Loading...
HomeMy WebLinkAboutWPO202000028 Correspondence 2023-02-14SHIMP ENGINEERING, P.C. Design Focused Engineering February 14, 2023 David James County of Albemarle Department of Community Development 401 McIntire Road, North Wing Charlottesville, Virginia 22902 RE: Response Letter #2 for WPO202000028 Regents school of Charlottesville (Amendment I Dear David, Thank you for your review the VSMP Plan Amendment for Regents school of Charlottesville [Amendment 1]. This letter contains responses to County comments dated December 06, 2022. 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. Update SWPPP with the approved plans. (Rev.1) Acknowledged. Please submit a revised Registration Statement (VAR10) form for the acreage increase, check modification with acreage increase. Revised, Registration statement has been submitted in these comments. B. Pollution Prevention Plan (PPP) The PPP content requirements can be found in County Code section 17-404. 1. Update PPP. (Rev.1) Acknowledged. C. Stormwater Management Plan (SWMP) VSMP Regulation 9VAC25-870-108 requires the VSMP authority to approve or disapprove a SWMP. This plan is denied, and the reasons are provided in the comments below. The stormwater management plan content requirements can be found in County Code section 17- 403. 1. Purchase of additional nutrient credits required prior to amendment aooroval. (Rev.1) Acknowledged; Purchase of credits required prior to plan approval. A nutrient credit letter for this amendment has been purchased and shown on sheet C15. 2. Utility crossings can be shown in the storm profiles. They m vie sanitary profiles. (Rev.1) Addressed. About 0.06ac additional F/OS is being added according to VRRM and must be protected to count towards Water Quality (TP) nutrient load reduction. This may require easement deed & plat revision & recording. a. Alternatively, you can purchase additional credits from the bank provider. Revise VRRM. (Rev.1) Acknowledged. Purchase of credits will need to be made at the closest downstream HUC. HUCO2080204 according to the hierarchy. The Rivanna River nutrient bank is within the same 8-digit HUC. There are no banks upstream of the discharge, nor within the same 12-digit or 30-digit HUC. New letter added to C15. SHIMP ENGINEERING, P.C. Design Focused Engineering ..."If the first assessed waterway downstream of the LDA has an applicable impairment (red) as shown on the dataviewer, credits should be purchased in accordance with the following hierarchy: a. Upstream of where the discharge reaches impaired waters, if credits are available; N/A b. Within the same 12-digit HUC, if credits are available; N/A c. Within the same 10-digit HUC, if credits are available; N/A d. Within the same 8-digit HUC, if credits are available;" Check 4. Provide revised drainage design, worksheet tables. Sheet C13 on the approved plan. (Rev.1) Addressed. 5. Provide SCC design, drainage maps for the new channels from Al & C1. (Rev.1) Addressed. 6. 'rovide revised SSC design for AO. Sheet C15 on the approved plan. (Rev.1) C14, etc.: Channel AO appears to have been modified. Revise: The width should be at least 15ft for the 10yr. The table lists a 5:1 side slope & design depth of 1.5 ft. The plan shows a loft wide flat bottom channel. Channel AO has been Revised. Ld 268 Design Computation table has been updated. Channel Design has been revised to include trapezoidal channel. See new, added SCC Table. a. Revise: The velocity at outlet AO & Al is excessive (>10 fps). Also, try to reduce / eliminate sharp bends from Al & Cl so that side channel scour is reduced into receiving channel. It was an error with the slope that has been updated. Velocity is now (>30 fps). Al now outlets with a 45 Degree bend. C3 Slightly re -aligned, both now reduce channel side scour. Table LD-229 is corrected now. Revise: Pipe AOb to AOa velocity is under the 3 fps (min) required self -flushing velocity (VDOT DM [9.5.6][9.3.51). Velocity has been revised and shown correctly now. a. Revise: LD-268 table lists a different project name. The name has been corrected. b. Confirm maximum 2-yr velocity from channel AO into stream is not excessive. Using a trapezoidal channel, the velocity has been updated. Please see Sheet C14 (LD -268 Ditch Design) D. Erosion and Sediment Control Plan (ESOP) 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. Please clarify what E&SC phase sheets are being revised per approved plan. Show phase 2 & (Rev.1) Acknowledged. SHIMP ENGINEERING, P.C. Design Focused Engineering (Rev.1) It appears you are creating / revising outfall channels. Include those areas in your disturbance. Thanks for the clarification, phase two has been reviewed and it has been corrected. Outfall is included in LOD. (Rev.1) C7: Revise: The permanent channels should not be shown installed before the trap / ST2. Upstream areas have not been completely stabilized yet. The channels appear to be directing runoff away or though ST2 bypassing it. The channels on Phase 2 have been updated to not be shown installed before the trap. (Rev.1) Revise your Sequence of Construction. Revised. Updated with new pipe & structure titles. (Rev.1) Note: ESC inspector may require additional or alternate controls that the plan does not show. Note has been added to sequence of construction on Sheet C2 ( Phase 3). If you have any questions or concerns, please feel free to email meat odria@shimp-enginee ring. com or you can contact Justin Shimp by phone at (434) 227-5140 or at justin@shimp-engineering.com to discuss in further detail. Best Regards, Odria Barefoot -Diaz Shimp Engineering, P.C.