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HomeMy WebLinkAboutWPO201500034 Calculations 2015-07-28 Glenn Brooks From: Glenn Brooks Sent: Tuesday, July 28, 2015 10:31 AM To: 'Graham Murray' Cc: John Anderson; Max Greene; Justin Deel Subject: Glenmore K2B Graham, Getting back to you regarding our meeting last Thursday and the plan and 2C worksheets you submitted for Glenmore K2C. I have a few points that may need work. Your computations assumed an impervious area per lot of 3000sf. I compute more like 7000sf using our GIS system, and noting that patios,walks and other features will add to this. A sample is shown below. This changes the computations somewhat. I have included an abbreviated version of the comp. I have also included the other lane of the road in the overall load computation, but not in the load to the facilities. The facilities themselves seem to make less sense now, with the largest facility not in the largest drainage area. 9 45-K2- 6-5 316 5-K2-C64 ,s51 s• ft 0.16Nicre. �,4 i43A54C2-6B-2 c r. 3434.tt • 0A54(2-0E3-1 Virginia 2C Method computations Total Pollutant Load and treatment A= 16.34 Iw=0.16 Lpre= [0.05+0.9*Iw]*A*2.28 Lpre = 7.2 Ip= (16*7000+2830*20)/43560/A Ip=_0.2369 Lpost= [0.05+0.9*Ip]*A*2.28 Lpost= 9.8 RR= Lpost-Lpre RR=_2.6 lbs/yr Required Effeciency 1 V EFF=(RR/Lpost) E '=_0, 29 BMP 1A bmpEFF=0.35 DA=2.88 acres Ida = [3*7000+750*10]/(DA*43560) Ida = 0.23 Lbmp= [0.05+0.9*Ida]*DA*2.28 Lbmp= 1.7 Lrem1= bmpEFF*Lbmp Lrem1= 0.5848 BMP2 bmpEFF=0.35 DA=3.64 acres Ida = [4*7000+800*10]/(DA*43560) Ida = 0.23 Lbmp= [0.05+0.9*Ida]*DA*2.28 Lbmp= 2.1 Lrem2= bmpEFF*Lbmp Lrem2= 0.7388 BMP 3 bmpEFF=0.35 DA=6.82 acres Ida = [6*7000+1280*10]/(DA*43560) Ida= 0.18 Lbmp= [0.05+0.9*Ida]*DA*2.28 Lbmp= 3.4 Lrem3= bmpEFF*Lbmp Lrem3= 1.1756 Lreml+Lrem2+Lrem3= 2.4992 Glenn Brooks, P.E. County Engineer VSMP Administrator Albemarle County 2 thous. PERFORMANCE-BASED WATER QUALITY CALCULATIONS APPENDIX 5D -c-acnv.si) swtA vINaLsrt Worksheet 1 S!tt %.1 Page 1 of 3 5v#,A TAL3L4.- To...cpolLo ..sv" vjg) TA(z LzLV ( A STEP 1 Determine the applicable area(A)and the pot-develop d imper ious cov r ('post)• —a- Applicable area(A)* = G acres — W10 rst. 3.GM x. 6,TIM. Post-development impervious cover: structures C4090 aefeo-4-- Lo 't-3 1-5A-.; 3 0 parking lot = N IN acres \ dc.0 (C-NPAo..t.cears i4) roadway = 30PC° -iter-es` '1O 6d. ‘10. Id LAK other: Vs 8,tico A cfgvs. cpczivi 16B- at A= 103° qteres--A-- 06 acres 4— kroanzfraG A,24A /, 0,2)87, (3,0 ri)g 7, xs GrtP'" c a 16).= .6 ) ' Q.noM. O."at 15.( Total = 3.Q1 acres =(total post-development impervious cover A) x 100= % The area subject to the criteria may vary from locality to locality. Therefore, consult the locality for proper determination of this value. STEP 2 Determine the average land cover condition ('watershed)DX the existing impervious cover(Lawn). Average land cover condition(I,atershek• If the locality has determined land cover conditions for individual watersheds within its jurisdiction,use the watershed specific value determined by the locality as'watershed' 'watershed Otherwise,use the Chesapeake Bay default value: 'watershed = 16% 01-117S 5D-5 C.D I Q a MO vl../V6 744( c: L, wvot, r -1-4cAl-co 71-ic DE-vetcw-AE.NI Pke:cis 1Al2 vA Thoo0-1. Ley swm all 315 SLSARK: .rei.A.koCt -Thegej--„„_c oc-szeiv c...0,10L/AArt Swm txmcs 's SCO trL71 &c T,e-szcv,c, Atzc .571-2 coMQL,TA141. (1) A avik."Crt'r A/QM...vs-Lc vvi 44_ Wot..z 0 0 f7-1,4-slks-fir.: 1X-A.E.L4(VAC."es riv COMazA/Van PERFORMANCE-BASED WATER QUALITY CALCULATIONS APPENDIX 5D Worksheet 1 Page 2 of 