NC0055221_Permit Flow Monitoring Requirements for WTP_20170327

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Water Resources a
Environmental Quality
March 27, 2017
Mr. Larry Carver, WTP Superintendent
City of Marion
P.O. Box 700
Marion, NC 28752
Subject: Permit Flow Monitoring Requirements for WTP >50,000 and
Continuous Flow Totalizing Devices
NPDES Application NCO055221
Marion Water Treatment Plant (WTP)
Buncombe County
Dear Mr. Carver:
ROY COOPER
Governor
MICHAEL S. REGAN
Secretary
S. JAY ZIMMERMAN
Director
In accordance with permit NC0055221, the City of Marion is required to install a continuous flow meter
18 months from the permit effective date of March 1, 2015. Therefore, continuous flow recording was
required by September 1, 2016.
In accordance with 15A NCAC 02B .0505 (b)(1), all water pollution control facilities shall install,
operate, and maintain continuous flow measuring devices or totalizing devices. Therefore, continuous
flow measurement can include totalizing devices. Additionally, the above rule and permit condition Part
II Section D. (3), requires the following for continuous recording devices or totalizing devices:
Appropriate flow measurement devices and methods consistent with accepted scientific practices
shall be selected and used to ensure the accuracy and reliability of measurements of the volume of
monitored discharges. The devices shall be installed, calibrated and maintained to ensure that the
accuracy of the measurements is consistent with the accepted capability of that type of device.
Devices selected shall be capable of measuring flows with a maximum deviation of less than 10%
from the true discharge rates throughout the range of expected discharge volumes. Flow
measurement devices shall be accurately calibrated at a minimum of once per year and
maintained to ensure that the accuracy of the measurements is consistent with the accepted
capability of that type of device. The Director shall approve the flow measurement device and
monitoring location prior to installation.
On-site calibration would be the preferred method, but it is our understanding that totalizing devices may
have to be shipped to the manufacture for calibration. Please note that General Permit Part II, Section A.
gives exceptions to when continuous flow measurement can be interrupted:
Continuous flow measurement
Flow monitoring that occurs without interruption throughout the operating hours of the facility.
Flow shall be monitored continually except for the infrequent times when there may be no flow or
for infrequent maintenance activities on the flow device.
<:�'N' of ing Compares!: L
State of North Carolina I Environmental Quality
1617 Mail Service Center I Raleigh, North Carolina 27699-1617
919-707-9000

Mr. Carver
March 27, 2017
Page 2 of 2
Removal of a totalizing devices for calibration is an infrequent maintenance activity. During such time,
flow monitoring may be an estimate or instantaneous. For instantaneous flow monitoring, the duration of
the discharge must be reported on the DMR in addition to the total flow. This can be reported in the
comments section of eDMR. The removal of a totalizing device for calibration must also be reported in
the eDMR comments section.
If you have any questions about this letter or your permit, please contact Derek Denard at 919-807-6307
or via e-mail at [e-mail].
S. cerely
S. Jay Zimmerman, P.G., Director
Division of Water Resources
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