SW6230807_Response To Comments_20231205

I-I FA
HARRISON FRENCH
& ASSOCIATES, P 1.I.C
5 December 2023
Brianna Holland
Environmental Engineer
DEMLR Post-Construction Stormwater Program
512 North Salisbury Street,Raleigh,NC 27604
RE: Request for Additional Information
Stormwater Permit No.SW6230807
Love's Travel Stop (Store 412)
Harnett County
Dear,Brianna:
We are writing this letter in response to the comments provided about the above project.
1. Consistency
a. The Project Area listed in the Application Section IV,7 and Supplement-EZ,Cover,Line 2 should be
the same. The project area has been revised on all forms.
b. Per Sheet C7.7,the post-development drainage area is 9.63 ac,but the drainage area utilized in the
calculations provided was 9.55 ac.The drainage area for the project has been recalculated and
verified.All reports and forms have been revised to show the corrected area of 9.55 ac,
c. The O&M Wet Detention Pond Summary states that the permanent pool elevation is 238,but the
Supplement EZ states that the permanent pool is at an elevation of 239. The permanent pool
elevation is 239 and these forms have been revised accordingly.
d. Please ensure the electronic repository is complete.The appendixes to the calculations were not
provided electronically that were submitted as a hard copy.Acknowledged.
2. Supplement-EZ
1x original Supplement-EZ Form and 1x hard copy with the following corrections made: (This item is
required per Sections V&VI,3 of the Application)
a. Drainage Areas,Entire Site,Line 21:The Rational Method is not a calculation method for the design
volume,it is a method for calculating peak flow.The calculation method that coordinates with the
minimum required treatment volume provided is the Simple Method(Schueler 1987),which was
found in the calculations. The Simple Method was used to calculate the required volume for the
proposed SCM. The Rational Method was used to calculate the peak runoff and discharge of the
SCM.Please refer to the revised Drainage Report for calculations and procedures.
b. Drainage Areas,Drainage Area 1,Lines 4-11,Lines 15-21:Please fill out.These lines are important
for confirming the drainage areas and BUA that is directed to the SCM and used in the sizing
calculations.These items were unable to be reviewed and therefore,comments may be made in
future submissions on these items. This information has been added to the EZ form.
Note:The"Entire Site"column is intended for the drainage area of the project area.The Drainage
Area 1 column is intended for the drainage area that will be treated by the SCM.Acknowledged.
c. Drainage areas:Please clarify in the"Additional Information"if the 21,100 SF of"Other"is the access
road,or if there is additional"Other"BUA. This row has been updated. The area for the existing
gravel road has been added row 15 and row 12"Other"has been updated to show the pond
surface area.
d. Wet Pond,Line 1:The Drainage Areas page of the Supplement-EZ has drainage area columns labeled
"entire site"and"1,2,3,4,etc."corresponding to the number of SCMs.This line is to identify which of
the columns from the previous page is being referenced.In this case,this should be filled in as"1."
This has been revised.
Harrison French &Associates, PLLC www.hfa-ae.com
1705 S. Walton Blvd, Suite 3, Bentonville, Arkansas 72712 p 479.273.7780 Page 1 of 3

