SW1190501_RESPONSE LETTER_7/12/2019

Corey Anen
Environmental Engineer
Stormwater Program
Please see our responses to comments:
1. Soil testing is required to determine the depth to the seasonal high water table to ensure
that the required 2-foot separation is maintained (Bioretention MDC 1). Were tests
conducted to identify the seasonal high water table?
An excavator was hired to excavate down to an elevation of 2190 in the middle of the
proposed bioswale. This would be at an elevation 5' below the underdrain for the proposed
system. The seasonal high water table was not encountered.
2. The bioretention cell detail on Sheet C-5.2 indicates that the internal water storage will be
1 foot below the planting surface. Bioretention MDC 4 requires that the internal water
storage be set at a minimum of 18 inches below the planting surface. In addition, the
detail appears to indicate that the orifice discharges directly into the outlet structure and
the pipe connected to the internal water storage is set at a higher elevation than the
underdrain.
The orifice was moved to a cap in the end of the upturned elbow attached to the underdrain
system. This cap was placed at an elevation of 2196.5 which is 18 inches below the planting
surface.
3. The plans and calculations indicate that the underdrain pipe has a diameter of 4 inches;
however, the outlet detail on Sheet C-5.2 labels it as 6 inches. Please update the detail to
match the plans.
The plans have been updated to provide a 6" underdrain.
4. Please complete and submit a Supplement EZ form for the bioretention cell. The
Supplement EZ form is an updated for of the supplement that was originally submitted
and better reflects the current stormwater regulations. The form can be found here:
https:Hdeg .nc. gov/about/divisions/energy-mineral-land-resources/energy-mineral-land-
permit-guidance/stormwater-bmp-manual.
See form in submission package
5. Provide pdfs of all revisions, 2 hardcopies of revised plan sheets, and 1 hardcopy of other
documents. Pdfs must be uploaded using the form at:
https:Hedocs.deg.nc.Gov/Forms/SW_Project_ Submittal
Plans/documents were uploaded