HomeMy WebLinkAboutWPO201600072 Correspondence 2021-04-26•
Engineering • Surveying • Planning
April 12, 2021
David James
Albemarle County
RE: WPO 201600072: WOOLEN MILLS AMENDMENT 4
Dear David:
Below are responses to the comments in your letter addressed January 27, 2021.
ENGINEERING— David James
D. Stormwater Management Plan
2. Sheet 14.
MERIDIAN
PLANNING GROUP, LLC
440 Premier Circle, Suite 200
Charlottesville, VA 22901
Phone: 434.882.0121
www.meric ienwbexom
a. Show the design storm W.S.E. in the SWM-2 Detail.
b. Show the 100-year W.S.E. in the SWM-1 Detail.
Rev.1 Show that the 25-yr storm W.S.E.
✓ C-612: 25-year W.S.E has been added. It does not rise above the embankment
3. SWM-1; Show the emergency spillway has been adequately designed. Due to site conditions (Dry
pond in the flood plain) provide that the riser structure contains the emergency spillway.
Rev.1 Show that the 25-yr storm will discharge from emergency spillway at a non -erosive
velocity for grass lining. Provide supporting calcs. Follow guidance from DEQ Design Spec.,
Appx. C.
✓ C-612/Detail 7: The 25-year discharge over the Emergency Spillway has been added. The
velocity is 2.23 fps.
✓ C-612/Detail 6: A note requiring the emergency spillway be planted with Tall Fescue has been
added.
9. Sheet 18: VRRM — Overall site area is 14.06 ac. 6.33 ac is listed as disturbed on current E&SC
plan; up from 5.71 on the original design plan. 7.39 ac disturbance is listed on VRRM. ? No new
area has been added or subtracted from the original site area, correct? I believe you can just modify
the original VRRM and come up with the new nutrient load requirements.
Rev.1 Land disturbance lies in A & D soils as well. The VRRM will need to be corrected.
✓ Surveys only show A & B soils on site. VRRM has been revised and a digital copy is attached.
13. Record deed & plat for the new/modified SWM easements.
Rev.1 Comment still valid.
✓ Plat has been recorded.
14. Rev.1 Sheet 9: Show/Label proposed SWM facility easements. Easement should be shown
outside of Public R/W. For underground detention system show that easement width equals
101(landing}+(Pipe Diameter)+2'+2(H-5'+). [ACDSM, p.151
✓ C-630: SWM-2 easement has been revised. Easement can extend into the access easement.
VDOT comment was to locate the structures outside of the access easement in case it is
dedicated to public R/W in the future.
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15. Rev.1 Sheet 7/9: The forebays look undersized. Provide sizing information meets forebay
design guidance from DEQ, Appx. D.
✓ C-611: Forebay has been appropriately sized. Gabion baskets have been added.
16. Rev.1 Sheet 12:
a. Label pipe runs for the profile. See comment #]] to address on the SDP.
✓ C-610: pipe runs have been labeled.
b. The rim elev. for Str-34 should be above finished grade.
✓ C-610: Str-34 rim has been revised.
c. Indicate two 42" pipes for SWM-2 or show profile for each.
✓ C-610: SWM-2 has been labeled as 2 pipes.
17. Rev.1 Sheet 14:
a. SWM-2 — Provide trash rack for orifice.
✓ C-612: Trash rack has been provided for orifice.
b. SWM-1— Show Anti -vortex device.
✓ C-622: Anti -vortex device has been labeled.
18. Rev.1 Sheet 15:
a. The 10-Year Flows chart for POA-1 appears to have incorrect value.
✓ C-620: 10-year flow chart has been revised.
b. Your RVpre value for E.B. is incorrect and should use 7.68 ac in the calcs instead of 7.09
ac for POA-L See POA-1 Pre-dev. hydrograph & DA-A on map.
✓ C-620: RVpre has been revised.
c. Provide further supporting calcs/analysis for the determination of Q„'d for POA-1 Post-
dev. Where does 0.21 come from?
✓ C-620: 0.23 is the Qpost required to meet Energy Balance. This is shown to prove that
Entirely Wooded pre -development conditions are greater than E.B requirements.
d. Provide supporting calcs/analysis for the determination of Qp,e values shown in E.B.
summary table.
✓ C-620: supporting calcs have been provided.
19. Rev.1 Sheet 17:
a. DA map shows pre-dev. areas adds up to 11.92 ac and post-dev. adds up to 12.32 ac.
Account for the difference (0.4 ac) in your pre-dev. analysis, make necessary changes, and
correct the map.
✓ C-622: the eastern half of SWM-1 picks up 0.4 acres of drainage area that is not included in
the pre -development drainage area.
b. Show Tc flow paths.
✓ C-622: Tc flow paths are shown.
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Erosion and Sediment Control Plan (ESCP)
2. Sheet 2-7: Areas of Forest/Open Space (F/OS) in easements are to be protected. Correct the sheets
to show these areas with TP around them. Provide acceptable signage. Areas of F/OS to be located
outside of the LOD.
Rev.1 I don't see signs. F/OS hatching needs to be shown on EC sheets C-501 & C-502.
✓ C-501 thru C-502: Hatching, YBBT (Yellow and Black Barricade Tape), and Signs are shown
around F/OS easements.
✓ C-602: sign Detail has been added.
5. Provide more information of SB-1 design. The completed worksheet in the ESC HB Spec. 3.14
shown on pages 1II-12 to IH-15 will do. Due to site conditions (SB in the flood plain) provide that
the riser structure contain the emergency spillway.
Rev.1 Partially addressed. Anti -vortex device not shown.
✓ C-612: trash rack was shown and is now labeled as Anti -vortex device is shown.
Please let me know if you need additional information.
Sincerely,
Timothy Miller, P.E., L.S.
Principal
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