HomeMy WebLinkAboutSDP201200001 Review Comments Minor Amendment 2012-02-22ALg�,��
�'IRGINZ�
COUNTY OF ALBEMARLE
Department of Community Development
401 McIntire Road
Charlottesville, Virginia 22902 -4596
Phone (434) 296 -5832 Fax (434) 972 -4126
Project: Stonefield Towncenter SWM and Minor Site Plan Amendment;
SDP - 2012 -00005 and WPO- 2011 -00059
Plan preparer: Mr. Herb White, PE; W & W Associates
Owner or rep.: Albemarle Place EAAP LLC
Date received: 28 December 2011
Date of Comment: 22 February 2012
Engineer: Phil Custer
The minor site plan and stormwater management amendments Stonefield Town Center (SDP- 2012 -00001
and WPO- 2011 - 00059), received on 28 December 2011, have been reviewed. The plans can be approved
after the following comments have been addressed:
A. Minor Site Plan Amendment Review Comments (SDP- 2012 - 00001)
An ESC amendment will need to be provided to keep the ESC plan updated with the current
proposed changes. None of these changes will drastically change the ESC plan. Please keep the
same ESC concept and submit revised sheets 25 and 26 and $180 fee at the time of the next
submittal.
2. Street furniture must be shown along District Ave.
B. Stormwater Management Amendment Review Comments (WPO- 2011 - 00059)
1. Please refer to the separate SWM memo provided at the same time as this comment letter.
2. The new biofilter is considerably undersized for watershed proposed to it. By my estimation there
is about 3lacres draining to structure 39.1 and the offline pipe system (please see following
comment as well). About 20 acres of this watershed is onsite drainage @ 90% impervious. The
remaining 11 acres is offsite area at 50% impervious. In total, there will be about 23.5 acres of
impervious surfaces in this facility's watershed which requires a biofilter bed of about 25,000sf to
treat at a removal rate of 50 %. The current bed area of 9,720sf is not sufficient. The biofilter bed
will need to almost triple.
3. Biorention facilities, as well as most BMPs in the Virginia Stormwater Management Handbook,
are volume -based facilities and achieve their specific removal rates by capturing the first flush
(1/2" or 1 ", depending on RR) of storm events. The full first flush volumes cannot be caught with
current configurations of structures 39.1 and 46.1. Please design the pipe system to the northern
biofilter so that the full flow can pass through it without diverting untreated.
4. Sediment forebays are required on all SWM quality facilities. Biofilter forebays should be
between 10% and 20% of the biofilter floor area.
5. Please provide details of the retaining wall in this set. The set of details should include a typical
cross - section and specific details for the pipe outlet through the wall.
6. The wall must be watertight up to the 100 -year storm elevation. No water should be able to escape
from the biofilter, above or below the bed material, through the drain beneath the wall's footer.
Please compare the 100 -year storm discharge coming into the facility with the stage /discharge
graph of DI -7 inlets in the Road Drainage Manual.
7. A planting plan for the biofilter is needed. The biofilter should have at least one plant for every
100sf of bed area and should have a variety of species of trees and shrubs.
8. This application will require that a new Stormwater Management Facility Maintenance Agreement
be recorded. Please complete this form and submit it to Ana Kilmer with a $17 recordation fee
after reading the instructions online. The applicant should wait until they are sure they are going
forward with this application to record this agreement.
9. A revised bond amount will be needed before the plan can be enacted. Please provide a completed
Bond Estimate Request Form to the county engineer to receive a new SWM bond.
File: E1_mia swm_PBC _ sdp- 2012 -00001 wpo- 2011 -00059 Town Center Amendment.doc