20051071 Ver 1_More Info Received_20050823

ROBERT M. CHILES, P.E.
417-ABROAD ST.
P.O. BOX 3496
NEW BERN, NORTH CAROLINA 28564-3496
Certified Mail Receipt No.
ENGINEERS, CONSULTANTS
8
MARINE SURVEYORS
August 1 b, 2005
7004 251 0 0000 31 03 6543
Mr. John Dorney
401 Oversight and Express Permits Unit
2321 Crabtree Blvd., Suite 250
Raleigh, NC 27604
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Re: DWQ Project #05-1071 Approval of 401 Water Quality Certification with Additional Conditions, for
B/S/H Logistics Center for H8~M Company.
General Certification WQC #3402, Condition 4.
NCDENR Stormwater Permit No. SW7050524
Dear Mr. Dorney:
This letter is in response to Additional Condition No. b of the. DWQ Project # OS-1071 Approval of
401 Water Quality Certification issued to the B/S/H Logistics Center for H8~M Company on August 8, 2005.
We request that our current's#ormwater management plan be accepted as an alternative design
and present the following supporting information:
Our Stormwater management plan, indicating. NSW classified receiving waters and 90% TSS
removal efficiency was issued DWQ Stormwater Perrrtit No. 7050524 based upon approval by the
Washington Regional Office o>• the DWQ. This satisfies the referenced Cond'ifion No. 4 via "approval by
other existing DWQ state stormwater programs," and alsr~ exceeds the 85%TSS removal design
requirement.
The design requirements for filterstrips contained in the current BMP Manual indicates that the
maximum drainage area flowing to individual filters "sheit be (es5 than or equgl to 5 acres." The existing
Stormwater management plan includes two wet detention basins, one serving 54 acres and the other 30
acres. Installing filter strips downstream of either' of these basins is not appropriate owing to the size of
the drainage areas. Footnote number 2 contained on NCDENR Stormwater Form SWU-102, Wet
Detention Basin Supplement states that "In the 20 coastal counties, the requirement for a vegetative filter
may be waived if the wet detention basin is designed to provide 90%TSS removal." Accordingly, we
utilized N.C. Coastal Regions SA/DA Percentages Chart 4 when designing the wet detention basins in
order to provide 90% TSS removdl.
Additionally, the stormwater management plan includes 5,760 linear feet of grassed swales, with
3,090 feet serving the 54 acre drainage area and 2,670 feet serving the 30 acre drainage area. This results
in approximately 57 feet per acre and 89 feet per acre in the respective drainage areas. If designed
according to the requirements contained in the current BMP manual, grassed swales are assumed to
provide a 35% TSS removal and a 20% total nitrogen (TN) reduction. Our swales meet all design criteria
contained in the BMP manual except for length. Assuming a linear correlation between length per acre
and treatment function, and allowing the provided 57 feet per acre to control, yields an assumed 20%
TSS removal and 1 1 % TN reduction for the proposed swales. When these treatment capacities are
considered in addition to the 90% TSS removal and 25% TN reduction provided by the basins, the result is
approximately 92% TSS removal and 33% TN reduction for the existing stormwater management plan.
MECHANICAL, CIVIL, AND MARINE ENGINEERING MARINE HYDROGRAPHIC AND LAND SURVEYS
COMMERCIAL, INDUSTRIAL, MARINE AND RAILROAD FACILITIES DESIGN
FORENSIC ENGINEERING AND FAILURE ANALYSIS BOUNDARY SURVEYS AND MAPPING SERVICE

In conclusion, we request that your office consider our existing stormwater plan acceptable in
accordance with the "alternative plan" provision contained in Condition No. 4 and as supported by the
information herein presented. Additionally, if accepted, we request that the modified stormwater plan
request contained in Condition 6 of the issued approval of 401 WQC be rescinded.
Should you require additional information or have any questions, please contact us your
convenience.
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Very truly your~~gN .~ A R O ~ir~
ROBERT M. ~JC~~SS/~y ~ ~~i
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Michael L. R>"~~G1N~ .~`G~~~`
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Mr. Alan Klimek, P.E., Director, DWQ, 1617 Mail Service Center, Raleigh, NC 27699-1617
Mr. Ai Hodge, DWQ Regional Supervisor, Washington Regional Office
Mr. Chris Carroll, H&M Company, 50 Security Dr., Jackson, TN'38305