HomeMy WebLinkAboutWPO201300002 Review Comments Stormwater Management Plan 2013-02-07�pF A
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COUNTY OF ALBEMARLE
Department of Community Development
401 McIntire Road, Room 227
Charlottesville, Virginia 22902 -4596
Phone (434) 296 -5832 Fax (434) 972 -4126
Project: Northtown Phase IIA -Final
Plan preparer: Collins Engineering [293 -3719]
Owner or rep.: United Land Corporation [975 -3334]
Plan received date: 7 Jan 2013
Date of comments: 7 Feb 2013
Reviewer: Michelle Roberge
A. Stormwater Management (WP0201300002)
1. It appears that the biofilter on site is now undersized due to the increase in drainage area from 7.5 acres
(from phase 1) to 10.95 acres (shown in this plan). Adding the forebay is great for pre - treatment, but it
also reduces the basin's volume capacity. For quality, the floor area of the biofilter should be 5% of the
impervious area. Based on these comments, the biofilter does not meet both the quality and quantity
criteria and a redesign is required.
2. Please include the drainage calcs for stormsewer in this WPO package when you resubmit.
3. For drainage inlet 28, the worst case scenario is to reduce the drainage area up to the wall. This will
reduce your time of concentration from 10 min to about 5 minutes. Please revise storm sewer
computations.
4. The curb cuts on the median should be treated like a curb opening inlets without depression and
analyzed for spread. Please provide analysis.
5. The stormdrain calcs show a CG -6 curb and gutter, but sheet 3 calls out CG -2 on travelways. Please
revise.
6. Please show all drainage easements, including the proposed stormsewer easements.
7. Please provide a scaled detail of the biofilter (preferably at a scale of 1 " =30' or 1 " =20'). Please show
just one bioretention basin detail which includes the cross section of the travelway, the spillway, the
54" culvert bypassing the system, the 10 yr and 100 yr elevations, the outlet, forebay, cleanouts, etc.
See details located on sheet 6.
8. Please provide the geotech fabric in basin.
9. The shape of the biofilter NW of site has slightly changed. Please differentiate between the existing
and the revised easements. The revise easement should encompass the 100 year high water mark.
10. Please show the approved site layout and drainage layout for the approved phase 1 on all sheets. If
there are changes to the phase 1, an amendment to phase 1 will be required. Phase 1 and 2 must be
looked at as a whole to ensure a well coordinated site layout, E &S plan, and SWM design.
B. Erosion Control Plan (WP0201300002)
1. Please provide a narrative for your project.
2. Please show the limits of clearing and grading. This must match the landscaping plans.
3. Sediment trap 2 is not necessary and I recommend providing another type of erosion control measure.
Provide soil stabilization blanket & matting with silt fence at the bottom of LOD.
4. The rip rap should not be placed at an angle from the pipe. Please revise.
Engineering Review Comments
Page 2 of 2
5. Please update the topo for the site. Also provide the as- builts for SB 1 or clarify if the basin will not be
reconstructed.
6. SB 2 is undersized. Please revise.
7. The wet storage volume is undersized for ST I.
If you would like to come in to discuss other BMP measures that could be explored, please feel free to
schedule a meeting on Thursdays from 2pm -4pm.
Sincerely,
1)16�
Michelle Roberge
File: EI_rp,esc,swm,fsp_GEB _ template.doc