3 Existing impervious cover(1eXst;,,g.2: Determine the existing impervious cover of the development site if present. Existing impervious cover: structures = acres parking lot = ) acres roadway = - acres other: acres ,.. �'4 acres ♦ � Total = 0 acres IC%isting=(total existing impervious cover± A*) X 100 = Q % * The area should be the same as used in STEP 1. STEP 3 Determine the appropriate development situation. The site information determined in STEP 1 and STEP 2 provide enough information to determine the appropriate development situation under which the performance criteria will apply. Check (• j the appropriate development situation as follows: Situation 1: This consists of land development where the existing percent impervious cover(Iixii1,t,g) is less than or equal to the average land cover condition ('watershed) and the proposed improvements will create a total percent impervious cover(Ir„,st) which is less than or equal to the average land cover condition (1„111ershed). I post 0�� • •'watershed 5D-6 ire a 4 .,t PERFORMANCE-BASED WATER QUALITY CALCULATIONS APPENDIX 5D Worksheet 1 Page 3 of 3 Situation 2: This consists of land development where the existing percent impervious cover(I ) is less than or equal to the average land cover condition (Iwa1C1.shed) and the proposed improvements will create a total percent impervious cover(1,,,,) which is greater than the average land cover condition (1,ater,heci)• Listing ( % ~(watershed lb` O %, and Ipost ___ % > (watershed too Situation 3: This consists of land development where the existing percent impervious cover(ltxist,,,g) is greater than the average land cover condition ('watershed)• existing n�� (watershed Situation 4: This consists of land development where the existing percent impervious cover(lexistmg) is served by an existing stormwater management BMP(s) that addresses water quality; If the proposed development meets the criteria for development Situation 1, than the low density development is considered to be the BMP and no pollutant removal is required. The calculation procedure for Situation 1 stops here. If the proposed development meets the criteria for development Situations 2,3, or 4,then proceed to STEP 4 on the appropriate worksheet. 5D-7 PERFORMANCE-BASED WATER QUALITY CALCULATIONS APPENDIX 5D Worksheet 2 : Situation 2 Page 1 of 4 Summary of Situation 2 criteria: from calculation procedure STEP l thru STEP 3, Worksheet 1: Applicable area (A)* = 45-x`' acres Ipost = (total post-development impervious cover_ A) x 100 = (' '! 'watershed = %�� Or Iuaternhed = 16% 'existing=(total existing impervious cover_ A*) x 100 = 'existing r' % 'watershed % and 'post a;' ' % 'watershed ' % STEP 4 Determine the relative pre-development pollutant load (Lpre). Lpre(watershed) = [0.05 + (0.009 x I�.�te1.,C,)] X A x 2.28 (Equation 5-16) where: L pre(watershed, = relative pre-development total phosphorous load (pounds per year) 'watershed = average land cover condition for specific watershed or locality or the Chesapeake Bay default value of 16% (percent expressed in whole numbers) A = applicable area(acres) Lpretwatershed) _ [0.05 + (0.009 X ( )] n ;6.31 Y 2.28 — pounds per year 5D-9 PERFORMANCE-BASED WATER QUALITY CALCULATIONS APPENDIX 5D Worksheet 2 : Situation 2 Page 2 of 4 STEP 5 Determine the relative post-development pollutant load (LPost). Lpost = [0.05 + (0.009 x lr )] X A X 2.28 (Equation 5-21) where: L = relative post-development total phosphorous load (pounds per year) 'p„,, = post-development percent impervious cover(percent expressed in whole numbers) A = applicable area(acres) Lposc = [0.05 + (0.009 X «d,6 )] x y. : x 2.28 = `j 1-Hi pounds per year STEP 6 Determine the relative pollutant removal requirement (RR). RR = L1.50,4'eLprowatershed) RR = ,49 ;f = pounds per year STEP 7 Identify best management practice (BMP) for the site. 1. Determine the required pollutant removal efficiency for the site: EFF = ( RR_ Lp,,,, ) x 100 (Equation 5-22) where: EFF = required pollutant removal efficiency (percent expressed in whole numbers) RR = pollutant removal requirement(pounds per year) Lp,,, = relative post-development total phosphorous load(pounds per year) EFF = ( Q.D\ - 9.44 ) < 100 = 3. i % 5D-10 I I PERFORMANCE-BASED WATER QUALITY CALCULATIONS APPENDIX 5D Worksheet 2 : Situation 2 Page 3 of 4 2. Select BMP(s) from Table 5-15 and locate on the site: BMP 1: Sw,M m& (DA iA' ° ç - 4 1��t cv,I aer ,Y BMP 2: SWM '.-rt< .`c as .. (bp Ex D o,.► ThcS+-rry BMP 3: Sw,A,‘, 1=ACaLxcti 3 xrti t,o Caca.* 3. Determine the pollutant load entering the proposed BMP(s): LBMp = [0.05 +(0.009 x IBMp)] x A x 2.28 (Equation 5-23) where: LBMP = relative post-development total phosphorous load entering proposed BMP(pounds per year) IBMp = post-development percent impervious cover of BMP drainage area (percent expressed in whole numbers) A = drainage area of proposed BMP(acres) LBMPI = [0.05 +(0.009 x ac),1 )] x -a:2 ' x 2.28 too ( oo t 11,50o fil.v)t-o.ao*. = 1..5D, a, w. pounds per year a0.1 LBMPI = [0.05 +(0.009 x )] x 3.6 ti x 2.28 o . 1c)o x (1a,000�i 4'52,402�tt q,5nc = 1.79 pounds per year 3.sti 19.25 V. LBMp3 = [0.05 +(0.009 x a4,a )] x 6.8a x 2.28 = Lt,16 pounds per year 19„4*3.1- 3- 100 X 9 1,9 3a ' 6.8a Ac, y.a .� 5D-11 PERFORMANCE-BASED WATER QUALITY CALCULATIONS APPENDIX 5D Worksheet 2 : Situation 2 Page 4 of 4 4. Calculate the pollutant load removed by the proposed BMP(s): Lremoved = EffHMI' X LHMI (Equation 5-24) where: Lrem,,,ed = Post-development pollutant load removed by proposed BMP (pounds per year) EffBMI, = pollutant removal efficiency of BMP (expressed in decimal form) LBMIp = relative post-development total phosphorous load entering proposed BMP (pounds per year) Lremoved/BMPI = '�' X ' ' = w-`=a pounds per year L'removed/BMP2 = °' 'J X 1 ? = G; pounds per year pounds per year Lremoved/BMP3 X '1 — 1 P P Y 5. Calculate the total pollutant load removed by the BMP(s): Lremoved/total = Lremm-ed/BMPI + Lremu∎ed'HMI'2 + Lreino%ed HMI'3 + • • • (Equation 5-25) where: Lremoved,„„,,, = total pollutant load removed by proposed BMPs LremovedHMP1 =pollutant load removed by proposed BMP No. I Lre,n„ved/BMP, = pollutant load removed by proposed BMP No. 2 Lremove&BMP3 =pollutant load removed by proposed BMP No. 3 Lremoved/total = c' + -{- ' • • • pounds per year 6. Verify compliance: Lremoved/total�RR d.F \ 5D-12 ,...te 6Leiw-tit.g 'Kan CD.AANrcaVi C A pi Nilo- :5, C7 LOS t,1-1.6 6Z9-`4:441. ar tat , '4 t b a-6's l'A-ctrii,:s) tit )6. 4 AaE•A 64°7 r44F) 7: \Gi 't"X) ar. I, Cte1/4,..i:' ..; -(3.37P,At. 4 0 C)c, ., 6. t ''t 3A 50 At CN 776"l' Ctek..,0 CI•10= 6-5.n (A'4 T-aciaiort.di) CNait: CJ v,st)ars) FraJA 1- Qat,Nyvi CA Lcw-Arups ?Roil,w't co rosERVA,1-4.,,MY i't ss1/4"ES C-Nw''7D 44- 'D f\ is : I f i c c). F A (rw, 1-j0 •1. 5 c.,15 J ''' ooa tr. 1 CNr- klY ■4 ..k. ' ' ' rg c 0,0= 9,06.c-ci5 GP.r.5s/LA'-•N5 '::,., '.4 ct,.. • IJo—o, A c . 0 AveANE t)-L,. Q Ct.'ovc, CAI LlSe15 aN, %NAL AVANTZTI CALCS Q, conSavAs1-.1\10.`1 A590141S. ..„, 4, • fs .-,. 