HomeMy WebLinkAboutWPO201000064 Review Comments Erosion Control Plan 2010-11-19ALg�,��
�'IRGINZ�
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.:
Date received:
Date of Comment:
Engineer:
WPO- 2010 - 00064, HTC Apartments ESC Plan
Mr. Scott Collins, PE; Collins Engineering
Uptown Village, LLC
6 October 2010
19 November 2010
Phil Custer
The ESC plan for Hollymead Towncenter Apartments, received on 6 October 2010, has been reviewed. A
review of the SWM and site plan will be provided at a later date. This ESC plan cannot be approved as
submitted and will require the following corrections before approval can be granted:
1. Before this plan can be approved, the offsite easements on TMP 32 -50 must be recorded. These
easements include a permanent stormwater facility easement, a permanent public sewer line
easement, and temporary construction easement to install these facilities.
2. Before this plan can be approved, the offsite private drainage easement on TMP 32 -49K must be
recorded.
3. The diversion through the middle of the construction site to reduce the drainage area to the east is
impractical to maintain throughout the filling of the site. Please remove this diversion and
accommodate the portion of site draining to the east in the existing condition. It appears that
structure 6 can be designed as a sediment basin riser and the stormsewer system 5 -3 -1 can be built
during Phase I. Sediment Basin 1 should remain as designed however, because the drainage area
will likely increase during fill operations.
4. It is my understanding that an ESC plan was recently approved for filling of the south side of
Towncenter Drive across from the apartment complex. In this plan, the construction of SB -2 was
authorized. However, because the apartment complex plan is much larger, it will supersede the
waste area plan for the sediment basin. At the time the bond is posted for the apartment complex
plan, the applicant should request a bond reduction of the waste area plan for the basin. Also,
please note in the construction sequence that Sediment Basin 2 should be constructed prior to
commencement of Phase II.
5. The ESC measures proposed to protect Phase III construction (IP and SF) are not adequate for the
watershed and the amount of work required in this phase on the north end of the site. I
recommend breaking Phase III into two phases. In Phase IIIA, the parking lot and drainage
structures north of the pool would be constructed. Below this work the sediment basin would be
filled in and converted to a sediment trap sized for the upstream watershed. Once the drainage
structures and curbing have been installed to direct the upstream construction area to S13-2, the rest
of the work to finish the site can be performed using silt fence at the tree preservation line.
6. Please grade sediment basin 2 and the stormwater management facility in such a way that the
Willow Glen Connector Road can be construction without impacts.
7. It is my understanding that the tree preservation areas are critical to the number of units proposed
on this site plan. Please provide a tree survey for the location, size, and type on the eastern side of
the property at the same scale as the plan.
8. Please fill as much as possible, ensuring positive drainage of the downhill diversion dikes, during
Phase II in the areas east and west of Sediment Basin 1. Please also relocate the diversions on the
east and west side of Sediment Basin 1 as close to the limits of disturbance as possible to ensure
positive drainage.
9. A construction entrance is needed for Sediment Basin 2.
10. Please show outlet protection in Sediment Basin 2 where pipe 1 outlets into the facility.
11. Please round down when computing the diameter of the dewatering orifice.
12. Please update the county erosion and sediment control notes. These notes can be found in the
latest edition of the design manual, available online.
13. The limits of clearing and grading do not appear to include Sediment Basin 2 and the sewer line
construction. Please update the limits and check to make sure all proposed construction is shown
within this line.
14. Please remove sediment trap 2. A trap cannot drain over a sidewalk and curb of a VDOT
roadway. Runoff from the construction entrance will drain to a sediment trapping measure with
both the existing and proposed contours so another trap is not needed.
15. Please provide a diversion dike along Towncenter Drive east of the eastern most entrance in
phases I and lI. By Phase III, this slope should be stabilized.
16. Engineering offers the following comments regarding the adequate channel analysis:
a. As stated throughout the plan, this project has a disturbed area of around 9 acres. The 1%
rule along Powell's creek is reached when the watershed is 900acres. It does not appear
that this is shown on sheet SWM -4. Please remove the note referencing the 1% rule.
b. The headwater on the Towncenter Drive pipe is extraordinarily high for a 10 -year storm.
Generally, a headwater of 1.5 x the diameter of the pipe for the 10 -year storm should be
designed for culvert crossing.
c. The slopes used in most of the computations appear to be underestimating the average
slope of the segment of the stream. When I measured the distances between the county's
4ft contours I found slopes greater than 2% for most of Powell's Creek.
17. The ESC portion of the WPO bond will be computed at the time of plan approval.
File: El_esc_PBC_WPO -2010 -00064 HTC Apartments ESC Plan.doc