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HomeMy WebLinkAboutSite Certifications - 03/19/2008March 17, 2008 ST0Wj'VVk ER RECEIVED MAR 1 8 2008 Mr. Jay Barber J•R ENGINEERING City of Fort Collins A Westrian Company Storm Water Utility 700 Wood Street Fort Collins, CO 80521 Re: Detention Pond Certification for Plymouth Church Renovation JR Project 39322.22 Dear Mr. Barber,�a)e�ZTC'O The purpose of this letter is to serve as a Detention Pond and Drainage Certification for the Plymouth Church Renovation project. JR Engineering has reviewed the following items through field observations and a survey completed March 13, 2008 by our crews: o Detention pond volumes/Water Quality Outlet Structures o Flowline Elevations o Erosion control measures The detention/water quality ponds and respective outlet structures were surveyed by JR Engineering after completion in early December. Regrading was required at that point and another survey was completed on March 13, 2008 by our crews. The results of this survey indicate that the East Pond Provides 0.042 acre-feet of Water Quality Volume at anelevation of 5024.32 which is less than the required 0.046 acre-feet as required in the Drainage Report. The East Pond provides the required 0.262 Acre-ft of detention storage at the 100-yr WSEL of 5026.25 with a freeboard of 0.04'. The total detention of the East Pond is 0.271 acre-feet at the overflow elevation of 5026.29'. East Pond shows a positive drainage towards the outlet sttuctufR It shall be noted that Northern Engineering requested a variance to allow 0.193 acre-feet of the Water Quality Volume to be included in the total detention and a variance requesting that the 1' freeboard requirement be waived for the site. The survey also indicates that the West Pond provides 0.015 Ac-ft of Water Quality Volume, which is less than the required 0.018 Ac-ft required by the DI- inage Report. The West Pond has a total detention volume of 0.0951 acre-feet_ with a freeboard of 0.02' at the 100-yr WSEL of 5026.20 which. is greater than the required detention volume of 0.0910 acre-feet as per the Drainage Report. The total detention of the West Pond is 0.122 acre-feet at the overflow elevation of '5026.22. West Pond shows a positive drainage towards the outlet structure. None of the West Pond Water Quality Volume was added to the detention volume. Detention volumes were adequate as shown above. The Water Quality Volumes were low despite the fact that the ponds were constructed almost exactly to plan. A calculation check was completed using the proposed contours provided by Northern Engineering. It was found that even though the Drainage Report requires 0.046 acre-feet of Water Quality Volume for 2620 Fast Prospea Road, Suite 190, Fort Collins, CO 80525 970A91-9888 • Fax: 970A91-9984 • wJrengineering.wm Mr. Jay Barber, March 17, 2008 Page 2 of 3 the East Pond and 0.018 acre-feet for the West Pond, the proposed contours provided by Northern Engineering did not provide this volume. The design checks show that the proposed condition as per the contours provided by Northern Engineering propose a Water Quality Volume of 0.0432 acre-feet for the East Pond and 0.0137 acre-feet for the West Pond. This is 0.0071 acre-feet short of the requirement set forth in the Drainage Report. The Contractor built the two proposed ponds within 0.18% of the proposed contours with a Water