SW6231205_Response To Comments_20240416

MORRIS & RITCHIE ASSOCIATES OF NC, PC . + _
• 171 • —/ • M
AN AFFILIATE OF MORRIS&RITCHIE ASSOCIATES, INC.WHICH
PROVIDES ENGINEERING,ARCHITECTURE, PLANNING, SURVEYING&
LANDSCAPE ARCHITECTURE THROUGHOUT THE MID-ATLANTIC REGION
Department of Environmental Quality
Division of Energy, Mineral, and Land Resources
225 Green Street, Suite 714
Fayetteville,NC 28301
Subject: Gardner Farms (SW6231205)
MRA Project: 22234
State Stormwater Response to Comments
Dear Jim Farkas:
We have received your review comments for the above referenced project dated March 27, 2024,
and made the changes as requested. Please find the updated plan set and response to comments
letter enclosed. The review comments are listed below and have been addressed as follows:
1. Please include the required vegetated setback from the existing on-site pond(surface
water) in the main set of plans in accordance with 15A NCAC 02H.1042(2)(g)(iii).
The existing on-site pond has been deemed non jurisdictional by the USACE and will be filled
in. A copy of the Notification of Jurisdictional Determination has been provided in this
resubmittal.
2. The provided drainage area map to the SCMs indicates that a portion of the existing on-
site pond is located within the SCM drainage area, which is not possible. Please revise the
drainage area map to accurately reflect the drainage area boundary to the SCMs. This
item is required per 15A NCAC 02H.1042(2)(g)(iv).
The drainage area maps have been revised per comment direction. See sheets C8.1-C8.2.
3. Please include the required SCM maintenance accesses and easements in the main set of
plans in accordance with 15A NCAC 02H.1042(2)(g)(vi) and General MDCs 8 & 9.
SCM access easements have been extended to encompass the tie in slope and outlet pipes of
the SCM's and extends to the Public R/W.
4. There appears to be a mismatch between the BUA information entered into the
Application/Supplement-EZ Forms and as shown in the calculations. For example,for SCM#2,
the BUA accounting as shown in the Application/Supplement-EZ Form indicates 189,705 sf of
BUA allocated to the individual lots, 21,040 sf of sidewalk BUA and 57,368 sf of roadway BUA
(189,705 sf+ 21,040 sf+ 57,368 sf= 268,113 sf). The calculations indicate a total of 333,421 sf
of BUA within this drainage area. Please revise as needed for consistency. NOTE: "Contingency"
BUA, as shown in the calculations, can be included in the Application/Supplement-EZ Form as
"Future"BUA. NOTE: The total BUA within the drainage area to the SCM should be able to be
calculated from the BUA information from the other BUA types as shown in the
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Re: Gardner Farms(SW6231205): Response to Comments Letter
April 16, 2024
Page 2 of 7
Application/Supplement-EZ Form (for example, the total BUA should be the sum of all of the
applicable types of BUA shown on the form).
The supplement-EZ Forms and Application have been revised to ensure all numbers match
what is shown in the calculations. See the revised forms and calculations provided in this
resubmittal.
5.
a. When calculating the volume of the main pool or forebay, the storage volume
provided in the sediment storage zone should not be included. For example, if the
excavated bottom of the main pool is at elevation 273.5'and the minimum 6"of
sediment storage is provided, the "bottom"of the main pool,for calculation
purposes, would be at elevation 274.0'since the "storage"provided between
elevations 273.5'and 274.0'is reserved for sediment storage (See guidance under
MDC 3 in Part C-3 of the Manual). Please revise as needed.
The grading for the SCM's have been revised to show an additional 0.5 feet for sediment
storage; but the SCM calculations will exclude this in the stage-storage tables and begin 0.5
feet higher than the bottom of the sediment storage elevation.
b. Please clearly indicate the elevation of the top of the sediment storage zone in the
cross-sectional view of the wet ponds and ensure that the contours in the plan view
extend to the excavated bottom of the wet pond. This item is required per Wet Pond
MDC 3 and per 15,4 NCAC 02H.1042(2)(h)(i).
The SCM cross sectional views have been revised to show the sediment storage zone. See
sheets D4.1 and D4.4.
c. The provided stage-storage tables for the wet pond forebays do not go all the way
up to the permanent pool. For example,for Wet Pond#1, the forebay stage-
storage table maxes out at elevation 263.0'whereas the permanent pool surface
elevation for Wet Pond#1 is at elevation 263.5'. Please revise as needed.
The stage-storage tables have been revised to ensure the max elevations match throughout
both SCM's.
d. Per the design, it is unclear if the drawdown orifices used will be 2.5"or 3.0"in
diameter. The notes on the outlet structure detail for each SCM reference both
values. Please revise as needed.
The outlet structure detail for each SCM has been revised to reflect the actual size of the
drawdown orifice. SCM A will have 3 inch orifice and SCM B will have a 2.5 inch orifice.
e. Wet Pond#1 —Plan sheet D4.2 indicates the "total plantings provided is 1,000"
which is less than the minimum number of plants required per Wet Pond MDC 11 b
(and less than the number that are shown to be provided). Please revise as needed.

