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HomeMy WebLinkAboutWPO202100001 Correspondence 2021-04-29 (3)SHIMP ENGINEERING, P.C. Design Focused Engineering April 29, 2021 David James County of Albemarle Department of Community Development 401 McIntire Road, North Wing Charlottesville, Virginia 22902 RE: Response Letter #2 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. (Rev. 1) Section II. a. C. Update —see comment D.6 below This section has been updated. Please see the registration statement included with the SWPPP file. b. F. Change `N/A' to `County of Albemarle'. This section has been updated. Please see the registration statement included with the SWPPP file. c. G. Please complete. This section has been updated. Please see the registration statement included with the SWPPP file. (Rev. 1) Sign & date. 2. Include all elements of the SWPPP [17-405] (Rev. 1) Seal, sign & date. Update sheets as needed. The SWPPP elements have been updated. B. Pollution Prevention Plan (PPP) The PPP content requirements can be found in County Code section 17-404. 1. Submit a PPP (exhibit sheet). (Rev. 1) Update as needed. The PPP exhibit sheets have been updated. SHIMP ENGINEERING, P.C. Design Focused Engineering C. Stormwater Management Plan (SWMP) 1. 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 (Rev.1) We want to have 3" min. orifice for maintenance purposes. What would be the post-dev. flowrate from the site? If the postdev. discharge is higher than allowable, then you will need to request an exception. Note the request should be a letter with a fee ($240) and the letter should compare the rates and provide justification for using a 3-inch discharge. Acknowledged, a variance request has been prepared and is attached with this submission. 2. 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). Response: We are still waiting on the ADS design, once we receive that from them then this will be provided. (Rev.1) Acknowleged. The MTFR is > gpTv. The calculations are included in the SWM Packet. 3. Show the pre -/post- development DA maps on the plans. (Rev.1) Partially addressed. See comment D.6. below. Show each DA to a POA. a. (Rev.1) Update SWM calcs to reflex any changes. The SWM Calculations have been updated. 4. Provide list of materials cost -estimate for the MTDs. (Rev.1) Acknowleged; please provide. A request to establish a bond is attached with this submission as well and bond estimate excel sheet has been emailed. 5. Note: Recording of Maintenance Agreement required prior to plan approval. (Rev.1) Acknowleged. Please provide us with the necessary documents and we will record immediately. 6. (Rev.1) Note: Nutrient credit purchase required prior to VSMP plan approval. Please coordinate with Ana (akilmer@albemarle.org) on the purchase document. We are working on the purchase and a new availability letter is attached with this submission. 7. (Rev.1) Sheet 5/6 —Add note that the underdrain from the Stormtech MC-3500 system should be non-preferated unless 6" stone sump is placed underneath. A note was added to sheet C5 and C6. SHIMP ENGINEERING, P.C. Design Focused Engineering 8. (Rev.1) Correct the VRRM, Plan sheets (narriative, etc.), SWM calcs as needed. See comment D.6. a. I measure longer dimensions for the StormTech than what's shown on the Pond calcs (pg. 8). NONE -' w I■■■■■■a ■■ ■I Your measurements are approximately correct, the stone shown in the calculation is less than what the drawing is, this is due to the change of the chamber's layout inside the stone. This just means that the calculations were more conservative. However, since we're updating the calculations with this submittal and applying for the energy balance waiver, the stone storage size has been updated as well. Below is a picture of the actual measurements for your reference. SHIMP ENGINEERING, P.C. Design Focused Engineering 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. Provide letter, or easement & deed bk/pg references for the offsite improvements. (Rev.1) Not addressed. Please show the off -site construction easements on the plan. The easement will need to be recorded prior to pre -con. VDOT entrance permit will also be needed prior. Also, see comment D.6. We submitted a request for recording the ACSA easement at the south of the property and we are waiting for the review & then the public hearing. 2. Sheet C8/C9/C10 — a. Add B/M symbols to graded areas over 3:1. (Rev.1) Partially addressed. B/M needed for 2:1 slope behind ST-2. B/M is now provided behind ST-2. 3. (Rev.1) Total Disturbed Acreage/LOD: 2.14 ac appears to be less area than accounted for in your LOD. It does not appear you're accounting for the disturbed area of san. sewer installation The total disturbed area without the offsite sanitary sewer is 2.14 ac, and the total disturbed area including the offsite sanitary sewer is 2.24. the plan, maps and VRRM calculations all have been updated to reflect the 2.24 ac. Initially, I thought since the offsite sanitary sewer area was already accounted for in the previous development, we wouldn't have to account for it this time, however, since I'm using the re -development VRRM spread sheet, I went ahead and counted for it with this submission. SHIMP ENGINEERING, P.C. Design Focused Engineering 4. (Rev.1) Sheet 2 — Show demo work for the san. sewer installation. The area has been labeled as to be removed and replaced. Please see Sheet C2. 5. (Rev.1) Sheet 10/11 —Provide h&SC stabilization & safety measures for the san. sewer work. Stabilization and inlet protections are now provided for the sewer work. 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.