SW1191201_Responce to Comments_20200414

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5410 TRINITY ROAD, SUITE 1 0 2 • RALEIGH , NC 27607 • PHONE [phone] • FAX [phone] • WWW.TIMMONS.COM

Project: NCNG Morganton Regional RRC Phase II Date: 04/14/2020
Case #: SW1191201
Contact: Frank Slinsky, PE
Phone: [phone]
Email: [e-mail]

Comments from NCDEQ review has been addressed below. Our responses are in red.

Construction Document Submittal Second Submittal Comments – 3/30/2020
NCDEQ REVIEW COMMENTS
Jim Farkas (919-707-3646, [e-mail])

1. Original Comment 12 – “Please provide riprap sizing calculations showing that the inlets
and outlet of the wet pond are stable during the 10-year storm event (General MDC 4).”
Please show how the 10-year peak flow value (Shown as 57.70 cfs for C1 on the riprap
sizing sheet is calculated.

Response: The value of the 10-year peak flow value has been updated to 56.84 cfs. This
value comes from the storm sewer calculations for line B1-C1(1). The updated riprap
sizing calculation and the storm sewer calculations have been added to the stormwater
narrative/calculations booklet (attached).
2. Sheet C4.8 indicates that there will be 7045 sf of future BUA located within the drainage
area to the proposed wet pond whereas the Supplement-EZ Form and Application indicate
that 7048 sf of BUA is proposed. Please revise for consistency.

Response: Sheet C4.8 has been updated with the correct value of 7048 sf. Updated
drawings are attached.
3. Please correct the following on plan sheet C8.14:
a. There appears to be a typo in the bottom of the forebay entrance/exit. The
entrance is shown lower than the exit, but the provided elevations indicate
otherwise (Entrance = 1197 ft, Exit = 1196 ft as shown on the plans). Please
revise for consistency.
b. Please include the sediment storage top elevation for the forebay (Similar to how
it is included for the main pool).

Response: The Wet Detention Pond Detail on sheet C8.14 has been updated such that
the elevation at the entrance of the forebay is 1197 ft and the elevation at the exit of the
forebay is 1198 ft. The detail has also been updated such that the forebay includes 1’ of
sediment storage similar to the main pool. The sediment storage in the forebay has a flat
bottom (elevation 1196) since sediment will settle level. The 1196 contour of the bottom of

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5410 TRINITY ROAD, SUITE 1 0 2 • RALEIGH , NC 27607 • PHONE [phone] • FAX [phone] • WWW.TIMMONS.COM
the sediment storage has also been added to the grading plan on sheets C4.0-C4.1.
Updated drawings are attached.
4. Please correct the following issues with the Supplement-EZ Form:
a. Cover Sheet:
i. Line 4 – Please list the surface water area located within the project area.
This value should correspond to Section IV, 6 of the Application.
ii. Line – 7 Please list the width of the provided vegetated setback. The
vegetated setback is provided from surface waters (“blue line” USGS
streams). Information can be found in 15A NCAC 02H .1017(10).
iii. Line 9 – If there is no non-exempt BUA located stream-side of the
required vegetated buffer, this item should be “No”.
Response: The surface water area on line 4 has been updated to 0.60 acres to
correspond with Section IV, 6 of the application. The vegetated setback is 50 feet
within the Catawba River basin, line 7 has been updated accordingly. All BUA on this
project is located out of the setback, Line 9 has been changed to “No” as
recommended. Updated forms are attached.
b. Drainage Area Sheet:
i. Line 10, Drainage Area 1 – There appears to be a mismatch in the
proposed parking area located within the drainage area to the wet pond.
The Supplement-EZ Form indicates that 456,802 sf is proposed while
Section IV, 10 indicates 465,306 sf. Please revise for consistency.
Response: The Supplement-EZ Form has been updated with the correct value of
465,306 sf. Updated forms are attached.
c. Wet Pond Sheet:
i. Line 43 – The depth of the forebay at entrance is the distance between
the permanent pool elevation (1201.5 ft) and the excavated bottom of the
forebay at its entrance (shown as 1197 on the plans, but please refer to
prior comment regarding this), expressed in inches. NOTE: Per Wet Pond
MDC 3, the forebay must have a minimum sediment storage depth of 6
inches (The distance between the sediment storage top elevation and the
excavated bottom of the forebay at its entrance must be greater than or
equal to 6 inches).
ii. Line 44 – The depth of forebay at exit is the distance between the
permanent pool elevation (1201.5 ft) and the excavated bottom of the
forebay at its exit (Shown as 1196 on the plans, but please refer to prior
comment regarding this), expressed in inches. NOTE: Per Wet Pond
MDC 3, the forebay must have a minimum sediment storage depth of 6
inches (The distance between the sediment storage top elevation and the
excavated bottom of the forebay at its entrance must be greater than or
equal to 6 inches).
Response: The depth of the forebay entrance and exit have been updated to reflect
1’ of sediment storage. Although the entrance of the forebay is lower than the exit of
the forebay, the bottom of the sediment storage (elevation 1196) is flat as sediment
will settle level. Line 43 and 44 have been updated with a depth of forebay at
entrance and exit of 66 inches. Updated drawings and forms are attached.

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5410 TRINITY ROAD, SUITE 1 0 2 • RALEIGH , NC 27607 • PHONE [phone] • FAX [phone] • WWW.TIMMONS.COM
5. NOTE: Per Diversion policy, the next review of this application will be the final review.
Failure to provide the requested information will result in the project being returned as
incomplete. The return of a project will necessitate resubmittal of all required items,
including the application fee.

Response: Noted.
6. Provide pdfs of all revisions, 2 hardcopies of revised plan sheets, and 1 hardcopy of other
documents. Pdfs must be uploaded using the form at:
https://edocs.deq.nc.gov/Forms/SW_Project_Submittal
Response: Revised calculations, revised forms and two copies of the revised plans are
attached. A pdf of all revisions has been uploaded to the above web address.