SW6240301_Response To Comments_20240709

G
LLC
STRONG ROC K STRONGROCK 83621 Six EForr s Rd.Suite P104
Raleigh, NC 27615
ENGINEERING GROUP Company License#P-2166
07/09/2024
To: Brianna Holland
DEMLR Post-Construction Stormwater Program
512 N. Salisbury Street, Office 625Y
Raleigh, NC 27604
RE: Request for Additional Information Stormwater Permit No. SW6240301 Ambrosia Farm
Phase 1 Harnett County
In response to review comments provided on 05/30/2024, I am providing the following comment
responses:
1. Revise the package for consistency.Ther's a conflict in project density classification.The
application states the project is low density,the supplement-EZ indicates it is high density, and
the narrative describes it as medium density. Notably,the program doesn't recognize "medium
density" as a permit type.
SREG Response: Package has been revised and all aspects should now reflect a low-density
classification.
2. Per 15A NCAC 02H.1042(2)(g)(ii):
a. Please provide dimensioned project boundary with bearings and distances. Please clearly
label the project area on the plans.
SREG Response: the project boundary for phase 1 is now clearly labeled with the correct
bearings and distances on the existing conditions plan sheet C-3.0.
3. Please correct the following issues with the application:
a. Section IV, 10
For low density,the total drainage area proposed is comprised only of an onsite
drainage area component, which is the total project area listed in the section IV.7.
Since only the property owned by the applicant can be used to calculate the
maximum allowed BUA, no offsite drainage area can be included.
SREG Response: Off-Site drainage has been removed from the application and is not
included in the projects BUA calculation.
ii. Please fill out the impervious area table with project impervious area information.
SREG Response:The impervious area table portion of the application is now filled
out.
4. Please correct the following issues with the supplement-EZ form:
a. Cover Page:
Line 7-8— Per 15A NCAC 02H.1017(10)the minimum required vegetated setback
width is 30 ft and must remain vegetated.
SREG Response: Lines 7-8 have been revised to reflect the information above.
b. Drainage Areas Page:
Line 1—Revise to "low"
SREG Response: Line 1 has been revised to reflect the information above.
ii. Line 2—Leave Blank
BUILD ON THE ROCK 1

G
LLC
STRONG ROC K STRONGROCK 83621 Six EForr s Rd.Suite P104
Raleigh, NC 27615
ENGINEERING GROUP Company License#P-2166
SREG Response: Line 2 on the drainage area page has been left blank.
iii. Line 3—Revise to "yes"
SREG Response: Line 3 has been revised to reflect the information above.
iv. Line 4—Revise to "1"
SREG Response: Line 4 has been revised to reflect the information above.
v. Once the above items are completed, click"Load Forms."This will generate the rest
of the supplement-EZ. Completely fill out the forms, do not leave them blank.
SREG Response: Load forms was clicked after inputting the revised information and
all subsequent pages have been filled out and included with this submittal.
5. Please correct the following issues with the calculations (Calculations are required per 15A NCAC
02H.1042(f):
a. The narrative states that the rational method was utilized to calculate the peak flow in the
swales, but this calculation could not be found. Please provide.
SREG Response:This calculation can be found in the summary table for permanent ditches
found on page 55 of the stormwater report.The equation used is Q=CiA and all 4 of the
variables of that equation can be found clearly labeled within the summary table.
b. Please indicate how the weighted rational coefficient(C value) is determined.
SREG Response:The C values for all ditches and pipes have now been included on their
respective summary pages within the stormwater report.A weighted average was used to
calculate each C value based upon the percentage of each drainage area a specific land use
covers. All reference C values for each land use were obtained from Tabel 1 in section B of
the stormwater manual.
c. Per part B of the manual, the Manning's n value for grass channel lining is 0.035. Please
indicate the source used for the 0.012 values.
SREG Response:The n value used in the grass channel calculations has been revised to 0.035
per the information above.
d. The rainfall intensity utilized in the pipe calculations is not consistent with the 5-minitue 25-
year intensity provided in the NOAA Atlas 14 rainfall data. Please provide time of
concentration calculations if a different duration was utilized. Please revise as needed.
SREG Response: 5-, 10-, and 25-year storm pipe calculations have been provided for pipe0l,
pipe02, and the existing off-site cross pipe. 25-year storm pipe calculations have been
provided for pipe03 and pipe04. All intensity values match those in the provided NOAA
rainfall data. All of the above-mentioned information can be found in the revised
stormwater report included in this submittal.
e. 15A NCAC 02H.1003(2)(c)(ii): Please provide the allowable velocity of the permanent liner
(assumed to be grass based on the plans) in order to demonstrate that the conveyances
have been designed to not erode during peak flow from the 10-year storm event.
SREG Response: Allowable velocity for the grass lined channels can now be found within the
table summary for the permanent ditches on page 55 of the stormwater report.
f. Please provide the sizing/design calculations for the riprap dissapators.
SREG Response: Due low velocities,the previously shown riprap dissapators have been
removed from the plans.
g. 15A NCAC 02H.1003(5): Please provide signed, sealed, and dated engineering calculations to
demonstrate that the outlets of the site have been designed to not erode downslope of the
discharge point during the peak flow from the 10-year storm event.
BUILD ON THE ROCK

G
LLC
STRONG ROC K STRONGROCK 83621 Six EForr s Rd.Suite P104
Raleigh, NC 27615
ENGINEERING GROUP Company License#P-2166
SREG Response: All outlet velocities have been provided within the signed and sealed
stormwater report and fall below the allowable velocity selected from Tabel 1 of section C-
11 of the stormwater manual.
6. Please correct the following issues with the O&M agreement form:
a. This project is applying for a low density permit however, "No" was selected for the low-
density category with "N/A" for the type. Filling these items out for the project and selecting
"load form" will result in the appropriate O&M agreement form being generated. Please
note that a complete O&M agreement form will have 2 or more pages and uses macros to
generate the relevant sheets based on the information entered into the cover page.
SREG Response:The information on the cover page of the O&M agreement has been
revised and the load form button clicked. All appropriate sheets(3 total) have been
provided in this submittal.
7. Please correct the following issues with the plans:
a. Please delineate the drainage areas to the proposed swales.This item is required per
section VI,8o of the application and 15A NCAC 02H.1042 (2)(g)(iv).
SREG Response:The swale drainage areas have now been delineated on sheet C-6.1 of the
plans provided with this submittal.They are also shown within the stormwater report.
b. Clearly specify the class and dimensions of permanent rip-rap-dissapators. (15A NCAC
02H.1003(5)).
SREG Response: Due low velocities,the previously shown riprap dissapators have been
removed from the plans.
8. 15A NCAC 02H.1003(7) and .1042(2)(k): Deed restrictions and protective covenants are required
to ensure the project will be maintained in perpetuity consistent with the approved plans and
specifications. Please provide a copy of the proposed deed restrictions and protective covenant
language along with a signed agreement to provide the final recorded versions.
SREG Response:The information requested above has been included with this submittal.
9. Please provide a response to comments letter indicating, in a point-by-point manner, how each
of the above comments has been addressed. This item is required per 15a NCAC 02H.1042(3)(b).
SREG Response:This letter will serve as the response to comments letter required.
10. Provide PDFs of all revisions, 2 hard copies of revised plan sheets, 1 hard copy of other
documents, and a response to comments letter briefly describing how the comments have been
addressed.
SREG Response: All the above items have been submitted to their respective places in a manner
that directly reflects the instructions provided.
Please let me know if you have any further questions.
Thank you,
Spencer Cashion
Strong Rock Engineering Group, PLLC
BUILD ON THE ROCK 3