For a coal-fired power plant operating under the Mercury and Air Toxics Standards (40 CFR Part 63, Subpart UUUUU), every CEMS exceedance is a federal compliance event — not a maintenance note. Mercury, hydrogen chloride, and non-mercury metal HAP emissions are measured continuously, and when the control equipment behind those readings — electrostatic precipitators, FGD absorbers, activated carbon injection systems — slips on its maintenance schedule, the CEMS data reflects it before the shift supervisor does. One Midwest coal plant had recorded CEMS exceedances in 7 of the previous 12 months, drawing two notices of violation and a compliance schedule from the state environmental agency. The root cause wasn't operational failure. It was a maintenance documentation gap: ESP rapper sequences, FGD slurry density checks, and mist eliminator wash cycles were being performed inconsistently — because the PM schedules weren't enforced and the records weren't traceable. Eleven months after deploying Oxmaint, the plant recorded zero CEMS exceedances — the first clean compliance year in four operating seasons. Sign up free to build the same compliance workflow, or book a demo for a live walkthrough of Oxmaint's emissions compliance templates.
CASE STUDY · COAL-FIRED POWER · MATS COMPLIANCE
From 7 Exceedance Months to Zero.
In 11 Months.
How a Midwest coal plant eliminated CEMS exceedances, cleared two notices of violation, and built a MATS-ready maintenance record system using Oxmaint's emissions compliance workflows.
BEFORE OXMAINT
7
Months with CEMS exceedances in prior 12-month period
2
Notices of violation from state environmental agency
0%
Traceable ESP and FGD maintenance records
AFTER OXMAINT
0
CEMS exceedances in 11-month post-deployment period
100%
ESP rapper, FGD, and ACI PM completion rate
Cleared
Both notices of violation closed with documented evidence
THE COMPLIANCE CONTEXT
Why MATS Maintenance Records Are a Regulatory Instrument
The 2012 Mercury and Air Toxics Standards established emission limits for mercury, acid gas HAP (measured as HCl), and non-mercury metal HAP from coal-fired electric generating units. Plants demonstrate compliance primarily through CEMS data — and CEMS data is only as clean as the control equipment behind it. When an ESP field trips, when FGD slurry chemistry drifts, when activated carbon injection rates aren't verified — the stack readings move. And in a MATS compliance framework, out-of-limit readings aren't maintenance events. They're federal records with NOV and penalty exposure.
Electrostatic Precipitator
Controls non-Hg metal HAP and particulate matter. Rapper sequence, field energization levels, and hopper evacuation intervals directly determine PM capture efficiency — and therefore CEMS PM readings.
Flue Gas Desulfurization
Controls SO₂ and serves as acid gas HAP surrogate for plants using the SO₂ CEMS alternate standard. Slurry density, pH, recirculation pump operation, and mist eliminator wash cycles determine SO₂ removal efficiency.
Activated Carbon Injection
Mercury-specific control. Injection rate verification, sorbent quality checks, and feeder calibration directly determine mercury capture effectiveness. Missed injection rate verifications are among the most common MATS documentation gaps.
Continuous Emissions Monitoring
The compliance measurement system itself requires daily calibration drift checks, quarterly relative accuracy test audits (RATA), and documented maintenance. An out-of-calibration analyser is treated as an exceedance for its entire data gap period.
ROOT CAUSE ANALYSIS
Why the Exceedances Were Happening
The plant's environmental engineer identified the exceedance pattern through a post-NOV root cause analysis. The findings pointed to a single systemic failure — not equipment degradation, but maintenance schedule enforcement and record integrity.
Finding 01
ESP Rapper Sequences Running on Paper Checklists
Rapper sequence adjustments and hopper evacuation checks were logged on paper shift sheets that weren't retained. When an EPA inspector requested 90 days of ESP maintenance records during the NOV investigation, the plant produced 11 days. The remaining period was undocumented — treated as unperformed.
Finding 02
FGD Slurry Density Checks Performed Inconsistently
Slurry density and pH monitoring rounds were scheduled verbally, not in a formal PM system. During high-load operating periods when operators were stretched, rounds were skipped. Three of the seven exceedance months correlated directly with periods of FGD slurry chemistry drift discovered only after the CEMS data flagged it.
Finding 03
ACI Injection Rate Verifications Without Timestamped Records
Activated carbon injection rates were being verified by operators but logged only in a shared notebook. No technician attribution, no timestamps, no systematic record. During the RATA audit period, the plant couldn't demonstrate continuous ACI operation at required injection rates — contributing to two of the seven exceedance months.
Finding 04
CEMS Daily Calibration Drift Checks Without Overdue Alerts
Daily CEMS calibration drift checks were required under 40 CFR Part 75. The checks were performed most days — but with no system to flag overdue checks in real time, drift events weren't caught and corrected within the regulatory window, turning maintenance gaps into exceedance records.
OXMAINT · MATS COMPLIANCE · COAL PLANT MAINTENANCE
Are Your ESP, FGD, and ACI Records Ready for an EPA Inspector Today?
Oxmaint's pre-built MATS compliance templates — ESP rapper schedules, FGD slurry PM, ACI injection verification, and CEMS daily drift checks — deploy in under a week and generate audit-ready records automatically.
