NC0085359_NOV-2022-LV-0237_20220422

EST. 1842
April 22, 2022
Department of Public Works
Water/Wastewater Division
4600 Goldmine Road
Monroe, NC 28110
T. 704-289-1434
F. 704-289-7395
www.unioncountync.gov
W. Corey Basinger,
Regional Supervisor
NCDEQ
610 East Center Avenue, Suite 301
Mooresville, NC 28115
Dear Mr asinger,
RECEIVED/NCDEQ/D1NR
APR 2 7 2022
WQROS
MOORESVILLE REGIONAL OFFICE
This letter is in response to NOV-2022-LV-0237, outlining the exceedance in monthly total
ammonia average that was experienced at our 12 Mile Creek WRF in February 2022. This
exceedance was a result of two separate mechanical issues that occurred concurrently:
• Failure of the Turblex blowers to achieve sufficient operating parameters and,
• Uneven distribution of solids between the grit facility and the influent distribution
structure.
Please see the attached copy of a letter from 12 Mile Creek Supervisor Jonathan Jordan, to
NCDEQ staff member Roberto Scheller, for a detailed explanation of the issues and the
methods used to correct them.
Since these issues were corrected we have consistently seen ammonia results well below
permit limits.
• February= 2.59MG/L (NOV)
• March= 0.013MG/L
If you have any questions or concerns please contact me at 704-296-4215.
Sincerely,
I /
Andrew Neff, PE
Water & Wastewater Division Director
Cc: Hyong Yi, Public Works Administrator
Josh Brooks, Asst. Div. Director, Water & Wastewater
Bart Farmer, WRF Superintendent

RECEIVED/NCDEQ/DWR
APR 2 7 2022
WQROS
MOORESVILLE REGIONAL. OFFICE; UN
Roberto Scheller
NC Department of Environmental Quality
Water Quality Regional Operations Section
610 E, Center AVE., Suite 301
Mooresville, NC 28115
■ -C=
Wm' TER
RE: NC0085359, February 2022 Monthly Average Ammonia Violation
Dear Roberto,
This Letter is a followup to our phone conversation on 3/28/2022 at 13:05.
Twelve Mile has exceeded it permit limitation for the Ammonia monthly average for the month of
February. There were multiple issues with the Howden Turblex Blowers, mechanically and
within their programing, Twelve Mile is equiped with 3 Howden Turblex Blowers, 2- 300HP and
1- 450HP. The blowers are designed to run in 5 different staging configurations to maintain
adequate pressuere in the aeration header. Stage 1- One 300HP blower, Stage 2- One 450HP
blower, Stage 3- Two 300HP blowers, Stage 4-One 300HP blower and One 450HP blower,
Stage 5- One 450HP blower and Two 300HP blowers. During our investigations with the Blower
we also found an issue with the disturbution of the Influent and RAS mix to the aeration basins.
Below is a time line beginning from when we started having issues with the blowers to present
as of this letter.
Blower Surge issue
On 11/23/2021 we experienced issues with the Aeration Blowers running all 3 blowers at once
in stage 5. Subsequently a workorder was put in to our maintenance workorder system. When
stage 5 was required, it would call the 450HP blower to run and immedately after the startup
sequence the blower would shut down on a surge alarm. The surge is similar to a water
hammer in a pipe and can cause significant damage to the equipment and associated piping. To
prevent damage to the equipment and piping we limited the blowers to run only to stage 4. After
our maintenance department investigated initially, the thought was that their was an issue within
our internal SCADA logic and how it was running the blowers. CITI (SCADA intergrader) was
contacted and brought on site. CITI could not find any issues with the logic but made changes to
the header pressure and lowered the max dynamic pressure for when 3 blowers are running
from 7,5PSI to 7,1PSI. Through the thanksgiving holidays this seemed to work but when flows
and loadings increased the blower started surging again.
On December 151" 2021, With direction from the manufacture and CITI, we attempted to run
blowers #1 and #2 (the 300HP blowers) in manual at 90% and put blower #3 (the 450HP
blower) in auto to regulate the header pressure. When blower #3 was put in auto it immedately
would ramp to 90% and would start to over pressurize the system. Once the pressure reached
an uncomfortable level we aborted to prevent damage to the diffusers. During this test we found
that we were not getting the expected/designed air flow from the blowers. The manufacture was
informed of our findings and stated that they have a new operating
Union County Water
500 North Main Street, Suite 400
Monroe, NC 28112
T 704,296,4210
unioncountync.gov/wcter
ar

