The 2024 EPA Effluent Limitation Guidelines for the Steam Electric Power Generating Point Source Category established zero-discharge requirements for three critical wastewater streams at coal-fired power plants: flue gas desulfurization (FGD) wastewater, bottom ash transport water (BATW), and combustion residual leachate (CRL). Effective July 8, 2024, these rules represent the most significant expansion of coal plant wastewater regulation since 2015, requiring facilities to eliminate direct discharge of pollutants including arsenic, mercury, selenium, and chromium into surface waters — pollutants that have contaminated drinking water sources and aquatic ecosystems near coal plants for decades. Compliance requires capital investment in zero liquid discharge (ZLD) technology, dry ash handling conversion, and engineered leachate collection systems, as well as ongoing O&M programs and discharge monitoring reports that must demonstrate continuous compliance. Sign up free on OxMaint to manage your wastewater treatment system maintenance schedules, inspection records, and DMR documentation in one audit-ready platform built for power plant ELG compliance.
EPA ELG · Clean Water Act · Steam Electric · FGD · Bottom Ash · ZLD
EPA Effluent Limitation Guidelines
for Power Plants: The ZLD Compliance Roadmap
The 2024 ELG Rule requires zero discharge for FGD wastewater, bottom ash transport water, and combustion residual leachate. Here's what that means for your operations, your wastewater systems, and your compliance documentation program.
Zero
Discharge limit for FGD wastewater, bottom ash transport water, and CRL under the 2024 rule
July 2024
Effective date of the 2024 Supplemental ELG Rule (40 CFR Part 423)
660M+ lbs
Estimated annual pollutant discharge reduction under the 2024 rule
Dec 2034
Proposed extended compliance deadline under EPA's 2025 deadline extension rulemaking
Regulated Wastewater Streams
The Three Zero-Discharge Wastewater Streams — What They Are and Why They Matter
Each regulated wastewater stream has a distinct source, treatment pathway, and compliance approach. Understanding the difference determines what capital investment and O&M documentation your facility needs.
FGD Wastewater
Zero Discharge Required
Source: Wet limestone FGD scrubbers — the blowdown from the scrubber recirculation loop that concentrates sulfates, chlorides, and dissolved metals including mercury, arsenic, and selenium.
Key Regulated Pollutants
Mercury
Arsenic
Selenium
Nitrate/Nitrite
Chlorides
ZLD Technology Pathway
Biological treatment (for selenium and nitrate removal) followed by physical-chemical treatment (evaporator/crystallizer system) to achieve zero liquid discharge. High-density sludge thickeners and brine concentrators are common upstream components.
O&M complexity: High — ZLD systems require continuous monitoring of biological reactor health, chemical dosing rates, and evaporator scale management.
Bottom Ash Transport Water
Zero Discharge Required
Source: Water used to hydraulically convey bottom ash (coarse coal combustion residuals) from the furnace bottom to a dewatering facility or ash pond. The 2020 rule had allowed some continued discharge; the 2024 rule eliminates it.
Key Regulated Pollutants
Arsenic
Boron
Thallium
Total Dissolved Solids
Compliance Technology Pathway
Conversion from wet sluicing to dry bottom ash handling (submerged scraper conveyor or vacuum pneumatic system) eliminates the wastewater stream at the source. For plants retaining wet systems, closed-loop water recirculation with zero discharge is required.
O&M complexity: Moderate — dry ash handling requires conveyor maintenance programs and bearing lubrication schedules, but eliminates the wastewater treatment system entirely.
Combustion Residual Leachate
Zero Discharge / CRL Limits
Source: Liquid that has percolated through or drained from coal ash storage areas (piles, ponds, landfills) and collected in sumps or drainage systems. At new sources, zero discharge applies; existing sources face numeric limits for mercury and arsenic from groundwater CRL.
Key Regulated Pollutants
Mercury
Arsenic
Boron
Radium
Compliance Technology Pathway
Leachate collection and containment systems (perimeter drains, sump pumps, liner systems), combined with evaporation or reuse as process water. For existing ponds, engineered closure with liner isolation or dry closure by removal eliminates the CRL stream at its source.
O&M complexity: Variable — sump pump maintenance, liner integrity inspection, and leachate volume monitoring are ongoing requirements throughout closure.
ELG Documentation with OxMaint
Your ZLD System Maintenance Records Are Your ELG Compliance Records
A zero-discharge system that isn't maintained doesn't stay at zero discharge. OxMaint links your FGD treatment system, dry ash conveyor, and leachate collection maintenance work orders directly to your ELG compliance program — creating auditable proof that your ZLD systems were operated and maintained to sustain the zero-discharge outcome required by the permit.
