After a lengthy period of speculation, the U.S. Environmental Protection Agency (EPA) has issued a Notice of Proposed Rulemaking signaling its intent to issue stricter effluent limitation guidelines (ELG) for three types of coal plant effluent — flue gas desulfurization (FGD) wastewater, bottom ash transport water, and combustion residual leachate (CRL). Here are a few key takeaways on these three areas addressed by the EPA under its authority granted by the Clean Water Act. Other considerations also are discussed below.

FGD Wastewater

The deadline for providing a formal Notice of Planned Participation (NOPP) and to permanently cease coal combustion operations by year-end 2028 has been extended to 90 days after the recent direct final rule has been published. This deadline applies to FGD wastewater as well as bottom ash limits.

This proposed rule eliminates subcategories for low utilization and high-flow facilities, while preserving previously defined limits under the Voluntary Incentive Program (VIP).

A new Early Adopter category has been established for electricity generating units (EGU) that generate FGD wastewater. To qualify for Early Adopter status, the plant operator must install biological treatment equipment or zero valent iron equipment and bottom ash handling equipment that meet all limitations by the date that this new proposed rule is published. In addition, the EGU must plan to permanently cease coal combustion operations no later than Dec. 31, 2032. To be an Early Adopter, an EGU must have compliant bottom ash and wet FGD streams. Units that have only a compliant bottom ash stream will not qualify as Early Adopters under this proposed subcategory.

All remaining sites with FGD wastewater effluent must install zero liquid discharge technology as soon as possible, but no later than Dec. 31, 2029.

Combustion Residual Leachate

Limits on combustion residual leachate are not to exceed daily 30-day limits of 11/8 µg/L arsenic, 788/356 ng/L mercury. These limits apply to CRL generated after the required date, but not to legacy CRL. The limits do not apply and were not included for surface impoundment decant or dewatering wastewater.

Under this subcategory, dischargers must meet leachate limits as soon as possible but not later than Dec. 31, 2029. EPA has suggested that all discharges of leachate through groundwater shall be included in National Pollutant Discharge Elimination System (NPDES) permits.

Two new terms have been created that apply to closure of an impoundment:

  • Surface Impoundment Decant Wastewater. This means the layer of a closing surface impoundment’s wastewater located between the upper water surface and the level above any coal combustion residuals that, when drained, does not resuspend the coal combustion residuals.
  • Surface Impoundment Dewatering Wastewater. This means the layer of a closing surface impoundment’s wastewater that is located below surface impoundment decant wastewater due to its contact with either stationary or resuspended coal combustion residuals.

Each facility treating CRL in groundwater must file an Annual CRL Monitoring Report each calendar year to the permitting authority. The report should address monitoring at the location where: (1) CRL is discharged to groundwater and (2) the point where the CRL enters a surface waterbody.

The ELG update includes a requirement to report a total of 18 pollutants, including these metals not already included in coal combustion residual (CCR) reporting: copper, magnesium, manganese, nickel, titanium, vanadium and zinc.

When permitting new analytes, permits typically have a “reopener clause” allowing the permitting agency to evaluate the data submitted and add limits including water quality-based effluent limitations (WQBELs) if the data indicates they are needed. Therefore, facilities should routinely evaluate if any collected data exceeds water quality criteria at the mixing zone.

Bottom Ash Transport Water

Unless the EGU meets the Early Adopter subcategory all bottom ash transport water will be required to be zero liquid discharge as soon as possible, but not later than Dec. 31, 2029.

EGUs meeting the Early Adopter subcategory can effectively continue to operate under the 2020 ELG restrictions (≤10% as justified and approved by the permit authority) until Dec. 31, 2032. After this date, Early Adopter units are to cease coal combustion.

EPA has requested comment regarding whether bottom ash quench water (water in contact with bottom ash but not used to transport bottom ash) should be covered as an ELG regulated flow.

Early Adopters must notify their permit authority 60 days after publication of the final rule [423.19(d)(1)].

Other Considerations

The proposed ELG guidelines include discharge to groundwater. EPA proposes that any discharge through groundwater that is the functional equivalent of a direct discharge under the Maui decision would be subject to the same BAT limitations as discharges that occur at the end of pipe.

EPA interprets the rule to apply to legacy wastewater at inactive and/or retired steam electric power plants. This opens the door to include CRL from legacy CCR units. This could be included in the Legacy CCR Impoundment rule that is expected to be released in May 2023.

While Waiting for the Final ELG

Operators should determine if any of the new definitions fit your plant or could fit your plant if the definitions were adjusted (e.g., if different deadlines were set).

It would also be prudent to determine if it is probable your plant will cease coal combustion operations by any of these announced deadlines.

Until the proposed rule becomes final, current NPDES permits will still apply for plants proceeding on a compliance schedule. Plants with compliance schedules in 2023 and 2024 should request clarification and are advised to submit comments about this Catch-22 before the comment period is up.

For streams that are not being currently treated, but will become regulated, operators should start:

  • Planning how to capture the stream.
  • Planning how to reduce the stream flow. This is often the most cost-effective method of treatment.
  • Planning how to treat the regulated streams.
  • Performing pilots for membrane alternatives (if you want to consider these options).
  • Determining time and cost to treat the streams.
  • Updating integrated resource plans to evaluate plant retirement scenarios, if applicable. These must be approved by appropriate agencies within one year of the final rule.
  • Evaluating leachate sources and discharges and begin a process to modify permits to address CRL discharged through groundwater to nearby surface waters.
  • Considering additions of new CRL constituents to CCR groundwater monitoring efforts.
  • Assessing the location of CRL entering a surface water body considering access, possible well location(s), data gaps, etc.
  • Continuing discussions with state permitting agencies to understand state-specific permitting timeframes and agency availability to approve modifications to existing permits, as well as permits to install and permit renewals.


Coal plants are required to comply with multiple CCR management rules and ELGs.

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Doug Randall is a chemical engineer working on air and water pollution control systems for power generation projects at Burns & McDonnell.