SW1220701_Response To Comments_20221128

November 28, 2022
North Carolina Department of Environmental Quality
Division of Energy, Mineral and Land Resources
512 North Salisbury Street
Raleigh, NC 27699
919-707-9200
Attention: Mr. Jim Farkas
RE: All About Plumbing Building Addition
Henderson County
Stormwater Permit No. SWSW1220701
Mr. Farkas:
Thank -you for your review comments regarding above referenced project.
Per our discussions, we have revised the submittal for low density stormwater requirements.
We have removed all stormwater pipe infrastructure and the bio-retention pond. The site will
convey the stormwater runoff via vegetated swale.
Below is an itemized list of the Stormwater Management Permit Application review
comments and how we have addressed them.
1) General Design Comments:
a) General MDC 3 — Per the provided detail on plan sheet C600 (the second one),
the vegetated side slopes of the SCM are shown to have a cross -slope of 2:1
while the MDC requires the side slopes to be 3:1 or flatter. NOTE: Steeper
vegetated side slopes can be allowed on a case -by -case basis, but this project
should be able to accommodate 3:1 or flatter side slopes.
Response: The project has been revised to meet low density requirements. The
proposed grass swale will have 3:1 side slopes.
b) General MDC 4 — Please provide calculations showing that the inlets and outlets
are stable/outlet protection is adequately sized.
Response:
The project has been revised to meet low density requirements. Grass Swale
calculations are included in Appendix D of the revised SWPPP.
c) General MDC 6 — Please ensure that the SCM has a means of being dewatered.
The Supplement-EZ Form indicates that the SCM will be dewatered using a
drawdown orifice, but this drawdown orifice device does not appear to be
indicated on the plans. If a tee with a removable screwcap (or other method) will
be added to the underdrain line to allow for the SCM to be drained, it needs to be
indicated on the plans/details.
9
U)
M
U
O
(n
U)
Q
c
�L
m
a�
c
0)
c
W
d
t
v
3
v
o
C (h
O N
: U
C U)
N 6)
c O
N �
>� C
1_
00
co U)
CT) 864 582 0585
@) www.mcc-ea.com

Response: The project has been revised to meet low density requirements.
d) General MDCs 8 & 9 — It is noted that the maintenance access/easement is shown
on the plans, however, this easement must not include any slopes steeper than 3:1
(8b), extend to the nearest public right-of-way (8c), and include the entire SCM
footprint (see guidance under MDC 9 in Part C-0 of the Manual). There is also a
proposed fence located in close proximity to the east side of the SCM which may
make it difficult to access/maintain the SCM from that side.
Response: The project has been revised to meet low density requirements.
e) Biorention MDC 1 — Please provide a SHWT boring so that the elevation of the
SHWT can be determined and the minimum separation verified.
Response: The project has been revised to meet low density requirements.
f) Biorention MDC 6 — Please note that the mixture values shown in the Manual
(and reproduced on plan sheet C600 (the second one)) are incorrect. The
maximum percent fines is 10% (15A NCAC 02H .1052(6)(b)) and the maximum
percent organics is 10%( 15A NCAC O2H. 1052(6)(c)). Sony for the confusion.
Response: The project has been revised to meet low density requirements.
g) Biorention MDC 10 — Please clarify if sod will be used as the vegetation for the
SCM. It is noted that the Supplement-EZ Form indicated that grass will be used,
however the plans are more ambiguous.
Response: The project has been revised to meet low density requirements.
2) Application Comments:
a) Section IV, 10 — The Drainage Area 1 column in this table is an accounting of the
drainage area to the SCM, not the entire project area. The information in this
column should correspond to the information shown in the DA 1 Column of the
Drainage Area Page of the Supplement-EZ form (see comments below).
Response: This section of the application has been revised per the comments
above & below.
3) Supplement-EZ Form Comments
a) Cover Page:
Please include the width of the vegetated setback (per 15A
NCAC 02H. 1017(10). It is noted that there are no surface
waters located on -site, however this value should be
included on the form (Lines 8 & 9 can be left as "N/a" since
there are no surface waters located on -site).
Response: The Cover Page has been revised to reflect the above
comments.