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Re: Gardner Farms(SW6231205): Response to Comments Letter
April 16, 2024
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The planting plan for Wet Pond 1 (SCM A)has been revised per comment direction. See Sheet
D4.2.
f As designed, the wet ponds appear to short-circuit. Short-circuiting is prohibited
per Wet Pond MDC 4. Please increase the flow length between the inlets and
outlets to better utilize the wet ponds. If berms or baffles will be added to increase
the flow path, they must extent to at least the temporary pool surface elevation.
Please revise as needed.
Berms/ spillways have been added to the forebay berms in both SCMs to increase the flow
length and prevent the SCM from short circuiting. See sheets D4.1 and D4.4.
6. Please correct the following issues with the Supllement-EZ Form
a. Cover Page:
i. Line 2— This value should correspond to Section IV, 7 of the Application (it
should not include the on-site surface water areas).
EZ form has been revised to match the Application.
ii. Line 3—Pleas include all of the on-site surface areas. This value should
correspond to Section IV, 6 of the Application.
EZ form has been revised to match the Application.
iii. Line 7—Please refer to 15A NCAC 02H.1017(10)for this value. Please
revise the plans as needed to ensure that the minimum required vegetated
setback from surface waters is being provided.
Vegetated buffers have been revised to be 30 feet per section 15A NCAC 02H .1017(10).
b. Drainage Area Page
i. Entire Site Column:
1. Please note that the entire site column is an accounting of the entire
project area, not necessarily a sum of the other provided columns.
All of the on-site BUA, whether it drains to an SCM or not, should
be included in this column and, typically, there are no off-site
components to this column (since off-site areas are not part of the
project area).
Entire site column has been revised per comment direction.Please note that we are capturing
most of the BUA, so some of values may be a summation of columns one and two.
2. Please note that Lines 19-21 are not required for this column.
Lines 19-21 have been revised per comment direction.

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Re: Gardner Farms(SW6231205): Response to Comments Letter
April 16, 2024
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3. The total amount ofBUA allocated to the individual lots (Line 9)
does not correspond to the total amount ofBUA allocated to the
individual lots as shown in the Deed Restriction Form. Please
revise as needed.
Total BUA allocated to each individual lot shall be 5,000 SF and has been revised on Line 9.
ii. SCM Drainage Area Columns:
1. DA 1 —Per 15A NCAC 02H.1003(3)(b), any off-site areas that are
not bypassed around the SCM must be accounted for at their full
build-out potential. Full build-out potential is determined by having
the property owners enter into a legal agreement limiting the
amount of drainage area and BUA draining from the off-site area to
the SCM, or by assuming that the off-site area is 100%BUA, its full
build-out potential. Please revise as needed.
The offsite area flowing towards SCM A will not be bypassed; moreover, SCM A has been
redesigned with the assumption that this offsite area will be 100% BUA. Please see sheets
D4.1-D4.6 and Appendix G3 of the Stormwater Report for the revised plans and calculations.
2. DA 2, Line 20— The design volume of a wet pond is the volume that
can be stored between the permanent pool surface elevation and the
invert of the lowest bypass device. Per the plans, the lowest bypass
device is the weir with invert of 280.5'. Please revise as needed.
The design volumes of both SCMs have been revised per comment direction.
3. General—Please ensure that all of the new BUA is fully accounted
for(there is more BUA shown on Line 8 than is shown in all of the
other lines combined). Please revise as needed.
The BUA has been revised as needed per prior comments/revisions.
c. Wet Pond Page:
i. Wet Pond 1:
1. Line 6—Per the plans, there appears to be an engineered side slope
(headwall) near the SCM outlet.
Line 6 has been revised to show that there will be a Headwall in SCM A.
2. Line 55—Please indicate that this SCM has two drawdown orifices.
NOTE:It is recommended to include one larger drawdown orifice
as opposed to two smaller drawdown orifices.
Line 55 has been revised to explain that SCM A will have two 2.5" drawdown orifices.