e. Wet Pond,Line 21:This would imply 8 ft of sediment storage and does not correspond to the plan
sheet. The sediment storage elevations have been revised.
f. Wet Pond,Line 25:The elevation of the temporary pool is set by the lowest bypass above the
drawdown orifice,which seems to be 240.25 per the cross section and provided calculations,please
clarify. The elevation of the Temporary Pool has been revised and is concurrent with the Pond
Plan and Profile.
g. Wet Pond,Line 34: Please include. This information has been added.
h. Wet Pond,Line 37: Please include. This information has been added.
i. Wet Pond,Line 54:A planting plan is required for the vegetated shelf per 15A NCAC 02H.1042 (2)(i).
This has been corrected.
3. Calculations:
lx signed,sealed,and dated hard copy of calculations with the following corrections made:(This item is required
per Section VI, 7 of the Application)
a. Provide engineering calculations demonstrating the inlets of the wet pond are designed to protect
the SCM from erosion resulting from stormwater discharges.The outlets of SCMs shall be designed so
that they do not cause erosion downslope of the discharge point during the peak flow from the 10-
year storm event.Rip-rap apron sizing calculations should be provided,and the class and dimensions
of the rip-rap aprons should be specified on the plans. The outlet as well as the inlets for the SCM
are being protected from erosion using Riprap Aprons. These aprons were sized using Chapter 6
of NC Erosion and Sediment Control Planning and Design Manual as well as the Municipal
Stormwater Management book(Debo&Reese,2nd Ed,pg. 695-698)and FHWA's Hydraulic
Design of Energy Dissipators for Culverts and Channels.Refer to Appendix H for calculations.
b. Per the Supplement-EZ,the bottom of sediment storage for the main pool is 231.Using this area in
the stage storage table overestimates the volume that will be stored within the main pool. It is
unclear what the storage elevation for the forebay is,so this comment may apply to the forebay stage
storage calculations as well.If 231.5 is the bottom of the pond/top of sediment elevation for the main
pool,please provide the surface area at this elevation so that volume calculations can be verified.A
separate Plan and Profile for each Forebay has been prepared and provided. The Drainage
Report has been updated to show the Stage-Storage information for each of the Forebays.
4. Plans
2x hard copies of revised sheets of the plans with the following corrections made:
(This item is required per 15A NCAC 02H.1042(2)(a)and per Section VI,1 of the Application)
a. The information shown in the Application,Supplement-EZ Form,and calculations should be
verifiable on the plans in the field without the use of a computer.You may wish to add a BUA table to
the plans or provide additional dimensions for easier verification of BUA. 15A NCAC 02H.1042 (2)
(g) (v).A new plan sheet"C7.8 SCM IMPERVIOUS AREA MAP"has been prepared. This sheet shows
a table for all the impervious areas draining to the proposed SCM,these areas have been color
coded for each type of surface.
b. Every SCM shall be accessible for maintenance and repair.Per 15A NCAC 02H.1050 8 and 9,
maintenance accesses shall:have a minimum width of ten feet;not include lateral or incline slopes
that exceed 3:1 (horizontal to vertical);and extend to the nearest public right-of-way.The entire SCM
shall be shown and labeled within the easement,including the emergency spillway.The 3ft block wall
around the perimeter of the SCM could provide issues with accessing the wet pond for maintenance.
A new 20ft access easement has been added near the SW corner of the property. This easement
will provide access to the SCM from the closest public ROW.In addition,a set of 6-steps have
been added at the north end of the pond to provide access for maintenance into the SCM.
c. Per 15A NCAC 02H.1042 (2) (h) (i),the plan details shall include labeled side slopes and a
benchmark for clean-out. This information has been added to the revised Pond Plan and Profile,
sheet C7.9.
d. Please include the drawdown orifice that sets the permanent pool in the details per 15A NCAC 02H
.1042 (2) (h) (ii). The drawdown orifice and outlet information have been added to the plans,see
sheet"C9.3 SITE DETAILS 2".
Harrison French&Associates,PLLC www.hfa-ae.com
1705 S.Walton Blvd,Suite 3,Bentonville,Arkansas 72712 p 479.273.7780 Page 2 of 3

e. Per Wet Pond MDC 5 (b),the forebay entrance shall be deeper than the forebay exit. The forebay
design has been revised to provide this requirement Flow from the pond inlets will flow from
west to east,deeper to shallower,for both forebays.
5. 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.
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:
Brianna Holland
512 N.Salisbury Street,Office 640E Raleigh,NC 27604
ii. For USPS:
Brianna Holland
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.
While not required to be addressed,the following was noted:
• A drawdown orifice should have a turned-down elbow in order to prevent trash or other material
floating on the surface from clogging the pipe.The drawdown orifice will have a"hooded"trash
screen/rack to prevent clogging.
• Emergency overflow spillways should be designed with hardened materials to prevent structural
failures.The Emergency Spillway will be protected by Turf Reinforcement Mats.
• The Application Section II 1b- la states that this project is"new"and not a"modification to an
existing state stormwater permit."Therefore,do not select"not started"because this means that this
application was a modification to an existing permit where the construction was not started. This
has been corrected.
Sincerely,
• 05.ae 2023
Diego Garcia P.E.,CFM
Civil Engineer
Harrison French&Associates,PLLC www.hfa-ae.com
1705 S.Walton Blvd,Suite 3,Bentonville,Arkansas 72712 p 479.273.7780 Page 3 of 3