SW6221101_Response To Comments_20230327

exp.federal
March 22, 2023
NCDEQ DEMLR
Post -Construction Stormwater Program
Attn: Jim Farkas
512 N. Salisbury Street, Office 640M
Raleigh, NC 27604
Subject: Response to Comments 91
Stormwater Permit No. SW6221101
Fort Bragg, North Carolina Technical Support Annex, PN79439.2
Cumberland County
Dear Mr. Farkas,
Please consider our response to your comments included in your letter dated February 14, 2023.
Comments have been addressed as follows:
As designed, this project does not appear to meet Runoff Treatment, as required per 15A
NCAC 02H .1003(3)(a) and defined in 15A NCAC 02H. 1002(43). Please ensure that the
net increase in BUA is being captured and treated in one or more primary SCMs. NOTE:
Dry Ponds are not considered to be Primary SCMs per 15A NCAC 02H .1002(37).
NOTE: The submittal items do not indicate any existing BUA associated with this
project. Please revise as needed.
RESPONSE: The proposed dry pond has been converted to a bioretention cell. The
runofffrom the three upstream bioretention cells, which were routed through the dry
pond, are now routed around the new bioretention cell instead of through it. The new
cell is sized appropriately for the entire drainage area discharging into the pond.
Although there may be credits available for existing BUA, the current design (treating all
proposed BUA) allows for better stormwater peak flow control during larger rainfall
events.
2. Please QA/QC the submission for consistency. For example, the drainage area to
bioretention cell B5 is shown as 47,916 sf (1.1 ac) in the Application (Section IV, 10),
1.07 ac in the calculations (Inlet Capacity for IN-135), and 1.0 ac in the plans (Plan sheet
CE602). Similar issues exist for the other SCMs and other aspects of the design. Please
revise as needed.
RESPONSE: Additional exhibits were prepared to better show where the information on
the forms came from and the submittal documents were checked for consistency across
all documents.
Page 1 of 5

p•0.
'°'� ,AFfederal
As previously indicated, a Dry Pond is not a Primary SCM and was not reviewed for
compliance with the MDCs. If you would like us to consider the treatment train provided
by the bioretention cells and dry pond in series as a combination of primary and
secondary SCMs that provides equal or better treatment then what is required per 15A
NCAC 02H . 1003 (2)(43), you will need to demonstrate this.
RESPONSE: The plans have been revised so that all proposed BUA is now routed
through a primary SCM.
4. The water quality volume for a bioretention cell is stored above the planting surface and
below the invert of the lowest bypass elevation (not within the bioretention media as
shown in the calculations). Please revise as needed. You will either need to provide a
stage -storage table for each bioretention cell or calculate the storage volume as the
bottom surface area of the bioretention cell multiplied by the ponding depth.
RESPONSE: The storage volume has been updated.
5. Please clearly indicate the project area in the plan set (required per 15A NCAC 02H
.1042(2)(g)(ii)). Typically, the project area corresponds to the property area, however, in
situations like this where the total property area is significantly larger than the project
area, a more suitable project area can be used (the limit of disturbance is commonly used
in situations like this, however, you can use any appropriate project area so long as it
includes the entire area to be covered under this permit and doesn't overlap the project
area of a different permit). Either way, please clearly indicate this project area boundary
on the plans.
RESPONSE: The project area is shown on the plan as a diamond -dash line and labeled
as "Construction Limits /LEED Boundary"
6. Please correct the following issues with the Supplement-EZ Form:
a. Cover Page:
Line 7 — Please include this value as required per 15A NCAC 02H
.1003(4) & .1017(10). It is noted that there are no surface waters located
on -site, however, we ask that this value is included on this form.
RESPONSE: This information was added to the form.
ii. Line 22 — Revise as needed.
RESPONSE: The form has been revised.
Page 2 of 5

