SW3220702_Response To Comments_20230703

LandDesign.
CREATING PLACES
THAT MATTER.
June 23, 2023
Jim Farkas
Environmental Engineer
North Carolina Department of Environmental Quality
Division of Energy, Mineral, & Land Resources—Stormwater Program
512 N. Salisbury Street
1612 Mail Service Center
Raleigh, NC 27699-1612
RE: Preserve at Forest Creek Phase 2
Stormwater Permit No. SW3220702
Dear Mr. Jim Farkas,
1. Prior Comment 2.e,— "Please provide the surface area of Zone 3 of the planting plan..."While the
surface area of the vegetated shelf for Wet Pond 7 was provided on the plans, the provided plant
density is inadequate to meet Wet Pond MDC 11b. Per the plans, the vegetated shelf area is shown as
1,992.6 sf and a total of 481 plants (161 + 160 + 160 =481)are proposed. This yields only 48.28 plants
per 200 sf of vegetated shelf area whereas the MDC requires 50 plants per 200 sf of shelf area. Please
revise.
LDI Response: Wet Pond 7 planting revised.
2. Prior Comment 5a—"The Supplement-EZ Form indicates that the BUA within the drainage area to this
SCM is 119,763 sf(2.75 ac)while the calculations show 2.49 ac. Please revise as needed."There
appears to be a discrepancy between the drainage area and BUA information shown in the
Supplement-EZ Form and as shown in the Application Form. Please revise as needed.
Value Application Supplement-EZ Form _
Drainage Area 521,855 sf 521,848 sf
On-site Drainage Area 260,931 sf 260,924 sf
Off-site Drainage Area 260,924 sf 260,924 sf
New BUA 93,360 sf 88,932 sf _
On-site Lots BUA 51,765 sf 47,337 sf
LDI Response: All pond information on Supplement-EZ form and Application have been revised.
3. Prior Comment#8— "There appears to be issues with the BUA accounting as shown on the Supplement-
EZ Form. For example, adding up the per lot BUA allocation from the Deed Restriction Form results in
1,645,153 sf of BUA while the Supplement-EZ Form only shows a total of 1,473,718 sf of BUA for the
entire site. Please revise as needed."This issue was not resolved,the Deed Restriction document still
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appears to show that the amount of BUA allocated to the individual lots is greater than the amount of BUA
shown for the entire project area in the Supplement-EZ Form (Entire Site Column, Line 8), which is not
possible since all of the BUA allocated to the individual lots(plus the common area BUA)must be included
within the project/entire site area. Please note that the Entire Site Column is an accounting of the entire
project area and all of the BUA located within the entire project area,whether or not these areas drain to
an SCM. Please also note that BUA allocated to the individual lots in the Deed restriction document
should not be double counted in the Application/Supplement-EZ Form. BUA either is allocated to the
individual lots (whereby it is listed on the"On-site Buildings/Lots"line of Section IV, 10 of the
Application/Line 9 on the Drainage Areas Page of the Supplement-EZ Form)or it is common BUA(listed
on the other lines of Section IV, 10 of the Application/Lines 10& 12 on the Drainage Areas Page of the
Supplement-EZ Form). Please revise as needed. Please also email me an Excel spreadsheet of the BUA
allocation table from the Deed Restriction document so that the BUA amounts may be added up/verified
quickly.
LDI Response: BUA allocation revised and corrected on corresponding documents.
4. Prior Comment 9biii— "Lines 25&35..."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(typically
a weir in the outlet structure). For example,for Wet Pond 7,the plans indicate that the permanent pool
surface elevation is at 644.0'and the invert of the lowest bypass is at elevation 646.3'. Per the provided
stage-storage table, approximately 62,000 cf of storage volume can be provided between elevations
644.0' &646.3'. This is the volume that should be reported on Line 35 and used to calculate the drawdown
time of the pond.The invert of the lowest bypass device should be used to set the temporary pool surface
elevation (Line 25). NOTE: While design volumes in excess of the minimum required treatment volume
are acceptable, the pond and drawdown orifice should be configured in such a manner that allows both
the minimum required treatment volume and design volume to be drawn down within the stipulated 2-5
day window per Wet Pond MDC 7.This isn't strictly specified in the rules, but it does prevent wet ponds
from being too oversized for their drainage area.All of the proposed wet ponds, except for Wet Pond 10,
appear to allow both the minimum required treatment volume and design volume to drawdown within the
2-5 day window. It is recommended to slightly reduce the size of the drawdown orifice or reconfigure the
weirs in the outlet structure for Wet Pond 10 to allow the minimum required treatment volume and design
volume to drawdown within the 2-5 d.
