SW6230603_Response To Comments_20240510

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May 10, 2024 civil engineering I land surveying
NCDEQ Division of Water Quality
Attn: Jim Farkas
512 N. Salisbury Street
Raleigh, NC 27604
RE: Storm water resubmittal, Aberdeen US 15-501 Dollar General, Hoke County, North
Carolina
Jim;
We received the review comments per email dated May 2, 2024. The comments have
been addressed as noted below.
- Plans:
o It appears that only 1 x hard copy of the revised plan sheets were provided (2x
are required per 15A NCAC 02H .1042(2)). Please ensure that we have 2x hard
copies of the plans. 2 hardcopies of the full plan set are enclosed.
- Calculations/SCM Design:
o As shown in the calculations,the minimum required surface area for the SCM is
10,627 sf. Per the stage-storage table (and as measured on the plans),the
cross-sectional area of the SCM at the bottom elevation (346.3 ft) is 10,354 sf
(which is less than the minimum required surface area). NOTE:The calculations
indicate that a bottom surface area of 10,753 sf is provided which does not
appear to be accurate. Please also include the minimum required surface area
equation in the calculations (only the values that go into the equation are
provided). Please revise as needed.The basin has been increased.The bottom
of the basin is 11,166 sf.The calculations have been updated to match the new
bottom surface area of 11,166 sf.The calculation for the minimum surface area
is embedded into the spreadsheet. Equation 2 from the Infiltration System
chapter was used.The equation has been shown as requested.
- Supplement-EZ Form:
o Drainage Area Page:
• Drainage Area 1, Line 6—The provided value(61,168 sf)does not
correspond to the on-site portion of the drainage area to the SCM as
shown in the Application (62,818 sf). Please revise as needed. NOTE:
The on-site&off-site portions of the SCM drainage area should add up
to the total drainage area. 62,818 sf is correct.Value has been updated.
• While not required for this project, it is recommended to remove the off-
site area/BUA component from the entire site column as the entire site
column is an accounting of the entire project area (and off-site areas are
t
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not a part of the project area). Offsite BUA has been removed from the
Entire Site column as recommended.
o Infiltration Page:
■ Line 29—The provided value(346.0 ft) does not correspond to the
bottom elevation indicated in the plans (346.3 ft). If you are considering
the bottom of the SCM to be the bottom of the 4" of clean sand provided
within the footprint of the SCM, please indicate this in the additional
information section (Line 46). Please revise as needed. Value has been
updated to show 346.30'.
■ Line 30—The provided value(346.33 ft) does not correspond to the
ponding surface elevation associated with the design volume (346.63 ft).
Please revise as needed.Value has been updated to 346.60.
■ Line 31 —The provided value(346.0 ft) does not correspond to the invert
of the bypass device indicated in the plans (346.63 ft). Please revise as
needed.The data entered into the spreadsheet cell is 346.60(same as
column 30). However,the spreadsheet is programmed to round and
don't have access to the spreadsheet to modify the formula. I have also
noted this in the additional information area.
■ Line 33—This value should correspond to the cross-sectional area of the
SCM at the elevation indicated in Line 30(346.63 ft).The provided value
(10,753 sf) is larger than the cross-sectional area of the SCM at elevation
346.8 ft(10,690 sf per the stage-storage table).The cross-sectional area
for this item should be closer to 10,570-ish sf. Please revise as needed.
The value has been updated based on the enlarged basin.
■ Line 44—The provided value(2,924 cf)does not correspond to the
design volume shown in the calculations(3,188 cf). Please revise as
needed.Value has been updated per new calculations
■ Line 45—Please provide calculations showing how this value was
determined and revise as needed. (Based on the minimum required
surface area calculation,the provided SCM configuration would take
more than 72 hours to draw down). Please revise as needed. The draw
down calculation is included. Equation#2 is used for the drawdown.The
drawdown can be computed from the minimum surface area equation.
The minimum surface area has a safety factor of 2 with a maximum
drawdown time of 72 hrs.Therefore,the compute drawdown time is in
agreement with the surface area required.
Please provide the following:
- Enough hard copies of the revised/most recent plan sheets so that we have 2x hard
copies (if you need to revise the 2/1/24 version of a plansheet provide 2x copies, if you
don't need to revise it, provide 1x hard copy(since we currently have 1x hard copy of
the 2/1/24 sheets)). 2 full plan sets enclosed
- 1x hard copy& 1x electronic copy of the revised calculation pages. done
- 1x hard copy& 1x electronic copy of the revised pages of the Supplement-EZ Form.
done
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- lx hard copy(2x hard copies for plans) & lx electronic copy of any items needed to
address these comments. done
I look forward to working with you on this project. If you have any questions or
concerns, please contact me at your earliest convenience.
Sincerely,
4D Site Solutions, Inc
Scott Brown, PE
[e-mail]
Enclosure
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