f �
expffederal
b. Drainage Area Page:
i. General:
1. Lines 7 & 11 — Off -site areas refer to areas that are located outside
of the project area. Portions of a drainage area that are located
outside of the project area must be accounted for at their full built -
out potential. Typically, this is accomplished by assuming that the
off -site area is 100% BUA (its full buildout potential) however,
since Fort Bragg will also own the off -site areas, this 100%
assumption does not need to be made.
RESPONSE: Offsite areas have been accounted for.
2. Lines 15 & 17 — Please ensure that any existing BUA is accounted
for on these lines (otherwise you don't get credit for these areas).
NOTE: you are only required to capture and treat the difference in
BUA from existing to proposed conditions.
RESPONSE: These values have been updated.
ii. Entire Site Column:
1. Lines 19-21 — These items are not required for this column.
RESPONSE: These cells have been cleared of input.
2. Revise as needed per earlier comments. NOTE: The entire site
column is an accounting of the entire project area (similar to how
the drainage area columns are an accounting of the drainage area to
the SCMs. When asked for the "drainage area" of the entire site, it
is asking for the project area.
RESPONSE: These cells have been revised. Total Drainage Area
is the site area plus any upstream areas draining toward the site.
iii. Drainage Area Columns:
1. Lines 5 & 6 — Please revise the drainage areas to the SCMs as
needed.
RESPONSE: Drainage Areas have been revised
2. Line 10 — This item should be a sum of the items in Line 12
RESPONSE: These cells have been updated.
3. Line 12, Other — Please include this information if located within
the drainage areas to the SCMs.
RESPONSE: The paved area around the building was classified
as other. (see additional information section)
Page 3 of 5

ei -,p.federal
c. Bioretention Cell Page:
i. Lines 12, 14, & 15 — Since this project is located at Fort Bragg, easements
and a standard O&M Agreement are not required. Please revise as needed
and provide a brief explanation in the Additional Information section
(Line 44).
RESPONSE: The cells were revised and explanation added.
ii. Line 18 — Please include the SHWT elevation. If the SHWT was not
encountered above a certain elevation, please list the lowest boring
elevation that the SHWT was not encountered at. For example, if the
boring terminated at elevation 100' without encountering the SHWT, you
can answer "100" or "<100" for this item.
RESPONSE: The cells were revised.
iii. Line 22 — See earlier comment.
RESPONSE: The cells have been revised
iv. Line 26 — Per the provided percolation tests, the soil infiltration rate is
closer to 0 in/hr. Please revise as needed so this information corresponds
with the soil boring information.
RESPONSE: The cells have been revised
v. Line 30, Column B5 — This value (267) does not correspond to the plans
or other submittal documents.
RESPONSE: The cells have been revised
vi. Line 32 — Per Bioretention MDC 5(b)(ii), the minimum required depth of
media for a bioretention cell with IWS and no trees/shrubs is 30" (24"
inches is provided in the design. Please revise as needed.
RESPONSE: The cells have been revised
vii. Line 43 — Please clarify how grass/gravel will be used as pretreatment for
the bioretention cells.
RESPONSE: Grass/Gravel is proposed at the top of slope of the pond
where runoff is sheet flowing into the pond.
Page 4 of 5

exp.federal
7. Provide PDFs of all revisions, 2 hardcopies of revised plan sheets, 1 hardcopy of other
documents, and a response to comments letter briefly describing how the comments have
been addressed.
RESPONSE: PDFs have been uploaded and hardcopies are enclosed.
a. PDFs must be uploaded using the form at:
https: [/edocs.deq.nc.gov/Forms/SW-Supplemental-Upload
b. Hard copies must be mailed or delivered to the following address:
i. For FedEx/UPS:
Jim Farkas
512 N. Salisbury Street, Office 640M
Raleigh, NC 27604
ii. For LISPS:
Jim Farkas
1612 Mail Service Center
Raleigh, NC 27699-1612
iii. Hand Delivery:
Please reach out to me prior to hand delivering a submission to make sure
that I (or someone else in my group) will be able to receive the
submission. Do not leave the package in the foyer with the security
guard. NOTE: Hard copies should not be sent to a Regional Office.
Doing so will delay the review process and the submission package may
be lost while being sent from
the Regional Office to me in the Central Office.
If you have any questions about the proposed responses, please feel free to contact Lorraine
Roberts with Exp Federal at Lorraine.Roberts(c�r�,expfederal.com.
Thank you,
' ► 'i
Lorraine Roberts
Director of Infrastructure
Exp Federal, Inc.
Page 5 of 5