Quality Volume of 0.0416 acre-feet in the East Pond and 0.0152 acre-feet in the West Pond. The As - Built condition is 0.0072 acre-feet short of the required water quality volume as per the Drainage Report. The water quality outlet structures are in general conformance with the approved plans. The water quality plate for West Pond and East Pond have the correct number and size of holes at the correct elevation to provide the volume as shown by the contours on the approved plans. The 100-yr detention volumes are met for the two ponds and therefore there are no negative impacts to the safety downstream of the project. It is noted that the shortage of Water Quality Volume is negligible and has no detrimental impacts downstream and we recommend that the ponds be certified as is. Enclosed with this letter you will find as -built stage -storage calculations for West Pond and East Pond. The required water quality capture volumes (WQCV) and 100-year detention volumes were obtained from the `'Final Drainage Report for Plymouth Church" (Northern Engineering March 12, 2007). As-builts of West Pond and East Pond have been attached. It should also be noted that the elevations for West Pond and East Pond might change subsequent to the date of the surveys due to natural and/or artificial actions, reseeding and landscaping. It is expected that these changes should be minimal. A survey was also completed obtaining spot elevations for curb and gutter flowlines to verify that the drainage intent of the approved plans was maintained. The spot elevations have been hand written on the approved plan included as an attachment to this letter. All elevations are flowline elevations unless otherwise noted. Overall, the site maintained the intent of the approved plan with the exceptions marked on the plan and listed below. It is recommended that these areas be addressed. 1) The proposed condition shows that the water should follow the curb and gutter to the north-west, but the as -built condition has a high point causing the water to flow across the asphalt to the north-east towards the parking island. 2) A low -point is causing the water to pond at this location. 3) A low point is causing the water to gather at this point and flow west along the asphalt. 4) A low point is causing the water to pond in this location. 5) A low point is causing the water to pond in this location. 6) It is recommended that the area beyond the drainage pan be filled in to prevent erosion and undermining. X:\3930000.all\3932222\Word\LettersWs-built Pond Cert.doc Mr. Wes Lamarque, March 17, 2008 Page 3 of 3 JR also observed that temporary erosion control measures such as silt fence and inlet protection were in place at the time of our field visit in early December, but no erosion control measures were present at the time of our field visit in March. The mulch and reseeding process was in progress during the time of the site visit in early December. Based upon our field visits and provided survey information, it is our opinion that the drainage facilities as noted above for Plymouth Church Renovation have been constructed -in general conformance to the approved plans with the exceptions listed herein. Sincerely, JR Engineering, LLC Prepared By: Eric Tracy Design Engineer �'DOREG M .... 0 .'• Reviewed By: 37953 " Ali 3 .