HomeMy WebLinkAboutWPO201200013 Review Comments Stormwater Management Plan 2012-05-22�� OF A
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COUNTY OF ALBEMARLE
Department of Community Development
401 McIntire Road, Room 227
Charlottesville, Virginia 22902 -4596
Phone (434) 296 -5832 Fax (434) 972 -4126
Project:
Old Trail Village Block 11 WP0201200013
SDP201200009
Plan preparer:
Scott Collins Engineering [293 -3719]
Owner or rep.:
March Mountain Properties, LLC
Plan received date:
8 February 2012
19 April 2012
Date of comments:
19 March 2012
22 May 2012
Reviewer:
Michael Koslow
Review Coordinator:
Megan Yaniglos
The second site plan and comps set (SDP201200009) and WPO plan and calculation set
(WP0201200013) submitted on and before 19 April 2012 have received Engineering Review and
do not appear to meet Albemarle County minimum checklist items for approval. Addressed
comments have been removed for clarity. Please adequately address the following comments for
final approval:
A. General (SDP201200009 and WP0201200013)
1. Final application for this review will need to be signed by the applicant.
(Rev2) Comment has been acknowledged but not addressed.
B. Final Site Plan and Comps set (SDP201200009)
C. Erosion and Sediment Control Plan (WP0201200013)
10. The baffle will not work as intended by the applicant.
(Rev2) Reconfigured baffle does not appear to provide a significantly increased flow path toward
outflow riser. Recommend lengthening baffle in northeast direction by 50 : This wouldprovide a
length -to -width ratio for the flow path greater than 2:1 as detailed in VESCHp. III -92.
12. Please provide an analysis of the downstream channel. Please refer to the design manual for all
expectations regarding a downstream channel analysis. The I% rule must be applied using the total
development acreage of Old Trail Village, not just that of this phaseiblock.
(Rev2) It appears the outlet for the proposed bioretention basin drains toward Slabtown
Branch. However, from the plan depicted on sheets SWM -1 and SWM -2, it is ambiguous
whether the outlet crosses the property line for this development's parcel. Please revise the
depiction of the proposed bioretention basin on sheets SWM -1 and SWM -2 to demonstrate an
adequate riprap ditch to Slabtown Branch (see also comment C13 below).
Per meeting with applicant on April 12, 2012, the demonstration of adequate channel for
Slabtown Branch will be waived due to additional detention for proposed Old Trail Village
projects in Lickinghole Basin if a proposed individual land disturbing project could meet the
pre- development condition's outfall detention (see also comment D5).
Engineering Review Comments
Page 2 of 2
13. (Rev2) Proposed land disturbance through the stream buffer for Slabtown Branch and
within the tree conservation area must be minimized. Please outlet the sediment basin /
bioretention basin to the road embankment for Old Trail Drive and provide a riprap channel
from the basin outlet to Slabtown Branch.
D. Stormwater Management Plan (WP0201200013)
3. (Rev2) Sheet SWM -2 depicts a Nyloplast 15 In. Standard Grate Assembly for the proposed
bioretention basin's inlet structure. Flat grates for trash racks are not acceptable [VSMH 3.02-
221. Please revise the proposed basin's inlet structure to include a concave inlet shape to
mitigate clogging.
4. (Rev2) The proposed routing calculations apply a reduction to the inflow hydrograph (fudge
factor) of 0.78. Use of inflow hydrograph reduction factors was not authorized by county
engineering when MS -19 requirements were discussed with Applicant on April 12, 2012.
5. (Rev2) The proposed biofilter bed is not large enough to meet treatment requirements.
Considering the three 3" diameter orifice elevations, only about 1,600 cft of runoff is treated
when 11,767 cft of runoff treatment is required. County engineering would also accept a
facility with a bed footprint of 7,060 sft for 282,396 sft of impervious area within it's watershed,
assuming 1 ft (maximum) of ponding [Albemarle County Design Standards Manual `Bio- filter
Combined with Detention Basin" detail].
6. (Rev2) Please remove sheets SWM -3 and SWM -4 from the plans. These sheets do not appear
to apply to the project.
7. (Rev2) Please propose a landscape planting plan for the proposed biofilter.
8. (Rev2) Proposed forebay gabion basket separators depicted on `Biofilter" section on sheet
SWM -2 must be laid on top of media mix. The gabion basket riprap appears as though it
would act as a draw for runoff to bypass the filter media.
Once the Erosion & Sediment Control and Stormwater Management [WP0201200013] comments have
been addressed, please submit 2 copies of the revised plans, calculations, and narratives to Community
Development Engineering along with the required review fee and transmittal form.
Community Development Engineering is available from 2:30 -4 PM on Thursdays to discuss these review
comments. Please contact Michael Koslow at 434 - 296 -5832 ext. 3297 or email mkoslowgalbemarle.org
to schedule an appointment.
[17- 204.f1 An application for an erosion and sediment control plan that requires modifications, terms, or conditions to be
included in order for it to be approved shall be deemed to be withdrawn if the owner fails to submit a revised plan addressing the
omitted modifications, terms or conditions within six (6) months after the owner is informed of the omitted information as
provided under paragraph (B).
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