SW3220306_Response To Comments_20230216

LandDes*n.
CREATING PLACES
THAT MATTER.
June 24, 2022
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 LID PN 1020233
Stormwater Permit No. SW3220306
Dear Mr. Jim Farkas,
Wet Pond Design:
a. General
Wet Pond MDC 5b — per this MDC, the forebay entrance must be deeper than the forebay
exit. Per the provided pond cross -sections, this appears to be the case (The forebay bottom is
shown with a slope and the deeper portion of the forebay near the entrance), but it is not clear
on the cross-section (Only a single forebay bottom elevation is provided and it is unclear if
this elevation refers to the entrance or the exit of the forebay). Please either add elevation
callouts for both the forebay entrance must be deeper than the forebay exit and specifying
whether the provided bottom elevation refers to the entrance or exit.
LDI Response: Forebay bottom elevations at entrance and exit called out.
Offsite portions of the drainage area to an SCM must be accounted for at their full build out
potential (15A NCAC 02H .1003(3)(b)). This can be accomplished by having the permittee
and off -site property owners enter into a legal agreement limiting the amount of BUA and
drainage area that can drain to the permitted system or the off -site area can be accounted for
at 100% BUA (its full build out potential). It is recommended to bypass off -site drainage
around the SCMs (so it doesn't have to be accounted for), but if it is not, it must be accounted
for. Please also make sure that the off -site portions of the drainage area are accounted for in
the table in Section IV, 10 of Application and in the Supplement-EZ Form.
LDI Response: Offsite areas have been accounted for at 100% BUA or full build out potential.
iii. Supplement-EZ Form, Wet Pond Page:
1. Line 2 — This Item is requesting the minimum required treatment volume for the SCM,
not the size of the drainage area (For example, per the calculations, the minimum
design volume for Wet Pond 1 is 18,580 cf).
LDI Response: Minimum required treatment volume has been updated.
LANDDESIGN.CDM

2. Line 8 — All of the proposed wet ponds appear to have outlet structures and emergency
spillways that would allow flows in excess of the design volume to bypass the SCM.
LDI Response: All Wet Ponds have been updated, confirming an overflow or bypass feature.
Line 26 — The combined permanent pool surface area for each wet pond was provided
for this item, however, this item is only asking for the main pool surface area which does
not include the surface area of the forebay. NOTE: Wet Pond MDCs 1, 2, &5a refer to
only the main pool, not the combined permanent pool, the forebay surface area/volume
should not be included when meeting these MDCs.
LDI Response: Surface area has been revised to only account for main pool.
4. Line 27 — Similar to the prior comment, this item is only asking for the volume of the
main pool, not the combined permanent pool (do not include the forebay).
LDI Response: Volume has been revised to only account for main pool.
5. Line 28 — Please recalculate these values based on the corrected main pool values.
LDI Response: Average depth of main pool has been recalculated with corrected values.
6. Line 34 — The cleanout depth of a forebay is the distance from the permanent pool
surface elevation to the top of the sediment storage zone in the forebay.
LDI Response: Cleanout depth has been revised.
Line 43 & 44 — The depth of the forebay is the distance from the permanent pool surface
elevation to the excavated bottom of the forebay. NOTE: the depth of the forebay near
the entrance must be deeper than the depth of the forebay near the exit.
LDI Response: Forebay depth has been revised.
b. Wet Pond 1:
The provided stage -storage table for the forebays starts at elevation 566.0', however, the
provided cross -sectional view of the wet pond indicates that the top of the sediment storage
zone is at elevation 570.0' (the sediment storage zone is not considered when determining
the provided volume of the forebay).
LDI Response: Cross-section forebay label has been revised to correct elevation of 566.0'.
Based on the prior comment, the actual provided forebay volume (provided between the top
of the sediment storage zone and the permanent pool) is approximately 4,350 cf. This results
in a forebay that is less than 15% of the main pool volume (4,350 cf / 45,122 cf = 9.6%) which
does not meet Wet Pond MDC 5a.
LDI Response: The combined forebay volume for Wet Pond 1 is 3,531 cf + 4,328 cf = 7,859 cf,
according to the Stage Storage Calculations table. This results in a combined forebay that is
(7,859 cf / 45,122 cf = 17.4%) 17.4% of the main pool volume.
LANDDESIGN.CGM

