SW6230705_Response To Comments_20240604

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June 4, 2024 ���� '
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NCDEQ Division of Water Quality civil engineering I land surveying
Attn:Jim Farkas
512 N. Salisbury Street e
Raleigh, NC 27604
RE: Serenity Subdivision Ph 3-5, Harnett County, North Carolina
Permit No. SW6230705
Jim,
We received the request for additional information dated May 29, 2024. We are resubmitting
the plans for Serenity Subdivision Ph 3-5 with the comments addressed as noted below.
1. Original Comment 6—"...Please ensure that the design calculations for the
curb outlet swale reflect the proposed,permanent site conditions. Please revise
as needed."The provided Vactual and flow depth values shown in the
Supplement-EZ Form reflect the temporary E&SC matting and not the
permanent vegetated cover(see attached). Please revise as needed.
o Supplement Low Density Tab has been updated.
2. Supplement-EZ Form,Wet Pond Page, Lines 43&44—The provided forebay
depths for each of the wet ponds do not appear to be correct. For example,for
Wet Pond 12(attached),the permanent pool is at elevation 312.5',the forebay
entrance is at elevation 305.59', and the forebay exit is at elevation 307.0'.The
depth of the forebay is measured from the permanent pool to the bottom of the
forebay. For the forebay entrance,this value would be equal to 82.9" (312.5'—
305.59' =6.91' =82.9") NOTE: 89" is shown. For the forebay exit,this value
would be equal to 66" (312.5'—307.0' =5.5' =66") NOTE: 73" is shown. Please
revise as needed for each SCM. NOTE: See later comment with regard to
forebay bottom elevations.
o Each of the pond forebays was looked at and updated.The callout
elevations for the forebay entrance and exits have been updated in the
sections and all forebay data is updated in the supplement.
3. Please update the information on the wet pond design page of the O&M
Agreement Form so that it is consistent with the other submittal items. For
example,for Wet Pond 12,the temporary pool surface elevation is shown as
313.98' (shown as 313.86'elsewhere),the forebay cleanout depth is shown as
4.5'=54" (shown elsewhere as 66"),the forebay sediment removal elevation is
shown as 308' (shown as 307'elsewhere), and the forebay bottom elevation is
shown as 306.5' (shown as 307'elsewhere). Please revise as needed for each
SCM.
o O&M has been updated.
4. Wet Pond MDC 3—Per the MDC,the forebay is required to have at least 6"of
sediment storage provided over its bottom. Per the provided cross-sectional
view,the forebay exit is shown to be at elevation 307.0' (NOTE:The plan
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appears to indicate that the exit is at elevation 306.5', however the callout
indicates 307.0', see attached)and the sediment cleanout is shown to be at
elevation 307.0' (resulting in zero inches of sediment storage for this part of the
forebay).This issue also appears to be present for Wet Pond 13, 15, &16. Please
revise as needed.
o All sections have been updated to accurately call out the entrance and
exit elevations at the forebays.All forebays have 0.5' or more of
sediment storage. It is sometimes difficult to position the cross section
such that it depicts ALL of the pond information accurately graphically.
This is improved in this submittal but may not be perfect in all cases.The
callouts are 100%accurate.
Please provide the following:
- lx hard copy& lx electronic copy of the revised pages of the Supplement-EZ Form.
- lx hard copy& lx electronic copy of the revised pages of the O&M Agreement Form.
- 2x hard copies & lx electronic copy of the revised plan sheets.
- lx hard copy(2x hard copies for plans) & lx electronic copy of any items needed to
address these comments.
https://edocs.deq.nc.gov/Forms/SW-Supplemental-Upload
Two copies of the revised plans sheets are enclosed as well as a copy of the revised calculations,
supplement form and application.This data has also been uploaded as requested. If you have
any questions or comments, please contact me at your earliest convenience.
Sincerely,
Scott Brown, PE
[e-mail]
Enclosure
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