HomeMy WebLinkAboutWPO201200058 Review Comments Stormwater Management Plan 2012-08-01� OF AL
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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:
CTS SWM Facility #5 Amendment; SDP -2010 -00019 and WPO- 2012 -00058
Plan preparer:
Justin Walton; VMDO Architects
Owner:
City of Charlottesville
Representative:
Mr. Scott Hendrix
Plan received date:
22 June 2012
Date of comments:
1 August 2012
Reviewer:
Phil Custer
The SWM plan amendment and letter of revision for the modification to Stormwater Management Facility
5, received 22 June 2012, has been reviewed. The plan can be approved after the following comments
have been addressed.
1. The Stormwater Management Calculations packet must be stamped and signed by a licensed
professional authorized in Virginia to design Stormwater Management Plans.
2. As identified in Table 12 of the originally approved SWM plan, the required removal rate of
facility #5 is 65 %, not 50% as currently proposed by the applicant. More stormwater treatment is
required in this watershed. Please either provide an aquatic bench around the stormwater facility
or add supplemental stormwater treatment facilities in the watershed.
3. The weighted C coefficient on Page 4 of the stormwater report is incorrectly calculated.
4. Please move the two Red Maples away from the embankment. [VSMH 3.01]
5. In essence, the applicant's proposal is to convert existing volume in the facility from providing
detention to providing water quality. The stormwater report provided to the county was lacking
the detailed detention calculations that are expected with such a modification. The assumption
that no runoff is discharged from the underground facility is the largest issue with this submittal.
The county has performed its own analysis of the two detention systems in series and found that
the combined runoff to the east is 3.02cfs and 5.86 for the 2 and 10 year storms, respectively (pre -
development rates were 4.34cfs and 5.86cfs). In addition, the combined effects of the 100 -year
storm results in an adequate freeboard on the embankment of the pond. Therefore, the county can
conclude that detention standards are maintained with the proposed amendment, just not to the
degree that the applicants' calculations claim.
6. The trash rack on the 2ft weir does not meet the minimum standards identified in VSMH
MS #3.02.
7. As stated in previous correspondence, since the drainage area to the facility is about half of the
minimum size required by the Virginia Stormwater Management Handbook, the county will need
to hold the bond longer to make sure the stormwater facility is viable. If problems arise after
construction, the applicant will be required to submit another amendment to the stormwater
management plan with a different concept that provides detention and treatment. No change is
required by this comment now.
8. Please review the State's Technical Bulletin regarding Vector Control to understand the risks
associated with the current SWM concept. No change is required by this comment.
9. The Planning Department has approved the modification to the Landscape Plan.