• � r— ONA1.E Timothy Halopoff, P. . Client Manager 0 X:13930000.all\39322221Word\LettersWs-built Pond Cert.doc As -Built Retention Ponds - Stage/Storage LOCATION: PLYMOUTH CHURCH RENOVATION PROJECT NO: 39322.22 COMPUTATIONS BY: ELT SUBMITTED BY: JR Engineering DATE: 3/17/2008 V = 113 d (A + B + sgrt(A-B)) where V = volume between contours, ft' d = depth between contours, ft A = surface area of contour WQCV Elevatior 100-Year WSEL Overflow Elm WQCV Elevatior 100-Year WSEI Overflow Ele, East Pond - As -Built Stage (ft) Surface Area (ft) Incremental Storage (ac-ft) Total Storage (ac-ft) Total Detention (ac-ft) 5023.25 0 5023.50. 549 0.001 0.001 5024.00 2876 0.018 0.019 5024.32 3303 0.023 0.042 0.0193 5024.50 3543 0.037 0.056 0.0290 5025.00 4082 0.044 0.099 0.0728 5025.50 5478 0.055 0.154 0.1274 5026.00 8701 0.081 0.235 0.2081 5026.25 10001 0.054 0.288 0.2617 5026.29 10209 0.063 0.298 0.2710 5026.50 11301 0.114 0.349 0.3226 West Pond -As -Built Stage (ft) Surface Area (ft) Incremental Storage (ac-ft) Total Storage (ac-ft) Total Detention (ac-ft) 5024.49 0 5024.50 91 0.000 0.000 5025.00 2291 0.011 0.011 5025.08 2395 0.004 0.015 0.0000 5025.50 2944 0.030 0.041 0.0257 5026.00 4917 0.045 0.085 0.0703 5026.20 5682 0.025 0.110 0.0951 5026.22 1 5742 1 0.027 1 0.137 1 0.1220 5026.50 1 6791 1 0.067 11 0.2075 WO Volume Required per Drainage Report West Pond 0.0180 East Pond 0.0460 Total 0.0640 WO Volume Design Check West Pond 0.0137 East Pond 0.0432 Total 0.0569 WO Volume Provided As -Built West Pond 0.0152 East Pond 0.0416 Total 0.0568 WQCV Elev 100-Year WSEL Overflow Elegy WQCV Elevatior 100-Year WSEI Overflow Elevatior East Pond - Design Check Stage (ft) Surface Area W) Incrementa Storage (ac-ft) Total Volume (ac-ft) Total Detention (ac-ft) 5023.25 0 5023.50 340.75 0.001 0.001 5024.00 3003 0.017 0.017 5024.35 3465 0.026 0.043 0.0193 5024.50 3664 0.038 0.055 0.0287 00 5025K6.2 4069 0.044 0.100 0.0731 564 0.055 0.1281 399 0.080 J�234 0.2077 0020 0.132 0.2604 0258 0.062 0.296 0.269716" 0.114 0.349 0.3220 West Pond -Design Check Stage (ft) Surface Area M Incramenta Storage (ac-ft) Total Storage (ac-ft) Total Detention (ac-ft) 5024.49 0 5024.50 192 0.000 0.000 5025.00 2305 0.012 0.012 5025.03 2358 0.002 0.014 0.0000 5025.50 3202 0.031 0.044 0.0284 5026.00 5162 0.048 01 1 0.0760 50%.11 5674 0.014 0.105 0.0911 5026.25 1 6326 1 0.033 1 0.138 0.1240 5026.50 1 7490 1 0.072 1 0,163 1 0.2259 Summary 100-yr Detention Volume Required per Drainage Report West Pond 0.0910 East Pond 0.2620 Total 0.3530 100-yr Detention Volume Design Check West Pond 0,0911 East Pond 0.2604 Total 0.3515 100-yr Detention Volume Provided As -Built West Pond 0.0951 East Pond 0.2617 Total 0.3568 2007.11.20 Western Detention Pond Volume.xls WEST POND AS -BUILT PLYMOUTH CHURCH JOB NO. 39322.22 3/17/08 SHEET 1 OF 2 20 10. 0 20 SCALE: 1" = 20' J-R ENGINEERING A Watrian Company 2620 East RwW Road 9We 190 • Fart Coos, Ca NO 9M-49-M-Fax — •wxwiaurvain= EAST POND AS -BUILT PLYMOUTH CHURCH JOB NO. 39322.22 3/17/08 SHEET 1 OF 2 20 10 0 20 V J'R ENGINEERING A Wa hi n Company 20 East ftpecl Road W SCALE: 1 " = 20' 9970-a Fax 970-4%- wwwW, a 1 December 3, 2007 Mr. Wes Lamarque City of Fort Collins Storm Water Utility 700 Wood Street Fort Collins, CO 80521 Re: Detention Pond Certification for Plymouth Church JR Project 39322.22 Dear Mr. Lamarque, J•R ENGINEERING A Westrian Company The purpose of this letter is to. serve as a Detention Pond Certification for the Plymouth Church project. JR