HomeMy WebLinkAboutWPO200900020 Review Comments Erosion Control Plan 2010-07-14� 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:
Rev. 2:
Rev. 3:
Date of comments:
Rev. 1:
Rev. 1:
Rev. 3:
Reviewer:
Rev. 1, 2 3 &:
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
14 June 2010
1 July 2010
3 Sep 2009
17 May 2010
21 June 2010
12 July 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. I) 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. I) Comment has been addressed.
3. "Clean water" diversions are not an approved variation. Basins should be sized for the contributing
drainage areas.
(Rev. I) 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. I) 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. I) Comment has been addressed.
Current Development
Engineering Review Comments
Page 2 of 3
B. Stormwater Management Plan
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 show a conceptual location of a pond for
future development.
(Rev. 3) Comment has been addressed.
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.
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.
- It appears that the CN numbers being used for Drainage Areas #1 and #2 are incorrect.
The GIS map shows that the existing areas are wooded, which should have a CN of 60.
- In order to treat at 65% for the bioretention basin, you need I" over all impervious area
(i.e., 199775 sf * I " /(12 "/') = 16,648cf).
For planning purposes, please use 4% or 5% (199775 sf *0.04 = 7991sf bed
area........ assuming Ift ponding your volume captured is like around 8200cf (well short
of goal. If 0.5 ft of ponding is used, you're down to around 4000cf which is 25% of the
actual intention of the Biofilter. Please refer to the VSMH
- For the retention wet pond, it is recommended that the conc. weir be moved to the other
side of the pipe as to provide access to the riser. It is also recommended not to install
the weir on fill.
(Rev. 3) Comment has been addressed.
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 1'.
(Rev. 2) Comment has been addressed.
Current Development
Engineering Review Comments
Page 3 of 3
The Erosion & Sediment Control and Stormwater Management Plans (WP0200900020)
submitted 1 July 2010 have received Engineering Review and meet Albemarle County minimum
checklist items for approval. Please submit 5 paper copies of the Plan to Current Development
Engineering.
The E &SC bond amount is $176,500. The SWM bond amount is $139,000. The forms and
instructions to post the Water Protection Ordinance Bond can be found on the Community
Development Department Web site on www.albemarle.oig.
A completed copy of the Standard Stormwater Maintenance Agreement and fee for recordation for
the stormwater facilities is required prior to final approval. [17-304E] The forms and instructions
can be found on the Community Development Department Web site on www.albemarle.org.
You may contact Ana Kilmer (Albemarle County Department of Community Development) at ext.
3246 for further information on bonding procedures and Maintenance Agreements.
Once the E &SC bond and the SWM bond have been posted, you may contact the Department of
Community Development to arrange a pre - construction meeting with a County Erosion &
Sediment Control Inspector. Should the County Inspector find the limits of disturbance increased
or the need for additional control measures required to protect the site, additional fees will be
required.
\\ Cob- dts01 \cityviewlnk\Docs \2009 \WPO \WPO200900020 University Village\ E3_ fsp_rp_esc_swm_JPD_WP0200900020
University Village.doc