20071888 Ver 1_Staff Comments_20081112

07-1888 Blake Commons
AML Comments
November 12, 2008
RETURN. The Request for More Information Letter that the DWQ sent on June 19,
2008 stated:
"Please provide a BMP Supplement Form for each BMP that will be used on the
site (including both worksheets, Design Summary and Required Items Checklist),
as well as all of the required items. The BMP Supplement Forms are available on
the DWQ web site at: http://h2o.enr.state.nc.us/sul'bmp_forms.htm. Failure to
provide an appropriate stormwater management plan in the next submittal will
result in a return of application."
The resubmittal failed to include the Required Items Checklist and many of the required
items.
When you resubmit, please address the following issues on the design of the wet
detention basin:
a. Check your calculation of the drainage area- it appears to be significantly
smaller than you have measured. However, the percent imperviousness for
this drainage area appears to be far greater than the 24 percent you have
calculated it to be. This will affect the pond sizing and the required SA/DA
ratio. Please redesign the pond after addressing the concerns about drainage
area.
b. The vegetated shelf is too steep - the plans show a two-foot change in its ten
foot width (instead of the one-foot change that is required per the BMP
Manual.) In addition, please provide an appropriate planting plan for the
vegetated shelf.
c. You must provide a soils report that documents the level of the seasonal high
water table (SHWT). The SHWT may not be lower than the proposed
permanent pool elevation of the wet detention pond.
2. In your resubmittal, please show the locations of every proposed stormwater
discharge point on the plans with a depiction of the drainage area of each outfall.
General Certification 3705 requires that you analyze the imperviousness of the
land draining to each stormwater outfall.