HomeMy WebLinkAboutWPO200900020 Review Comments Stormwater Management Plan 2010-05-17� OF AL
,. vIRGI1`IZP
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.:
Plan received date:
Rev. 1:
Date of comments:
Rev. 1:
Reviewer:
Rev. 1:
University Village, Phase 1; SDP - 2009 - 00033, WPO- 2009 -00020
Mr. Scott Collins; Collins Engineering
Next Generation, LLC
6 Aug 2009 (activated 19 Aug with the ZMA variation approval)
13 April 2010
3 Sep 2009
17 May 2010
Glenn Brooks
John Diez
The erosion control plan and stormwater management plan for Phase 1 of the University Village
Retirement Community project have received engineering review.
A. Erosion and Sediment Control Plan
1. Site plan approval is required.
(Rev. 1) Comment has been addressed.
2. Revise the plan to place sediment collection facilities downhill of major fill sections, and in the
low points of the topography.
(Rev. 1) Comment has been addressed.
3. "Clean water" diversions are not an approved variation. Basins should be sized for the contributing
drainage areas.
(Rev. 1) Comment has been addressed.
4. Regarding the MS -19 analysis:
a. Location 3 does not appear to be a channel. This outfall and basin should be
moved to discharge to a channel.
(Rev. 1) Basin has been removed. Please disregard.
b. Location 1 and 2 need to go further downstream and look at the pond.
C. Locations 2 and 3 appear to have been impacted sometime in the past, and are
deeply entrenched. They appear inadequate for the flows to them. Calculations
should use varying, lower n- values and have higher velocities, instead of one n-
value and an oversimplified, average velocity for the section.
(Rev. 1) Comment has not been addressed. Please provide calculations for the given
locations.
5. Additional comments may be issued once comments have been revised.
B. Stormwater Management Plan
1. The layout does not appear to address the overall plan. Areas of future development will need to
be captured.
(Rev. 1) Comment has not been addressed. Please provide conceptual plans as to have the
future development will be captured.
2. The embankments must be wide enough to drive in order to reach forebays, and there are too many
2:1 slopes. See VSMH 3.01.
(Rev. 1) Comment has been addressed.
Current Development
Engineering Review Comments
Page 2 of 2
3. Both biofilters are short - circuited.
(Rev. 1) Comment has been addressed.
4. The computations and drainage areas appear to be over - manipulated. There must be some attempt
to honor existing drainage divides. The change to the basin two area, and its placement, are an
extreme example. Removal rates must be computed by drainage area. There is not enough control
of depth in a weir built with class II rip -rap to obtain the results as shown. Why is a fudge factor
used in the 100 year routing? 24hr storm distributions should be used, and routed above the WQV
volume. Some of the drainage areas are in error.
(Rev. 1) Comment has not been addressed. It appears that lines and dimensions are missing in
the Retention Basin detail. please revise. Additional comments may be forthcoming.
5. The 5% sizing guideline falls short of providing the volume of 1" of runoff over impervious
surfaces to achieve a 65% removal rate. For example, basin 1 provides a capture volume of 2071
cf as designed. The required volume is about 189000 sf (1 "/12) = 15750cf.
(Rev. 1) Comment has been addressed. However, the ponding depth must be I'.
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University Village.doc