Regulatory Timeline
ELG Compliance Timeline — Key Dates, Deadlines, and What Changes When
The ELG compliance timeline has evolved across three major rulemakings (2015, 2020, 2024) with EPA's 2025 proposed deadline extension adding further complexity. This timeline shows where your facility likely stands today.
2015
Original ELG Rule
First federal limits set for FGD wastewater and bottom ash transport water. Zero discharge for fly ash transport water. Beginning of technology-based limits for the steam electric sector.
2020
Revised ELG Rule
Trump administration revised FGD and BATW requirements, eliminating zero-discharge for bottom ash transport water and relaxing FGD standards. Retirement subcategory created for plants retiring by 2028.
July 8, 2024
2024 Supplemental ELG Rule Effective
Zero-discharge requirements reinstated and expanded for FGD wastewater, BATW, and CRL. CRL numeric limits for mercury and arsenic added. Estimated $536M–$1.1B annual compliance cost across the industry.
Now (2025–2026)
Compliance Pathway Assessment Period
EPA's proposed rulemaking would extend the compliance assessment deadline to December 31, 2031. Facilities must evaluate zero-discharge pathways, update NPDES permits, and begin capital project planning. Current ELG requirements remain enforceable.
Proposed Dec 2034
Zero-Discharge Compliance Deadline
Under EPA's proposed 5-year extension, full zero-discharge systems for FGD wastewater, BATW, and CRL must be operational by December 31, 2034 (extended from 2029). Permitting, engineering, and construction must begin now to meet this deadline.
Compliance Requirements Matrix
ELG Requirements by Wastewater Stream and Source Type
Compliance requirements differ between new sources (greenfield or recommissioned units) and existing sources, and between direct dischargers and indirect dischargers (those using municipal treatment systems).
Common Questions
EPA ELG Frequently Asked Questions for Power Plants
Is the 2024 ELG Rule still in effect given Trump administration rollback activity?
As of mid-2026, the 2024 ELG Rule remains effective (July 8, 2024 effective date). EPA has proposed extending compliance deadlines but has not proposed repealing the zero-discharge requirements themselves. The compliance deadlines are under active rulemaking, but the underlying zero-discharge standards for FGD wastewater, BATW, and CRL are current law. Facilities should plan for compliance while monitoring EPA's proposed deadline extension rulemaking for updated timelines.
OxMaint can help track your ELG compliance milestones as deadlines evolve.
What qualifies for the retirement subcategory and what does it allow?
Plants that have committed to permanently cease burning coal by a specific deadline may be eligible for alternative, less stringent wastewater pollution limits. The retirement subcategory allows qualifying facilities to continue meeting the less stringent 2015 or 2020 ELG requirements rather than implementing full ZLD technology. Qualifying requires a binding commitment to retire (e.g., a FERC filing or state permit condition specifying the coal retirement date) and continued compliance with the applicable alternative standards until closure.
How do ELG and CCR rules interact for ash pond closure compliance?
The ELG and CCR rules were deliberately coordinated by EPA to avoid duplicative compliance requirements. CCR rules govern the structural integrity, groundwater monitoring, and closure of coal ash storage units under RCRA. ELG rules govern the wastewater discharges that flow from those units under the Clean Water Act. For surface impoundments subject to closure, both programs apply simultaneously — CCR governs the physical closure, while ELG governs any leachate or wastewater discharge during and after the closure process.
What ongoing O&M documentation does a ZLD system require to support ELG compliance?
Zero liquid discharge systems require continuous documentation of biological reactor performance (for selenium/nitrate removal), evaporator scale management and cleaning intervals, chemical dosing rates, and effluent quality at the recycle return point. DMR (Discharge Monitoring Report) submissions to NPDES authorities require monitoring data traceable to calibrated instruments. Any ZLD system upset that results in a bypass to surface water creates an immediate permit deviation requiring notification and documentation.
Book a demo to see how OxMaint structures ZLD O&M records for ELG compliance.
What pollutants in FGD wastewater make it the most regulated of the three streams?
FGD wastewater from wet limestone scrubbers concentrates pollutants absorbed from flue gas, including mercury, arsenic, selenium, boron, bromide, and nitrate/nitrite. Selenium toxicity to aquatic species is particularly acute — a few parts per billion can cause reproductive failure in fish populations downstream of discharge points. Mercury and arsenic present drinking water contamination risks. These ecological and public health impacts drove EPA to prioritize FGD wastewater as the most stringently regulated stream in the ELG rule.
Build Your ELG Compliance Program Today
Zero Discharge Means Zero Room for Maintenance Documentation Gaps
When your ZLD system has an upset and a permit authority asks for your maintenance records to demonstrate the event was unforeseeable and properly corrected, your answer is only as good as your documentation. OxMaint keeps every service record, calibration log, and inspection report organized, timestamped, and immediately retrievable for your FGD, dry ash, and leachate systems.
