SW6220202_Response To Comments_20221213

underfoot 1149 Executive Circle -Suite C-1 Cary, NC 27511
_ 919.576.9733 1 NCBELS C-3847
ENGINEERING
August 5, 2022
North Carolina Department of Environmental Equity
Division of Energy, Mineral and Land Resources - Stormwater Program
512 N. Salisbury Street, Office 640E
Raleigh, NC 27604
Re: Messer Parcels (HARNE-2022-060)
State Stormwater Permit No. SW622020
Plan Review # 1 Response Letter
Dear Mr. Farkas,
Please find comment responses to the review dated May 3, 2022 for the above reference project.
Staff comments from the staff reviews have been transcribed for ease of review. Comment
responses are shown in green below.
Comments
1. Application:
a. Section II, 5 - This project appears to be located within 5 miles of Harnett Regional
Jetport. Please revise.
This section has been updated appropriately to reflect this.
b. Section III, 4 - Please provide a point of contact for the local building permits. Please
revise.
This section has been updated with the appropriate information.
c. Section IV, 10:
i. Receiving Stream Name, Classification, & Index Number - These items do not
appear to be correct. Please use the map at the following address
(https://ncdenr.maps.arcgis.com/apps/webappviewer/index.html?id=6el25
ad7628f494694e259c80dd64265) to determine the name, classification, and index
number of the first classified surface water that runoff from this project area enters.
This section has been updated with the appropriate information.
ii. Total/On-site/Off-site Drainage Area - The drainage area to the proposed SCM
(451,962 sf) does not match the drainage area shown in the calculations & plans
(418,798 sf / 9.61 ac). Please revise as needed.
The drainage areas have been updated throughout the DA maps, sizing
spreadsheet, CN calcs and routing.
iii. Proposed Impervious Area (and Impervious Surface Area breakdown table) -
The BUA located within the drainage area shown here (166,442 sf) does not match
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Cary, NC 27511
919.576.9733 1 NCBELS C-3847
the BUA within the drainage area as shown in the calculations (169,978 sf). Please
revise as needed and ensure that the BUA breakdown (lower half of the table)
adds up to the proposed impervious area.
The drainage areas have been updated throughout the DA maps, sizing
spreadsheet, CN calcs and routing, as well as on the app.
iv. To Impervious Area - The To Impervious Area of the drainage area shown here
(36.87o) does not match the To Impervious Area of the drainage area as shown in
the calculations (40.597o). Please revise as needed.
The drainage areas have been updated throughout the DA maps, sizing
spreadsheet, CN calcs and routing, as well as on the app.
d. Section VI, 2 - Please revise to indicate that deed restrictions have been provided.
This section has been updated to reflect this.
2. Design:
a. Please provide a stage -storage table for the portion of both the main pool and forebay
below the permanent pool so that Wet Pond MDCs 1, 2, & 5a can be verified. NOTE: the
main pool and forebay of the wet pond are mutually exclusive and add together to form
the total permanent pool. NOTE: The sediment storage zone does not count towards the
volume of either the main pool or the forebay.
Stage -storage tables have been created and added to the calculations for both forebay
and main pool.
b. Wet Pond MDC 3 - Please show the top of the sediment storage zone for the main pool
on plan sheet C-600 (similar to how the top of the sediment storage zone is shown for the
forebay.
The sediment storage zone is now shown as requested.
c. Wet Pond MDC 4 - The location of the inlets and outlet are too close together and this
results in short-circuiting. Please increase the length of the flow path between the inlets
and outlets (This can be accomplished by moving the location of the inlets and/or outlets
and/or adding berms and/or baffles to the pond).
A berm has been added to the SCM to increase the flow path from the inlets to the outlet
as required. Refer to sheet C-600.
d. Wet Pond MDC 5a - Based on the provided information, it appears as though the
forebay may be larger than 207o of the main pool (main pool only, not combined
permanent pool) volume. This cannot be verified until the stage -storage tables for the
portions of the pond below the permanent pool are provided, but it appears to be the
case. Please revise as needed.
The stage -storage tables are now provided and the forebay has been modified to be less
than 207o of the main pool. It is +/- 197o.
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e. Wet Pond MDC 5b -The entrance of the forebay must be at a lower elevation than the
exit of the forebay. Please refer to Figure 5 in Part C-3 of the Manual for more information.
The bottom of the forebay should be deeper near the inlets than in the other parts of the
forebay. Please also include callouts in the cross-section on plan sheet C-600 indicating
the elevation of the forebay entrance and exit
The forebay has been adjusted to be deeper at the inlet locations and these callouts have
been added to sheet C-600 as requested.
f. General MDC 3 - Please place a label on the cross-section on plan sheet C-600
indicating the side slope(s) of the vegetated areas of the wet pond.
