HomeMy WebLinkAboutSDP202200029 Review Comments Final Site Plan and Comps. 2022-07-12From: John Anderson
To: Ben Hol
Cc: Ammv George; Jim Taggart; Tim Duncan
Subject: Planning Application Review for SDP202200029 S.L. WILLIAMSON ASPHALT PLANT AT RED HILL QUARRY -
FINAL - DIGITAL . [ Engineering review comments]
Date: Tuesday, July 12, 2022 1:31:35 PM
The Review for the following application has been completed
Application Number = SDP202200029
Reviewer = John Anderson
Review Status = See Recommendations; comments, below
Completed Date = 07/12/2022
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Ben,
Thanks for your patience. I copy RGA since: 1) Engineering is last reviewer to comment; 2) we were
alerted the WPO plan was submitted, earlier today. Engineering hopes to review the WPO plan application,
expeditiously.
Ammy, Tim,
Thank you for submitting the WPO plan, for coordinating with Jen Smith, earlier today, and for
coordinating with Engineering and Planning on S.L. Williamson asphalt plant at Red Hill quarry:
CV comments:
Sheet 4:
Provide existing spot shot elevations to delineate /establish there is an existing berm along
west edge of (S.L. Williamson) lease area not precisely reflected by existing topographic
contours. FSP does not indicate proposed change to berm along west edge of lease area.
Without such grade change, existing topography will direct site storm runoff to proposed
settling basins, which then in turn may (on rare occasion) fill to the point that detained
volume crests proposed settling basin rim (please provide spot elev. for each proposed
settling basin to establish low point of rim, sheet 8), at which point, given existing
topography, Engineering anticipates shallow flooding of the asphalt plant could occur (as it
may at present) prior to breaching overall perimeter lease area berm. This is important:
existing perimeter grade prevents storm runoff reaching a stream to the west without first
passing through a settling basin. The manner of settling basin pass -through is via shallow
flooding with detained basin volume first breaching existing settling basin rim, and then
(which may occur infrequently, or perhaps never during a 10-yr storm event) ponded
elevation may rise until such point detained runoff may crest lease area perimeter elevation.
During site visit 4/15/22, Engineering observed no trace or pattern of detained storm runoff
escaping lease area. Rather, ponded runoff level does not appear to exceed existing settling
basin capacity. Drawdown of settling basin ponded volume appears to occur via infiltration
to earth, or evaporation. Ref email to Applicant (J. Anderson to Planning Div. coordinator
/RGA: April 19, 2022 4:27 PM; ISP/FSP review comments, SDP202100092) for additional
information. The purpose of discussing settling basin elevations with RGA in such detail is
to affirm Engineering understanding of design, which is: site storm runoff will in fact reach
one of two proposed settling basins depicted on sheet 8 prior to reaching the stream to the
west (unnamed tributary to North Fork Hardware River). Also, item 2 , below (from
4/19/22 Engineering review comment email).
2. -C7 [Now Sheet8 Grading Plan with SDP202200029]
a. Provide spot elevations that indicate all site storm runoff reaches proposed settling basins, and
that establishes relative grade as close as possible to existing vertical interval between rims of
existing settling basins and perimeter site grade before slope falls steeply to the creek. (Rev.
1) Addressed via revised Grading plan sheets: 9A, 9B, 9C, 9D, sent via email July 11, 2022
2:37 PM.
b. With WPO plan: (Rev. 1) Persists. Note: Email states the WPO plan is submitted (July 12,
2022 11:07 AM, Tim Duncan to J. Anderson). Items i., it., below, will be evaluated with
WPO plan application.
i. Provide mitigation plan (with proposed plantings) for proposed improvements within
landward 50' of stream buffer.
ii. Compare (via table) existing volume and proposed volume of settling basins. Total
proposed settling basin volume should exceed total existing settling basin volume.
iii. Recommend submit WPO plan /application at earliest convenience.
iv. Note: site visit 15-Apr by county engineering indicates volume of existing settling
basins, existing basin rim elev., inlet design, site perimeter elevation, and
circulation patterns appear to provide adequate storm runoff management for
routine operations at the plant, and as discussed /outlined in correspondence with
RGA (email, Friday, April 15, 2022 1:03 PM), design that mimics current basin
volume, rim elevation/s, and site perimeter elevation are goals that may alleviate
nearly entirely storm runoff concerns relative to adjacent stream water quality.
3. An approved WPO plan (ESC, SWM, Mitigation) is required prior to FSP approval. (Rev. 1)
Persists.
Note: Settling basins are not SWM facilities, per se, but rather serve an industrial site runoff settling
/filtering function. Water evaporates from basins. Ex. settling basins have no outlet. Engineering
anticipates similar design with WPO plan: details that provide basin volume, profiles, with no outlet."
Thanks, again, best, J. Anderson
John E. Anderson, PE I Civil Engineer II
Department of Community Development I County of Albemarle, Virginia
401 McIntire Road I Charlottesville, VA 22902
434 296 S832 ext 306