SW6230606_Response To Comments_20230906

NCDENR REVIEW
Benhaven Emergency Services
Stormwater Management Permit Application
The following are the NCDENR comments(dated August 28, 2023), applied corrections, and our
responses for the above referenced Application/Plan.
Department Status Reviewer Phone Email
NCDEQ Correction Brianna Holland 919.707.9218 [e-mail]
required (Environmental Engineer)
1. Bioretention Cell (Plans,Supplement-EZ, Calculations)
Comments: a). Bioretention MDC 4-An underdrain with internal water storage shall be installed unless it is
demonstrated that the in-situ soil infiltration rate is two inches per hour or greater immediately prior to the
initial placement of the media.The top of the internal water storage zone shall be set at a minimum of 18
inches below the planting surface. Per this MDC, an internal water storage zone is required for any
bioretention cell that has an underdrain system. Please provide internal water storage or revise the design
of the bioretention cell. If revising to include IWS, please provide a detail of the outlet structure so that the
IWS depth may be verified (The detail should include the invert of the IWS).
RESPONSE:The bioretention cell has been modified to include the internal water storage zone. The top
of the IWS proposed is 18"below the planting surface. The Plan set,sheet C7.2 SCM profile shows the
new design details.
Comments: b). Bioretention MDC 5-Bioretention cells that are planted with grass may have a shallower media
depth, either 30 inches with an underdrain or 24 inches without an underdrain. Note that, per MDC 4,the
only time that a bioretention cell would not require an internal water storage zone is when the in-site soil
infiltration rate is two inches per hour or greater. Note if the desire is to not include IWS,that using the same
footprint as the location for the skimmer basin would impact infiltration rates and can lead to compaction
during construction.
RESPONSE:Thank you for the comment.A revision to a bioretention cell to add IWS is designed, and
the filter depth of 30"is proposed.
2. Application
2x hard copies of the Application with the following corrections made is required per 15A NCAC
02H.1042(2)(a)and per Section VI, 1 of the Application:
Comments: a)The previous Application Section II,4b listed the E&SC permit information,with your permission, I
can write this on the hard copy. Please upload a revised PDF with "Benhaven Emergency Services 13,
HARNE-2023-020, 2-8-23, E&SC Permit to match the previously provided permit information.
RESPONSE: Yes,please revise hard copy. Application has been revised to show the "Benhaven
Emergency Services 13, HARNE-2023-020,2-8-23, E&SC Permit"and uploaded.
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3. Supplement-EZ
1x hard copy of the complete, original Supplement-EZ Form is required per Sections V& VI, 3 of the
Application
Comments: a) Drainage Area Information, Line 20:This is the actual volume of the pond that is designed, not the
minimum required treatment volume (that is provided in Line 2 of the next page). Please revise.
RESPONSE: Drainage Area Information, Line 20 is modified to 2,850 CF(actual volume designed),
which is shown on drawing plan(see sheet C7.2).
Comments: b) Drainage Area Information, Line 21: It appears in the calculations the"simple method"was used.
Please revise.
RESPONSE: "simple method"is stated on the line#21.
Comments: c) Bioretention Cell, Line 26: Please revise to include an infiltration rate if it is desired to avoid IWS
per MDC 4-5.
RESPONSE:It is not desired to use underlying soil infiltration rate. It is now reflected on new design
and drawing.
4. Plans
2x signed&sealed hard copies of a plan sheets showing the following corrections made:
(This item is required per 1SA NCAC 02H.1042(2)(a) and per Section VI, 1 of the Application)
Comments: a) Please clarify if the 50' road easement on Dunrovin Lane is a public ROW. Per 15A NCAC 02H
.1050 (8)(c), SCM easements must extend to the public right-of-way. Ensure consistency across plans,
sheets C1.0 and Sheet C5.0 show variability in where the easement ends. It should include the entire
footprint of the SCM (including side slopes and associated structures)plus an additional 10 ft around the
footprint to allow for access.The outlet exiting the SCM's rip rap protection is past the treeline shown,which
may make it difficult to maintain depending on field conditions.
RESPONSE:Dunrovin Lane is not public ROW. The SCM easement now extended to the NC 27 W. The
new easement includes the entire footprint of the SCM plus additional 10'around footprint for access.
The existing treeline modified to include the SCM rip rap protection.
Comments: b) Per the Supplement-EZ and Application, the project area is less than the property area. Please
clearly indicate the project area in the plan set(required per 15A NCAC 02H .1042(2)(g)(ii)). You can use
any appropriate project area so long as it includes the entire area to be covered under this permit, but the
project area boundary should be shown on the plans.