11-*. MA (N01 -‘1,A ) :-. aci L-%a)..i4 -,. g W 0.41 RC. ,:i CA/ ' clii) t':: (:),,,2 0,Oct -Wic COr5.5/1-#‘14A6 Ziti 60p0 caksi)• T. SP{PC- 9.9-7 t-I.: 1 - an, j C._1•1=61 rk y ..t Cr' .r. 65, 2 el r Ct,i,= 3 VI al* ...,_0 €.1-EV.icao' 331:45 C rJa\c co kAt.4N.)'F4r.ifi_ (9604•Wt cALfS Nap_o•kgxa) coNsovitcvayst,-( Assvews Civ.,i'/i) '.=A 5: ui\K IA Ame60 Qi3-, 5,ai 4Vs Qlp r 4.D.,5 -Ti ifs 4 C)■.)C.Iztl Li. Sc (Alec(a4A) qb5c-Cal'A) Q'pRE (P4a) 045-2,.'..• (''s S • /Dflc 11...k 3.‘c1 /Al'IiN Gal op, a5.61 cr5 R.06-- 0.v9 1)A a.ci3, I I.a6 cs 4.05-1 9,33 ms c.F5 \.•5'a DP*. a 01 --- ___ toi. 3 8.96 cr5 5, c .s t,,,,14 .... , \1,c‘k crs 135 as U.S.Department of Agriculture FL-ENG-21A Natural Resources Conservation Service 06/04 TR 55 Worksheet 2:Runoff Curve Number and Runoff Project: Glenmore Lots 1&7-16(Removal of ditches in lots 2-6) Designed By:FGM,PE Date: 7/24/2015 Location: Glenmore Subdivision,Alb.County Checked By:SRC,PE Date: 7/24/2015 Check One: Present X Developed X 1.Runoff curve Number(CN) Soil name and Cover description Drainage Area (Cover type,treatment,and hydrologic condition; Area Product of CN(weighted)= Description hydrologic group CN total product/total Calculated'5' percent impervious;unconnected/connected (Acres) CN x Area (Appendix A) ( ) area Value impervious area ratio) Impervious Areas D.A.#1B B 98 0.22 21.6 63.8-Caculated (Developed) Woods in Good Condition 55 0.00 0.0 (Conservatively 4.08 Grass/Lawns in Good Condition(75%+Groundcover) 61 2.68 163.5 assumed to be 71) 2.Runoff 2-Year Storm 10-Year Storm Drainage Area Description Frequency-years 2 10 n/a Rainfall,P(24 hour)-inches 3.7 5.6 n/a Runoff,Q-inches 1.19 2.58 D.A.#18(Developed) U.S.Department of Agriculture FL-ENG-21A Natural Resources Conservation Service 06/04 TR 55 Worksheet 3:Time of Concentration(I,)or Travel Time(1 t) Project: Glenmore Lots 1&7-16(Removal of ditches in lots 2-6) Designed By: FGM,PE Date: 7/24/2015 Location: Glenmore Subdivision,Alb.County Checked By: FGM,PE Date: 7/24/2015 Check One: Present X Developed X Check One: T, X T, Through subarea n/a DA 1A D.A.#1B Segment ID: (Developed) (Developed) Sheet Flow:(Applicable to T,only) 1 Surface description(Table 3-1) Dense Grass 2 Manning's roughness coeff.,n(Table 3-1 0.24 3 Flow length,L(total L<100)(ft) 100 4 Two-year 24-hour rainfall,P2(in.) 3.7 5 Land slope,s(ft/ft) 0.04 6 Compute T,=[0.007(n*Lp 8]/P20.5 s0 4 0.17 Shallow Concentrated Flow: 7 Surface description(paved or unpaved) Unpaved 8 Flow Length,L(ft) 540 9 Watercourse slope,s(ft/ft) 0.100 10 Average velocity,V(Figure 3-1)(ft/s) 5.1 11 Tt=L/3600*V 0.03 Channel Flow: 12 Cross sectional flow area,a(ft 2) 13 Wetted perimeter,P (ft) 14 Hydraulic radius,r=a/P*,(ft) 15 Channel Slope,s(ft/ft) 16 Manning's Roughness Coeff,n 17V=[1.49i2'3s05]/n 18 Flow length,L(ft) 19 T1=L/3600*V 20 Watershed or subarea T,or TT (Previously Approved) (Add T5 in steps 6,11 and 19) I 0.20 I 0.16 I I s•.Ile U,S.Department of Agriculture FL-ENG-21C Natural Resources Conservation Service 06/04 TR 55 Worksheet 4:Graphical Peak Discharge Method Project: Glenmore Lots 1&7-16(Removal of ditches in Designed By: FGM,PE Date: 7/24/2015 Location: Glenmore Subdivision,Alb.County Checked By: SRC,PE Date. 7/24/2015 Check One: Present X Developed X Drainage Area 1.Data Description D.A.q1B (Developed) Drainage Area(Am)in miles '= 0.0045 Runoff curve number CN= 1 71.0 Time of concentration(Tc)= 0.20 Rainfall distribution type= U Pond and swamp areas spread 0 throughout the watershed= 2.Frequency-years 2 10 3.Rainfall,P(24 hour)-inches 3.7 5.6 4.Initial Abstraction,la-inches 0.817 0.817 5.Compute la/P 0.22 0.15 6.Unit peak discharge,Qu-csm/in 750 775 7.Runoff,Qfrom Worksheet 2-inches 1.19 