HomeMy WebLinkAboutWPO200800038 Review Comments Erosion Control Plan 2008-05-30ALg�,��
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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:
Plan preparer:
Owner or rep.:
Date received:
Date of Comment:
Engineer:
WPO- 2008 - 00038, Westhall V ESC and SWM Plan
Mr. Doug March, PE;
Shiflett Farm, LLC
15 April 2008
30 March 2008
Phil Custer
W & W Associates
fax 434.978.1444
fax 434.975.3542
The SWM and ESC plans for Westhall V, received on 15 April 2008, have been reviewed. The plans
cannot be approved as submitted and will require the following corrections before approval can be granted:
A. General Review Comments
1. The work proffered in item 1.3 of ZMA- 2006 -00001 should be shown in this set.
2. Please provide the county with all state and federal permits.
3. Before this plan can be approved, all necessary easements on adjacent TMP 56 -53 must
be recorded. These easements include, but are not necessarily limited to, the SWM
facility, drainage -ways across all channels from the Westhall property, and the access
path to the facility.
4. This WPO plan is currently being reviewed independent of any subdivision plat because,
at the time of the WPO submittal, all plats for this area were either withdrawn or not yet
submitted. Additional WPO comments may be given in the reviews to follow based on
required changes or review of the plat and road plans.
B. ESC Plan Review Comments
1. Please perform adequate channel analyses for the channels downstream of the forebay and
pond outlets. The single calculation for the channel immediately after the pond outlet is
not extensive enough.
2. Please provide a Phase 1 ESC sheet with the initial clearing of land and the installation of
the perimeter control measures. This sheet should show the existing drainage areas to the
traps and basins with the current site topography before grading operations begin. It is
hard to review the adequacy of the current plan and future comments may be forthcoming
based on the new sheet.
3. Please provide drainage area lines on ESC -2 for all sediment trapping measures.
Sediment trapping measures should be sized for the largest drainage area that could
possibly be draining to it. This could be in the initial disturbance phase, final site grading
phase, or an intermediate phase between the two. Again, please be sure that drainage area
lines are provided for both existing and proposed grading.
4. Please provide letters of intent for all off -site work. From my initial review of the plans,
letters are needed from the owners of lots 57 -61, lot 7, TMP 56 -48, and TMP 56 -53.
5. Grade lines go over and through sediment traps. Please tie site grading into the sediment
traps. The final as -built grade lines should not appear on the ESC plans.
6. Provide diversion dikes north and south of ST3 rather than silt fence. Please be sure to
direct the area of disturbance required to construct the extension of Westhall Drive into
the sediment trap.
7. The construction entrance cannot be placed on fill. I recommend moving the construction
entrance off of the temporary turnaround area on Brookwood Road. Moving the CE
would reduce the limits of construction for the Phase I operation to the area needed to just
construct the perimeter controls. To place the construction entrance in its current
proposed location, the volume of the existing basin would be reduced by significant
amounts of fill and the ESC plan for Phase III would become inadequate.
8. The embankment for the sediment basin is not shown to be wide enough. [VESCH]
9. Please provide a safety fence around all sediment traps and basins with signs stating:
"danger, quick sand, do not enter ".
10. A baffle is required in the sediment basin.
11. I do not see where Culvert Inlet Protection is used on the plan though a detail was
provided in the set.
12. Please correct the sediment basin table to show that only 810.7 cy are provided as
opposed to the total volume provided at this elevation. Please note that the 12.1 drainage
has not been confirmed by engineering review because it has not been shown on the plan.
(Please also see ESC comment #3) If it appears that the drainage area is in fact larger
than 12.1 acres in the next review, the sediment basin will be undersized.
13. Please modify the C coefficient used for the routing of the sediment basin. The entire
drainage area is not bare earth and contains some impervious area from existing
developed phases.
14. Considering the time of concentration calculation on sheet SWM -2, the sediment basin
time of concentration should be around 10 -11 minutes.
15. Please divert SCC D into ST2.
16. Please provide blowup details for the review of the sediment traps. It is hard to check the
traps for compliance with the state's design standards (regarding embankment heights,
embankment widths, volumes, etc.) with the plan at 60 scale.
17. Please use diversion dikes on the south end of the property to direct water into sediment
traps 1 and 2.
18. Please provide a calculation for the dewatering orifice of the sediment basin. My
calculations indicate the orifice should be 5 ".
19. The ESC portion of the WPO bond will be computed once all comments have been
addressed.
C. SWM Plan Review Comments
1. A Lickinghole basin pro -rata share fee will be calculated when the plans are closer to
approval.
2. Signed Stormwater Management Facilities maintenance agreements and recordation fees
will need to be submitted for both parcels. Please contact Pam Shifflett (x 3246) for
questions regarding this procedure.
3. Engineering review staff will not approve this SWM plan for proposed development of
the TMP 56 -53 parcel. This review is for the development of the Westhall V subdivision
SWM plan only. At the time of the development of TMP 56 -53, the existing SWM
facility will need to be checked for adequacy by the applicant.
4. Please improve the "existing unimproved road" to the standards specified in the design
manual for maintenance paths to SWM facilities.
5. In addition to the Lickinghole basin pro -rata share, SWM facility C needs to provide
stormwater quality treatment to be consistent with the approved rezoning plan. Please
provide these calculations. The sediment forebay sizing calculations should also be
provided when the pond calculations are submitted.
6. Please show a trash rack on the riser weir.
7. The maximum slope allowed around the sediment forebay facility will be 3:1, including
the downstream slope on the embankment.
8. The downstream slope of the SWM pond must be 3:1 or shallower.
9. The minimum pipe diameter permissible in SWM facilities is 15 ". For the forebay
facility, please make the pipe 15" and provide an orifice plate at the inlet to the pipe.
10. Please specify on Sheet SWM -3 the elevations for the crests for both riser structures.
11. On sheet SWM -5, please provide information for the sediment forebay drainage area so
that routing calculations can be confirmed.
12. The SWM portion of the WPO bond will be computed once all comments have been
addressed.
File: El esc swm PBC 08 -038 Westhall V ESC and SWM