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Home My WebLink AboutWPO202000017 Correspondence 2021-03-30 (2)SHIMP ENGINEERING, P.C. Design Focused Engineering March 30, 2021 David James County of Albemarle Department of Community Development 401 McIntire Road, North Wing Charlottesville, Virginia 22902 RE: Response Letter #2 for WPO202000017 — Proffrt Road Townhomes South Dear David, Thank you for your review of the VSMP request for Proffit Road Townhomes South. This letter contains responses to County comments dated August 24, 2020.Our responses are as follows: A. General 1. (Rev. 1) Complete VSMP application form with each resubmittal. The VSMP application is included with this submission. B. 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. 2. Complete Sect. 9 —Signed Certification (Rev. 1) Comment still valid. Sect. 9 & Sect. 10 are now completed and included in the SWPPP packet. C. Pollution Prevention Plan (PPP) The PPP content requirements can be found in County Code section 17-404. 3. Submit a PPP exhibit sheet. (Rev. 1) Please include offsite area on the PPP. Also, add a Staging area & symbol. The offsite area is now showing on the PPP exhibit. Staging area has been added to the PPP near lot 9 and a symbol was added to the PPP key. D. Stormwater Manasement 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. 4. Provide proposed inlet drainage area map. (Rev. 1) Acknowledged. Provide on map for each inlet: drainage area size, time of concentration, flow path, C value. The drainage area size, TOC, Flow path & C-value are now provided on the Inlets DA map. 912 E. High Sr. Charlottesville, VA 22902 1434.227.5140 1 shimp-engineering.com 5. You will need to confirm that the off -site `Biofilter' facility's will handle this site's drainage area since you are diverting stormwater directly to it. (Rev.1) Not currently addressed. Need to investigate the original design plans. Please show current DA to bio£dter. Any increase volume, or Bow may need to be diverted around facility to a receiving channel or alternative. The design has been diverted from the biofilter. Therefore, no analysis of the existing bio-filter is required. 6. Show WSE on the weir plate in str. A4. (Rev.1) Partially addressed. Indicate the design storm elevation for the 1-,2-,10-yr storm.\ All WSE are now shown on detail 6 on Sheet C9. 7. Provide minimum easement width for the SWM pipes to follow sizing, [ACDSM, p.151. (Rev.l) H is measured from grade to the top of foundation. It looks like you might have measured from grade to the top ofpipe. EASEMEN-r WIDTH. DIAMETER • 2' a 21H-S'1 ♦ 10' 120' NIM.1 The easement calculations have been revised so that H is measured from the grade to the top of foundation. Al to A2: A2 to A3: A3 to A4: A4 to A5: A5 to A6: A7 to All: A8 to A9: A9 to A10: A10 to All: A9C to A9B: A9B to A9A: A9A to A9: 2+2+2*(7.11-5) +10 =18.22 ft (20 ft provided) 2 + 2 +2 *(6.25-5) +10 =16.5 ft (20 ft provided) 2 + 2 +2 *(11.12-5) +10 =26.24 ft (26.5ft provided) 3 + 2 +2 *(6.76-5) + 10 =17.04 ft (20 ft provided) 3 + 2 +2 *(11.77--5) + 10 =18.54 ft (20 ft provided) 1.25 + 2 +2 *(6.50-5) + 10 =16.25 ft (20 ft provided) 1.25 + 2 +2 *(8.0-5) +10 =19.25 ft (20 ft provided) 1.25 + 2 +2 *(8.0-5) +10 =19.25 ft (20 ft provided) 1.25 + 2 +2 *(6.50-5) +10 =16.25 ft (20 ft provided) 1.25 + 2 +2 *(6.0-5) +10 =15.25 ft (20 ft provided) 1.25 + 2 +2 *(7.40-5) +10 =18.05 ft (20 ft provided) 1.25 + 2 +2 *(7.60-5) +10 =18.45 ft (20 ft provided) 8. Record the SWM maintenance agreement prior to approval. [Sec. 17-4151(Rev.1) Comment still applies. Please provide us with the maintenance agreement and the owner will sign it. 912 E. High St. Charlo"sville, VA 22902 1434.227.51401 shimp-engineering.com 9. A recorded SWM facility easement plat & deed prior to permit issuance. (Rev.l) Comment still applies. This is a subdivision and we will record this with the subdivision plat of the property. 10. Provide letter of availability from the off -site nutrient bank provider. Currently 1.16 TP load credits required. [Sec. 17-403 A. 9] (Rev.l) Acknowledged. Currently 1.37 credits needed The letter of availability is provided with this submission. 11. (Rev.l) Sheet 9 (Weir plate detail) — Orifices under 3" are susceptible to clogging & increase maintenance. Increase diameter, provide anti -clogging device/feature. The orifice size has been revised to be 2.2". a trash rack has been provided to prevent clogging. Detail is now provided on Sheet C10. 12. (Rev.l) Show/provide how this circled area will drain to Str. A8 The area circled in the image was included to drain into structure A8 was an error. This area would have not drain into A8. We have revised the drainage area map, added another drop inlet structure by lot 8 and routed the water to go into the detention system through pipes. E. 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. 13. Provide offsite easement for proposed drainage connection to offsite SWM facility. A letter from off -site property owner is enough for this plan review, but any legal easements will need to be signed by the property owners. [ACDSM, p.221(Rev.1) Partially addressed. You can also record an easement plat. We will record the easement along with recording all of the easements on site when the subdivision plat is recorded. 912 E. High St. Charlottesville, VA 22902 1434.227.5140 1 shimp-engineering.com 14. Sheet 6- b. Provide SCC (3.17) instead of DV & CIP. That way you have both outlet & inlet protection. DV not meant to receive concentrated flow. (Rev.1) Partially addressed. Provide channel design and determine appropriate liner needed. Velocity below 4fps will require EC-2 or equivalent, 4-10fps will need EC-3. The silt fence shown is enough, so CIP not needed. The CIP has been removed. Included with the SWM packet is an LD-268 & a drainage map for the temporary SCC. If you have any questions or concerns about these revisions, please feel free to contact me at Stephanie akshimp-en ing eering com or by phone at 434-227-5140. Regards, Stephanie Paul Shimp Engineering, P.C. 912 E. High St. Charlottesville, VA 22902 1434.227.5140 1 shimp-engineering.com