HomeMy WebLinkAboutWPO201000064 Review Comments Stormwater Management Plan 2010-12-03ALg�,��
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COUNTY OF ALBEMARLE
Department of Community Development
401 McIntire Road
Charlottesville, Virginia 22902 -4596
Phone (434) 296 -5832 Fax (434) 972 -4126
Project:
Plan preparer:
Owner or rep.:
Date received:
Date of Comment:
Engineer:
WPO- 2010 - 00064, HTC Apartments ESC Plan
Mr. Scott Collins, PE; Collins Engineering
Uptown Village, LLC
6 October 2010
3 December 2010
Phil Custer
The SWM plan for Hollymead Towncenter Apartments, received on 6 October 2010, has been reviewed.
The reviews of the ESC and site plan have been provided in separate documents. This SWM plan cannot
be approved as submitted and will require the following corrections before approval can be granted:
1. Before this plan can be approved, the stormwater management easement on TMP 32 -50 must be
recorded.
2. The plan cannot be approved until the applicant provides a Stormwater Facility Maintenance
Agreement and fee to the county for the BMP located on TMP 32 -50.
3. It is unclear what the intention of this SWM plan is regarding the mobile home portion of the
project. The southern boundary of drainage area 4 appears to be between Forest Spring Lane and
Haven Lane, but the line is drawn adjacent to the property boundary. To simplify the review of
this project, please accurately show the existing drainage area limits for this section of the site and
update all calculations accordingly.
When updating the calculations, please note that if the exclusion of a portion of the watershed
results in a greater discharge, the calculations should ignore this area.
4. Since there is only one stormwater facility being proposed, please use one modified simple
spreadsheet for the BMP analyzing the total post - development watershed. For water quality
analysis, the only existing impervious area for this watershed will be the area of lawns, roads, and
buildings within the mobile home portion of the site.
5. Please remove Towncenter Drive and accompanying sidewalks from the pre - development water
quality analysis. (The road has been correctly excluded from the quantity analysis.)
6. Please provide the source for woods in good condition in B soils possessing a CN value of 66.
Most references seem to use a value of 55 for woods in good condition.
7. For the pre - development drainage area 1, please use woods for at least 90% of the groundcover.
The land was recently cleared by the land owner when the roadway was constructed.
8. The existing pond that was removed with the recently approved grading plan was providing
detention for approximately half of the mobile home site, as was likely required at the time of
construction. Therefore, the new pond must provide for this detention and the pre - development
landcover for DA 4 must use woods in good condition unless another CN value can be justified
with the original calculations for this facility. (The water quality analysis can consider the existing
impervious area because the water quality requirement was added to the ordinance after the
construction of the mobile home park.). Please remove "Therefore stormwater
management... proposed SWM facility" from the note regarding drainage area 4 on sheet SWM -1.
9. A small portion of the Willow Glenn Connector will be draining to the facility and the stormwater
plan appears to correctly account for this impervious area in its design. Please remove the note on
SWM -2 that insinuates otherwise.
10. The downstream slope of the stormwater facility must be 3:1.
11. The retention basin detail correctly shows the construction of an impervious core and cutoff trench
for the embankment. However, the applicant also has provided notes on many other sheets that the
embankment was not to be disturbed except for grading on the west side. Please clarify. Is the
applicant certifying that the facility was constructed to the detail shown in this plan when it was
constructed two years ago as a sediment basin?
12. The flow path is within the retention facility is too short.
13. The facility should be graded in a manner so that the construction of the Willow Glen Connector
road and sidewalk will not require an alteration to the pond.
14. Please correct the rightmost column on the "Summary of Drainage Areas Table" on sheet SWM -2
to read "Post- Development Drainage Areas ".
15. I recommend raising the elevation of the forebay spillway. The 2ft depth will allow more sediment
into the main cell and cause a higher frequency of maintenance within the majority of the pond.
16. The SWM portion of the WPO bond will be computed at the time of plan approval.
File: El_swm_PBC_WPO- 2010 -00064 HTC Apartments SWM Plan.doc