20140843 Ver 1_More Info Requested_20151118

From: Price, Zan (George)
Sent: Wednesday, November 18, 2015 4:58 PM
To: 'Wanda Austin'; '[e-mail]'
Cc: Higgins, Karen; Payne, John; [e-mail]; Walker, Fred; Davidson,
Landon
Subject: Jule Noland Road Phase II (DWR 14-0843) - Stormwater Management Plan
The Division of Water Resources (DWR) Asheville Regional Office (ARO) has performed a review of the revised Stormwater
management plan (SMP) for the Jule Noland Road Phase II project (DWR 14-0843) received at the ARO on November 6,
2015. We appreciate the revisions based on previous comments from DWR. Please address the following comments to
meet all the requirements specified in the North Carolina Stormwater BMP manual (Manual):
Major Design Element #12 in the Manual specifies "Ponding depth shall be 12 inches or less. Nine inches is
preferred". The submitted bioretention cell checklist and bioretention cross section on plan sheet SW2 state a 9 -
inch ponding depth. However, the invert of the primary outlet device for each bioretention cell is 24 -inches
above the sod floor of each cell. Therefore, the ponding depth at each cell could reach 24 -inches, which exceeds
the maximum depth allowed in the Manual. Page 12-17 of the Manual states "The first available outlet on the
outlet structure should therefore be placed at the height of the first flush, which is the ponded level of the
bioretention cell." This can be fixed on the plans by either raising the elevation of the sod floor for each cell or
lowering the elevation of the primary outlet invert so that the ponding depth is between 9 and 12 -inches. Make
sure the adjusted outlet depth provides at least the minimum storage volume required for each cell (e.g. 2,812 cu
ft for cell #1). The storage volume is measured from the bioretention cell floor to the invert of the primary outlet
and not the top of the bioretention cell berm. For example, the storage volume provided for cell #1 for a 12 -inch
ponding depth is 2,711 cu ft based on the submitted stage storage volume calculations.
It is difficult to determine the primary outlet device for the drainage area 4 bioretention cell. The plans specify an
emergency overflow elevation of 2585 which is the same elevation as the contour line around the entire
cell. Therefore, Stormwater could discharge or overflow the berm surrounding the entire cell comprising the
structural integrity of the cell. This can be fixed by including a primary outlet box similar to drainage areas 1
through 3 or sizing an emergency overflow at an elevation that provides sufficient freeboard beneath the
surrounding bioretention cell berm. Make sure to design the appropriate ponding depth per comment #1
above. See Section 12.3.7 on page 12-7 of the Manual for guidance on overflow structure design.
The submitted water table report completed by the NC Division of Soil and Water Conservation states "A total of
four soil boring were dug and examined. The borings were done at the four locations marked by a
surveyor." Please provide a map with the locations and ground surface elevations of the four soil borings so DWR
can confirm that each bioretention cell meets Major Design Element #6 of the Manual.
In order to expedite our review of the required revisions, feel free to send me an electronic copy of the revised plans and
supporting documentation. I would also like to follow up with a telephone conversation with Ms. Austin in the next
couple of days to make sure we are clear on the required revisions. Please provide some dates and times that would work
in the next couple of days (weekend or evening is fine). Our goal is to receive a set of approvable plans as soon as
possible.
Please forward this email to Mr. Harmon. I could not find his email address.
Regards,

Zan Price, P.E.
Assistant Regional Supervisor —Asheville Regional Office
Water Quality Regional Operations Section
NCDEQ — Division of Water Resources
828 296 4500 office
828 231 9634 mobile
email: [e-mail]
2090 U.S. Hwy. 70
Swannanoa, N.C. 28778
r
Email correspomYence to amY from this a�Y�Yress is subiect to the
lVoill`? Carolina PublicReconYs Law amY n7ay �Yiscl se�Y to thi Y path s,