RESPONSE:The project area was shown in the Plan (Sheet C3.0)as "Proposed Bioretention Drainage
Area", now it is modified and relabeled as "Project Area/Proposed Bioretention Drainage Area".
Comments: c) Please specify the type of sand in the media mix is ASTM C33,AASHTO M 6/M 80,ASTM C330,
AASHTO M195,or the equivalent per 15A NCAC 02H .1052 (6). (A note can be added saying the specific
type, or the above options.)
RESPONSE:The type of sand in the media mix is specified as per MDC 6,please see SCM Profile,sheet
C7.2
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Comments: d) Please specify the inverts/slopes of all storm drain pipes including underdrains per 15A NCAC
02H .1042 (2)(g)(vii)
RESPONSE:Invert and slope of 15"RCP outlet is noted on Grading Plan, C3.0 and has been added to
Detail Sheet C7.2. The slope of the underdrain as well as outlet invert of the underdrain is noted on
Detail Sheet C7.2
5. Calculations
1x signed, sealed, and dated hard copy of calculations with the following corrections made:
(This item is required per Section VI, 7 of the Application)
Comments: a)General MDC 1 —Per the Supplement-EZ, Drainage Area Information Table Line 5,the total
drainage area to the SCM is 68,400 SF, but the calculations for the design volume used 62,984 SF. Please
revise calculations for consistency.The design volume of SCMs shall take into account the runoff at build
out from all surfaces draining to the bioretention cell. (Revise the minimum required treatment volume
accordingly.)
RESPONSE:Sorry for the confusion. The area 68,400 SF is the drainage area to the Point of Analysis for
modeling peak flow discharge. This area includes a small area that by-passes the SCM. The 62,984 SF
is the drainage area for SCM. The EZ Bioretention Cell Drainage Area, Line#5, is revised to 62,984 SF.
Comments: b)General MDC 4—Please provide calculations showing that the inlets and outlets of the SCM are
stable/outlet protection is adequately sized.
RESPONSE:Two swales are the inlets of the SCM. These swale design and protection sheet was
provided on Stormwater Calculation Report(see Annex C:Drainage Swale Design). The additional rip
rap near the inlet of the SCM provides extra protection in addition to the lining proposed. The design
calculation for outlet protection was not shown as the outlet discharge for 10-yr storm(design storm)
was only 0.5 cfs(very low). Now, the outlet protection design is added to the Annex C.
Comments: c) In the underdrain calculations, please show how the flow rate, Qf was found, provide the assumed
roughness factor as well as the internal slope.
RESPONSE:The Qf,infiltration to underdrain is the product of filter bed area times infiltration rate of
the filter(1 in/hr). The assumed roughness(manning's coefficient)is assumed as 0.011 and slope of
0.5%.All these factors are now adequately shown on Bioretention Design Sheet(See Storm water
Calculation Report Annex D).
6. 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
RESPONSE:PDFs will comply with the requirement.
b)Hard copies must be mailed or delivered to the following address:
i. For Fed Ex/UPS:
Brianna Holland
512 N. Salisbury Street, Office 640E
Raleigh, NC 27604
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ii. For USPS:
Brianna Holland
1612 Mail Service Center
Raleigh, NC 27699-1612
iii. Hand Delivery:
Please reach out to me prior to hand delivering a submission to make sure that I
(or someone else in my group) will be able to receive the submission. Do not leave the package in the
foyer with the security guard.
RESPONSE:Hard copies will be Hand Delivered.
NOTE: Hard copies should not be sent to a Regional Office. Doing so will delay the review process and
the submission package may be lost while being sent from the Regional Office to me in the Central
Office.
While not required,the following is recommended:
-The elevations on the cross section that are located in hatched areas are hard to read, recommend putting a
"mask"behind the text for legibility or showing the text outside of the hatched area.
RESPONSE:Now a mask is placed behind the text to show the text outside the hatched area. Thank
you for your comment.
-Please verify in the calculations that the surface area being used is the bottom surface area of the bioretention
cell.A volume calculation of the bottom surface area times the ponding depth can be used to demonstrate
compliance with General MDC 1.
RESPONSE:The SCM profile shown on site plan set Sheet C7.2 is modified to show the vertical cut for
the SCM up to planting surface.Surface area of the filter media is 2,850 SF
If you have any questions concerning this matter please feel free to contact me at
[e-mail] or(919) 707-9218.
RESPONSE:Thank you Brianna for all comments.
Please call if you have any questions. 919-851-1980
Sincerely,
BOBBITT DESIGN BUILD, INC.
eda
Blair Pittman, PE
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