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Home My WebLink AboutWPO201900051 Correspondence 2020-02-24TIMMONS GROUP YOUR VISION ACHIEVED THROUGH OURS. February 19, 2020 David James County of Albemarle Dept. of Community Development 401 McIntire Rd, Rm 227 Charlottesville, VA 22902 608 Preston Avenue P 434.295.5624 Suite 200 F 434.295.8317 Charlottesville, VA 22903 www.timmons.com RE: Scottsville ES Addition — VSMP Permit Plan Review — WP0201900051 - Comment Response Letter Dear Mr. James: We have reviewed all of your comments from February 6, 2020 (Rev.1) and made the necessary revisions. Please find our responses to the comments below in bold lettering. 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. Sign the registration statement. Acknowledged. The registration statement will be signed once a contractor has been selected. (Rev. 1) Acknowledged. Comment still valid. The registration statement will be signed by contractor once selected for the project. 2. Complete Sections: 2 — Provide copy of DEQ permit coverage letter when obtained (before pre -con). 9 & 10 — Sign Signed Certification and complete Delegation of Authority (before Pre -con). 11-Copy of CGP. Acknowledged. A copy of the DEQ permit coverage will be added to the SWPPP when obtained. (Rev.1) Acknowledged. Comment still valid. A copy of the DEQ permit coverage will be provided once obtained. B. Pollution Prevention Plan (PPP) The PPP content requirements can be found in County Code Section 17-445. CIVIL ENGINEERING I ENVIRONMENTAL I SURVEYING I GIs I LANDSCAPE ARCHITECTURE I CONSTRUCTION SERVICES 1. Show paving operations, landscaping operations, staging, stockpile, borrow, fueling, waste disposal, vehicle/equipment washing locations on the PPP. Also, show locations where concentrated stormwater discharges. The PPP has been updated. Stockpile areas have been shown on PPP. Cut and fill areas are shown on grading plan (Rev.1) Addressed. C. Stormwater Management Plan (SWMP) VSMP Regulation 9VAC25-870-108 requires the VSMP authority to approve or disapprove a SWMP. This plan is disapproved, 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. Sheet 6: a. Show land cover map with percent surface areas. Sheet C6.0 shows pre and post land cover conditions with surface conditions shown to match hatches and callouts on C4.0 Layout Plan for post condition and C2.0 Existing Conditions Plan for Pre. Areas of land cover are shown in the VRRM spread sheet and in the Stormwater Quality Calculations summary on C6.0. (Rev. 1) Acknowledged. b. How are you satisfying water quantity, part 1113 for this area? I think this area should be routed (CNpost>CNpre). What is the flow? The pond and upstream bioretention areas have been designed to over detain the routed stormwater to satisfy energy balance for the unrouted area as well. The POA is the ditch downstream of the pond where the routed and unrouted flow come together. The POA has been labeled on C6.0 and is downstream of that area. The Energy Balance Equation on C6.0 and the routing calculations include that area. (Rev. 1) Not addressed. Let's meet to discuss. Stormwater Management Plan and calculations have been updated so that the pre and post areas add up per comment #6. Calculations and pond riser design have been updated accordingly to meet Channel and Flood Protection Requirements at the POA. c. Show the downstream POA. The Point of Analysis is the ditch directly downstream of the pond outfall and has been labeled on sheet C6.0. (Rev. 1) Addressed. d. Add a trash rack to bottom orifice to prevent larger objects from clogging hole. Trash racks have been added to the plans. See sheets C1.1 and sheet C6.0 (Rev. 1) Addressed. e. Bioretentions — Indicate 1-2% slope for underdrain to outlet structure. Specify filter media & surface cover. Specify planting plan requirements. Specify maintenance requirements. 