NC0024911_NOV-2019-PC-0251 Response_20190422

Metropolitan Sewerage District
OF BUNCOMBE COUNTY, NORTH CAROLINA
VF ONNTY, 0\"
April 22; 2019
Landon Davidson, P.G.
Regional Supervisor Asheville Regional Office
Water Quality Regional Operations Section
NCDEQ - Division of Water Resources
2090 U.S. Hwy. 70
Swannanoa, N.C. 28711
Dear Mr. Davidson:
Metropolitan Sewerage District (MSD) received the Notice of Violation & Intent to Assess Civil
Penalty dated April 11th, for the bypass occurring February 26, 2019, at the new headworks fine
screens. The bypass occurred following a sequence of over -torque alarms on all three (3) fine
screens placed in service February 19th. The new PLC control logic, commanding automated
actions of moving parts, was thoroughly tested in the last week of January. That testing did not
indicate any issues with the proper operation of the screens, flow control gates, or any associated
appurtenances. The over -torque alarms experienced are related below:
Fine Screen 1 had a screen over -torque alarm at: 3:47:19 2/26/19
Fine Screen 3 had a screen over -torque alarm at: 3:53:22 2/26/19
Fine Screen 2 had a screen over -torque alarm at: 4:04:26 2/26/19
Based on the duty assignment of the fine screens; Screen 1, should have been the last screen to fault
since it was assigned Lag2 responsibility. Screen 3 was the assigned the Lead responsibility, Screen
2 the Lag responsibility.
After the by-pass occurred, MSD promptly contacted the General Contractor (Judy Construction),
equipment supplier (EnviroCare) and the systems integrator, (CITI). This initial contact was to
begin scheduling additional logic and equipment troubleshooting and testing. The scheduling
proved difficult due to the heavy workload of the equipment supplier and system integrator. The
earliest all parties could be on site was not until March 11th. In the interim, MSD has placed one
fine screen channel in a constant open/operational state to prevent the possibility of another
bypass.
On -March 11, 2019, representatives from EnviroCare and CITI,along with MSD staff conducted
equipment and,control logic testing. This testing carried over to March 12, 2019, -with no
deficiencies identified. Below is the list of testing, changes and outcomes;
• .The logic of PLC14 was re -checked but no changes to the program were made before the
test. .
• For, testing, Screen 3 was the lead, Screen 2 the lag and Screen 1 was lag2.
Protecting Our Natural Resources
2028 RIVERSIDE DRIVE, ASHEVILLE, NORTH CAROLINA28804 TELEPHONE: [phone] FAX: [phone] WEBSITE: www.msdbc.org

• Jeff (Envirocare) lowered the trip set point for the over -torque relay on the LCP panels so
that the screen would fail in an over -torque each time it was turned on.
• We ran different scenarios where only the lead failed, then the lead and lag failed, and
finally all the screens. In addition, tests were performed only with the lead running and
then, by changing the influent flow set point, with two screens running. In every test, PLC14
behave' as expected. When one of the screens failed, the influent and effluent gates remained
open for 5 minutes, while the next screen opened its gates.
• A critical high level situation was simulated, all screen gates opened under this condition,
even when the screens were faulted.
• It was found that the set point for the high critical alarm was set at 7 feet, comparing it to
the elevation at which the sensor was installed; this set point would not be reached during a
high flow/level situation.
• After the tests were completed, Jeff reconfigured the over -torque setting to its original set
point and Dale changed the critical high level alarm to 6.5 feet. In addition, after discussion
with Operations, the 5-minute timer to maintain the gates open after a screen failure was
increased to 8 hours.
• It was confirmed that all the over -torque alarms were generated at the LCP panels. Jeff
could not identify the reason why screens 2 and 1 failed in over -torque, and the behavior of
the gates on February 26 was not possible to replicate.
• The logic of PLC14 with respect to the influent and effluent gates was not modified as it
worked as expected and the gates did not close immediately after the LCP panel torque
over -torque alarms were generated.
Since thepost testing did not duplicate the over torque situation experiences on February 26, 2019,
MSD has undertaken operational controls to eliminate the likelihood of another by-pass from the
fine screens. This is as follows;
• All flow control gates, influent and effluent, are maintained in the open position
• All PLC set points are set so operational control must be manually changed by an
operator
• The washing of fine screens is controlled by flow differential from influent side of
fine screen to effluent side of side of fine screen. This is the only, somewhat,
automatic operation of the fine screens in place.
MSD believes the actions taken prior to the bypass of the fine screens were within industry
standard for startup of new equipment. The followup of the bypass was detailed and complete even
though the over torque was not re -creatable. Furthermore, MSD believes the operational changes to
the fine screens will prevent another bypass barring any extraordinary operating conditions.
Respectfully,
Peter C. Weed
Director of Operations, MSD
Cc: Thomas E. Hartye, General Manager; MSD
File