North Carolina Agricultural Sciences Center - C16123-comment response

Project North Carolina Agricultural Sciences Center
Permit NCDEQ Stormwater
Permit#SW5180902
Date 10.12.2018
Reviewer Corey Anen
Number Comment Response
1 The low density regulations allow for only a
minimal amount of piping for driveways or
culverts under a road. Because this project
proposes treatment of all surfaces using
bioretention systems it can be permitted as a
high density project if the applicant so chooses.
This site meets low density regualtions per the
NCDEQ Stormwater Design Manual (E-1 Low
Density Projects) based on the total built upon area
percentage; however, the reviewer has determined
that the project is considered to have both high and
low density areas
based on the length of pipe proposed. We are
proceeding with high density permiting.
2 Much of the proposed parking and roadway are
designed as curb and gutter but do not have
catch basins. How is runoff going to be
conveyed to the bioretention systems?
The north parking area includes turned-down curb
to allow sheet flow into the bioretention devises.
This is consistent with low-density efforts to
maximaize dispersed flow.
3 In accordance with Bioretention MDC 3, the
maximum depth for peak attenuation in a
bioretention system is 24”.
Peak attenuation of the 1-year storm is provided in
both bioretention cells with less than 24" of
ponding. Additional Flood control is provided at
higher elevations. The MDC specifies that it is up to
the designer to determine appropriate storm for
peak attenuation. Plans have been revised to clarify
the 1-year, 24-hour storm is the target for peak
flow.
4 Sheet C5.10 refers to a planting plan, L1.00,
which was not submitted. Please submit the
planting plan.
Sheet L1.00 is included with this submittal.
5 Internal water storage is required for all
bioretention systems with an in-situ soil
infiltration rate less than 2 inches per hour. Soil
testing results indicating the infiltration rate is
greater than 2 inches per hour must be
submitted or internal water storage must be
added to the design. (Bioretention MDC 4)
Internal water storage is shown in the north
bioretention devise and has been added to the
south bioretention devise.
6 The minimum depth of the bioretention media
is 36 inches for all cells with trees and shrubs.
Bioretention cells without trees and shrubs are
required to have a minimum media depth of 24
inches if they have no internal water storage or
30 inches with internal water storage.
(Bioretention MDC 5)
The north bioretention devise includes media depth
of 36". The media depth in the south bioretention
devise has been increased to 30". The south
bioretention devise does not proposed the use of
trees or shrubs. The bioretetention swales have a
media depth of 18".
7 The calculations for the northern bioretention
cell use a design depth of 1 foot. However, the
details show that the first outlet from the
bioretention cell is 6” above the planting soil.
Therefore, there will not be enough storage for
the design volume.
The first available outlet in the north bioretention
cell has been raised to 1' above planting soil.
8 The bioretention mix does not match the media
mix required by Bioretention MDC 6.
The media mix has been adjusted to reflect 75-85%
medium to course washed sand, 8-15% fines, and 5-
10% organic matter
9 On Sheet C5.12 Details 1 and 4, multiple
elevations are stated as 339’ instead of 439’.
The four typos were corrected, thank you for
pointing out this inconsistency.
10 The nutrient calculations show a sand filter
rather than a bioretention system. In the Neuse
River Basin Model bioretention cells receive
only 25% nitrogen removal credit.
The sand filter reference was a typo that has been
corrected. Per page A-5 of the MDC crediting
document, Bioretention cells receive 35-65% TN
removal in the Neuse River Basin. 40% TN is credit
for IWS in Piedmont Region.
11 Please provide calculations showing that the
post-construction peak flow from the 1-year, 24-
hour storm does not exceed the pre-
construction peak.
1-year, 24-hour storm calculations have been
included as requested.
12 Please explain the intent of the runnel in the
stepped bioretention system.
The runnel is intended to evenly distribute the
inflow between the three stepped bioretention
areas.
13 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 November 11,
2018, 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.