HomeMy WebLinkAboutWPO200800054 Review Comments Stormwater Management Plan 2008-07-02ALg�,��
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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- 2008 - 00054, Faulkner Falls Subdivision
Plan preparer: Mr. Brian Smith, PE; Brian Smith Engineering fax 434.296.2041
Owner or rep.: Faulkner Falls LLC fax (unknown)
Date received: 19 May 2008
Date of Comment: 2 July 2008
Engineer: Phil Custer
The SWM, ESC, and road plans for Faulkner Falls Subdivision, received on 19 May 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
Please provide a benchmark on the plan.
2. Please state what datum the topography has been generated with.
3. The scale of sheet E -1 appears to be F' =50' and not 1 " =40'.
B. ESC Plan Review Comments
1. Please provide adequate channel analyses for all concentrated discharge points. It appears
adequate channels are needed from the detention facility to the stream and from the roadside swale
on lot 7.
2. Please provide a brief construction sequence for the plan. It appears that after the ROW is cleared,
cut needs to be taken in the second half of the road to fill the first half.
3. Please call out the roadside ditch on the east side of the roadway as a diversion (DV).
4. The wet storage calculations appear to indicate vertical soil walls between elevation 439.5 and
441.99. The maximum slope in wet storage is 1:1. Please modify grading on sheet ESC -2 to
match the calculations sheet.
5. The wet storage calculations appear to be incorrect. For instance, between the first two elevations
439.5 and 441.99, I calculated the incremental volume to be close to 69cy. Similarly, the volume
between the 2 °d and 3`d elevations (441.99 and 442) was found to be close to ley. Unless the
sediment basin grading below the 442 elevation is hollowed, the dewater orifice needs to be placed
at a higher elevations.
6. The cleanout elevation of the basin must be located at the elevation when half of the wet storage is
filled with sediment. At elevation 442, according to the calculations sheet, 522cy of 635cy will
have settled.
7. When determining the diameter of the dewatering orifice, the value should be rounded down (5 ")
to ensure that the drawdown is not less than 6 hours.
8. Please specify outlet protection (OP) at the outfall of the sediment basin.
9. Please move the sediment trap inline with the roadside swale.
10. Please show the grading for the sediment trap.
11. Why isn't the permanent structure specified in the SWM plan used for ESC purposes?
Engineering review maintains a policy that "structures and embankments match permanent design
for facilities to be converted to permanent stormwater management facilities. [DM]
12. Please show the safety fences around both the sediment trap and basin.
13. Please note that a grading permit will be withheld until a copy of the state VSMP permit is given
to the county. Please contact Mr. Matthew Grant, DCR, at 804.225.3068 for more information.
14. The ESC portion of the WPO bond will be computed once all comments have been addressed.
C. SWM Plan Review Comments
1. Please provide a SWM facility south of the roadway at Sta. 3 +00. [17- 314.C]
2. Please provide modified simple spreadsheets for both SWM facilities.
3. Please provide on the plan the standard county notes for SWM management.
4. All quality SWM facility must have sediment forebays for each discharge point. Forebays must be
sized to VSMH standards.
5. The SWM computations do not appear to compare routed peak flow rates to the pre - development
condition.
6. The detail states that the bed elevation is 443.60 but the grading indicates a bed area of 443.
Please clarify.
7. Please dimension the outlet protection from the biofilter detention basin.
8. Gravel layer in the biofilter must be 18 ". [DM]
9. Underdrain pipe must be 6 ". [DM]
10. Please change all callouts for Luckstone biofilter mix to "state approved mix." [DM]
11. The SWM portion of the WPO bond will be computed once all comments have been addressed.
D. Road Plan Review Comments
1. An application for a road plan review was not received with this submittal. A county review of the
road plan was performed, but copies were not sent to VDOT until July Ist, 2008.
2. VDOT approval is required. At this time, VDOT comments have not yet be received.
3. Please provide traffic control signage on the road plan.
4. Please provide street name signs on the road plan.
5. Please show a culvert at the driveway to the existing house and callout VDOT Standard PE -1.
6. It appears a crossdrain is needed at Sta. 1 +50.
File: E1_esc swm rp_PBC_08 -054 Faulkner Falls Subdivision