HomeMy WebLinkAboutWPO201100064 Review Comments Stormwater Management Plan 2011-10-07ALg�,��
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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- 2011 - 00064, HTC Apartments ESC and SWMPlan
Plan preparer: Mr. Scott Collins, PE; Collins Engineering
Owner or rep.: Uptown Village, LLC
Date received: 23 August 2011
Date of Comment: 7 October 2011
Engineer: Phil Custer
The ESC and SWM plans for Hollymead Towncenter Apartments, received on 23 August 2011, have been
reviewed. These plans can be approved after the following comments have been addressed:
A. Erosion and Sediment Control Plan Review
1. Please show on the plan the deedbook and page number of all offsite permanent and temporary
easements on TMP's 32 -49K and 32 -50K needed to carry out this plan. These easements should
appear on each applicable sheet within the site plan, ESC, and SWM sheets.
2. Please provide dewatering orifice calculations for the basins. For sediment basins 1 and 3, I found
required orifices to be 3" (rounded down if <4 "). Also, dewatering orifice calculations should
sized based on the 6hour release of the dry storage required, not provided, when the difference
between the two volumes (and elevations) are significant.
3. DCR has informed the county that permanent drainage systems cannot be used as a conveyance
system of sediment -laden water to settling facilities. The current plan relies on this practice to
transfer water to Sediment Basin 2 in Phases II, IIIA, and III. The plan must be revised
conceptually so that water only enters permanent drainage system when an inlet's watershed has
been stabilized with grass and stone and that all overland sediment -laden flow can be directed to
settling facilities.
4. There is a problem in the current construction sequence between Phases II and IIIA. Sediment
trap 1 will not be able to handle the runoff northeast of the parking lots and building constructed in
Phase H. Trap 1 (or another facility based on comment A.3) must be expanded and kept in place
while buildings 5 and 7 are constructed.
5. Please show outlet protection on all stormsewer outlets. This includes the existing storm drain
outfalls in Sediment Basin 2.
6. Construction entrances are needed on all construction phases.
7. Please provide an analysis of the downstream channel. A map, SWM -4, was provided in the sheet
set that was submitted with the site plan, but calculations were not included with the new WPO
application.
8. A diversion at the south end of the site in Phase H appears to release sediment -laden water off the
property untreated.
9. After all comments have been addressed, please provide a Bond Estimate Request Form to the
County Engineer to receive a SWM bond estimate.
B. Stormwater Management Plan Review
1. Please show on the plan the deedbook and page number of all offsite permanent and temporary
easements on TMP's 32 -49K and 32 -50K needed to carry out this plan. These easements should
appear on each applicable sheet within the site plan, ESC, and SWM sheets.
2. The plan cannot be approved until the applicant provides a Stormwater Facility Maintenance
Agreement and fee to the county for the BMP located on TMP 32 -50.
3. The borrow /waste area plan (WPO- 2010 - 00068) has been underway for some time and the
topography on the south side of Towncenter Drive is no longer accurate. Please provide updated
topography of this land.
4. Why doesn't the area listed in the modified simple spreadsheet on page SWM -1 (19.72acres) equal
Drainage Area 1 plus Drainage Area 4? According to this plan, the watershed for this facility
should be 22.15acres.
5. The downstream slope of the stormwater facility must be 3:1.
6. The retention basin detail correctly shows the construction of an impervious core and cutoff trench
for the embankment. However, the applicant also has provided notes on many other sheets that the
embankment was not to be disturbed except for grading on the west side. Please clarify. Is the
applicant certifying that the facility was constructed to the detail shown in this plan when it was
constructed two years ago as a sediment basin? If so, please provide this statement on SWM -3,
below the cross - section detail.
7. The flow path within the retention facility is too short.
8. Please provide the profiles of the two existing pipes directed into the pond to show how far up the
VDOT storm drain system the pond will backwater storm discharge. VDOT approval may be
necessary. If the backwater is not acceptable, the pond elevation may need to be lowered.
9. The existing sediment basin currently does not hold water at this location. Will this facility, when
converted be able to hold any water as a wet pond? What is the reason that the sediment basin
does not hold any water permanently?
10. Please relocate the spillway farther to the north, closer to existing grade.
11. After all comments have been addressed, please provide a Bond Estimate Request Form to the
County Engineer to receive a SWM bond estimate.
File: E1_esc swm_PBC_WPO- 2011 -00064 HTC Apartments.doc