SW6231103_Response To Comments_20240306

CurryENGINEERING
March 6,2024
Brianna Holland
Stormwater Engineer
NCDEQ
1612 Mail Service Center
Raleigh,NC 27699
RE: Godwin Subdivision,Cumberland County
Request for Additional Information
Stormwater Permit No.SW6231103
High Density—Wet Pond
Dear Brianna:
The purpose of this letter is to provide comment responses to comments that were provided to Curry
Engineering on February 6,2024. Below represents responses to comments.
1. Built-Upon Area
a.The sum of the BUAallocated to the individual lots in the deed restriction document is
equal to 348,000 SF whereas the Application,Supplement-EZ,and calculations use the
value 348,046 sf(Section VI,2&Section VIL Please revise as needed for correctness and
consistency.
This has been revised.
b.Please provide additional information clarifying the built-upon area for each impervious
per 15ANCAC 02H.1042(2)(f).Examples of ways to present this information
calculations,or clarification in the Supplement-EZ,Drainage Area Page,Line 22.The
main items needing to be clarification are category the pump station BUAis
accounted for and the difference between the"roof'and BUAon subdivided lots in
the Supplement-EZ.It is assumed that his difference is the driveways,but please
show that it is accounted for in one of the other.
See revised EZ form for additional impervious detail.
2. Confirm the drainage areas shown on the plans correspond to the actual drainage areas.
Note that drainage areas do not always correspond to property lines but are based on the
existing and proposed grades.Please revise package as needed.
The area is very flat. See updated calculations for clarification on impervious areas,
however,the overall drainage area to the pond is unchanged.
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a. Unless otherwise diverted,it appears off-site areas may drain to the SCM 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 15ANCAC 02H.1003(3Xb)).Full
build-out potential is determined by either having the property owner and
permittee enter into a legal agreement limiting the amount ofBUAand 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 SCMs 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). Please revise package as needed.
Off-site areas do not drain toward the site or pond.There is a ditch that conveys
drainage through the site in the existing draw and wetland,but the subdivision
does not affect this drainage system and it continues to drain through the
property.
3. General MDCs 8&9—It is noted that the maintenance access/easement is shown on the
plans,however,this easement must not include any slopes steeper than 3:1 (8b),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,currentlythe outlet/outlet protection is
not included in the easement).
This has been revised.
4. Wet Pond
a. Per General MDC 3,side slopes of SCMs stabilized with vegetated cover shall be
no steeper than 3:1.Portions of the side slopes appear to be steeper.Please
revise.
See revised slopes that are now no steeper than 3:1.
b. Per Wet Pond MDC 1,the volume of the main pools and the forebays should not
include the sediment storage zone since this portion of the pond is intended to be
filled up with sediment and can therefore not count towards provided storage
volume.Please revise the stage storage tables,associated volumes,and
calculations (such as average depth).Revise the Supplement-EZ accordingly.
This has been revised.
c. Please ensure that the forebay entrance is deeper than the forebay exit(Wet Pond
MDC 5b).The entrance and exit elevations should be indicated on the cross-
sectional view.NOTE:Aminimum of 6"of sediment storage must be provided for
the entrance and exit of the forebay,please refer to Figures 2 and 5 in Part C-3 of
the Manual.
This has been revised.See wet pond section.
d. 15ANCAC 02H.1042(2Xi)(i-ii)states that the following are required as part of a
planting plan:plant layout with species names and locations and total number and
sizes of all plant species.The plant a list of plant species was provided in the plan,
but the number and size of each of the species was not specified. Additionally,
woody shrubs were included on the shallow land plant list,and would not be
permissible for a wet pond per Wet Pond MDC 11 (b)
See updated planting plan with shrubs removed.The quantities are shown on
the planting plan detail sheet.
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5. Supplement-EZ
lx hard copy ofthe complete,original Supplement-EZForm is required per Sections V&
g 3 of the Application
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 15ANCAC 02H.1017(10),
the vegetated setback shall be at least 30 feet in width.3.
This has been revised.
b. Drainage Areas Page,Entire Site Column: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.
This has been revised.
c. Wet Pond Page—Line 6:Per the provided plans,the SCM appears to have a
retaining wall.Please revise.
This has been revised.
d. Wet Pond Page—Lines 43 &44:The depth of the forebayat the entrance is the
distance from the permanent pool to the excavated bottom of the forebay near the
entrance of the forebay.The depth of the forebay at the exit is the distance from
the permanent pool to the excavated bottom of the forebay near the exit of the
forebay
This has been corrected.
6. Calculations
a. Please verify the area of the bottom of the vegetated shelf used in the average
depth calculation(providing this information in the stage-storage table would
make verifying the calculations simpler in the future.)The bottom of the vegetated
shelf is 137.50.Per the provided stage storage table,the area of the 137.0 contour
is 22,788 SF,and the area of the 138 contour is 25,639 SF.The bottom of vegetated
shelf provided in the calculations appears to correspond to the 137.0 surface area.
Please revise.
This has been revised.
b. In the rip-rap calculations associated with FES100,a smaller pipe diameter was
used in the zone determination chart than what was shown on the plans.When
using a 48"diameter pipe,it appears that the appropriate zone would be Zone 3.
Please revise.
This has been corrected.
c. In the rip-rap calculations associated with HDWL200,a note stating that the
analyzed flow is half of total flow due to two culverts.The provided riprap
dimensions correspond to the dimensions shown on the plan,ensure that the
sizing of the riprap shown on the plans is appropriate for the flow from both
culverts.
This has been revised.
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7. The provided O&M Form is outdated and therefore incomplete.Please use the most up to
date form,which can be found on our website at the following address:
https://www.deq.nc.gov/about/divisions/energy-mineral-and-land-
resources/stormwater/stormwater-rogram/stormwater-design-manual(O&M EZ Form).
NOTE:It is recommended to get a second copy of this form signed&notarized for the
Applicant's records (it will be helpful when they go to record it with the Register of Deeds)
shown on the design plans. They will be recorded prior to approval of the site plan.
This form has been updated.
8. When uploading the response,ensure that the electronic repository is complete.The
documentation showing the LLC is an active corporation in good standing with the NC
Secretary of State and confirming the titles held by the person who signed the
application,was noted to be missing.
This information was included in the hard copy submittal but is now also included in the
electronic information as well.
9. Provide PDFs of all revisions,2 hardcopies of revised plan sheets,Application,and
Supplement-EZ, 1 hardcopyof other documents,and a response to comments letter
briefly describing how the comments haw been addressed.
Acknowledged.
Should you have any questions during your review of this site plan for construction drawings please
feel free to contact me. We sincerely appreciate your review of this project.
Sincerely,
The Curry Engineering Group,PLLC
tam/Xelfre „
Donald L.Curry,PE
President
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