete reported by John Fleming ir half the actunl infiltration rate,thereforc, providing t2OO"/o factor of safety.,It-t,LILAppendix B Page 8
r-nt-ErIIaPretreatment - Water Quality Infiltration Trenches must be preceded by a pretreatmert BMP. SeeChapter I-4 for selecting appropriate pretreatment BMPs.Ans. Both biofilhation and a sediment trap are being utilized ae pretreatment forsediment removal,oDrawdown Time - Iafiltration trenches shall be designed to empty the 6-month, 24-hour stormevent within one day (24 hours). This will ensure that the nece$ary aerobic conditions exists inorder to provide effective treatment of pollutants. If a Presettling Basin (BMP RD.10) precedes theinfiltration trenclr, the combined drawdown time for both BMPs should be 24 hours.Ans. Ilrawdown time for the 6-month storm is lcss than 24 hours.aBackfill Material - The aggregate material for the infiltration trench shall consist of a cleanaggregate with a maximum diameter of 3 inches and a minimum diameter of 1.5 inches. Theaggregate should be graded such that there will be few aggregates smaller than the selected sizo.Void space for these aggregates is assumed to be in the range of30 percent to 40 percent.Ans. Aggregale will be washed drain rotk of approximately 1.5" diameteraFilter Fabric - The aggregate fillmaterial shall be completely surrounded as shown in Figure III-3.9with an engineering filter fabric. In the case ofan aggregate surfacg filter fabric should surroundall ofthe aggregate fill material exce$ for the top one foot.Ans. Accommodated in design.aOverflow Channel - In general, because ofthe small drainage areas controlled by an infiltrationtrench, an emerge{rcy spillway is not necessary. In all cases, the overland flow path ofsurfacerunoffexceeding the capacity of the trench should be evaluated to preclude the development ofuncorrtrolle4 erosive, concentrated flow. A nonerosive overflow channel leading to a stabilizedwatercourse shall be provided.Ans. Facility is located in e closed deprcsrion. Should the capacity of the trench beexceeded, the water will pond at the inlots at San Juan Avenue and Lopcz street' acondition now existentaSeepage Analysis and Control - An analysis shall be made to determine any possible adverse effectsof seqpage zones when there are nearby building foundations, basements, roadg parking lots orsloping sites. Developments on sloping sites often require the use of extensive cut and filloperations. The use of infiltration trenches on fill sites is not petmitted.Ans. Fecility is located in at I higher elevation than the Middle School. The brse of thetfench is 6 feet lower than the first floor of the school. No impact from the trench isanticipated.aBuildings - Infiltration trenches should be located 20 feet downslope and 100 feet up slope frombuilding foundations.Ans. Facility is located more than 100 feet up slope from all building foundations.Observation Well - An observation well shall be installed for every 50 feet of infiltration trenchI["oAppendix B Page 9
Ilength. The observation well will serve two primary functions: it will indicate how quickly thetrench dewaters following a storm and it will provide a method of observing how quickly the trenchfills up with sediments. Figure III-3.16 illustrates observation well details.The observation well should consist of perforated PVC pipe, 4 to 6 inches in diameter. It should belocated in the center of the structure and be constructed flush with the ground elevation of thetrench as shown in Figure III-3.9. The top ofthe well should be capped to discourage vandalismand tampering.Ans. Tho observntion wells will be established elong with the construction of this facility.Construction and Maintenance CriteriaConstruction TimingAn infiltration trench shall not be constructed or placed into service until all of the contributing drainage areahas been stabilized and approved by the responsible inspector.Trench PreparationExcavate the trench to the design dimensions. Excavated materials shall be placed away from the trench sidesto enhance trench wall stability. Care should also be taken to keep this material away from slopes,neighboring property, sidewalks and streets. It is recommended that this material be covered with plastic if itis to be left in place for more than 30 days (see BMP El.20 in Volume II).Fabric Lay downThe filter fabrio roll must be cut to the proper width prior to installation. The cut width must includesufficient material to conform to the trench perimeter irregularities and for a 72 inch minimum top overlap.Place the fabric roll over the trench and unroll a sufficient length to allow placemeflt of the fabric down intothe trench. Stones or other anchoring objects should be placed on the fabric at the edge ofthe trench tokeep the lined trench open during windy periods. When overlaps are required between rolls, the upstreamroll should overlap a minimum of 2 feet over the downstream roll in order to provide a shingled effFect. Theoverlap insures fabric continuity and allows the fabric to conform to the excavated surface during aggregateplacement and compaction.Stone Aggregate Placement and CompactionThe stone aggregate should be placed in lifts and compacted using plate compactors. As a rule of thumb, amaximum loose lift thicknpss of 12 inches is recommended. The compaction process ensures fabricconformity to the excavation sides, thereby reducing potential soil piping, fabric clogging" and settlementproblems.Overlapping and CoveringFollowing the stone aggregate placement, the filter fabric shall be folded over the stone aggregate to form a12 inch minimum longitudinal overlap. The desired fill soil or stone aggregate shall be placed over the lap atsufficient intervals to maintain the lap during subsequent bacldlling.Appendix B Page l0
(IIPotential ContaminationCare shall be exercised to prevent natural or fill soils from intermixing with the stone aggregate, AIIcontaminated stone aggregate shall be removed and replaced with uncontaminated stone aggregate.Voids Behind FabricVoids may be created between the fabric and excavation sides and shall be avoided. Removing boulders orother obstacles from the trench walls is orte source of such voids. Natural soils should be placed in thesevoids at the most convenient time during construction to ensure fabric conformity to the excavation sides.Soil piping, fabric clogging and possible surface subsidence will be avoided by this remedial process.Unstable Excavation SitesVertically excavated walls may be difficult to maintain in areas where the soil moisture is high or where softor cohesionless soils predominate. These conditions require laying back of the side slopes to maintainstability; trapezoidal rather than reotangular cross-sections may result. This is acceptable, but any change inthe shape ofthe stone reservoir needs to be taken into consideration in size calculations.Traffic ControlHeavy equipment and traffic shall be restricted from traveling over the infiltration areas to minimzecompaction ofthe soil. The trench should be flagged or marked to keep equipment away from the area.Observation WellAn observation well, as described in the previous section on design criteria and shown in Figure III-3.16shall be provided. The depth of the well at the time of installation will be clearly marked on the well capMaintenanceInspection ScheduleThe observation well should be monitored periodically. For the first year after completion ofconstruction, the well should be monitored aftor every large storm (>l inch in 24 hours), and,during the period October I through March 31 inspections shall be conducted monthly. From AprilI through September 30, the facility should be monitored on a quarterly basis. A log book shall bemaintained by the responsible person designated by the local government indicating the rate atwhich the facility dewaters after large storms and the depth of the well for each observation. Oncethe performance characteristics ofthe structure have been verified, the monitoring schedule can bereduced to an annual basis unless the performance data indicate that a more ftequent schedule isrequired.Sediment RemovalaSediment buildup in the top foot of stone aggregate or the surface inlet should be monitored on thesame schedule as the observation well. A monitoring well in the top foot of stone aggregate shallbe required when the trench has a stone surface. Sedimont deposits shall not be allowed to build upto the point where it will reduce the rate of infiltration into the trench.oILiAppendix B Page 1l
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