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HomeMy WebLinkAboutWPO202100001 Correspondence 2021-03-11 (2)SHIMP ENGINEERING, P.C. Design Focused Engineering March 11, 2021 David James County of Albemarle Department of Community Development 401 McIntire Road, North Wing Charlottesville, Virginia 22902 RE: Response Letter #1 for WPO202100001 - 999 Rio Road VSMP Dear David, Thank you for your review of the VSMP plan for 999 Rio Road. This letter contains responses to County comments dated February 22, 2021.Our responses are as follows: A. Stormwater Pollution Prevention Plan (SWPPP) The SWPPP content requirements can be found in County Code section 17-405. A SWPPP must contain (1) a PPP, (2) an ESCP, (3) a SWMP, and (4) any TMDL measures necessary. 1. Please complete the newer version of the registration statement. The newer version of the registration Statement is now provided with the SWPPP. 2. Include all elements of the SWPPP. [17-405] All SWPPP elements are provided. B. Pollution Prevention Plan (PPP) The PPP content requirements can be found in County Code section 17-404. 1. Submit a PPP (exhibit sheet). PPP Exhibit is included in the SWPPP. C. Stormwater Management Plan (SWMP) 1. Cover — Add WPO# to title. WPO202100001 has been added to the Sheet Cl. 2. Provide letter of availably from the nutrient source provider on plans. -Currently, 0.93 Ib/yr TP credit needed Availability Letter is attached with this submission. 3. Sheet C3 — SWM easement should extend over structures AIA & Alas well. SWM easement has been extended to the property line. 4. Sheet C5 — a. Part of the text is cutoff in the details. The viewport has been fixed so that the text is visible. SHIMP ENGINEERING, P.C. Design Focused Engineering b. Orifices under 3" are suseptable to clogging & increased maintenance. Current design not acceptable; especially with the grate over weir in Al. May be acceptable with some sort of trash/debris separater. With this design it is critical that the orifice Structure Al has been modified to doghouse manhole to prevent leaves from entering the system and clogging it. Since the 100-yr water surface elevation is higher than the weir top elevation, the 100-yr storm water is going to flow backwards towards structure Al. Thus, the design has been modified so that structure AlA will be the release for the 100-yr storm event instead of structure Al. The doghouse size has also been modified to 5 ft instead of 4 ft to allow better accessibility. c. The orifice in Al detail is above the 10-yr design & is incorrectly labeled V� Az W N IN 5IHUUIUN! 41. M 4I • .16 D6 iW Lf Pi .]ADD 5" 10-M Aln¢ OM].W =d�O° m r°`sIi -° ai]°si==788-d�JkSS ou'r°< i.8' I W DLnCE QLnCE 0.6].5] P -EOUIREEiR SM R4Cx ..M(6 e. v°Accn nc65 ]D WPED � The orifice elevation has been revised accordingly. The elevation is now 465.20 ft. d. Revise design: You're showing an invert out of 464.80' & invert in of 464.15' in Al, 464.8-464.15=0.65. The hole in the bottom of weir will be underwater. This will make visual inspection impossible & lead to increase maintenance issues. Therefore, raise Al bottom to the minimum allowed of bottom invert. The invert out of structure Al has been corrected to 464.00 the 464.80 was a typo. WEIR- 1464.W N, Al 464.1k , e. The current design based upon the 10-yr WSE will create a pressure situation in the system. The existing pipe and joints before the weir will need to be made water tight. Engineering recommends replacement with new water tight pipes & joints. All pipes going to structure Al and structure A2 have been modified to have water tight pipes & joints. SHIMP ENGINEERING, P.C. Design Focused Engineering 5. These �J esg0 �x xi !s/Loints should be made water -tight. i. iDexe nowu ue muue wxmo-u¢m. ur uxi]9 Y � k ]0 `6 fto a _ O b �?I i The pipes/joints have been modified to be water -tight. 6. Provide MTD details/specs for the installation, inspection, long-term operation, and maintenance requirements on the plans. MTD details are now provided, please see sheet C18. Show that the MTD is sized for the project (https:Hswbmp.vwrrc.vt.edu/bmps/filteringdevices/ - VADEQ Practice 17: Filtering Devices. Sizing information): a. Calculate the treatment volume to the device (TvBMP). The calculated TvBMP can be obtained from the Virginia Runoff Reduction Method (VRRM) spreadsheets. The TvBMP is calculated in the VRRM and is 4,556ft;. The Sheet is included in the SWM Packet with this submission. b. Calculate the peak discharge of the obtained treatment volume (gpTv). DEQ's preferred method to calculate the peak discharge for a BMP drainage area is described here. gpTv=1.78 cfs, calculations are included in the SWM packet. c. Work with the MTD vendor to ensure that the obtained peak discharge to the device (gpTv) is less than or equal to the maximum treatment flow rate (MTFR) of the device (gpTv < MTFR). We are still waiting on the ADS design, once we receive that from them then this will be provided. 