20100063 Ver 1_Staff Comments_20100627

10-0063 Franklin County HUB, take 2
AML comments
June 27, 2010
A Wet Detention Pond does not provide an adequate level of total nitrogen removal (25%)
to be used in place of a level spreader (a minimum of 30% total nitrogen removal is
required). At Outlets 1 and 4/5, please replace the proposed wet detention ponds with
stormwater wetlands. A stormwater wetland will work in an area with a high SHWT and
also provide sufficient total nitrogen removal to be used in place of a level spreader (40%).
For the level spreader designs, please address the following issues:
a. Per Item 2 of the Required Items Checklist, please provide custom plan details at a
1" = 30' scale or large with 1' topographic lines, showing proposed topo and its
connection to existing topo. On these details, please include specific details on the
proposed flow splitting devices with correct swale dimensions, invert elevations,
etc.
b. The flow splitting devices must be equipped with concrete weirs to split flow
between the input and bypass swales. Please clearly show the weir elevations on
the plan details and provide the calculations used to set the weir elevations.
c. The filter strip must be straight in plan view (an issue for level spreaders 6 and 7).
d. The bypass channel must enter the stream at an angle (an issue for level spreader
6).
e. For level spreader 7, please show 1' contours downslope of the level lip. Please
explain the choice of discharge location for the bypass channel (for example, it could
be an existing natural draw).
3. The Operation and Maintenance Agreements must be signed and notarized.