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Re: Gardner Farms(SW6231205): Response to Comments Letter
April 16, 2024
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ii. Wet Pond 2:
1. Line 2— The provided value, 9,010 cf, does not appear to be
correct. Please revise as needed. The minimum required treatment
volume is calculated based on the drainage area to the SCM and
the design storm depth using either the Simple or Discrete NRCS
Curve Number Method.
Line 2 has been revised to match SCM B's calculation spreadsheet.
2. Line 26— The provided value, 22,267 sf, does not correspond to the
value shown on the stage-storage table, 26,098 sf. Please revise as
needed.
Line 26 has been revised to match SCM B's calculation spreadsheet.
3. Line 35—See earlier comment with regard to the design volume of
the SCM.
Line 35 has been revised per prior comments.
4. Line 40—See earlier comment with regard to the design volume of
the SCM, Since the design volume is changing, the drawdown
calculations will need to be revised.
Line 40 has been revised per prior comments.
iii. General:
1. Line 8— This item is required per General MDC 5.
Line 8 has been revised per General MDC 5.
2. Line 20—Per the plans, the lowest excavated bottom elevation of
the main pool for Wet Pond 1 is 257.5'and for Wet Pond 2 is
273.5'. Please revise as needed.
Wet Pond 1 has been graded down to 257.0' to account for 0.5' of sediment storage, and Wet
Pond 2 has been graded down to 273.0' to account for 0.5' of sediment storage.
3. Line 21 —Please indicate the top of the sediment storage zone on
the cross-sectionalview of the SCMs. NOTE: The top of the
sediment storage zone (Line 21) must be at a higher elevation than
the bottom of the sediment storage zone (Line 20) and must be at
least 6"higher (per Wet Pond MDC 3).
The SCM cross sectional views have been revised to show the sediment storage zone. See
sheets D4.1 and D4.4.

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Re: Gardner Farms(SW6231205): Response to Comments Letter
April 16, 2024
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4. Line 25—See earlier comment with regard to the design volume of
the SCM. The temporary pool surface elevation is determined by the
invert of the lowest bypass device.
Line 25 has been revised per prior comments.
5. Line 27—See earlier comment with regard to the sediment storage
zone and excluding it from the main pool volume.
Line 27 has been revised per prior comments.
6. Line 28—revise this calculation per the prior comment.
Line 28 has been revised per prior comments/revisions.
7. Line 32—See earlier comment with regard to the sediment storage
zone and excluding it from the forebay volume.
Line 28 has been revised per prior comments.
8. 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.
Line 34 has been revised to accurately represent the depth of the forebays.
9. Line 37—See earlier comment with regard to the orifice diameter.
Decimal values cannot be entered into this cell so if the orifice
diameter is 2.5",please indicate this information in the additional
information section (Line 55).
Line 37 has been revised per prior comments and an explanation of SCM B's orifice has been
provided in line 55.
10. Line 42—Berms and baffles provided to increase the flow length
through the wet pond must extend up to at least the temporary pool
surface elevation.
Berms/ spillways have been added to the forebay berms in both SCMs to increase the flow
length and prevent the SCM from short circuiting. See sheets D4.1 and D4.4.

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Re: Gardner Farms(SW6231205): Response to Comments Letter
April 16, 2024
Page 7 of 7
11. Lines 43 & 44— The depth of the forebay is measured from the
permanent pool to the excavated bottom of the forebay near either
the entrance or exit. Per Wet Pond MDC 5b, the bottom of the
forebay near the entrance must be deeper than the bottom of the
forebay near the exit and per Wet Pond MDC 3, there must be at
least 6"of sediment storage provided above the bottom of the
forebay (near the exit). See Figure 5 in Part C-3 of the Manual for
more information.
Line 43 & 44 has been revised to accurately represent the depth of the forebays.
12. Line 48—Per the detail, there is a downward curved elbow, the
purpose of which is to drawdown from below the permanent pool
elevation.
Line 48 has been revised to show that there will be a downward curved elbow.
13. Line 53—Specify the type of turfgrass that will be planted on the
dam and embankments on this form and on the plans.
Hybrid Bermuda has been added to line 53 and has been called out on the plan sheets.
Thank you for your consideration of this resubmittal. Please do not hesitate to contact us
directly at(984) 200-2103 or at [e-mail] with any questions you
may have.
Sincerely,
Morris &Ritchie Associates of NC, PC
Edgar Rodriguez-Diaz
DirectI984-200-2103
[e-mail]
CC: Jeremy Keeny, PE, PLS