20091346 Ver 3_Staff Comments_20100820

09-1345v2 Granville Medical Center-take 2
AML Comments
August 20, 2010
1. The depiction of the storm drainage system remains unclear. Some of the issues of concern are:
a. On the northern, 0.27 acre parking lot, it appears that a ditch or curbing along the east
side of the parking lot will need to be added to direct the stormwater to the BMP.
b. On the southern, 0.91 acre parking lot, please provide calculations that show whether
the curb will be overtopped during the one inch storm. If the curb is likely to be
overtopped during the design storm, then additional inlet structures must be provided.
2. The sediment basin and sand filter do not appear to have enough capacity to store the entire
adjusted water quality volume. Please re-design to provide this additional volume and submit
calculations to support the design. Please also provide calculations of the draw down rate.
3. The pipes conveying water from the sediment basin to the sand filter is at a very steep slope
(over ten percent). In your redesign of the sand filter, please significantly reduce the slope of
that pipe to prevent scouring in the sand filter.
4. The embankment that separates the sediment basin from the sand filter looks likely to have
stability issues above the PVC pipes. In your redesign of the sand filter, please ensure that there
is a continuous, unbroken side slope of no greater than 3:1.