Coal Combustion Residuals
Coal Combustion Residuals (CCR)
EPA's 2015 Coal Combustion Residual Rule
The U.S. Environmental Protection Agency published its final rule for the Disposal of Coal Combustion Residuals from Electric Utilities (CCR Rule) on April 17, 2015. This final rule was the culmination of extensive study on the effects of coal ash on the environment and public health. The rule establishes that coal combustion residuals (CCR) are a non-hazardous waste and addresses the risks from CCR disposal into surface impoundments and landfills. The CCR Rule is not applicable to SJGS as there are no CCR impoundments or landfills at the site nor is it applicable to mine placement of CCR and thus, San Juan Coal Mine.
Management of CCR at SJGS and San Juan Mine
During coal combustion operations at SJGS to produce electricity, CCR generated at the SJGS was placed into trucks operated by the San Juan Coal Mine, which transported the CCR back to the mine for mine reclamation purposes. Coal combustion at SJGS ceased on September 29, 2022.
In the reclamation process, the CCR is returned to the former surface mine pits where coal was mined. Use of CCR in this manner reduces mine reclamation costs because not as much new fill material is required. A portion of the CCR in the form of gypsum, is sold for beneficial use to a third party.
The San Juan Coal Mine is required to have a reclamation plan that is approved by Mining and Minerals Division (MMD) of the New Mexico Energy, Minerals and Natural Resources Department. MMD receives oversight for its programs from the Office of Surface Mining Reclamation and Enforcement (OSMRE). Use of the CCR from SJGS is specifically approved for mine reclamation at the San Juan Coal Mine. The mine reclamation plan is intended to reconstruct as many of the pre-mining conditions as practical.
The CCR generated by SJGS is sent to the former surface mine pits for reclamation at San Juan Coal Mine where they are placed in mine pits and covered with at least 10 feet of overburden and topsoil. This process minimizes CCR contact with surface water. In addition, because the San Juan Coal Mine is located in an arid region, the opportunity for the CCR to be impacted from precipitation is lower compared to wetter climates. Monitoring equipment is placed above and below the CCR in the mine pits to detect any movement of water into and out of the CCR. Mine operators are required to post bonds to ensure that mine reclamation is properly performed.
Westmoreland San Juan Mining developed a groundwater-monitoring plan to monitor changes in the quality of the groundwater resource during mining and subsequent reclamation. The monitoring plan includes collection of groundwater information from specified hydrogeologic units. The goal is to collect data on groundwater quality and quantity and to monitor any changes that may occur as a result of past mining and current reclamation and if changes are detected, operations can be adjusted to prevent adverse effects. As such, the monitoring includes adaptive management to either adjust operations or adjust the monitoring. Monitoring reports are reviewed by MMD, who has the authority to require additional monitoring wells during mining or reclamation. Further, prior to bond release after reclamation, OSMRE reviews monitoring reports and, if necessary, works with MMD to adjust the groundwater monitoring plan to ensure potential effects are avoided or minimized.
PNM’s Groundwater Recovery Systems
In 2008, PNM chose to proactively install a groundwater recovery trench below the plant. This trench is designed to capture any potential release of discharges from SJGS. The trench became operational in January 2010 and quarterly monitoring data is provided to the NMED via a discharge plan monitoring report. At the end of 2018, PNM completed installation and began operating a second groundwater recovery system as part of a 2012 consent decree among PNM, San Juan Coal Mine and the Sierra Club. This groundwater recovery system, consisting of an impermeable, underground concrete-like slurry wall and groundwater recovery trench, is designed to capture groundwater downstream of SJGS and the San Juan Mine. Groundwater quality data is provided to the NMED quarterly via a discharge plan monitoring report.
Studies of the Impacts of CCR to Groundwater at the San Juan Coal Mine
Multiple studies have been conducted to determine whether the CCR from SJGS have the potential to come in contact with groundwater at the San Juan Mine and affect the underlying groundwater quality. In 2017, the USGS published the Hydrologic Reassessment & Numerical Simulation of Groundwater Flow, San Juan Mine, San Juan County, 2010-13, which indicates that the rate of re-saturation of the mine spoil is expected to be extremely slow due to New Mexico’s arid climate and the low rate of recharge to the aquifer. The USGS Report discusses how the low groundwater volume and velocity in the coal seam combined with the high dilution potential of the San Juan River alluvium (soils and sediment deposited by the river) would greatly reduce any potential impacts to the river in the unlikely event that the CCR affected the groundwater quality. In addition, constituents are not released from CCR in high concentrations when CCR are exposed to ground water and these constituents are likely to attenuate through chemical and physical mechanisms to negligible concentrations in ground water well before reaching the arroyos and the San Juan River.
After the USGS published their 2017 report, and based on USGS recommendations, San Juan Coal Mine implemented additional best management practices in the reclamation process. These practices included increasing the amount of spoil material surrounding and between coal ash layers placed in the surface mine pits to further minimize the potential for restoration of the mine pits.
Four Corners Power Plant
PNM owns 13% capacity of Four Corners. Arizona Public Service (APS), the operator of Four Corners, currently disposes of CCR in surface impoundments and dry storage areas. The disposal of CCR at Four Corners is subject to the EPA’s CCR rule. Prior to implementation of the rule, Four Corners, located on the Navajo Nation, was already subject to federal regulatory requirements designed to monitor for potential groundwater and surface water impacts of plant operations. On December 19, 2019, EPA released a proposed rule establishing a federal permitting program for the handling of CCR within the boundaries of American Indian land boundaries. Permits for units within the boundaries of American Indian lands would be due 18 months after the effective date of the rule. The final rule is expected in October 2023.
Four Corners is in compliance with the CCR rule and is meeting all applicable requirements. For facilities like Four Corners, the rule requires ongoing, phased groundwater monitoring. In addition, the rule specifies that, by October 17, 2017, electric utility companies that own or operate CCR disposal units, such as APS, must have collected sufficient groundwater sampling data to initiate a detection monitoring program. To the extent that certain constituents were identified through this initial detection monitoring at levels above thresholds provided in the CCR rule, the rule required the initiation of an assessment monitoring program by April 15, 2018. In 2018, APS completed the statistical analyses for its CCR disposal units that triggered assessment monitoring. APS determined that some of its CCR disposal units at Four Corners will need to undergo corrective action.
APS completed an assessment of corrective measures needed for its CCR disposal, which identified several units that require corrective action or cessation of operations and initiation of closure by April 11, 2021. All units subject to corrective action are monitored until closure and/or groundwater mitigation objectives have occurred.
In January 2023, APS released the Annual Groundwater Monitoring and Corrective Action Report for 2022. This report is the formal regulatory method for releasing annual groundwater monitoring data.
