North Carolina Agricultural Sciences Center - C16123-comment response (2)

Project North Carolina Agricultural Sciences Center
Permit NCDEQ Stormwater
Permit#SW5180902
Date 01.02.2019
Reviewer Corey Anen
Number Comment Response
1 The square footage of impervious surfaces
varies throughout different documents.
The variation in square footage is due to the
difference between peak folw calcuations that
account for entire drainage area, and nutrient
calculations that only account for area within the
property line.
1a The existing impervious surface on the plans
and in the nutrient calculations is 11,250 sf
(0.258 acres). On the application, the total
existing impervious surface is 123,109 sf (2.83
acres).
The 11,250 sf refers to the project area and the
123,109 sf refers to the drainage area.
1b The total impervious surface, per the
application, draining to the north and south
bioretention cells is 290,872 sf (6.68 acres) and
131,521 sf (3.02 acres), respectively. In the
sizing calculations, it is 250,660 sf (5.75 acres)
and 65,588 sf (1.51 acres).
The application includes impervious sf within the
entire drainage area of the analysis point so that
pre- and post- development conditions can be
compared where flow is concentrated. The
stormwater control measure sizing spreadsheets
only account for the area draining to each device.
1c The total impervious area shown in the
nitrogen calculations is 7.36 acres. In the
application it is 10.22 acres.
The 7.36 acres refers to the impervious area within
the parcel and the 10.22 acres refers to the
impervious area within the drainage area (including
offsite impervious from Edwards Mill Road).
2 The calculations in the Stormwater Impact
Analysis show the north bioretention surface
area as 20,413 ft2. The surface area shown on
the plans is significantly smaller. Note that the
bioswales cannot be counted as they do not
meet the minimum design criteria for
bioretention systems. However, it is likely that
as designed, the project could meet the Volume
Match standard in lieu of the Runoff Treatment
standard. This would be done by completing the
Storm EZ spreadsheet and showing that the
annual runoff volume in the post-development
condition is less than 10% greater than the pre-
development condition. For more information,
please see Chapter A-1 of the Stormwater
Design Manual.
The Storm-EZ forms have been filled out and
demonstrate a reduction in annual runoff volume.
3 The nitrogen calculations in the Stormwater
Impact Analysis do not show the nitrogen
loadings leaving the SCMs. Note that if the
Volume Match approach is taken, the 35%
reductions should only be applied to the
volume of water that can be stored below the
first outlet of the bioretention cell, as any
overflow will not be treated.
With the volume match approach, the 1" storm is
still the target for nitrogen removal. Our model
shows no outfloe in the water quality event. All
water is contained below the first outlet.
4 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://edocs.deq.nc.gov/Forms/SW_Project_S
ubmittal
Pdfs have been provided as requested.
NOTE Please note that this request for additional
information is in response to a preliminary
review. The requested information should be
received by this office prior to January 13, 2019,
or the application will be returned as
incomplete. The return of a project will
necessitate resubmittal of all required items,
including the application fee.
Acknowledged
NOTE If you need additional time to submit the
information, please submit your request for a
time extension to the Division at the contact
below. The request must indicate the date by
which you expect to submit the required
information. The Division is allowed 90 days
from the receipt of a completed application to
issue the permit.
Acknowledged
NOTE The construction of any impervious surfaces,
other than a construction entrance under an
approved Sedimentation Erosion Control Plan,
is a violation of NCGS 143-215.1 and is subject
to enforcement action pursuant to NCGS 143-
215.6A.
Acknowledged
NOTE If you have any questions concerning this
matter please feel free to contact me at
[e-mail] or [phone].
Thank you for meeting with us in person. It was very
helpful to discuss the best way forward for
permitting this project.