NC0027103_Flow Proportional Sampling_20000321

NORTH CAROLINA DEPARTMENT OF
ENVIRONMENT AND NATURAL RESOURCES
March 21, 2000
Ms. Karen Dial
Town of Pembroke WWTP
PO Box 866
Pembroke, NC 28372
DIVISION OF WATER QUALITY
FAYETTEVILLE REGIONAL OFFICE
SUBJECT: FLOW PROPORTIONAL COMPOSITE SAMPLING
Town of Pembroke WWTP
NPDES Permit No. NC0027103
Robeson County
Dear Ms. Dial:
Based on a recent survey and an on site review of sampling techniques at
your facility it has been determined that the Town of Pembroke's WWTP does not
collect effluent samples flow proportionally. 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 obtained by methods given below, however,
the Director may designate the most appropriatemethod, 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
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
225 GREEN STREET, SUITE 714 / SYSTEL ELD. FAYETTEVILLE, NORTH CAROLINA 28301-5043
PHONE [phone] FAX [phone]
AN EQUAL OPPORTUNITY / AFFIRMATIVE ACTION EMPLOYER - 50% RECYCLED/10% POST -CONSUMER PAPER

-continued-
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.
Due to the possible cost involved with the installation or modification of
effluent flow and sampling equipment this office requests that the Town initiate flow
proportional sampling on or before March 15, 2001. Please reply to this office as to what
measures will be required to facilitate flow proportional composite sampling on or before June
1, 2000.
If you have any questions or comments do not hesitate to contact me at
910-486-1541.
Sincerely, .
; nd . )
Belinda S. Henson
Environmental Chemist
/bsh
cc: DWQ, NPDES Compliance Group

iv• .ry . r_6. .., L1 LJTJ
•
•
•
•
•
•
r GI*ID ww I r
TOWN OF PEMBROKE
WWTp LAB
P.O. BOX 866
PE BROKE, NC 28372
' Ts, Y.t...=`tinc°r� ' •�� ;��ny y:nz k_ rry
r o, I 0. i� � p n" `-F
,a: sI ,yld�yti'�1��"
To: BELINDA HINSON
FAX: [phone]
rHUt CI
iUh -6
FAYE T TEV LL E
REG, O FFICF
Frorn: KAREN T. DIAL Date: 06/16/00
Re; ' FLOW PROPORTIONAL Pages:
SAMPLING
CC; FILES
As per the requirements of the State of North Carolina, Division of Water Quality, our ..
• 'sampler for the wastewater treatment plant is now picking up samples on the flow proportional cycle. This
. change in sampling was implemented on February 25th, & 28t , 2000.