2.58 8.Pond and Swamp adjustment factor,Fp 1 1 9.Peak Discharge,Qp-cfs where Qp=Qu Am Q Fp 4.05 9.06 SWM Facility No. 1- UPDATES LIMITED TO DA BasinFlow printout INPUT: Basin: SWM Facility No. 1- UPDATES LIMITED TO DA 7 Contour Areas Elevation(ft) Area(sf) Computed vol . (cy) 292.00 3.00 0.0 294.00 127.00 3.7 295.00 269.00 10.9 296.00 544.00 25.6 298.00 1187.00 88.2 300.00 2057.00 206.9 302.00 3016.00 393.6 Start_Elevation(ft) 292.00 vol . (cy) 0.00 5 Outlet Structures Outlet structure 0 Orifice name: 30hr Drawdown Orifice area (sf) 0.005 diameter or depth (in) 1.000 width for rect. (in) 0.000 coefficient 0.600 invert (ft) 292.000 multiple 1 discharge out of riser Outlet structure 1 Orifice name: Mid-Flow Orifices area (sf) 0.196 diameter or depth (in) 6.000 width for rect. (in) 0.000 coefficient 0.600 invert (ft) 298.680 multiple 5 discharge into riser Outlet structure 2 Wei r name: Proposed Spillway length (ft) 20.000 side angle 45.000 coefficient 3.300 invert (ft) 300.500 multiple 1 discharge through dam Outlet structure 3 Culvert name: Barrel multiple 1 discharge out of riser D (in) 18.000 h (in) 0.000 Length (ft) 88.000 Slope 0.011 Manning's n 0.013 Inlet coeff. Ke 0.500 Equation constant set 3 Invert (ft) 289.000 Page 1 Now SWM Facility No. 1- UPDATES LIMITED TO DA Outlet structure 4 Curve name: Anti Vortex multiple 1 Invert (ft) 300.000 discharge into riser file: twentyfour.txt 3 Inflow Hydrographs Hydrograph 0 SCS name: 2-Year, SCS 24-hour Storm Area (acres) 2.880 CN 71.000 pe rainfall , PT(in) 2 3.700 time of conc. (hrs) 0.2000 time increment (hrs) 0.0210 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 3.739 peak time (hrs) 11.970 volume (cy) 461.499 Hydrograph 1 SCS name: 10-Year, SCS 24-hour Storm Area (acres) 2.880 CN 71.000 pe rainfall , PT(in) 2 5.600 time of conc. (hrs) 0.2000 time increment (hrs) 0.0210 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 8.087 peak time (hrs) 11.970 volume (cy) 998.050 Hydrograph 2 SCS name: 100-Year, SCS 24-hour Storm Area (acres) 2.880 CN 71.000 pe rainfall , PT(in) 2 9.100 time of conc. (hrs) 0.2000 time increment (hrs) 0.0210 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 17.389 peak time (hrs) 11.970 volume (cy) 2146.047 Page 2 4,00, SWM Facility No. 1- UPDATES LIMITED TO DA OUTPUT: Routing Method: storage-indication Hydrograph 0 Routing Summary of Peaks: 2-Year, SCS 24-hour Storm inflow (cfs) 3.739 at 11.97 (hrs) discharge (cfs) 3.191 at 12.05 (hrs) water level (ft) 299.386 at 12.05 (hrs) storage (cy) 163.478 Hydrograph 1 Routing Summary of Peaks: 10-Year, SCS 24-hour Storm inflow (cfs) 8.087 at 11.97 (hrs) discharge (cfs) 6.808 at 12.05 (hrs) water level (ft) 300.240 at 12.05 (hrs) storage (cy) 225.633 Hydrograph 2 Routing Summary of Peaks: 100-Year, SCS 24-hour Storm inflow (cfs) 17.389 at 11.97 (hrs) discharge (cfs) 17.084 at 11.99 (hrs) water level (ft) 300.651 at 11.99 (hrs) storage (cy) 259.920 Fri Jul 24 12:46:52 EDT 2015 Page 3 Nwe Nino, SWM Facility No. 2- UPDATES LIMITED TO DA BasinFlow printout INPUT: Basin: SWM Facility No. 2- UPDATES LIMITED TO DA 5 Contour Areas Elevation(ft) Area(sf) Computed vol . (cy) 334.00 4211.00 0.0 336.00 6722.00 401.3 338.00 9686.00 1005.7 340.00 12250.00 1816.3 341.00 13438.00 2291.8 Start_Elevation(ft) 334.00 vol . (cy) 0.00 5 Outlet Structures Outlet structure 0 Orifice name: 30hr Drawdown Orifice area (sf) 0.012 diameter or depth (in) 1.500 width for rect. (in) 0.000 coefficient 0.600 invert (ft) 334.000 multiple 1 discharge into riser Outlet structure 1 Orifice name: Mid-Flow Orifices area (sf) 0.136 