expected air flow both in independent and combined operations. A summary of these tests are
below:
Blower #1
O 45% capacity — 112 HP, 2366 CFM @ 5.66 PSI header pressure
O 100% capacity — 233 HP, 5660 CFM @ 6.28 PSI header pressure
Blower #2
O 45% capacity — 111 HP, 2361 CFM @ 5.66 PSI header pressure
O 100% capacity — 232 HP, 5662 CFM ©6.27 PSI header pressure
Blower #1 and #2 together
O 100% capacity -- 229 HP (ea.), 11,290 CFM @ 6.39 PSI header pressure
O 100% capacity — 223 HP (ea.), 10,745 CFM @ 7.02 PSI header pressure
This test was ran at two different discharge pressures to confirm that
blower performance remained as expected when pressure increased.
Once testing was completed on Blower #1 and #2, similar testing was performed on Blower #3
(the 450 HP). Similar to above, the IGVs were found to be off by a few degrees and corrected,
but Tess error than the others. The results of the high -end tests on Blower #3 are as follows:
Blower #3 (before IGV adjustments)
O 100% capacity — 278 HP, 7276 CFM @ 6.38 PSI header pressure
Blower #3 (after IGV adjustments)
O 100% capacity — 269 HP, 7022 CFM @ 6.15 PSI header pressure
From the above you can see that the IGV adjustment provided no positive benefit (actually
worsened the performance slightly). Howden did not find any other mechanical issues with
Blower #3, but does agree with the team that Blower #3 (the 450 HP) is not performing as it
should, as it appears to only be providing about 80% of its designed air capacity.
Mike Lindsey (the Howden tech onsite) is consulting with Howden engineering over this
weekend and hopes to be able to return to the site Monday March 14th with some programming
adjustments. We are currently awaiting further information from Howden at this time.
March 15th 2022, Howden returned for a test that the factory asked for. Howden manipulated the
blower to intake more air by opening the Inlet Guide Vanes via a setting in his computer. We
preformed this test previously but the local control panel was only allowed to go up to a 1.0
factor via the screen. The Howden changed this setting to a 5.0 factor gradually, we cannot
achieve this factor on the screen at the blower. The baseline of blower 3 running at 100%
capacity for vane diffusers was 299HP/7992SCFM
The following numbers were collected at separate points in the testing as Howden increased the
IGVs ability to open more, while keeping the VD position the same. It was understood that these
4 other readings came from Howden changing the IGV opening setpoint to 2, 3, 4, and 5.
1. 299HP/7992SCFM (baseline)
2. 331 HP/8806SCFM
urlioncountync.gov/water

On February 8th 2022 After consluting with our engineers we determined that the piping size
was adequate to handle influent and RAS flow through one pipe. We closed the second valve
and saw positive results. The west side TSS was 3358mg/L and the east side TSS was
3991 mg/L,
In conclusion, we are able to utilize the full capacity of the two 300 HP blowers and can utilize
the 450 hp up to 80% of its capacity. Solids distribution at the Influent Distribution Structure has
been corrected. Currently this is providing sufficient air and we have not had any blower surge
issues since the changes were made. As of February 21st the Effluent Ammonia has been less
than 2.0mg/L and the plant is back into compliance.
If you have any questions please feel free to reach out to me directly.
Sincerely,
Jonathan Jordan
Treatment Plant Supervisor
Jonathan.JordanAunioncountync.gov
704-562-4542
Union oUn ync,gov/welter