iii. Due to the proximity between FES-111 and the outlet structure, flow from this inlet appears to
short-circuit the wet pond. Please increase the length of flow from FES-111 to the outlet (this
can be done by moving the inlet, moving the outlet, adding berms/baffles, or a combination of
these options). Placing the inlets and outlets too close together does not allow for a sufficient
amount of time for the TSS to settle out, thus short-circuiting the wet pond.
LDI Response: Outlet has been relocated to be further from FES-111. Distance between the two
structures has been increased.
c. Wet Pond 2:
i. The provided forebay is larger than 20% of the provided main pool volume (4,641 cf / 19,756
cf = 23.5%) which does not meet Wet Pond MDC 5a.
LDI Response: Forebay has been revised. New forebay volume is 3,999 cf. New main pond
volume is 20,418 cf (3,999 cf / 20,418 cf = 19.6%).
d. Wet Pond 3:
i. The provided forebay is larger than 20% of the provided main pool volume (14,740 cf / 60,927
cf = 24.2%) which does not meet Wet Pond MDC 5a.
LDI Response: Forebay has been revised. New forebay volume is 12,584 cf. New main pond
volume is 63,261 cf (12,584 cf / 63,261 cf = 19.9%).
ii. Due to the proximity between FES-346 and the outlet structure, flow from this inlet appears to
short circuit the wet pond. Please increase the length of flow from FES-346 to the outlet (this
can be done by moving the inlet, moving the outlet, adding berms/baffles, or a combination of
these options).
LDI Response: Outlet has been relocated to be further from FES-346. Distance between the two
structures has been increased.
e. Wet Pond 5:
i. The provided forebay is larger than 20% of the provided main pool volume (11,514 cf / 54,794
cf = 21%) which does not meet Wet Pond MDC 5a.
LDI Response: Forebay has been revised. New forebay volume is 10,966 cf. New main pond
volume is 55,343 cf (10,966 cf / 55,343 cf = 19.8%).
f. Wet Pond 6:
i. The provided forebay is larger than 20% of the provided main pool volume (7,398 cf / 34,701
cf = 21.3%) which does not meet Wet Pond MDC 5a.
LDI Response: Forebay has been revised. New forebay volume is 6,121 cf. New main pond
volume is 35,783 cf (6,121 cf / 35,783 cf = 17.1%).
2. It appears as though some of the plans (such as plans C104-208 &C500+) are not signed (Section VI,8
and 15A NCAC 02H .1042(2)(g)). Please provide signed copies of the applicable plans.
LDI Response: All sheets submitted have appropriate signatures.
LANGGESIGN.CGM

3. There appears to be an issue with the BUA amounts shown in Section IV, 10, the Supplement-EZ Form,
and/or the Deed Restriction Document. Adding up the BUA allocated to the individual lots in the Deed
Restriction Document results in a total of 1,325,240 sf of BUA which is larger than the total amount of
BUA shown to be in the entire project (entire site column of the Supplement-EZ Form). Please revise as
needed. Please also provide the BUA per lot allocation table as an excel spreadsheet (please email this
to me instead of uploading it).
LDI Response: Application, Supplement-EZ Form, and Deed Restriction document updated to match 100%
BUA buildout. One lot did get removed so BUA SF has been adjusted.
4. Please ensure that the SCM maintenance access and easements are sufficiently large to allow for
access and maintenance to the entire SCM (General MDCs 8 & 9). The entire footprint of the SCM
system must be included in the access and maintenance easement, plus an additional 10 ft or more (25
ft is recommended for wet ponds due to the nature of their maintenance requirements) around the SCM
to provide enough room to complete maintenance tasks. This SCM system includes the side slopes,
forebay, riser structure, SCM device, and basin outlet, dam embankment, outlet, and emergency
spillway.
LDI Response: SCM easements have been adjusted to include all SCM system components.
5. In order to meet Runoff Treatment, the net increase in BUA must be captured and treated in one or
more SCMs. The BUA associated with lots 130, 131, & part of 132, part of the street in front of these
lots, parts of the trail, etc... is not being captured and treated. Please demonstrate that the uncaptured
BUA is less than or equal to the existing BUA (i.e., the net increase in BUA is being captured and
treated), reconfigure the design to capture and treat the net increase in BUA, or permit the portions of
the project that do not drain to the SCMs as a low -density area (provided that it meets the low -density
requirements).
LDI Response: BUA associated with lots 130, 131 & 132, parts of the street and sidewalk have been
included in the drainage area for BMP 6. Calculations revised for this BMP. There are no proposed trails in
this drainage area to be included in the BUA.
6. The proposed asphalt trail appears to be located within the vegetated setback from the on -site surface
waters. Please either demonstrate that this BUA meets one of the exemptions outlined in 15A NCAC
02H .1003(4)/.1017(12) or reconfigure the design so that this BUA is not located within the vegetated
setback.
LDI Response: Asphalt trails are a requirement of the rezoning documents which are regulated by the Town
of Waxhaw and Union County. These municipalities are requiring the trails and material in the locations
depicted on the plans.
7. Please correct the following issues with the Application:
a. Section II, 4a — This project requires an E&SC permit. Please indicate this on the Application and
provide the relevant information.
LDI Response: E&SC permit will be permitted through Town of Waxhaw and not NCDEQ.
LANGGESIGN.CGM