diameter or depth (in) 5.000 width for rect. (in) 0.000 coefficient 0.600 invert (ft) 336.750 multiple 3 discharge into riser Outlet structure 2 Wei r name: Emergency Spillway length (ft) 20.000 side angle 78.460 coefficient 3.300 invert (ft) 339.750 multiple 1 discharge through dam Outlet structure 3 Culvert name: Barrel multiple 1 discharge out of riser D (in) 18.000 h (in) 0.000 Length (ft) 64.000 Slope 0.005 Manning's n 0.013 Inlet coeff. Ke 0.500 Equation constant set 3 Invert (ft) 330.320 Page 1 SWM Facility No. 2- UPDATES LIMITED TO DA Outlet structure 4 Curve name: Anti Vortex multiple 1 Invert (ft) 338.750 discharge into riser file: twentyfour.txt 3 Inflow Hydrographs Hydrograph 0 SCS name: 2-Year, SCS 24-hour Storm Area (acres) 3.640 CN 71.000 pe rainfall , PT(in) 2 3.700 time of conc. (hrs) 0.1600 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 4.989 peak time (hrs) 11.938 volume (cy) 583.252 Hydrograph 1 SCS name: 10-Year, SCS 24-hour Storm Area (acres) 3.640 CN 71.000 Type 2 rainfall , P (in) 5.600 time of conc. (hrs) 0.1600 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 10.788 peak time (hrs) 11.938 volume (cy) 1261.334 Hydrograph 2 SCS name: 100-Year, SCS 24-hour Storm Area (acres) 3.640 CN 71.000 Type 2 rainfall , P (in) 9.100 time of conc. (hrs) 0.1600 time increment (hrs) 0.0200 time limit (hrs) 30.000 fudge factor 1.00 routed true peak flow (cfs) 23.197 peak time (hrs) 11.938 volume (cy) 2712.180 Page 2 Nue it SWM Facility No. 2- UPDATES LIMITED TO DA OUTPUT: Routing Method: storage-indication Hydrograph 0 Routing Summary of Peaks: 2-Year, scs 24-hour Storm inflow (cfs) 4.986 at 11.94 (hrs) discharge (cfs) 0.085 at 14.96 (hrs) water level (ft) 336.135 at 17.38 (hrs) storage (cy) 435.491 Hydrograph 1 Routing Summary of Peaks: 10-Year, SCS 24-hour Storm inflow (cfs) 10.783 at 11.94 (hrs) discharge (cfs) 1.315 at 12.38 (hrs) water level (ft) 337.335 at 12.40 (hrs) storage (cy) 780.087 Hydrograph 2 Routing Summary of Peaks: 100-Year, SCS 24-hour Storm inflow (cfs) 23.187 at 11.94 (hrs) discharge (cfs) 7.529 at 12.14 (hrs) water level (ft) 339.245 at 12.14 (hrs) storage (cy) 1487.657 Fri Jul 24 12:54:22 EDT 2015 Page 3 ww PERFORMANCE-BASED WATER QUALITY CALCULATIONS APPENDIX 5D 5 W'\4 a r Worksheet 1 iRcn0 wf Crouu:.i �� Page 1 of 3 5vur1 Fnls�tt 8Y7'nsyc� (•r?C V»,s<c.+}VA") poc-0 tr� SWM Fltf's l.:i•4Y STEP 1 Determine the applicable area(A)and the pot-develop d imper ious cov r U"e'61"6 eo) (Ipust)• 3 Applicable area(A)* = I€>-'< acresk- a,$$ ,cu ft. 3.GLix. 6,glAc. Post-development impervious cover: L.csi 5 =.Qo9Q aefes-e-- Lcs>\-3 L.r45 9-6 Las /7-\o parking lot = N 1 rN acres + t, .7,0-z,, ( 4c .C4.V S 14) roadway = 30,000 -aefek,rk..- Go'.'6, other: atio x to E}6PR6aF1`�v+M TN=t y {'t'& �sr- $,1-tc0 16:. R3,•34'q A fltrc= tick 3°' -uere3 I,G( k ReAftipzr re Pat 5S6c0.55 re 8/"P= 0.66 acres 4— (a.9oK�8% (Q61}A7.)8?. (3�"1,K)?1, tt t' Q'sO Pe, Q. Ac. Total =3,Q1 acres I�st=(total post-development impervious cover-A) x 100= ao2.7 % * The area subject to the criteria may vary from locality to locality. Therefore, consult the locality for proper determination of this value. STEP 2 Determine the average land cover condition (Iwatershed)Qr the existing impervious cover(Iextseng)• Average land cover condition(Iwatershed); If the locality has determined land cover conditions for individual watersheds within its jurisdiction,use the watershed specific value determined by the locality as Iwatershed' 'watershed = Otherwise,use the Chesapeake Bay default value: 'watershed = 16% N OTC S Q) R�/�J 5D-5 E mov2./v6 '-{O( S vee.5::.TG:dy511)110- 1J rea,EAs.i mde.... NJ C./<i l�St.a f3 i �'� .