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HomeMy WebLinkAboutWPO202000017 Correspondence 2020-07-20 (2)SHIMP ENGINEERING, P.C. Design Focused Engineering July 17, 2020 David James County of Albemarle Department of Community Development 401 McIntire Road, North Wing Charlottesville, Virginia 22902 RE: Response Letter #1 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 May 71, 2020. Our responses are as follows: A. General Cover — Add WPO202000017 under title. Acknowledged, the WPO202000017 has been added to Sheet C1 under the title. 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 ESOP, (3) a SWMP, and (4) any TMDL measures necessary. Registration Statement: a. Update the Start & End dates under Section IV. Acknowledged, the start and end dates have been updated in the registration statement. b. Add `County of Albemarle' for Section IV._ Acknowledged, "County of Albemarle" has been added to Section IV.E in the registration statement. 2. Complete Sect. 9 — Signed Certification Acknowledged, we will send the signed Sec. 9 and Sec. 10 in an email upon receiving them from the owner. C. Pollution Prevention Plan (PPP) The PPP content requirements can be found in County Code section 17-404. 1. Submit a PPP exhibit sheet. Acknowledged, the PPP is included with this submission in the SWPPP document and as a separate attachment. D. 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. Provide LD-347 or equivalent Cates & show HGL in the storm sewer profiles. 912 E. High Sr. Charlottesville, VA 22902 1434.227.5140 1 shimp-engineering.com Acknowledged, the LD-347 is provided with this submission, and the HGL is shown on the storm sewer profiles. 2. Show drainage area for the entrance and show that the entrance will be free of flooding during the 25-yr storm. The entrance is at a high point of the road and therefore, the water is flowing away from it. 3. Provide curb to keep stormwater on -site: u u — -� r�nee3ed here I VIA rc ncnroo �urc I LOT 31 20 FFEE 527.5 I nT Zn X, I ,� Water is flowing into the site such that very small drainage area from off site would flow into the site and we've accounted for that in our Stormwater calculations. 4. Provide ditch or berm: Win needed_ here-tO-dir6C�w2terf w—••,—°"—°"—'°- inlet(s) on -site Inn i { y �y 3a I� � [ FFLCr 3F &. 53 Acknowledged, the water is flowing away from the back of the site; thus, a berm is not needed. 5. Provide proposed inlet drainage area map. Acknowledged, Inlets Drainage area map is provided with this submission. 912 E. High St. Charlottesville, VA 22902 1434,227,5140 1 shimp-engineeringcom 6. 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. The offsite "biofilter" will not be affected because the stormwater is already being filtered on our site and is out -letting into a channel not the bio£dter. 7. Show WSE on the weir elate iii str A4 Acknowledged, the WSE are now shown on the weir plate in str. A4. See detail 6 on Sheet C9. 8.Sheet 9—IIUiIUc L„_11 Acknowledged, Al to A2 profile is now provided. Please see detail 9 on Sheet C9. 9. I was unable to find this Stormtech MC-4500 system listed on DEQs approved list posted on the BMP Clearinghouse website. Acknowledged, the certificate is provided with this submission. Please see attacked. 10. VRRM — Please verify (with DEQ) the pollutant removal eff /o of this Stormtech system. Acknowledged, the pollutant removal eff is 40% based on TP performance data, you can find this information in the Stormtech MC-4500 system certificate provided for comment 9. 11. Show that the MTD is sized for the project (https://www.swbmp.vwrrc.vt.edu/bmps/hydrodynamic-devices/ - VADEQ Practice 16: Hydrodynamic Devices, Sizing information): Note: Our proposal actually falls into Practice 17: Filtering Devices not Practice 16: Hydrodynamic Devices, a. Calculate the treatment volume to the device (TvBMP). The calculated TvBMP can be obtained from the Virginia Runoff Reduction Method (VRRM) spreadsheets. Acknowledged, TvBMP is 7,053 Fe. Please see the VRRM sheets included in the SWM Packet. 