b. Section IV, 6 — Please include the on -site surface water area (there are multiple surface waters
located on -site).
LDI Response: Total surface water area has been provided
c. Section IV, 7 —The provided project area seems small. I measured the provided project area on
one of the provided PDFs and it was closer to 100 ac than 70 ac (This also makes sense since the
project area takes up most of the 124 ac property whereas 70 ac would only take up about half of
the property area). Please ensure that this value is correct and that the project area is accurately
reflected on plans.
LDI Response: Total property area and total project area have been revised.
d. Section IV, 10:
i. Please ensure that the off -site portions of the drainage areas are accounted for.
LDI Response: Off -site drainage areas have been accounted for.
ii. The "On -site Buildings/Lots" item corresponds to Line 9 of the Drainage Areas Page of the
Supplement-EZ Form (see later comment) and refers to the BUA allocated to the individual
lots. The other items (street, parking, etc...) refer to the common BUA not allocated to the
individual lots. Please revise as needed.
LDI Response: BUA quantities have been revised in Supplement-EZ form.
8. Please Correct the following issues with the Supplement-EZ Form:
a. Cover Page:
i. Line 4 — Please include the on -site surface water area (there are multiple surface waters
located on -site).
LDI Response: Project area and surface water area revised.
b. Drainage Areas Page
i. General:
1. Line 5, 7, & 11 — Please ensure that the off -site portions of the drainage areas are
properly accounted for.
LDI Response: Off -site drainage areas have been accounted for.
2. Line 9 — This item should only include BUA that is allocated to the individual lot (it
should not include any common BUA such as the BUA associated with the roadways).
LDI Response: Individual lot BUAs have been revised.
3. Line 10 — This item should include all of the common BUA not allocated to the individual
lots.
LDI Response: Common BUA has been added to line 10.
LANGGESIGN.CGM

4. Line 12 — These items are a breakdown by type of the common BUA not allocated to the
individual lots. The sum of these items should equal line 10. NOTE: "Roof' BUA does
not refer to the individual homes (since the BUA allocated to the individual lots is
already accounted for in Line 9), the same also applies to driveways, sidewalks, etc...
that are covered under the Deed Restriction Document.
LDI Response: "Roof' BUA has been removed. Common BUA listed in Line 12 now sums up
to quantity listed in Line 10.
5. Lines 15 & 17 — Please be sure to include any existing BUA in order to get credit for it.
LDI Response: There is no existing BUA on site.
ii. Entire Site Column:
1. The Entire Site Column is an accounting of the entire project area (similar to how the
drainage area columns are an accounting of the drainage areas), not just a sum of the
drainage area columns. All BUA located on -site (whether it drains to an SCM or not)
should be included in this column.
LDI Response: Additional BUA not located within existing wet pond drainage areas added to
Entire Site column.
2. Line 5-7 — The "drainage area" of the entire site is equal to the project area.
LDI Response: Entire site "drainage area" has been revised.
3. Line 18 — This item should correspond to Section IV, 8 of the Application. Revise either
as needed.
LDI Response: Overall BUA percentage has been revised on application.
c. Wet Pond Page:
i. Please see earlier comments.
LDI Response: Items on Wet Pond Page have been addressed and 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.
Sincerely,
Mason Greeson, PE for LandDesign, Inc.
Director
LANDDESIGN.CGM