6" diameter underdrain recommended. {VADEQ SW Design Spec. 91. Minimum slope has been called out in the detail on sheet C6.0. Both bioretention areas will be mown turf and bioretention #2 will have trees as well satisfying the requirements for bioretention. Multiple underdrains have been provided so 4" diameter should be sufficient. (Rev. 1) Addressed. f. Bioretention facility 2 — The grading for the sideslope should be 3:1 or flatter (2:1 shown). Pre-treatment cell needed for piped inlet & curbcuts equal to 15% of Tv. {VADEQ SW Design Spec. 91. Bioretention facility 2 side slopes have been updated to be 3:1. Gabion basket forebays have been added to achieve pretreatment cells of 15%. See C5.0 and calculations on detail on C6.0. (Rev. 1) Addressed. What is the L/We ratio for pond? Will runoff not short-circuit to the riser opening from the curbcut & pipe outlets? Gabions at each outlet or another solution should be added. The dry pond is designed only for quantity detention to meet the Channel Protection and Flood Protection requirements, so the L/w ratio does not apply. There are no quality credits being generated from the dry pond and no extended detention, so this pond is not required to be designed to the extended detention requirements of the BMP clearinghouse. The riser outlet structure serves as the control structure to release the 1- and 10-year storms per the routing calculations. (Rev. 1) Acknowledged. 3. Calculations: The outlet velocities (Str 100, 200 & 400) are considered excessive (>10fps) and should be lowered. Pipes have been adjusted to reduce the outlet velocities. (Rev. 1) Addressed. 4. Provide general description of SWM facility operation and maintenance. SWM facility and operation maintenance information has been added to sheet C6.1 (Rev. 1) Addressed. 5. Include this checklist in the plan set. Checklist has been added to sheet C3.0. (Rev. 1) Addressed. 6. Design calc. packet & related Sheet 6 — Pre-dev. Runoff area (4.30 ac) should be the same as the Post-dev. Runoff area (4.21 ac). Calculations have been updated accordingly. 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. Show location of all existing and proposed utilities and easements with deed book references. Existing and proposed utilities and any easements that were marked by miss utility or found incidental to the survey boundary research are shown on the plans. (Rev. 1) Addressed. 2. Show the existing contours for the site where not shown and next to property line where not shown. Existing Contours are now shown on the plans (Rev. 2) Addressed. 3. Engineering recommends replacement of existing barrel with a new one due to planned compaction above barrel for road & embankment fill. Pipe has been replaced as recommended. (Rev. 1) Addressed. 4. Sheet 3.3/5: a. Tie in the grading along SW corner of disturbance. Grading has been updated to tie into new survey area. (Rev. 1) Addressed. b. B/M recommended on slope areas where mulch won't hold. {VADEQ ESC HB, Spec. 3.35,3.361 Acknowledged. Blanket matting has been added to areas where slope is greater than 3:1. (Rev. 1) Addressed. c. Tie in grading here. Grading has been revised accordingly. (Rev. 1) Addressed. d. Grading next to steps will require B/M and low -maintenance ground cover specified on plans. {DSM, pg. 221. Blanket Matting has been added to this area as required. (Rev. 1) Addressed. e. Call out any ditches created due to grading and provide cross-section detail & lining required. Ditch cross-section and detail can now be found on sheet C5.2 (Rev. 1) There appears to be an 85 ft ditch created next to entrance road that needs to be analyzed as well. A ditch analysis on this channel has been added to sheet C5.2. Please note this ditch is existing and energy balanced is addressed at the POA so this or further analysis should not be necessary. 5. Provide OP shape & stone size calcs (see VADEQ ESC HB Spec. 3.18). OP shape and stone size calcs are provided on the sheet C5.0. (Rev. 1) Addressed. 6. (Rev. 1) Sheet 3.1: Provide the paved wash rack (CE) detail. [DSM, pg. 8]. A paved wash rack is included on plans sheet C3.1. We have included PDF copies of the plans and calculations for your review. If you have any questions or comments, please feel free to give me a call at 434.295.5624. Sincerely, Jonathan Showalter, PE Project Manager