SW1231201_Response To Comments_20240325

FAShaping Communities Together
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March 25, 2024
Jim Farkas
State Stormwater Engineer
North Carolina Department of Environmental Quality
512 N. Salisbury Street, Office 640M
Raleigh, NC 27604
RE: Project name: Bobby N. Setzer State Fish Hatchery Renovation
Project No.: SW1231201
Location: Transylvania County
Disapproval date: March 4, 2024
Dear Mr. Farkas,
Thank you for your review of the stormwater permit submittal for this project. Below are our
responses to your comments that I received via email on March 4, 2024. Your comments are
shown in italics followed by McGill's bolded responses.
1) 15A NCAC 02H.1003(5) and General MDC 4— Please provide the calculations showing that
the stormwater outlets and SCM inlets are adequately sized/designed to prevent erosion.
Calculations are required per 15A NCAC 02H .1042(2)M.
According to wetland MDC 6, the forebay is best colonized by plants. In order to
accommodate this and to ease maintenance of the forebay, no rip-rap outlet
protection was provided for the forebay. Appendix L demonstrates that the
velocity of the submerged influent storm water is greatly reduced within the
forebay and will not cause erosion.
A rip-rap outlet protection is now provided for the stormwater wetland discharge
into Grogan Creek; see Appendix L. Due to less bury depth and less steep
stream side slopes, rip-rap outlet protection outside of the stream is feasible for
the wetland discharge.
Rip-rap protection is not provided for HW A or HW C for multiple reasons as
follows:
■ Rip-rap stabilization in the stream or along the streambank is
discouraged during our concurrent, 401 and trout buffer waiver
permitting processes.
■ Due to the depth of our storm and the topography in the areas of our
outfalls, it is not practical or feasible to cut out a channel to discharge
the pipes into a rip-rap apron before reaching the 30' vegetated setback
or even the edge of the river. The streambanks at both outlets are 8'-10'
MCG ILL ASSOCIATES 55 BROAD STREET, ASHEVILLE, NC 28801/828.252.0575/MCGILLAS50CI ATE S.COM

high and have an approximate 1H:1V slope. The grading that would be
required to install an outlet would have a much larger impact on the
natural streambank than the current proposed design.
■ The justification used for our original submittal was that the existing
conditions of the outfalls today have not caused erosion problems in the
stream and our proposed improvements have lowered discharge
velocities due to our increased pipe size with only minimal impervious
area increases. To increase the factor of safety with our plan, we have
added an impact curb to both HW A and HW C to further reduce the
velocity. Appendix L shows the velocity calculations with the curb
added for each outfall and those are 2.75 ftls for HW A and 2.92 ftis for
HW C. A typical stable streambed velocity for the observed
characteristics of the Davidson at our outfalls is 5 ftlsec and the flow
rate observed during a normal flow depth was 3 ftlsec. Based upon this
data, the receiving streambed will be stable at the outfalls A and C.
2) Stormwater Wetland MDC 14 -- Per the proposed planting plan, there is an insufficient plant
density proposed for the temporary inundation zone. The planting plans shows a total of 114
shrubs (45 VD and 69 XS) and a total of 256 herbaceous plants (60 AT and 196 SR). This
does not meet the herbaceous minimum planting requirements as only 2 herbaceous species
are provided and a planting density of 50 plants per 200 sf of area would require a minimum
of 956 plants (256 provided). This does not meet the shrub minimum planting requirements
as a planting density of 8 plants per 200 sf of area would require a minimum of 153 plants
(114 provided). Please revise as needed.
The planting plan on Sheet L-103 has been revised. Our design is intended to
meet MDC 14, Option #2 (8 shrubs per 200 sf). 157 shrubs are provided (153
required). Additional herbaceous plants have been provided in the temporary
inundation zone to provide additional vegetation.
3) Per 15A NCAC 02H.1003(4)(e), stormwater runoff that has not been treated in an SCM may
not be discharged through a vegetated setback, it needs to be released at the edge of the
vegetated setback and allowed to flow through the setback as dispersed flow. Per the
proposed design, headwalls NW A & NW C appear to discharge untreated runoff through the
vegetated setback. Please revise as needed.
Due to the depth of our storm and the topography in the areas of our outfalls, it
is not practical or feasible to cut out a channel or bench to disperse the pipe
flow before reaching the 30'vegetated setback.The streambanks at both outlets
are 8'-10' high and have an approximate 1H:1V slope. The grading that would
be required to install an outlet would have a much larger impact on the natural
streambank than the current proposed design. Therefore, we request a variance
per 15A NCAC 02H .1003(6)(b). We can demonstrate that the project provides
better stormwater control and better protection of waters than what the code
requires.