`.'. k:�y t�iVN:' -1"K�/S'�E� k'vN �= �EVELC�P/'1���f 5'T/1s. P.kc4--ts In/Al R vA t—rl y p:��R2-M�ASs ►0644 SwM FACSC3'T° �s 5 5 .. A DX o; AIM a�: ;<•° t -Re&CeaE "ThC aers-This t:, � (�..>r�`cf�, rs s7Zt� cQl`1Ptxr'�nFi: (.9 S1nt m Ft1Cx to acs 1 4S 5\-IaAR.(}\fi e,iL�ASit:.s� �s 6'F I C t 'j'}{i r'-i'.t.�1tF, Tr AE �3P�cNS` DESTGnb V2F 5C3 t( CoMkgAait. a) A QVAcnr' -N A/'ALyssi W=6C 3k �/�144ZY}4: s:i4c rxl(_' -r te 7E L4(/-lct't 35 STSC� sN CcJkva.:AiveC. Nevi PERFORMANCE-BASED WATER QUALITY CALCULATIONS APPENDIX SD Worksheet 1 Page 2 of 3 Existing impervious cover(1 existing"): existingl• Determine the existing impervious cover of the development site if present. Existing impervious cover: structures = D acres parking lot = 0 acres roadway = 0 acres AsSuM�,, Lo-, a-6 4-k4,dc. other: 154 C t,4 xvt ice: acres A55uttirs ecgo acres go wRy rM002,0 u5 Pi CAS FROM, 11.0Ayaveivf Tr) �QE- Total = 0 acres Dc-oe svkie 'existing=(total existing impervious cover-A*) x 100= 0 * The area should be the same as used in STEP 1. STEP 3 Determine the appropriate development situation. The site information determined in STEP 1 and STEP 2 provide enough information to determine the appropriate development situation under which the performance criteria will apply. Check(• )the appropriate development situation as follows: • Situation 1: This consists of land development where the existing percent impervious cover(Iexisting)is less than or equal to the average land cover condition (Iwatershed) and the proposed improvements will create a total percent impervious cover(Inns!)which is less than or equal to the average land cover condition (Iwatershe i). 'post % • •'watershed 5D-6 '*.r PERFORMANCE-BASED WATER QUALITY CALCULATIONS APPENDIX SD Worksheet 1 Page 3 of 3 Situation 2: This consists of land development where the existing percent impervious I g p p ous cover ( existing)is less than or equal to the average land cover condition ('watershed) and the proposed improvements will create a total percent impervious cover(Ipost)which is greater than the average land cover condition('watershed)• 'existing Q % 1_'watershed l %; and 'post Q'11 %�0>'watershed /6 Situation 3: This consists of land development where the existing percent impervious cover(Iexisting)is greater than the average land cover condition(I T watershed)• Iexisting % >'watershed Situation 4: This consists of land development where the existing percent impervious cover(Iexisting) is served by an existing stormwater management BMP(s) that addresses water quality. If the proposed development meets the criteria for development Situation 1, than the low density development is considered to be the BMP and no pollutant removal is required. The calculation procedure for Situation 1 stops here. If the proposed development meets the criteria for development Situations 2,3,or 4,then proceed to STEP 4 on the appropriate worksheet. 5D-7 Neale PERFORMANCE-BASED WATER QUALITY CALCULATIONS APPENDIX 5D Worksheet 2 : Situation 2 Page 1 of 4 Summary of Situation 2 criteria:from calculation procedure STEP 1 thru STEP 3, Worksheet 1: Applicable area (A)* = 16.a4 acres (post =(total post-development impervious cover_A) x 100= aa.r1 (watershed = % Or(lwatershd = 16�o 'existing=(total existing impervious cover_A*) x 100= C.