20091085 Ver 2_More Info Letter_20100127

A.
NCDENR
North Carolina Department of Environment and Natural Resources
Division of Water Quality
Beverly Eaves Perdue Coleen H. Sullins Dee Freeman
Governor Director Secretary
January 27, 2010
DWQ EXP # 09-1085v2
Iredell County:
CERTIFIED MAIL: RETURN RECEIPT REQUESTED
Mr. Brian Fletcher
124 Iron Gate Circle
Mooresville, NC 28117
Subject Property: Troutman Towne Center (under North Point Resources Property)
STORMWATER MANAGEMENT PLAN (SMP)
REQUEST FOR MORE INFORMATION
Dear Mr. Fletcher:
On January 25, 2010, the Express Review Program of the Division of Water Quality (DWQ) received a
complete stormwater management plan (SMP) application signed and dated January 22, 2010. The
supporting information had already been submitted by Ms. Beverly Rosenbloom and Mr. Matt Edwards,
PE of Kimley-Horn and Associates on January 20, 2010. The submitted documents included stormwater
management plan sheets dated January 19, 2010 (Engineer's Seal), design calculations, subsurface
exploration (soil) report as well as operation and maintenance (O & M) agreements for the two proposed
wet ponds. 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 211.0506:
Additional Information Requested
Wet Pond 1:
a. Short-circuiting of flows:
i. OPTION 1: Please look into the possibility of combining the two forebays into a
larger one and locate it at the present location of the smaller forebay. There appears
to be enough relief from 91-MH to the smaller forebay to bring the flow to that
location. This way, you will have a single forebay weir, have additional space and
volume, minimize grading and maintenance issues with two forebays and berms and
eventually resolves the short-circuiting issue.
ii. OPTION 2: Please extend about three-quarters length of the longer portion of the
forebay weir to the temporary pool elevation so as to elongate the flow path from the
eastern inlet to the outlet. Please ensure the following requirements are maintained as
you extend the berm: 2:1 side slope, minimum 5ft width at the top of the weir, and
percentage of forebay volume to overall pond volume should fall within 18 -22%.
b. Please provide documentation to support the reported the 10-year storm elevation in the pond.
401 Oversight/Express Review Permitting Unit
1650 Mail Service Center, Raleigh, North Carolina 27699-1650
Location: 2321 Crabtree Blvd., Raleigh, North Carolina 27604
Phone: [phone] FAX: [phone]
Internet: http://h2o.enr.state.nc.us/ncwetiands/
NoithCarolina
Wuraffi
An Equal Opportunity 1 Affirmative Action Employer
Troutman Towne Center (North Point Resources Property SMP)
Brian Fletcher
Page 2 of 3
January 27, 2010
c. This office recommends that the secondary spillway be designed for the excess discharge
(9.55cfs) from the next available storm (i.e. 25-year storm) since almost all the routed flow
fr om the 10-year storm outlets through the primary control structure to the Level Spreader.
d. One of the major design elements (#15) of a wet pond states that "the BMP shall not be
located to produce adverse impacts on the water levels in adjacent wetlands". The BMP
Manual then states under Section 10.3:2 (Siting of BMP) that the Permanent Pool
Elevation (PPE) shall be located no more than 6 inches above or below the Seasonal
High Water Table (SHWT). Two major issues with wet pond 1 arising from the above
statements are:
i. The BMP has been located very close to a wetland.
ii. The Soil report indicates that the actual groundwater table elevation ranges from 867
to 869 feet from bore holes (D 1 -D4) installed at the location of the BMP. This
implies that the SHWT would, at a minimum, be 2 feet above the permanent pool
elevation of 867 feet.
Because of the issues stated above, please submit the following:
OPTION 1: Detailed engineering measures necessary to prevent impacts to the wetland
during the construction stages of the BMP and also during its use as sediment basin and
subsequently as a wet pond. This should include a narrative of the sequence of
construction or installation activities, necessary structures or devices (both temporary
and permanent) and supported plans or diagrams that will be put in place. Section 10.3.8
of the BMP Manual may be helpful.
OPTION 2: On the other hand, if you are convinced that the location will not adversely
affect the wetland, please submit engineering calculations and hydrogeological analysis
to demonstrate and/or support your assertion. Please refer to Section 10.3.2 of the BMP
Manual for guidance.
Another possible solution would be to raise the bottom of the pond and the permanent
pool elevation if the required surface area can still be achieved, in addition to providing
a liner, irrespective of whichever option you choose.
2. Level Spreader for Pond 1:
a. Please provide photos of the vegetation down slope of the Level Spreader that is being used
as the filter strip.
b. Please re-orient your outlet control structure and the discharge pipe such that the incoming
flow from the pond shall be discharged at an angle to the "blind swale" of the Level Spreader.
This was discussed in detail with Ms. Beverly Rosenbloom on January 20, 2010.
c. Please submit a completed Operation and Maintenance Agreement for the Level Spreader -
Filter Strip System.
3. Wet Pond 2:
a. The drawdown time of the water quality volume is approximately 4.7 days and not 2.6 days
as reported on the Supplement Form.
b. Since there were no borings at this location, and with no information of the seasonal high
water table, please add a liner to this pond.
4. Wet Ponds 1 and 2:
a. The temporary pool volume under Section II (Design Information) of the Supplement Form
should be the storage volume provided between the primary orifice and the next available
opening (orifice, weir) on the control structure
Troutman Towne Center (North Point Resources Property SMP)'
Brian Fletcher
Page 3 of I
January 27, 2010:
b. Please ensure that the provided storage. volume described in (a) above equals or exceeds the
required minimum water quality treatment volume. In addition, please make sure they
correctly match the values reported in the stage-area-storage table.
Please respond within five (5) days of the date of this letter by sending two (2) copies of the above
information and any revisions in writing. The Express Review Program is a process that requires all
parties to participate in a timely manner.
This letter only addresses the application review and does not authorize any impacts to wetlands, waters or
protected buffers. Please be aware that any impacts requested within your application are not authorized (at %
this time) by the DWQ.
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 call Joseph Gyamfi or Lia M. Gilleski at 919-733-1786.
Sincerel ,
Cyndi Karoly, Supervisor
g)---4-101 Oversight/Express Review Program
CBK/jg
cc: File copy
USACE Asheville Regulatory Field Office
Alan Johnson, DWQ Mooresville Regional Office
Matt Edwards, PE, Kimley-Horn & Assoc., 1919 South Blvd, Suite 100, Charlotte, NC 28203
24 • • • •u• • •? • l?•i'
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Mr Brian Fletcher 1/27/10
124 Iron Gate Circle
Mooresville NC 278117
EXP 09-1085 V2 Iredell Co
3. Service Type
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2. Article Number
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UNITED STATES PQSTAL SER-V.IC.E
• Sender: Please print your name, address, and ZI
NC DENR Division of Water Quality
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