20060973 Ver 4_Staff Comments_20091217

06-0973v4 Birchwood Homes
AML Comments
December 17, 2009
The soils report provided does not include the level of the SHWT in close
proximity to the proposed dry detention basin. Please provide in-field soil testing
to determine the level of the Seasonal High Water Table (SHWT).
2. The information given in the soils report does not support the depth and
placement of the dry detention basin. The soils report states: "Based on soil
morphology the seasonal high water table can be considered to be within 2 ft. of
the bottom of the dry detention basin for unknown (but probably brief) periods
during the wetter seasons of the year."
Based on this information, the pond will have to be redesigned such that it does
not dewater the natural wetlands on the site. Chapter 17 of the DWQ BMP
Manual, the SHWT must be at least two feet below the invert of the dry detention
basin. Given the proximity of the dry detention basin to the wetland, it is
extremely unlikely that this separation exists. Per the DWQ BMP Manual, the
only detention devices that may be used in an area with a high SHWT are wet
detention basins and stormwater wetlands.