SW6231104_Response To Comments_20240221

PARAMO uNTE
E N G 1 N E E R 1 N G . INC PaPe 1 of 3
February 21,2024
Attn:Brianna Holland
NCDEQ-DEiti1I,R
512 N.Salisbury Street,Office 6251'
Raleigh,NC 27604
postconstru c tion(a)deq.nc.gov
RE: Request for Additional Information
Stormwater Permit No. SW6 231104
Tractor Supply Store—West End—Moore County
Dear Ms.Holland,
On behalf of West End Development Group,LLC,we are submitting a response to your comments emailed
at 5:51pm from [e-mail] on the statutory 90th day of the standard review. Please find
your comments listed below with our response provided in bold. In addition,due to the development of the
design,a few changes have occurred from the original design documents. Some grading has been adjusted and
storm drainage upstream of IIW-100 has been shifted over to the curb. A new storm table is provided,and the
two driveway culverts and swales were added for offsite drainage bypass flow. This project will install the
driveway culverts and swales as proposed to carry the offsite water. The plans have been revised per the
comments and to include the existing conditions and site plan. Sheets SV-1 and S-1 thru S-3 are included for
the permit file. The rules do not indicate you need water,sewer,erosion control,or other sheets,but grading,
drainage,and site plans along with respective details. If we need additional information.please let us know
upon your completeness check,
1. Please ensure that the off-site portions of the drainage areas to the SCMs are correctly accounted
for at their full build-out potential(per 15A NCAC 02H.1003(3)(b)). Full build-out potential is
determined by either having the property owner and permittee enter into a legal agreement
limiting the amount of BUA and drainage area being directed from the off-site area to the SCM or
by assuming that the off-site area is 100%BUA,its full build-out potential.It is recommended to
bypass off-site drainage areas around proposed SCI\Is as the permittee has no control over how
off-site areas are developed(which is why they are required to be accounted for at their full build-
out potential).Indicate which option is being pursued,and revise the package as necessary.See
additional information on this item at the conclusion of this letter.
RESPONSE: Offsite areas have been bypassed with DOT ROW drainage swales
and two driveway pipes. The swales and the driveway culverts as part of the
driveways off NC 211 and NC 73 will be installed through this project. The
Drainage Area has been reduced from 285,000sf to 221,500sf and calculations
have been revised. See DA-Map and Sheet S-3.0.
2. Consistency:
a.The Bl A provided in the design calculations is different than what is provided in the
Supplement-EZ and Application.28,000 SF+22,200 SF+5,000 SF= 55,200 SF< 139,300 SF.
RESPONSE: The BUA has been revised to 139,300sf from the original 155,300sf
which included 16,000sf of DOT roadway pavement.
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b.Per the provided riprap calculations,the minimum apron width the outlet end for HW 200 is
12 ft,but 10 ft was provided in the details.
RESPONSE: Revised the detail to show 12-ft of apron width on Sheet S-3.0.
3. Application
a.Section I,4—Please verify the coordinates of the project.Note that the application requests this
in degrees,minutes,seconds format.When entering the location,it appears that the coordinates
provided are for a South Carolina location.
RESPONSE: Revised the coords. to 35°14' 28.92" and 79°33' 55.76".
b. Section II, 1, 2—Please till in.
RESPONSE: Revised the SWU-101.
c.Section III,2a—Provide all property owners,per Moore County GIS and the provided ALTA
survey,the property owners are Southern Golf and Land,LLC and lames D.Williams.
RESPONSE: Revised the SWU-101 to include both Southern Golf and James
Williams on page 2 of the application.
d.Section IV,10—For the Impervious Surface Area Table,ensure that the total(sf)is the sum of
the rows above.
RESPONSE: Revised the SWU-101 according to the revised BUA per Item #2
above.