Engineering has reviewed the following items through field observations and a survey completed November 26, 2007 by our crews: o Detention pond volumes o Trickle channel size and slopes o Erosion control measures The detention/water - quality ponds and respective outlet structures were surveyed by JR Engineering after completion. The results of this survey indicate that the East Pond Provides 0.041 Ac-ft of Water Quality Volume which is less than the required 0.046 Ac-ft. The East Pond provides more than the required 0.289 Acre-ft of total storage with a total of 0.298 Ac-ft and shows that the detention volume for the 100-Year storm is 0.289 Ac-ft at an elevation of 5026.25' with 0.04' of freeboard.. East Pond shows a positive drainage towards the outlet structure. It shall be noted that Northern Engineering requested a variance to allow 0.0193 Ac-ft of the Water Quality Volume to be included in the total detention for East Pond and a variance requesting that the 1'_ freeboard requirement be waived for the site. The survey also indicates that the West Pond provides 0.025 Ac-ft of Water Quality Volume, which is more than the required 0.018 Ac-ft required by the Drainage Report. The West Pond has a total storage volume of 0.143 Ac-ft, which is greater than the required 0.109 Ac-ft and shows that the detention volume for the 100-Year storm is 0.109 Ac-ft at an elevation of 5026.10' with 0.15' of freeboard. West Pond shows a positive drainage towards the outlet structure. The water quality outlet structures are in general conformance with the approved plans with the exception of non -galvanized steel being used for portions of the structure. The water quality plate for West Pond and East Pond have the correct number and size of holes. It is noted that even though East Pond does not provide the required Water Quality Volume, the ponds in.conjunction provide more Water Quality Volume than required for the site and therefore it is anticipated that the existing condition will be accepted. In all, it is anticipated that West Pond and East Pond are adequate wd.will perform as -intended. 2620 Fast Prospect Road, Suite 190, Fort Collins, CO 80525 970-491-9888 • Far: 970-491-9984 • wwwjrengineering.wm Mr. Wes Lamarque, December 3, 2007 Page 2 of 2 Enclosed with this letter you will find as -built stage -storage calculations for West Pond and East Pond. The required water quality capture volumes (WQCV) and 100-year detention volumes were obtained from the "Final Drainage Report for Plymouth Church" (Northern Engineering March 12, 2007). As-builts of West Pond and East Pond have been attached. It should also be noted that the elevations for West Pond and East Pond might change subsequent to the date of the surveys due to natural and/or artificial actions, reseeding and landscaping. JR Engineering has reviewed the permanent erosion control measures and it appears that trickle pans have been installed in general accordance with the design plans. JR also observed that temporary erosion control measures such as silt fence and inlet protection were in place at the time of our field visit. The mulch and reseeding process was in progress during the time of the site visit. Based upon our field visits and provided survey information, it is our opinion that the drainage facilities as noted above for Plymouth Church have been constructed in general conformance to the