HomeMy WebLinkAboutSW3210301_Add Info_20210609ROY COOPER
Governor
DIONNE DELLI-GATTI
Secretary
BRIAN WRENN
Director
Matthew S. Kiker, PE
1020 Euclid Avenue
Charlotte, NC 28203
NORTH CAROLINA
Environmental Quality
June 9, 2021
Subject: Request for Additional Information
Stormwater Permit No. SW3210501
Cresswind — Phase 3
Union County
Dear Mr. Kiker:
The Division of Energy, Mineral and Land Resources (DEMLR), received a Stormwater
Management Permit Application for the subject project on May 5, 2021. A review of that
information has determined that the application is not complete. The following information is
needed to continue the stormwater review:
1. Please indicate that, in addition to being a high -density project, this project drains to an
off -site stormwater system (Section II, 2). I understand that the form says to "select one"
however both are being utilized by this project so both should be selected.
2. Please indicate that a portion of this project area will be draining to an off -site SCM,
Pond 3 in Phase 2 (Section IV, 1).
3. Please list the number of drainage areas for this project as 2 (Section IV, 9). The first
drainage area will be the drainage area to Pond 4 and the second drainage area will be the
portion of this project area (Phase 3) that drains to Pond 3 (from Phase 2). Do not include
the entire drainage area to Pond 3, only the portion of the drainage area to Pond 3 that
corresponds to Phase 3 (The "off -site drainage area" portion of the Pond 3 drainage area
in the Phase 2 submission will correspond to the "second" drainage area in this Phase 3
submission).
4. As noted above, please include the portion of this project (Phase 3) that will drain to the
off -site (Phase 2) SCM (Pond 3) as its own drainage area (Section IV, 10).
5. The impervious area information for drainage area 1 does not appear to add up correctly
(Section IV, 10). The "On -site Buildings/Lots" refers to the BUA that is allocate to the
individual lots. "On -site Streets" refers to the BUA associated with streets (roadways,
D E Q�� North Carolina Department of Environmental Quality I Division of Energy, Mineral and Land Resources
512 North Salisbury Street 1 1612 Mail Service Center I Raleigh, North Carolina 27699-1612
NORTH CAROLINA _
Depar ntofEnvimnmmdlDwllry 919.707.9200
curb & gutter, etc...) that is not located on the subdivided lots. "On -site Parking" refers
to the BUA associated with parking (parking lots, driveways, etc...) that is not located on
the subdivided lots (For example, the portion of the driveway that is located on a
subdivided lot would be counted under "On -site Buildings/Lots" and would count against
a lots BUA limit). "On -site Sidewalks" refers to the BUA associated with sidewalks that
is not located on the subdivided lots (Like with the "On -site Parking" any sidewalks that
are located on a subdivided lot be counted under "On -site Buildings/Lots" and would
count against a lots BUA limit). All of the impervious area listed in the lower table
should add up to the "Total" (i.e, do not "double count" impervious areas in this table)
and the "Total" should match the "Proposed Impervious Area" in the upper table.
6. Please dimension the project area (Phase 3) boundary with bearings and distances in the
main set of plans (Section VI, 8i).
7. Please identify and dimension all BUA for this project (Section VI, 8j). The information
shown in the application and Supplement-EZ Form should be verifiable from the plans.
8. Please place a note on the main set of plans stating the identity of the person that made
the wetland determination (Section VI, 8m).
9. Please delineate the drainage area to the proposed SCM (Pond 4) and the on -site areas
that will drain to the off -site SCM (Pond 3 of Phase 2) (Section VI, 8o).
10. Please ensure that maintenance accesses and easements are clearly shown on the plans
and extend to the nearest public right-of-way (General MDCs 8 & 9). It was noted during
review that the roads associated with this project will be private roads.
11. The following issues were noted with the design/calculations for the proposed wet pond.
These issues prevented the design from being reviewed in its entirety, but I reviewed
what I could.
a. The drainage area used in the water quality calculations (19.87 ac) does not match
the drainage area used in the post -development drainage calculations (19.86 ac).
Please revise for consistency.
b. The impervious area within the drainage area is shown as 13.54 ac in the water
quality calculations, 13.52 ac in the post -development drainage calcs, 18.41 ac
(802,000 sf) in Section IV, 10 of the Application, and either 13.54 ac or 13.25 ac
in the Supplement-EZ Form (depending on how it is calculated since Line 8 does
not equal the sum of Lines 9 & 10).
c. The stage -storage information for the main pool and forebay starts at elevation
564.5 whereas the plans indicate that the top of the sediment storage zone is at
elevation 563.5.
d. The cross -sectional area of the main pool at the permanent pool elevation used in
the average depth calculation ("SA Designed @ Elevation") incorrectly includes
the surface area of the forebay (Wet Pond MDC's 1 & 2 are for the main pool
only).
e. The cross -sectional area of the main pool at the bottom of the vegetated shelf used
in the average depth calculation ("Area of wet pond at the bottom of the shelf')
does not match the value provided in the stage -storage table (16,789 sf).
f. It is recommended to interpolate the SAIDA value from the table for situations
where the calculated average depth and/or percent impervious cover do not
exactly match the table values. If you do not wish to interpolate, you can use the
more conservative values shown in the table (Rounding down the average depth
to the nearest whole number and rounding the percent impervious cover up to the
nearest 10%). Either way, the SAIDA value used is too small and as a result, the
provided surface area of the main pool is too small.
g. Plan sheet C3.30, both the forebay entrance and exit are shown at elevation 563.5.