4. Supplement-EZ
a. Cover Page—Line 7-8:While there is no surface water,and therefore no vegetated setbacks
associated with this project,please fill in.Per 15A NCAC 02H.1017(10),the vegetated
setback shall be at least 30 feet in width.
RESPONSE: Revised the Supplement Cover Page.
b.Drainage Areas Page,Entire Site Column: Please complete.The drainage area,BUA,etc.of the
entire site column should refer to the total project drainage area,not only the drainage area to the
SCM.
RESPONSE: The Entire Site Column is filled in that includes the total site area
of 6.14 acres (267,458 sf).
c.Infiltration System—Line 46:Line 20 indicates that the type of pretreatment is"other,"please
clarify here,
RESPONSE: Pretreatment 'Other' is explained in the comments at the bottom—
catch basin sumps will be a part of every box on site. See notes on Sheet S-2.0
and S-3.0 for the 12" sump in the storm drainage structures.
5. Plans
a. Provide the complete cross-section view of the infiltration basin detail per 15A NCAC 02H
.1042(2) (h) so that all\[DC requirements can be verified.
RESPONSE: Cross-section expanded on Sheet S-3.0.
b.Per 15A NCAC 02H.1042(2) (g) (vi) and General MDCs 8&9,maintenance and access
easements must be shown on plans.This easement must not indude any slopes steeper than 3:1
(8b),must extend to the nearest public right-of-way(8c),and include the entire SCM footprint
(see guidance under MDC 9 in Part C-0 of the Manual).
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RESPONSE: Access Maintenance Easement shown on the plans that connects
to the NC 73 right-of-way and covers the entire infiltration basin. See Sheet S-
1.0.
6. Calculations
a.Verify the drawdown calculations.The calculations seem to indicate that drawing down to the
586 contour takes more time than drawing down to the bottom contour.
RESPONSE: The spreadsheet had an error. We have checked the drawdown
using alternative equations and Equation #2 below. The Darcy Equation
drawdown is 1.60 days (39 hrs). The time-volume drawdown calculation
resulted in 1.78 days. The minimum surface area was met per the Equation
below in part b. In addition, the stage-area-storage was added for clarity and
revised with a curving of the basin contours to better reflect the construction
conditions.
b. Part C-1 of the Manual recommends using the equation SA=FS* (DV*12)/(K*T)where: SA
=required minimum surface area of infiltration system(ft2) FS=factor of safety(minimum
of 2 is recommended)DV=design volume(ft3)K=hydraulic conductivity of soil(in/hr)T
=maximum dewatering time(72 hours).
Although some infiltration will likely occur from the sides of an infiltration system,the DEQ
recommends sizing the infiltration system's bottom surface area per this equation and
considering infiltration from the sides as a factor of safety.A factor of safety is crucial in
infiltration system design due to the following:
•The inherent uncertainty in soil testing;
•The likelihood that the soil will be compacted during construction,which can reduce soil
infiltration rates by more than an order of magnitude;and
•The likelihood that sediment will enter the infiltration system after it is constructed and
diminish the infiltration rate.If the system does not drain within 72 hours throughout its
operational life,then it will be out of compliance with this MDC.
RESPONSE: The minimum surface equation has been calculated in the
spreadsheet and found to be less than the provided. Provided surface area is
2,850 sf> 1,687 sf min. from the equation referenced above.
7. When uploading the response,ensure that the electronic repository is complete. Plan sheets
showing required information per 15-k NCAC 02H.1042 were not provided,only the grading
sheet and stormwater detail sheet were provided, and the soils investigation was not provided.
RESPONSE: Existing Conditions (SV-1) and site plan (S-1.0) included as part of
the stormwater permit. In addition, the soil report from ECS for the infiltration
testing and seasonal high-water measurements is included.
If you have any questions regarding any of this information or require additional material,please feel free to call
or email in advance of the approximate May 20th response time.
Sincerely,
Paramounte Engineering, Inc.
J.Branch Smith E
Cc:Gavin Melia,West End Development Group
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