approved plans. Sincerely, JR Engineering, LLC Prepared By: ?5;1- Eric Tracy Design Engineer Reviewed By: Michael D. Walker, P.E. Project Manager X:\3930000.all\3932222\Word\Letters\As-built Pond Cert.doc Proposed Retention Ponds - Stage/Storage LOCATION: PROJECT NO: COMPUTATIONS BY: SUBMITTED BY: DATE: WQCV E/evatior, 100-Year WSEL Overflow EleN WQCV Elevation 100-Year WSEL Overflow Elevatior PLYMOUTH CHURCH RENOVATION 39322.22 ELT JR Engineering 12/3/2007 V = 1 /3 d (A + B + sgrt(A*B)) where V = volume between contours, ft3 d = depth between contours, ft A = surface area of contour East Pond - As -Built Stage (ft) Surface Area W) Incremental Storage (ac-ft) Total Storage (ac-ft) 5023.50 227 5024.00 3161 0.016 0.016 5024.32 3505 0.024 0.041 5024.50 3699 0.039 0.056 5025.00 4087 0.045 0.100 5025.50 5538 0.055 0.155 5026.00 8685 0.081 0.236 5026.25 9856 0.053 0.289 5026.29 10043 1 0.062 0.298 5026.50 1 11026 1 0.113 0.349 West Pond Stage (ft) Surface . Area (fe) Incremental Storage (ac-ft) Total Storage (ac-ft) 5024.00 61 5024.60 778 0.004 0.004 5025.00 2260 0.017 0.021 5025.08 2380 0.004 0.025 5025.50 3009 0.030 0.051 5026.00 5137 0.046 0.097 5026.10 5765 0.012 0.109 5026.26 6789 0.034 0.143 5026.50 1 8441 0.077 0.174 - Required 0.046 Ac-ft > Required 0.018 Ac-ft 2007.11.20 Western Detention Pond Volume.xls 20 10 0 20 SCALE: 1" = 20' WEST POND AS -BUILT PLYMOUTH CHURCH JOB NO. 39322.22 12/3/2007 SHEET 1 OF 2 . lIZw ,j•R BNGnvaMNG ANM [w Caopnyr 20 East Rospea R3 4 See 0-Fan Cams co 8M r 5024- I RETAINING WALL 1e 1902 CHASE TOW ELEV-302&50 (TYP) I_Qi WATER QUALITY OUTLET STRUCTURE WOCV ELEV-3024.32 5' MOLE INV. ELEV-5024.32 i ?r HOLE INV. BEV-302123 .EAST POND —� 100-YR WSEL - 5026.25 �- CONCRETE PAN ry \ . VERTICAL Of AS -BUILT \ CURB A' CUPS CUT h GUTTER (TYP.) / \ �� CONTOURS (TYP.) ,����� 100-YR WSEE PROPOSED / SO26\ - CONTOURS (TYP.) \lam \ 20 10 0 20 SCALE: 1 " = 20' ml � IiT l 11 EAST POND AS -BUILT PLYMOUTH CHURCH JOB NO. 39322.22 12/3/2007 SHEET 1. OF 2 f •R ENGINEERING AW4sfflm0w4wq -20 Eag fl'O5W ROA W180• Fat C41M 00 B0625 9m-0-M-Fa( 0-0-sea•WWWiixonemimco(D CONTRACTOR TO WAWA BOOSTING WALK EIM MN 4-OA 4CTRM, WAYCH ENI GRACE AT BAIX BY W" AND EIO END AT A 0I TO SOUTH. WE EETK a„ W BNDNum iE W N 4k* 0 IWM_® AIM T Dud amw BEN u NIOPHC WALL EM OEIFHTIDN TEMPORARY VEGETATION SPECIFICATIONS: WARM SEASON TEMPORARY VEGETATION TABLE SPECIE W./ACRE R MI% MIXED (mBex.) YILLET ]0 7" f2.5 SDRDHIIY 10 ass 2.5 OTAL 250 - THE AROW YIX R A YW W RG INERA MAY AND ANAL, BE AMIIED g.1RE11 MAY 16 AND JUDY 31. COOL SEASON TEMPORARY VEGETATION TABLE SPECIES WC/ACRE i YI% mccm (IBS./TROD ANBAI BTE ZO 50.S 10 WINIFR WEATJ M ISO1E w OTA .1D �FY� MIX 5 A %;00L WELOW Mlw AND 4Wi RR E .WIW aYM3E4 MO Y SI M NOTES: I) EEW SMALL K pOYED TO A DETAIN BE 1/2' TO J/N•AAND PWY INK A RON EFIIX Nm TO EW R•. TARE oRLL sHV1 eE EgIPFFD ATI sJ1,pl ECR FIFMwc mE sfa QER M EMLV HILJAIID SEED. 2) NEEDED AREAS SNLL W MNJYIm WITH DHSS WN AT THE RATE OF IS (NM) ED zD BM.) IONS/ AI HE TEENSDAY SUALL BE CAU LENGTH A- ORE NATO THE SON, T LEAST W[ HE THE FINEFS SHARE BE 0 OR MORE DETERRED AREAS SEEDED WITH PERMANENT GRAW SMALL BE MULCHED IMMEDIATELY AfIER SEm NC. 3) IF PERMANENT CW55 SEED IS PONIED AT A ONE OTHER BAN "1 6 RECOMMENDED. RI, FIBER HYCNUNC MULCH OR EROSON CCNYCL BLANKET SIUIL RE USED TO REDUCE EROSION AMID PROTECT SEEM. 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