This label has been provided on the SCM # 1 - Wet Pond Cross Section. Refer to sheet C-
600.
g. General MDC 4 - Please provide calculations showing that the inlets to the wet pond
are protected from erosion. It is noted that the outlet calculations are provided in the
calculation book. While not required, you may wish to increase the elevation of the inverts
of the inlet pipes so that the sediment stored in the sediment storage zone is not
resuspended when water enters into the forebay.
These calculations have now been provided in the SIA as requested. Refer to sheet C-600
for the dissipator summary table. It is preferred to have the inlets under the normal pool for
aesthetics, as well as to have the water help dissipate the in -flow.
h. General MDC 8 & 9 - Please show the maintenance access & easement for the
proposed wet pond in the main set of plans.
SCM maintenance and access easement is now shown and labeled as requested. Refer
to sheets C-200 and C-600. The easement boundary is clearly shown on the portion
downstream of the dam and extends to property lines, lot lines, and R/W out side of that
back line.
3. Supplement-EZ Form:
a. Drainage Areas Page:
i. Please fill in the drainage area 1 column. The entire site column is an accounting
of the entire project area and the drainage area 1 column is an accounting of the
area draining to the wet pond. For the entire site column, the "drainage area" is
equal to the project area and Lines 19-21 are not required. The information in the
drainage area 1 column will correspond with the information shown in Section IV,
10 of the Application (once revised).
Comment noted. This column has been filled out appropriately as required.
ii. Lines 5-7 - Please express these values in square feet.
These values have been provided in square feet as required.
iii. Lines 8-21 - Please revise as needed in accordance with earlier comments.
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These lines have been revised accordingly.
1149 Executive Circle - Suite C-1
Cary, NC 27511
919.576.9733 1 NCBELS C-3847
b. Wet Pond Page:
i. Line 19 - As mentioned in a prior comment, please provide the stagestorage
tables for the portions of the main pool and forebay that are below the permanent
pool surface.
These tables are now provided as requested.
ii. Line 21 - As mentioned in a prior comment, please show the sediment storage
top elevation for the main pool in the plans so that this value may be verified.
This elevation is now shown on the plans as required.
iii. Line 26 - This value should only include the surface area of the main pool, not
the combined surface area of the main pool and forebay (permanent pool).
Please revise.
This cell has been updated appropriately as requested.
iv. Line 27 - This value should only include the volume of the main pool, not the
combined volume of the main pool and forebay (permanent pool). Please revise.
This cell has been updated appropriately as requested.
v. Line 28 - Please recalculate the average depth based on the prior two
comments.
This cell has been recalculated and updated appropriately as requested.
vi. Line 32 - As previously mentioned, the volume of the forebay appears to be too
large. Assuming that the volume of the permanent pool is 63,862 cf, this results in a
forebay volume of 12,490 cf (shown on this Line) and a main pool volume of 51,372
cf (63,862 cf - 12,490 cf) . 12,490 cf / 51,372 cf = 247o > 207o. Please revise.
This cell has been recalculated and updated appropriately as requested.
vii. Line 34 -The cleanout depth of the forebay is the distance from the permanent
pool surface elevation to the top of the sediment storage zone, expressed in
inches.
This cell has been recalculated and updated appropriately as requested.
viii. Line 35 - The design volume of the wet pond is the volume that can be held
above the permanent pool surface and below the bypass weir. Please revise.
This cell has been updated appropriately as requested.
ix. Lines 43 & 44 - As mentioned in a prior comment, the entrance of the forebay
must be at a lower elevation than the exit of the forebay. The depth value shown
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on these Lines is calculated as the distance from the permanent pool surface
elevation to the excavated bottom elevation of the forebay at either the entrance
of the forebay (Line 43) or the exit of the forebay (Line 44).
These cells have been recalculated and adjusted appropriately as requested.
4. While it is not required, it is recommended to increase the BUA limit per lot. Currently, this amount
is set at 2,100 sf per lot and this includes any BUA located within the lot (house, driveway, garage,
patios, sheds, walkways, sidewalks, etc...). NOTE: This will require the SCM to be resized and the
submittal materials will need to be updated.
Comment noted. While the BUA limit is relatively low, we are unable to increase this number based
on BUA percentage requirements of the Town of Coats. Additionally, the developer and builder
are aware of the limit and the product planned for this neighborhood will (be required to) fall
within the per lot limits.
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.
These items are provided with this submittal as required.
I am hopeful that your comments have been adequately addressed and approval of this project
is forthcoming. If you have questions or concerns, please contact our office at 919.576.9733.
Respectfully:
Landon M. Lovelace, PE
Principal
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