THE SOLUTION
What Oxmaint Replaced and What It Built
The environmental engineer led deployment in three weeks — migrating existing PM schedules, building MATS-specific compliance work order templates, and configuring mobile access for field operators. No IT project. Live within 21 days of kickoff.
Paper rapper sequence checklists with no retention
Daily ESP rapper work orders with timestamped technician sign-off, retained permanently in asset history
Verbal FGD round scheduling, skipped during high-load periods
Auto-generated FGD slurry density and pH rounds on shift intervals, with overdue alerts before rounds are missed
ACI injection logs in a shared notebook, no attribution
Mobile ACI injection verification work orders — technician-attributed, timestamped, exportable for RATA audit periods
CEMS calibration drift checks with no overdue flag system
Daily CEMS drift check work orders with 2-hour overdue alert — corrective action triggered before the regulatory window closes
Quarterly RATA prep as a manual scramble
RATA deadline auto-scheduled 30 days out, with pre-RATA checklist and documentation package generated from Oxmaint records
THE RESULTS
11 Months of Clean Compliance
Zero
CEMS Exceedances
in 11 Months
Both
Notices of violation closed — documented evidence package submitted to state agency, compliance schedule satisfied
100%
ESP rapper PM completion rate maintained across 11 months — first time this metric was measurable at all
3 days
Time to generate next RATA documentation package vs. two-week prior manual process
Zero
CEMS calibration drift events that exceeded the regulatory correction window in the post-deployment period
$0
Additional NOV penalties incurred — prior two-year period had accumulated $94,000 in civil penalties
"
We'd been doing the maintenance. The problem was we couldn't prove it. After Oxmaint, I can pull a 90-day ESP maintenance history in about 30 seconds. That's the difference between a NOV and a clean inspection — not what you did, but what you can document.
— Environmental Compliance Engineer, Midwest Coal Plant, 600 MW unit
COMPLIANCE TEMPLATE LIBRARY
Oxmaint's Pre-Built MATS Maintenance Templates
Every work order template below is pre-built in Oxmaint and deployable the same week you sign up — no configuration required. Each maps directly to a MATS compliance documentation requirement.
ESP
Daily Rapper Sequence Verification
Daily · Shift-based trigger
Non-Hg metal HAP / fPM control documentation
ESP
Hopper Evacuation & Field Energization Check
Weekly · Auto-generated
ESP performance assurance record
FGD
Slurry Density & pH Monitoring Round
Per shift · Overdue alert at 2 hrs
SO₂ / acid gas HAP surrogate control
FGD
Mist Eliminator Wash Cycle Verification
Daily · Timestamped sign-off
FGD efficiency and opacity compliance
ACI
Injection Rate Verification & Sorbent Check
Per shift · Technician-attributed
Mercury (Hg) control documentation
CEMS
Daily Calibration Drift Check
Daily · 2-hr overdue escalation
40 CFR Part 75 analyser calibration integrity
CEMS
Quarterly RATA Preparation Checklist
Quarterly · 30-day advance scheduling
Relative accuracy test audit documentation
ACI
Carbon Feeder Calibration & Maintenance
Monthly · Preventive schedule
ACI system reliability for Hg compliance
FREQUENTLY ASKED
Oxmaint for Coal Plant MATS Compliance
How quickly can Oxmaint MATS compliance templates be deployed at a coal plant?
Pre-built MATS templates for ESP, FGD, ACI, and CEMS are available immediately upon signup and can be live with your asset structure in under a week. Most plants have all compliance work orders generating within 5–7 days of deployment.
Sign up free to see the template library.
Can Oxmaint records be used as evidence in response to an EPA or state NOV?
Yes. Oxmaint work order records are timestamped, technician-attributed, and permanently stored — meeting the documentation standard required by EPA and state environmental agencies for MATS compliance demonstration. Records are exportable in structured formats for regulatory submission.
Does Oxmaint integrate with CEMS data systems directly?
Oxmaint manages the maintenance and calibration record layer — work orders, completion records, drift check documentation — that supports CEMS data validity. Integration with CEMS historian or DCS systems is available for automated alert triggering.
Book a demo to discuss your plant's CEMS configuration.
What happens when a CEMS drift check is overdue?
Oxmaint generates an overdue alert — configurable to 1–4 hours after the required check window — and escalates to the designated environmental engineer. A corrective work order is auto-generated, creating a documented response record before the regulatory data gap window is exceeded.
How does Oxmaint help with quarterly RATA preparation?
Oxmaint auto-schedules RATA preparation work orders 30 days before each quarterly RATA window. A pre-built RATA checklist walks technicians through CEMS pre-test maintenance. Oxmaint then generates the maintenance documentation package — CEMS calibration history, control equipment PM records — needed for the RATA test period.
Sign up free to review the template.
OXMAINT · COAL PLANT CMMS · MATS COMPLIANCE
Stop Running MATS Compliance on Paper Checklists
Oxmaint's pre-built ESP, FGD, ACI, and CEMS maintenance templates give coal plant environmental and O&M teams the timestamped, technician-attributed records they need to demonstrate MATS compliance — and clear NOVs before they become penalties.