While the state requires treatment of only the net increase in impervious area to
the project,we have captured and treated above that; net increase in impervious
1.88 acres, treated impervious = 3.06 acres, therefore, we are treating 1.18
acres more than required. Additionally, HW A and HW C stormwater systems
outlet at existing stormwater system discharges and their drainage areas
include only an additional 0.64 acres of impervious area.
These calculations can be found in the narrative and Appendix E of the revised
stormwater calculations report.
4) Per 15A NCAC 02H.1021(7), the minimum required width of a vegetated setback from
surface waters is 30 ft(a 25 ft buffer appears to have been provided) NOTE: If the 25 ft
buffer is required for other programs/permits, please ensure that both setbacks from
surface wafers are included on the plans. Please revise as needed.
A 30 ft vegetated setback has been added to the revised site sheets. There are
no new proposed surfaces within the vegetated setback. Note that we have
received a Trout Buffer Zone Waiver (TB-TRANS-2024-002).
5) Please correct the following issues with the Application:
a. Section IV, 10-- Please revise the receiving stream information to reflect the first
named stream that runoff from the proposed SCM enters. Per the provided USGS
topographic map, the first named surface water downstream of the SCM appears to be
Cedar Rock Creek (labeled as "Grogan Creek"on the plans).
The downstream surface water has been adjusted to Cedar Rock Creek. Note
that Grogan Creek and Cedar Rock Creek combine just upstream of the
hatchery and that Grogan Creek is the common name recognized by locals and
hatchery staff. 'Grogan Creek' label will remain on plans.
b. Section IV, 10—Please revise the drainage area information to reflect the area
draining to the proposed SCM. The shown drainage area appears to correspond to the
entire project area and should only refer to the areas that are draining to the SCM (the
BUA information for the entire project area is shown in the Supplement-EZ Form).
Please revise as needed.
The drainage area has been adjusted to reflect the proposed SCM drainage
area. Based on previous experience with this process, a revised page 4 of the
application is being provided to replace the original.
6) Please correct the following issues with the Supplement-EZ Form:
a. Drainage Areas Page:
i. Please complete the drainage area 1 column. The information in this column
corresponds to the area draining to the SCM.
The entire site drainage area and Site 1 drainage area have been appropriately
adjusted.

ii. Please ensure that the BUA is accounted for correctly. For this project, Line 8 = Line 10 +
Line 15, Line 10 is equal to the sum of the items on Line 12 and corresponds to the new (net
increase) in BUA from existing to proposed conditions. Line 15 corresponds to BUA that is
present on-site in existing conditions (it does not matter if it is modified/relocated during the
proposed project). Please revise as needed.
Drainage areas have been appropriately adjusted.
iii. NOTE: Lines 19— 21 are not required for the entire site column.
Lines 19-21 have been removed for the entire site column.
b. Stormwater Wetland Page:
i. Line 18—Per the stage-storage table, the SCM only provides 9,308 cf of storage (between
the permanent pool and the temporary pool @ elevation 2334.25').
Design Volume of SCM has been updated to 9,308 cf.
ii. Line 20 — This item refers to berms/baffles that reach above the temporary pool surface
elevation that increase the flowpath from the inlet to the outlet. The proposed design does not
appear to include these.
Response has been changed to `No'.
iii. Lines 28 & 29—Please provide spot elevations on the plan view or indicate the elevations
on the cross-sectional view in the main set of plans so that these values may be verified.
The cross-sectional view on sheet C-140 has been adjusted to show the
indicated elevations.
iv. Lines 32— 35— The sum of these items is equal to 10,204 sf(it should be equal to 10,203
so. This appears to just be a rounding issue but needs to be revised. Please revise as needed.
The total surface area has been adjusted to 10,204 sf, the sum of Lines 32-35.
v. Line 40— This value is equal to the difference between Lines 24 and 25.
Line 40 has been adjusted accordingly.
A Line 43— This value is equal to the difference between Lines 26 and 28.
Line 43 has been adjusted accordingly.
vii. Line 44— This value is equal to the difference between Lines 26 and 29.
Line 44 has been adjusted accordingly.
viii. Line 45— This value is equal to the difference between Lines 26 and 30.
Line 45 has been adjusted accordingly.
ix. Line 46— Per the plans, the drawdown orifice diameter is equal to 1.5"(2"is
shown). If the cell does not allow a decimal value to be entered, please enter the
actual value in the additional information section (Line 57).
The actual value (1.5") has been noted in the additional information section.
x. Lines 46 and both Lines 47 & 48 are mutually exclusive as they refer to the lowest bypass
device (designs typically only have one lowest bypass device). Please revise as needed.
Lines 47 & 48 have been removed.
A Line 53—Please provide this value. If the cell does not allow for a value to be input,please
include this information in the additional information section.
The response to Line 53 has been added to the additional information section.
7) Please be aware that, in accordance with 15A NCAC 02H .1003(1)(b), projects with existing
BUA may exclude the existing BUA from the project density calculations.
Project density calculations have been adjusted in the stormwater report to
account for existing BUA.

8) Provide PDFs of all revisions, 2 hardcopies of revised plan sheets, 9 hardcopy of other
documents, and a response to comments letter briefly describing how the comments have
been addressed.
All applicable updated documents shall be provided on paper to Jim Farkas and
as PDFs uploaded to the provided link.
If you have any questions or require additional information, please feel free to give me a call at
828-252-0575.
Sincerely,
McGILL ASSOCIATES, P.A.
Ben Cathey, PE
Senior Project Manager/Practice Area Leader
P:120t9119.00124-NCWRC-Bobby N Setzer State Fish HatchelDesignlPermits,.Stormwatcr,2024-03-15 RcsubmittallSourcesl19.00124-Response
Later-Storm-03 2524.docx