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November 20, 2000
Mr. Robert Geddie, WWTP
E. I. Dupont
22828 NC Hwy. 87 West
Fayetteville, NC 28306
SUBJECT: FLOW PROPORTIONAL COMPOSITE SAMPLING
E. I. Dupont de Nemours & Company, Inc. WWTP
NPDES Permit No. NC0003573
Bladen County
Dear Mr. Geddie:
Based on a recent on site review of sampling techniques at your facility it
has been determined that the Dupont Company's WWTP does not collect effluent
samples flow proportionally. The facility was sent a survey September 9. 1999
and it appears an error was made with the information submitted by the facility to
our office concerning effluent flow proportional sampling. The requirements for
flow proportional composite sampling is stated as follows in the Administrative
Code: 15A NCAC 2B .0503 -Surface Water Monitoring: Reporting
(4) "Composite sample means: a sample gathered over a 24 hour period by
continuous sampling or combining grab samples in such a manner as to result in a
total sample which is representative of the wastewater discharge during the sample
period. This sample may be obtained by methods given below, however, the
Director may designate the most appropriate method, number and size of aliquots
necessary and the time interval between grab samples on a case-by-case basis.
Samples may be collected manually or automatically.
a. Continuous - a single, continuous sample collected over -'a 24 hour period
proportional to the rate of flow.
b. Constant time/variable volume - a series of grab samples collected at equal
time intervals over a 24 hour period of discharge and combined
proportional to the rate of flow measured at the time of individual sample
collection, or
-continued-
225 GREEN STREET, SUITE 714 I SYSTEL BLD. FAYETTEVILLE, NORTH CAROLINA 28301-5043
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C. Variable time/constant volume - a series of grab samples of equal volume collected over a
24 hour period with the time intervals between samples determined by a preset number of
gallons passing the sampling point. Flow measurement between sample intervals shall be
determined by use of a flow recorder and totalizer, and the preset gallon interval between
sample collection fixed at no greater than 1/24 of the expected total daily flow at the
treatment system, or
d. Constant time/constant volume - a series of grab samples of equal volume collected over a
24 hour period at a constant time interval. This method may be used in situations where
effluent flow rates vary less than 15 percent. The grab samples shall be taken at intervals
of no greater than 20 minutes apart during any 24 hour period and must be of equal size
and of no less than 100 milliliters. Use of this method requires prior approval by the
Director." The Director has given the regional water quality supervisors authority to
approve this.
Our office requests that your facility initiate flow proportional effluent sampling on or
before March 15, 2001. Please reply to this office by December 31, 2000 as to what measures
will be facilitated to incorporate flow proportional effluent composite sampling.
If you have any questions or comments do not hesitate to contact me at
910-486-1541.
Sincerely,
Belinda S. Henson
Environmental Chemist
/bsh
cc: DWQ, NPDES Compliance Group