Coal Ash Constituents in Groundwater and Regulation Under the Clean Water Act

摘要

Background/Objectives. Should the Clean Water Act (CWA) regulate discharges to groundwater? It’s a matter of significant debate. According to the U.S. Environmental Protection Agency (EPA), CWA permits for discharges to groundwater may be required if pollutants from point sources to jurisdictional surface waters that occur via groundwater or other subsurface flow have a direct hydrologic connection to the surface water. As such, EPA has stated that determinations are fact-specific, leading courts to rule on both sides of the issue. On February 20, 2018, EPA issued a request for comment on the technical elements of the matter and whether the agency should consider clarification or revision of previous statements. As administrators of the CWA’s National Pollutant Discharge Elimination System (NPDES) program, some states oppose permitting groundwater discharges under the CWA. Officials from those states contend that such permitting contorts the law, creates unnecessary challenges, and could undermine states’ abilities to regulate groundwater contamination through other programs already in place. Historic disposal of coal ash in unlined earthen impoundments or landfills presents a situation in which permitting discharges to groundwater could apply. Approach/Activities. When impounded surface water overlying coal ash infiltrates the subsurface and encounters natural groundwater, coal ash constituents can migrate to jurisdictional surface water bodies, sometimes 'daylighting' as a seep on a stream or river bank or upwelling through sediments. Coal ash constituents dissolved in groundwater can be conservative (unreactive with soil or native groundwater) or reactive, which means migration and attenuation are influenced by adsorption-desorption, cation exchange, precipitation-dissolution, or oxidation-reduction processes, often making transient or seasonal seeps challenging to characterize. Coal ash impoundments are subject to cleanup under the 2015 federal Coal Combustion Residuals (CCR) rule. Results/Lessons Learned. Mandated closure of coal ash impoundments includes removal of ash and overlying water and capping ash in place. It is anticipated that those activities will substantially reduce or eliminate seeps. In the interim, an option may be to permit constructed seeps, such as toe drains, as NPDES outfalls. Non-constructed seeps, by contrast, are challenging if not inappropriate to permit because of inconsistent flows and characteristics. Non-constructed seeps are seasonal and transient in nature, and may or may not have direct hydrologic connection to surface water. In those cases, non-constructed seeps may be addressed outside of NPDES through consent agreements, compliance monitoring, and corrective action.