� 'existing Q %‘"Iwatershed 1'6 %; and 'post '7 %>'watershed 1.6 STEP 4 Determine the relative pre-development pollutant load (Lpre). Lpre(watershed)= [0.05 +(0.009 x 'watershed)] x A x 2.28 (Equation 5-16) where: Lpre(watershed) = relative pre-development total phosphorous load(pounds per year) 'watershed = average land cover condition for specific watershed or locality or the Chesapeake Bay default value of 16% (percent expressed in whole numbers) A = applicable area(acres) Lpre(watershed)=[0.05 +(0.009 x f )] x 16.a9 x 2.28 = 7.1$ pounds per year 5D-9 PERFORMANCE-BASED WATER QUALITY CALCULATIONS APPENDIX 5D Worksheet 2 : Situation 2 Page 2 of 4 STEP 5 Determine the relative post-development pollutant load (Lposi). Lpost = [0.05 + (0.009 x Ipos)] x A x 2.28 (Equation 5-21) where: Lpost = relative post-development total phosphorous load(pounds per year) Ipost = post-development percent impervious cover(percent expressed in whole numbers) A = applicable area(acres) Lpost = [0.05 +(0.009 x aa.? )] x t 6.a■ x 2.28 = q' 1'd- pounds per year STEP 6 Determine the relative pollutant removal requirement (RR). RR = Lpost Lpre(watershed) RR = q,4a -- = pounds per year STEP 7 Identify best management practice(BMP)for the site. 1. Determine the required pollutant removal efficiency for the site: EFF = (RR_Lpost) x 100 (Equation 5-22) where: EFF = required pollutant removal efficiency(percent expressed in whole numbers) RR = pollutant removal requirement(pounds per year) Lpost = relative post-development total phosphorous load(pounds per year) EFF = ( a.a t - q.y a ) x 100 a3.'8 % 5D-10 PERFORMANCE-BASED WATER QUALITY CALCULATIONS APPENDIX 5D Worksheet 2 : Situation 2 Page 3 of 4 2. Select BMP(s)from Table 5-15 and locate on the site: BMP 1: Suit-1 C91, cx'r-s-ms Or,i ''FAeat -E"`t BMP 2: SWM T<x. -/ t'c.. -'x r a DEr TSC 1-4e=1.1-Ty BMP 3: 5\41-k CZL I`( 3 A : C ON FACS47,11 3. Determine the pollutant load entering the proposed BMP(s): LBO = [0.05 +(0.009 x IBMP)] x A x 2.28 (Equation 5-23) where: LBMP = relative post-development total phosphorous load entering proposed BMP (pounds per year) IBMP = post-development percent impervious cover of BMP drainage area (percent expressed in whole numbers) A = drainage area of proposed BMP(acres) LBMPI = [0.05 + (0.009 x aU,1 X 2.28 a ') _ too 9,000 fi, t �I,SOO fih tO.av+,c t.5 pounds 3.2> per year ac.\ 'l. LBMP2 — [0.05 +(0.009 x N. )] x 3.6 4 x 2.28 -[ " s.,,Av vt9s. t \moo (t ,„„o B,yoo;At.Oa5►c = 1,q9 pounds per year 3 s4 4=c, = 19. V. LBMP3 = [0.05+(0.009 x a4,a )] x 6.ga. x 2.28 k 6 pounds per year Wig q . 100 x, 9 1,9 V8 . Ac. 5D-11 Igoe 1 PERFORMANCE-BASED WATER QUALITY CALCULATIONS APPENDIX 5D Worksheet 2 : Situation 2 Page 4 of 4 4. Calculate the pollutant load removed by the proposed BMP(s): Lremoved = EffBMP X LBMP (Equation 5-24) where: Lremoved = Post-development pollutant load removed by proposed BMP (pounds per year) EffBMP = pollutant removal efficiency of BMP(expressed in decimal form) LBMP = relative post-development total phosphorous load entering proposed BMP(pounds per year) LremovedlBMPI = 0.35 x \. 5d = 0.53 pounds per year Lremoved/BMP2 = a 35 X \'21 = ©.66 pounds per year I'removed/BMP3 — 0'35 x y•16 = 1.9.6 pounds per year 5. Calculate the total pollutant load removed by the BMP(s): Lremoved/total = Lremoved/BMPI +Lremoved/BMP2 +Lremoved/F3MP3 +• • • (Equation 5-25) where: Lremoved/totai = total pollutant load removed by proposed BMPs L removed/BMPI =pollutant load removed by proposed BMP No. 1 =pollutant load removed by proposed BMP No. 2 Lremoved/BMP2 L'removed/BMP3 =pollutant load removed by proposed BMP No. 3 Lremoved/total = 0'53 + O,66 + I '`IC + . . . = a•6`-3 pounds per year 6. Verify compliance: 7 Lremoved/total ERR 'a.GS w a,ait 5D-12