b) Drainage Area Page:
i) Entire Site Column:
l . Line 12, Parking & Roof — These items should
add lip to Line 10. Existing BUA (even if it is
changed fi•om one type to another) is already
accounted for in Line 15 so it should not also be
accounted for with these items.
2. Line 16 — This item should not be included since
the site was not previously permitted.
3. Line 19 & 20 — These items are not required for
the entire site column.
Response: The Drainage Area Page Entire Site Column has been
revised for the above comments
ii) DA 1 Column
1. Please complete this column. This column is an
accounting of the drainage area/BUA to the
SCM.
2. Lines 5 & 6 — These items should correspond to
the drainage area of the SCM (0.94 ac,
expressed in square feet).
3. Line 8 — This item is the total amount of BUA
located within the SCM drainage area (0.65 ac,
expressed in square feet).
4. Lines 10, 12, & 15 — Similar to above, the BUA
within the drainage area to the SCM should be
categorized as either existing BUA (Line 15) or
new BUA (Line 10). New BUA should be
further be broken down by type (Line 12). The
sum of the items of Line 12 should add up to
Line 10 and the sume of Line 10 and 15 should
equal Line 8 (for this project).
5. Line 18 — Calculate this value based on the
drainage area to the SCM (Line 8 / Line 5).
6. Line 19-21 — Please include these items
Response: The Drainage Area Page Column 1 has been revised for
the above comments.
c) Bioretention Page
i) Line 2 — See below optional comment, revised if needed
ii) Line 5 — As mentioned above, the plans indicate that the
vegetated side slopes of the SCM are 2:1. Please revise as
needed.
iii) Line 9 — As mentioned above, there does not appear to be a
drawdown orifice shown on the plans. Please revise as
needed.
iv) Line 18 — Please provide this value.

v) Line 21 — The plans indicate that the surface area of the
bioretention cell (@ elevation 1003') is 3,612 sf (3,890 sf
shown). Please revise as needed. Please also ensure that the
forebay area & volume are not included in the bioretention
cell surface area & volume (A forebay is provided in
addition to, not as part of, a bioretention cell). Line 22 may
need to be adjusted as well.
vi) Line 26 — The in -situ soil infiltration rate was not provided
(it appeals that the shown value, 3 fps, may refer to the
media mix (which does not need to be reported on this
form)). An in -situ soil infiltration rate is only needed if you
are proposed to eliminate the INS from the design (per
Biorention MDC 4).
vii) Line 31 — See earlier comment, please revise as needed.
Response: The project has been revised to meet low density
requirements. The Supplement EZ Form has been revised to include
vegetated conveyance
4) Optional Comments:
a) Application, Section IV, 8 — While not required, you may utilize the
methodology outlined in 15A NCAC 02H .1003(1)(b) to calculate the
project density since this project has Existing BUA [Net Increase in
BUA] / ([Project Area] — [Existing BUA])
Response: Utilizing this method, the project density calculation yields
15.35%. Therefore, we have revised the plans to meet the low density
stormwater requirements.
b) While not required to be addressed, the calculated minimum required
design volume may be larger than it needs to be. Per Part B of the
Manual, the Simple Method, or Discrete NRCS method can be used to
calculate the minimum required design volume (The provided
calculations calculates this value as 1.0 inches of rainfall over the entire
SCM drainage area (which is similar to the Simple Method, but is more
conservative since it assumes that the entire 1.0 inches of rainfall will
turn into runoff)).
Response: The project has been revised to meet low density
requirements.
c) While not required, it is recommended to reduce the available storage
depth provided in the bioretention basin. The current configuration
provides 4 ft of ponding (basin bottom is @ elevation 1003' and the top
of the embankment is @ elevation 1007'). This may harm the vegetation
due to prolonged inundation during large storm events.
Response: The project has been revised to meet low density
requirements.

d) While not required, it is recommended to include an emergency spillway
for the bioretention basin so that if the embankment overtops during
large storm events (and/or if the outlet structure gets clogged), it does so
nondestructively and in a controlled manner.
Response: The project has been revised to meet low density requirements.
5) Provide PDFs of all revisions, 2 hardcopies of revised plan sheets, 1 hardcopy of
other documents and a response to the comment letter briefly describing how the
comments have been addressed.
a) PDFs must be uploaded using the form at:
httos:Hedocs.dea.nc.eov/Forms/SW-Sunnlemental-Unload
b) Hard copies must be mailed or delivered to the following address:
i) For FedEx/UPS:
Jim Farkas
512 N. Salisbury Street, Office 640E
Raleigh, NC 27604
Response: Attached you will find a digital copy of the revised plans, SWPPP, and
supplemental documents and applications as well as 2 hardcopies of the revised plans
and 1 hardcopy of the supplemental documents.
Sincere Regards,
McCutchen Engineering Associates, PC
Tommy Karnes, P.E.
Project Manager