8. Show current/proposed land uses and tabulation of percentage of each surface area. Land Use Schedule is provided on Sheet Cl. 9. Show the pre -/post- development DA maps on the plans. The SWM maps have been added to the VSMP plan, please see Sheet C13, C14, C15, & C16. 10. Show drainage patterns on the plans: a. drainage divides, inlet eas, flow lines/paths Flow directions have been added to all the SWM maps, drainage divides are shown on the inlet drainage area map and inlet areas are on sheet C14. SHIMP ENGINEERING, P.C. Design Focused Engineering 11. Provide list of materials cost -estimate for the MTDs. We have been preparing the bond estimates for projects for the County, we can continue to do that. We do not have the material quotes at this time but we will provide that with bond estimates once we get the quote. 12. Show the areas treated by each BMP on the plans. The area treated by limp is now shown on the post development VRRM map. Please see Sheet C16. 13. Note: Recording of Maintenance Agreement required prior to plan approval. We are working with Anna Kilmer to get the maintenance agreement. 14. Note: Recording of deed & easement required prior to Pre -con. The project is part of a subdivision plat, and in the past, the Albemarle County policy has been to record the deed of easement with the subdivision Plat. Please advise of that policy has changed. 15. Note: Coordinate landscaping trees to be outside of any public SWM & drainage easements. All landscaping is outside of the easements. The landscape plan is included in the Site Plan submission but not in the VSMP submission. D. Erosion and Sediment Control Plan (ESCP) Virginia Code §62.1-44.15:55 requires the VESCP authority to approve or disapprove an ESCP. This plan is disapproved, and the reasons are provided in the comments below. The erosion control plan content requirements can be found in County Code section 17-402. 1. Cover — Visually field verify topography & existing site show on sheet 2 and provide date of field verification. A note has been added to Sheet C1 under "Benchmark" regarding a field verification. Justin & I both went to the site and verified it. 2. Provide letter, or easement & deed bk/pg references for the offsite improvements. We understand this is required prior to grading permits are issued. However, all offsite work is being done within the Public Right of Way and ACSA easement. The grading at the South West corner of the property has been modified so that there is no disturbance on the adjacent property (County of Albemarle DB 4830 PG 20). 3. SheetC8/C9/C10— a. Add B/M symbols to graded areas over 3:1. Blanket & Matting symbol has been added to all graded areas over 3:1, Blanket & matting definition has been added to the narrative on Sheet C8 and the details have been added on Sheet C12. SHIMP ENGINEERING, P.C. Design Focused Engineering b. Extend the diversion to the CE RE i ZOxF: TEK lRRE RE 1- � i uses rwnlr aslon+nu F19'911( The diversion has been extended to CE. c. Correct diversion here ©S The diversion has been revised. d. Extend the diversion here The Diversion has been extended. SHIMP ENGINEERING, P.C. Design Focused Engineering 4. Sheet 11 — a. Remove standard CIP detail. Show the CIP sediment trap detail. [VADEQ ESC HB Spec. 3.08,111-50] The CIP detail has been corrected. Please see detail 2 on Sheet C12. b. Remove CE detail. Show the County's CE detail. [ACDSM, pg. 8] The CE detail has been revised to PCE. c. The bottom elevation should be 466.5' for ST-1 The sediment trap table has been corrected. 5. Provide low maintenance (not grass) ground cover specified on the plans where grades are steeper than 3:1. [ACDSM, Sect 8A] Low maintenance ground cover is now provided. Please see Sheet C4 & Sheet C11. Detail 4 on Sheet C12 has been updated so that it has the low maintenance ground cover notes included. If you have any questions or concerns about these revisions, please feel free to contact me at Stephaniekshimp-en ing eering com or by phone at 434-227-5140. Regards, Stephanie Paul Shimp Engineering, P.C.