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. Acknowledged, gpTv = 2.86 cfs 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). Acknowledged, the MTFT = 3.2 CFS > 2.86. Therefore, requirement met. 12. Show TvBMP area of the Stormtech. Acknowledged, the TvBMP area is now shown on the Post Dev map. A legend was provided to eliminate any confusion. Note: On the drawing, the term "Onsite Drainage Area" means the TvBMP drainage area. 13. Sheet 12 - Show these post-dev areas of runoff on the map. 912 E. High St. Charlohesville, VA 22902 1434.227.5140 1 shimp-engineering.com Acknowledged, the post-dev areas are now shown on sheet C12. A legend was provided to eliminate any confusion. 14. Show/label `SWM facilir Isements for the underground detention and Stormtech system. Acknowledged, the SWM Facility easement for the underground detention and Stormtech is shown on Sheet C4, C7, & C12, as well as on the Post Dev DA map. 15. Provide minimum easement width for the SWM pipes to follow sizing, [ACDSM, p.15]. EASENU.\T WIDTH. DLOtETER . S' . 21H-5'I *IV 19M NEM.1 Below are the easement calculations based on the formula provided: Al to A2: A2 to A3: A3 to A4: A4 to A5: A5 to A6: A7 to A8: A8 to A9: A9 to A10: 2+2+2*(4.10-5) +10 =12.2 ft 2 + 2 +2*(3.23-5) +10 =10.46 ft 2 +2 +2*(7.74-5) +10 =19.48 ft 3+2+2*(6.76-5) +10=18.52ft 3+2+2*(7.07-5)+10=19.4ft L25 + 2 +2*(4.12-5) + 10 =11.49 ft L25 +2 +2*(6.27--5) +10 =15.79 ft z25 + 2 +2*(4.25-5) +10 =11.75 ft Since all the results of the calculations are less than 20 ft, the easements are kept as 20ft easement. 16. Record the SWM maintenance agreement prior to approval. [Sec. 17-415] Acknowledged. 17. A recorded SWM facility easement plat & deed prior to permit issuance. Acknowledged. 18. Provide letter of availability from the off -site nutrient bank provider. Currently 1.16 TP load credits required. [Sec. 17-403 A.9] Acknowledged, we will send this via email upon receiving it from the owner. 19. Provide list of materials auu P1,oc Icl tiIo �IDlmlcLit MC-4500 s) stciii wi uIo DOW est. Acknowledged, please see the document provided with this submission that has the MC- 4500 Site Calculator. E. Erosion and Sediment Control Plan (ESCP) 912 E. High St. Charlottesville, VA 22902 1434.227.5140 1 shimp-engineering.com Virginia Code §62.1-44.15:55 requires the VESCP authority to approve or disapprove an ESOP. 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 3 and provide date of field verification. Acknowledged, Justin Shimp, P.E. has field verified the site on June 4' 2020. A note was also added to Sheet C1 under Source of Boundary and Topography. 2. Show location of all existing utilities and easements with deed book references. Acknowledged, all existing easements are shown on Sheet C3, C4, C5, C6, C7, & C11 and the text of the easements is shown on Sheet C2, C3, C4, C5, & CIL 3. 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.22] Acknowledged, the offsite easement is provided, it is located right on the limits of disturbance, therefore, it is not showing clearly. However, it is labeled as "20' Drainage Easement" and this is shown on Sheet C4, and C12 as well as on the Post DA Map. 4. Sheet 4 —Please show all grading elevation labels (a few missing). Acknowledged, more grading elevations were added. 5. Sheet 6 — a. Provide CRS (3.03) for the road. Acknowledged. Please see #4 of sequence of construction notes on Sheet C6. The road will be stabilized with 1.5-inch stone. b. Provide SCC (3.17) instead of DV & CIP. That way you have both outlet & inlet protection. DV not meant to receive concentrated flow. under title. Acknowledged. The DV have been replaced with SCC. The CH' is still necessary because the SCC is proposed with only the filter cloth without stone. Please see Sheet C6. 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. 912 E. High St. Charlottesville, VA 22902 1434.227.5140 1 shimp-engineering.com