Per Wet Pond MDC 5b, the forebay must be deeper at the entrance than at the
exit.
h. The stage -storage table for the temporary ponding zone appears to be incorrect.
For example, the depth shown between elevation 568 and 569 is shown as 0.5 ft.
It appears as though the contour elevations are incorrectly labeled, but it is
unclear.
12. Please correct the following issues with the Supplement-EZ Form:
a. Drainage Area Page:
i. Please complete the "Entire Site" column. This column should be an
accounting of the entire site (the "drainage area" of this column is the
project area). Any BUA located on the site (whether it drains to an SCM
or not) should be included in this column.
ii. Line 2 — As mentioned earlier, please include the portion of this project
that drains to an off -site SCM (Pond 3 in Phase 2) as a drainage area.
iii. Line 12 — This line is a breakdown of the BUA that will be located in the
common areas (i.e., not located on the subdivided lots). The sum of these
items should add up tolbe shown on Line 10.
iv. Line 9 — This line shows the BUA that will be allocated to/located on the
individual lots. For the entire site column, this value should equal the per
lot BUA (as shown in the deed restriction document) multiplied by the
number of lots in this phase.
v. Line 8 — This item should be the sum of both the BUA on subdivided lots
(Line 9) and the BUA outside of subdivided lots (Line 10).
b. Wet Pond Page:
i. Line 5 — Please include this item. Per the MDCs, the typical maximum
allowable side slope is 3:1.
ii. Line 20 — This value (564) does not match the excavated bottom elevation
of the main pool as shown on plan sheet C3.30 (563.0).
iii. Line 21 - This value (564.5) does not match the top elevation of the
sediment storage zone of the main pool as shown on plan sheet C3.30
(563.5).
iv. Line 25 — The elevation of the surface of the temporary pool should be
based on the design volume (47,842 cf) and should be above the
permanent pool surface elevation (568).
v. Line 28 — Per Wet Pond MDC 2, the average depth of the main pool of a
wet pond must be at least 3.0 ft.
vi. Line 34 — The cleanout depth of the forebay is the distance between the
permanent pool elevation and the top of the sediment storage zone in the
forebay.
vii. Line 43 — The depth at the forebay entrance is the distance between the
permanent pool elevation and the excavated bottom of the forebay near the
entrance.
viii. Line 44 - The depth at the forebay exit is the distance between the
permanent pool elevation and the excavated bottom of the forebay near the
exit.
13. Please correct the following issues with the O&M Agreement Form:
a. Per the plans, the proposed wet pond does not appear to incorporate a vegetated
filter strip (a vegetated filter strip is typically located downstream of the outlet
structure and is different than the vegetated shelf).
b. The temporary pool elevation for both the forebay and main pool appears to be
incorrect. This value should be based on the design volume and should match
Line 25 of the Wet Pond Page of the Supplement-EZ Form.
c. The sediment storage elevation item should be the elevation of the top of the
sediment storage zone in the forebay and main pool. The provided values (both
561) appear to be lower than the lowest excavated part of the pond per plan sheet
C3.30.
d. The bottom elevation item should be the lowest excavated elevation (i.e., bottom)
of the forebay and main pool. The provided values (both 560.5) appear to be
lower than the lowest excavated part of the pond per plan sheet C3.30.
e. The cleanout depth should recalculate based on the other values, but if it does not,
it is the distance between the permanent pool elevation and the sediment storage
elevation in feet.
14. It is recommended to include an emergency spillway for the proposed wet pond (The
cross-section on plan sheet C3.30 shows an emergency spillway, but the plan view does
not appear to have one).
15. 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.
a. Pdfs must be uploaded using the form at:
https:,[/edocs.deq.nc.gov/Forms/SW-Supplemental-Upload
NOTE: This is a new link. The online form has been updated.
b. Hard copies must be mailed or delivered to the following address:
i. For FedEx/UPS:
Suzanne McCoy
512 N. Salisbury Street, Office 640K
Raleigh, NC 27604
ii. For LISPS:
Suzanne McCoy
1612 Mail Service Center
Raleigh, NC 27699-1612
Please note that this request for additional information is in response to a preliminary review.
The requested information should be received by this Office prior to July 9, 2021, or the
application will be returned as incomplete. The return of a project will necessitate resubmittal
of all required items, including the application fee. Please reference the State assigned project
number SW3210501 on all correspondence.
If you need additional time to submit the information, please submit your request for a time
extension to the Division at the contact below. The request must indicate the date by which you
expect to submit the required information. The Division is allowed 90 days from the receipt of
a completed application to issue the permit.
The construction of any impervious surfaces, other than a construction entrance under an
approved Sedimentation Erosion Control Plan, is a violation of NCGS 143-215.1 and is subject
to enforcement action pursuant to NCGS 143-215.6A.
If you have any questions concerning this matter please feel free to contact me at
Jim.Farkas@ncdenr.gov or (919) 707-3646.
Sincerely,
V" "I
Jim Farkas
Environmental Engineer
Stormwater Program
cc: Mooresville Regional Office