20110446 Ver 1_More Info Letter_20110524

~~~
~~~
NCDENR
North Carolina Department of Environment and Natural Resources
Division of Water Quality
Beverly Eaves Perdue Coleen H. Sullins Dee Freeman
Governor Director Secretary
May 24, 2011
Mr. Erich Hahne
137 Cross Center Drive, Suite 246
Denver, NC 28037
Subject Property: Cottonwood Village -Phase 1
REQUEST FOR MORE INFORMATION (Stormwater Management Plan)
Dear Mr. Hahne:
DWQ #: 11-0446
Lincoln County
On Apri16, 2011, the Wetlands, Buffers and Stormwater Compliance and Permitting Unit of the Division of Water
Quality (DWQ) received your stormwater management application along with supporting information for the subject
project in Lincoln County. Please provide the following information so that we may continue to review your
project and prevent return of your application as required by 15A NCAC 2H .0506:
Additional Information Requested:
1. Wet Detention Pond:
a. Current configuration of proposed wet detention pond has two forebays in close proximity to the outlet
structure. This does not provide sufficient flow path length (FPL) to meet the required minimum of 1:5
(L:W ratio). We highly recommend 3:1 (L:W ratio) FPL.
b. Wet detention ponds designed for 85%TSS removal must discharge up to 2.0 cfs of the 10-year discharge
from the pond to a Level Spreader -Vegetated Filter Strip (LSVFS). Unless designed for 90%TSS
removal, please provide an appropriately sized LSVFS system and aflow-splitting device to convey up
to 2.0 cfs to the LSVFS, and discharge larger flows through a bypass structure (pipe, riprap channel, etc).
Detailed design and installation information of the flow splitting device must be provided.
c. As you reconfigure your BMP to meet the flow path requirement, please pay attention to the minimum
average depth requirement. Using Option 2 on Supplement Form to compute the average depth, our
calculation yields 2.42 ft which is less than the recommended 3.0 ft minimum. This is because you have
set the top of sediment cleanout elevation at 709 ft. Setting the top of sediment cleanout at 708 ft yields an
average depth of 3.22ft. Please note that when designing for either 85% or 90%TSS, your average depth
to be used in either table will then be 3.0 ft (rounding 3.22 ft to the nearest .Sft), and by interpolation your
required Surface Areas are 16473 ft2 and 24,016 ftz for the 85% and 95%TSS respectively. In summary,
your BMP is undersized.
d. Please provide a minimum of 6 inches top soil on the clay liner.
e. Planting Plan: Please provide local nursery supplier information for proposed native plant species.
401 OversighUExpress Review Permitting Unit
1650 Mail Service Center, Raleigh, North Carolina 27699-1650
Location: 512 N. Salisbury St, 9~^ Floor, Raleigh, North Carolina 27604
Phone; 91907-6301 1 FAX: [phone]
Internet: http:llportal.ncdenr.orglweblwglswplws1401
NonithCarolina
~atura!!t~
An Equal Opportunity 1 Affirmative Action Employer

Cottonwood Village Phase 1 (Linco111 County)
Page 2 of 2
May 24, 2011
f. Please note that this is a high density project and therefore the BMP must be in place once Phase 1 is
stabilized. The impervious amount does not have to reach 24% before the BMP is installed.
Please respond within 30 days of the date of this letter by sending two (2) copies of the above information and any
revisions in writing. This letter only addresses the application review and does not authorize any impacts to wetlands,
waters or protected buffers. Thank you for your attention to this matter. If you have any questions or wish to discuss
these matters further please do not hesitate to contact Joseph Gyamfi at [phone] or me at [phone].
Sincerely,
'~c.,l~.~/V1
Karen Higgins, Supervisor
Wetlands, Buffers and Stormwater Compliance
and Permitting (WBSCP) Unit
~Ig
cc: File copy
-Alan Johnson, DWQ Mooresville Regional Office
USACE Asheville
Jonathan Carter, P.E., 128 Overhill Drive, Suite 105, Mooresville, NC 28117