DAQ-2025-000035

RioTinto Rio Tinto K6nnecott
4700 Daybreak Parkway
South Jordan, Utah
84009
Tel: [phone]
November 12,2024
Mr. Bryce Bird, Director
Department of Environmental Quality
Division of Air Quality
195 N 1950 W
Salt Lake City, UT 84116
Attention: Mr. Joe Randolph
Subject:R307-107 and l.S.2.c: Smelter Main Stack Particulate
Breakdown
Kennecott Utah Copper - Smelter Facilitv
Title V operatinq Permit 3500030004
Dear Mr. Bird,
This letter provides a report of a breakdown event that occurred on October 27 ,2024,
at the Kennecott Utah Copper, LLC (Kennecott) Smelter. This report is intended to
satisfy the requirements of Permit Condition 1.S.2.c, deviation reporting, including
deviations due to breakdowns in accordance with R307-107.
Background
The Main Stack (SME011) is the exhaust stack for gases from the acid plant,
secondary gas system, rotary dryer, powerhouse superheater, matte grinding plant,
anodes area, and hydrometallurgical plant. To monitor particulate emissions,
Kennecott operates a continuous particulate sampler (CPS) to collect a daily sample
which provides a calendar-day average for particulate emissions in pounds per hour
(lbs/hr). The sample is a filter installed in the CPS, operated for between 20-28
hours, samples are then removed from the CPS, and desiccated in the Smelter
laboratory for 24 hours or more. For this reason, Main Stack particulate emission
results are provided to Kennecott personnel between 25-30 hours after the sample
has completed.
Description of lncident
On October 30,2024, the Smelter laboratory results indicated that the Main Stack
particulate emissions measured on October 27, 2024 were 152.5 lbs/hr exceeding
the particulate matter less than 10 microns (PM10) permit limit of 89.5 lbs/hr. Mr.
Sean Daly called Mr. Joseph Randolph of the Utah Division of Air Quality on
October 30,2024 to provide initial notification of the breakdown event.
Rio Tinto Kenne@tt, 4700 Daybreak Parkway, South Jordan, Utah, 84009
D[I'NIIIMLNT
ENVIHONMTN IAL OUALITY
fland rltl ,verc4
REVIEWED
Initials JBR Date 7/8/2024
Comp Status Meets
File # 10346 Blue 2
matte house damper
reading off and damper
aligned and bags replaced.
NFA
Analysis of Events
On October 28th the RTK Technicalteam noticed a very dark PM filter result for
October 27th thal is typically indicative of issues with the Matte Grinding baghouse
(SME011g). While the official results would take a few days to analyze, they alerted
RTK operations to start to look into potential baghouse issues, including dye testing.
It was determined that around 14 bags were blown out due to damper/draft
mismanagement and over pressurization. The baghouse was taken down and the
bags were replaced immediately and then put back into service. On October 30th the
result for October 27ih was complete and it was determined that there was a PM10
exceedance. ln the days following, there was a separate issue with the CPS that
required Kennecott to invalidate the results from October 28th to November 1$.
Because of these invalidated samples it was difficult to determine if the original
baghouse issue was resolved. Eventually once the separate CPS issue was resolved
and results for November 2nd came back under the limit, it was determined that the
issue had been resolved. A timeline of the particulate emissions sample results and
corrective action is provided in the table below:
Data Evaluation
As discussed above, the CPS is the permitted monitoring toolfor daily compliance
with the PM10 emissions limit. However, the CPS operation is based on an
Environmental Protection Agency Method 5 procedure and for that reason; it
measures all Total Suspended Particulate (TSP) rather than the PM'10 fraction. For
comparison with the permitted PM10 emissions limit, Kennecott also performs an
annual PM 1 0 stack test. The 2023 stack test performed on November 9-1 0, 2020,
measured 5.4 lbs/hr of PM10 compared to the CPS result of 27.6lbs/hr for the
same day. The 2021 stack test performed on November 17th 2021, measured
6.7lbs/hr of PM10 compared to the CPS results o'f 23.4 lbs/hr for the same day.
Based on this comparison, approximalely 24 percent of the emissions measured by
the CPS were PM10 emissions. lf this same comparison is applied to the sample
from October 271h, the actual PM10 emissions would be 36.6 lbs/hr which is less
than the PM10 emission limit. ln the past five years, the comparison of the CPS
data and the stack test results have indicated that the PM 10 fraction of the CPS
measured value ranges from 24-59 percent, all of which would suggest that the
Preliminary look at filter for10127 determined very
heavy/dark filter - eventually
emissions result was 152.5
lb/hr
RTK Technical team noticed dark filter,
alerted Operations to dye test baghouse to
determine if any broken bags. Found
around 14 broken bags and replaced and
put baghouse back into service
lnvalid results due to CPS
sampling issue
Sampling issue was noticed and resolved
by Environmentalteam on 1111124
27.21 lblhr
Baghouse and CPS sampling issues
resolved
PM10 emissions from the Main Stack during the breakdown event were below the
limit.
Additionally, as outlined in the permit, Kennecott monitors differential pressure (dP)
on the Matte Grinding baghouse. During the days preceding and following the
event, baghouse dP remained within the permitted range.
Corrective Action Summary
Kennecott believes the Matte Grinding baghouse and related process equipment are
maintained and operated in a manner consistent with good practices for minimizing
emissions. To the maximum extent possible, air pollution control equipment and
process equipment are maintained and were operated per standard procedures and
in a manner consistent with good practice for minimizing emissions, including
minimizing bypass emissions. Kennecott conducts monthly maintenance inspections
and dye testing on the baghouses to try to minimize breakdowns and catch issues
that could affect performance of the pollution control systems.
All practicable steps were taken to minimize potential impacts on ambient air
quality. Kennecott responded to the elevated particulate emissions on October 27th
by scheduling offline time to perform additional corrective actions. Review of events
suggests that corrective actions on October 28th reduced emissions below the PM10
emissions limit. Once the equipment was restarted on October 29th, Kennecott used
available process data to ensure that no additional excess emissions were emitted
from the Matte Grinding baghouse.
Based on information and belief formed after reasonable inquiry, the statements and
information in this document are true, accurate, and complete (R307-415-5d).
Should you have any questions regarding this report or need further information
regarding the event, please contact me or Sean Daly at 801-204-2563.
Yours sincerely,
Matt Tobey
General Manager - Metals