HomeMy WebLinkAboutWPO201000062 Review Comments Erosion Control Plan 2011-01-20ALg�,��
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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: WPO- 2010 -00062 SUB - 2008 - 00138, Westhall V Construction Set
Plan preparer: Mr. David Jensen, PE; W & W Associates
Owner or rep.: Shiflett Farm, LLC
Date received: 3 September 2010 (application received 21 September 2010)
(Rev. 1) 17 December 2010
Date of Comment: 3 November 2010
(Rev. 1) 20 January 2011
Engineer: Phil Custer
The Construction Set (ESC, SWM, and Road Plans) for Westhall V, received on 17 December 2010, has
been reviewed. The previous WPO plan for this property had expired due to inactivity and a new
application number was assigned to this project. The previous ESC, SWM, and Road Plans were reviewed
under WPO- 2008 - 00038. The ESC and SWM plans are now be reviewed under WPO- 2010 - 00062. The
road plan will be tracked using the final plat application, SUB - 2008 - 00138.
A. Road Plan comments (SUB- 2008 - 00138)
1. The applicant has provided an approval email from Joel Denunzio at VDOT dated 26 September
2008. I have forwarded a copy of the latest submittal to Joel and am awaiting confirmation of
approval. Please note that the ditch work within the VDOT ROW is a new element to this plan
and must be approved by Joel as well.
(Rev. 1) A copy of the latest Westhall plan has been forwarded to VDOT.
2. A road bond must be posted prior to final plat approval. To request a road bond estimate, please
complete the request form and submit it to the county with a $250 fee. Before posting the road
bond, a schedule of completion must be approved by the County Engineer.
B. Stormwater Management Plan Comments (WPO- 2010 - 00062)
1. The pro -rata contribution for Westhall V has been computed to be $9,788.63. If this payment has
not be posted prior to the Board of Supervisors modifying the rate early next year, a new amount
will need to be calculated that may be more expensive.
(Rev. 1) The pro -rata contribution to the Lickinghole Basin has been updated per Board of
Supervisors policy. The fee is now $9,945.25.
2. Stormwater facility C has been verified to have met the requirements for the development of
Westhall V. When TMP 56 -53 is developed however, the owner will need to verify the adequacy
of the pond at that time.
3. A Stormwater facility maintenance agreement will be needed for each parcel with a stormwater
facility. Please submit this document to Ana Kilmer after reviewing the guidelines online. The
agreement should reference the current WPO plan, WPO- 2010 - 00062.
(Rev. 1) Comment has not been addressed.
4. The SWM portion of the WPO bond will be computed at the time of plan approval.
(Rev. 1) To receive a SWM bond estimate, please submit the Bond Estimate Request Form to
the County Engineer.
C. Erosion and Sediment Control Plan Comments WPO- 2010 -00062
1. This submittal shows the offsite work on Park Road covered in Proffer 1.3. Though Current
Development Engineering review may approve the proposed plan, the proffer will remain
unaddressed until the County Engineer is satisfied with the construction. For this offsite work,
please make the following changes to DP -5:
a. Please show and calculate the limits of disturbance. The ESC narrative should be updated
considering this disturbance as well.
b. Show culvert inlet protection where applicable.
c. Show Permanent Seeding throughout the plan.
d. Please define the property lines more boldly. If work outside of the ROW is necessary,
construction easements will be required.
e. Please provide calculations showing that the new channels will be non - erosive for the 2-
year storm and with carry the 10 -year storm within its banks.
f. I recommend using riprap, concrete, or a similar material for channel SCC -1 because it
appears that the establishment of grass in this location will be difficult.
(Rev. 1) Comment has been addressed.
2. The adequate channel calculations must be updated to satisfy the requirements detailed in pages V-
122 through V -141 of the VESCH. The cross - section should be irregular and taken from a field
survey. I walked these downstream channels earlier this week and had difficulty locating cross -
sections E -E, F -F, and G -G. Each segment of each channel cross - section should have a computed
n -value (Table 5 -16 to 5 -21), permissible velocity (Table 5 -22), and computed velocity. Since
these channels are natural, only the 2 -year storm must be analyzed for erosion and capacity.
As an alternative to providing an analysis on the channel between the forebay and pond, the
applicant may provide a pipe instead. This would require an additional easement from the
downstream property owner. If this alternative is chosen by the applicant, I recommend designing
the outlet structure from the forebay in a manner that allows a minimal amount of water into the
existing channel to keep the wetland area alive, though this is not a requirement.
(Rev. 1) The MS -19 analysis does not show separate computed n- values, permissible velocities,
and computed velocities for each segment of each channel cross - section as mentioned above.
For each channel section, the calculations account for only one n -value when typically there is
a difference in n -value between the bottom, banks, and overbanks. Similarly, the material of the
channel usually differs between the bottom, sideslopes, and overbank which results in varying
permissible velocities. The analysis shows only one averaged velocity for each cross - section,
when higher velocities are expected in the deeper segments of the cross - section.
Between the outlet of the forebay and cross - section E -E, the channel is sloped at 7 -8% and will
likely erode much more rapidly than the current cross - sections. Please provide calculations on
two cross - sections in this reach of the channel while considering the above technical comments.
3. The county has updated the General Construction Notes for ESC plans since this plan was
prepared. Please modify the general notes to match the latest list from the Design Manual.
(Rev. I) Comment has been addressed.
4. Please provide the county with all of the state and federal permits within the streams and wetlands.
(Rev. 1) The permit provided by the applicant refers only to the disturbances to construct the
sewer line on the north end of the property and the construction of the forebay facility. The
work to convert the existing pond to a Storm water Facility seemed to be a change to design that
occurred after approval. However, I have correspondence from Vinny Pero of the Army Corps
of Engineers that this work can be performed under the existing permit.
5. All offsite easements must be recorded prior to issuance of a grading permit.
(Rev. 1) Comment has been noted by the applicant.
6. The ESC portion of the WPO bond will be computed at the time of plan approval.
(Rev. 1) To receive an ESC bond estimate, please submit the Bond Estimate Request Form to
the County Engineer after the ESC plan is approved.
File: E2_rp esc swm_PBC_WPO- 2010 -00062 Westhall V Construction Set.doc