LDI Response: Lines 25 and 35 of the Supp-EZ form have been revised.All wet ponds now drain
within 2-5 days.
5. Prior Comment 9bviii—"Lines 43 &44—The depth of the forebay is measured from the permanent pool
surface elevation to the excavated bottom of the forebay."The values provided in the Supplement-EZ
Form do not appear to be correct. For example,for Wet Pond#9, the permanent pool surface elevation is
at 654.0',the excavated bottom of the forebay near the entrance is at elevation 649.17',and the
excavated bottom of the forebay near the exit is at elevation 649.5'.The depth of the forebay at the
entrance (Line 43)is equal to 58" (654.0'—649.17' =4.83' =58")whereas 50"is shown.The depth of the
forebay at the exit(Line 44)is equal to 54"(654.0'—649.5' =4.5' =54")whereas 44" is shown. Please
revise these values for all of the wet ponds as needed.
LDI Response: Lines 43 and 44 of the Supp-EZ form have been revised.
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6. Prior Comment 12—"Provide PDFs of all revisions..."Submittal items,such as revised plansheets(from
the 1/20/23 revision), revised calculations(1/20/23), revised supplement-EZ Form (1/27/23), and the
revised O&M Agreement Form (2/9/23)were not electronically uploaded. Please upload these electronic
files(electronic files are required per 15A NCAC 02H .1042(2)).
LDI Response: PDFs from previous submittal uploaded.Will upload new revised documents as
well.
7. Off-site components were added to the drainage areas for SCMs 9, 10, 11, & 12. Off-site areas are
portions of the drainage area to the SCM that are located outside of the project area (the provided
drainage area maps do not appear to indicate the amount of off-site drainage area to the SCMs as is
shown in the Application and Supplement-EZ Form). Any off-site areas that are not bypassed around
the SCM must be accounted for at their full built-out potential per 15A NCAC 02H .1003(3)(b). The full
build-out potential of an off-site area can either be limited 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 (more information
can be found following these comments). Please revise as needed
LDI Response: Off-site drainage areas revised to show assumed 100% BUA. Off-site drainage
areas called out on drainage sheets.A permanent ditch has been proposed along the northeast
perimeter of the site to divert offsite drainage around BMP-12 and into the existing stream.
8. Please correct the following issues with the Wet Pond Page of the Supplement-EZ Form:
a. Line 40— Please recalculate these values in accordance with the earlier comment.
b. Lines 25, 35, 43, &44—See earlier comments
LDI Response: All relevant lines on the wet pond page of the Supp-EZ form have been revised.
9. 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.
LDI Response: Noted. Revised plans will be uploaded as well as hard copies sent.
a. PDFs must be uploaded using the form at:
https://edocs.deq.nc.gov/Forms/SW-Supplemental-Upload
b. Hard copies must be mailed or delivered to the following address:
i. For Fed Ex/UPS:
Jim Farkas
512 N. Salisbury Street, Office 640M
Raleigh, NC 27604
ii. For USPS:
Jim Farkas
1612 Mail Service Center
Raleigh, NC 27699-1612
iii. Hand Delivery:
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Please reach out to me prior to hand delivering a submission to make sure that I (or someone
else in my group)will be able to receive the submission. Do not leave the packaae in the
foyer with the security auard.
NOTE: Hard copies should to be sent to a Regional Office. Doing so will delay the review
process and the submission package may be lost while being sent from the Regional Office to
me in the Central Office
Sincerely,
Frank McMahan, PE for LandDesign, Inc.
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