SW3231102_Unaddressed Comments_20241009.pdf

In addition to these comments, the digital repository remains incomplete. All project
documentation must be submitted in both physical and digital form,per 15A NCAC 02H
.1042(2). The following comments remain unresolved.A brief description of the reason is
included with each.
l. Previous Comment—"The response to comments indicates that Runoff Treatment is being
pursued for this project. Per the definition of Runoff Treatment(15A NCAC 02H .1002(43)),
the net increase of the BUA of a project must be captured and treated in one or more
primary SCMs (If it is not possible to direct all BUA to an SCM, the bypassed area of the
project can be permitted as a low-density area,provided it meets all of the requirements
outlined in 15A NCAC 02H .1003(2)). Please revise the package accordingly.
• NOTE: The design volume of SCMs shall take into account the runoff at build out
from all surfaces draining to the system. Drainage from off-site areas may be
bypassed. The combined design volume of all SCMs on the project shall be
sufficient to handle the required storm depth(15A NCAC 02H .1050 (1)).
Existing BUA is not required to be directed to an SCM, but if the drainage
area to the SCM includes existing BUA,it must be sized accordingly.
• NOTE: The narrative refers to the gravel on-site as "partially pervious."In order
to not be considered impervious, the gravel must be number 57 stone, as
designated by the American Society for Testing and Materials, laid at least
four inches thick over a geotextile fabric per N.C.G.S.143-214.7(b2)."
The exception outlined in the response to comments was not shown on the main set of
plans, therefore the location and dimensions of the portions of the gravel surface that
are to be considered pervious surfaces could not be verified. All proposed BUA must be
identified and dimensioned on the main set of plans, per Section VI, 8j of the
Application. In addition, the grading provided seems to indicate drainage from off-site
areas, which was not bypassed, accounted for, or delineated. Therefore, this comment
remains unaddressed.
2. Previous Comment—"Please revise the design so that the following MDCs are met:"
a. `Bioretention MDC 1 —"The lowest point of the bioretention cell shall be a minimum of
two feet above the SHWT. However, the separation may be reduced to no less than one
foot if the applicant provides a hydrogeologic evaluation prepared by a licensed
professional." The SHWT elevation was found to be 772.42,the minimum separation
is at least 2 feet which would make the lowest elevation of the bottom allowable
774.42, unless a hydrogeologic evaluation is prepared."
The revised plan sheets that were submitted indicate that the bottom of the SCM
will be at elevation 774.08. The SHWT was identified to be at elevation 772.42,
resulting in a separation of 1.66 feet. In addition, the provided hydrogeologic
evaluation does not address the criteria noted in Section A-2 of the Design Manual
with regard to making an exception for SHWT separation. As a result, this
comment remains unaddressed.

b. "Previous comment unaddressed: Bioretention MDC 2—Please provide a bypass
mechanism to limit the design volume of the bioretention cell to no more than 12". The
invert of the bypass mechanism sets the ponding elevation associated with the design
volume." The design volume for a bioretention cell is equivalent to the volume that is
contained above the planting surface to the invert of the bypass mechanism for the design
storm. (A visual aid from the Chapter 2 of the manual is provided below.) This MDC is
used to calculate the required surface area of the bioretention cell, which is equal to the
required treatment volume divided by the ponding depth. The ponding depth above the
media and mulch shall be 12 inches or less (however 9 inches or less is recommended if
the site will allow this much space to be devoted to the bioretention cell). The 12-inch
limitation on depth is based on the typical inundation tolerance of the vegetation used in
bioretention facilities, as well as the ability of the ponded water to drain into the soil. Per
the provided detail (included below), it appears that 6" (776.50-776.00) is the height
between the invert of the bypass mechanism and the planting surface. 6" is acceptable,
but this design volume needs to be reflected throughout the remainder of the package.
Please provide a stage storage table so that the design volume can be verified."
Stage storage tables could not be found in the provided project documentation. As a
result, the Design Volume of the SCM could not be verified, and this comment
remains unaddressed.
c. "Previous comment unresolved: "General MDCs 8 & 9—Please include the maintenance
access and easement in the main set of plans (required per 15A NCAC
02H .1042(2)(g)(vi)).and ensure that it meets the applicable requirements outlined in
the MDC."It is not clear on the provided plans that the maintenance access/recorded
easement includes the entirety of the SCM with a minimum width of 10' and slopes less
than 3:1."
The maintenance access and easement indicated on the main set of plans is
identified to be 5 feet in width, and therefore does not meet the MDC. As a result,
this comment remains unaddressed.
3. Previous Comment—"Please correct the following issues with the Supplement-EZ Form:"
a. Cover Page
i. "Lines 7, 9: Per 15A NCAC 02H .1017 (10), the vegetated setback shall be at least
30 feet in width. If BUA is proposed in the vegetated setback. Please confirm that
BUA is proposed in the vegetated setback as indicated by Line 9, if there is no BUA in
the setback, please indicate N/A."
Line 7 should reflect 30 feet of vegetated setbacks, to demonstrate compliance
with the listed statute.
b. Drainage Areas Page:

i. "Previous comment unaddressed: Line 2—Please use 1 drainage area per SCM.
NOTE: You can also include two bypass drainage areas (one for each receiving water)
if you like."
The Drainage Areas Page of the Supplement-EZ still refers to four drainage
areas. As a result, this comment remains unaddressed.
c. Bioretention Cell Page:
i. Line 9—Please show the drawdown orifice used to dewater the SCM in the plans (this
must completely dewater the SCM for maintenance).
The structure on plan sheet C210 identified as a drawdown orifice does not
appear to serve the purpose of completely dewatering the SCM for maintenance.
There does not appear to be any orifice present that will be able to completely
dewater the SCM for maintenance. This comment remains unaddressed.