Differentiation of Coal and non-Coal Sources of Constituents in the Environment

Current EPA rules for disposal of coal combustion residuals (CCR) provide opportunities to demonstrate alternative sources of constituents when monitoring programs suggest a statistically significant increase in CCR-related constituents at downgradient locations. Failing to accurately identify alternative sources, when present, can lead to ineffective corrective action and financial loss, because the target of this action is misplaced. A combination of advanced geochemical and statistical techniques can help pinpoint whether CCR contributes as a source, differentiate between CCR sources, and if present, quantify the proportion of CCR contributions to constituents. Here, we provide examples of how isotopic ratios of various elements, such as osmium, neodymium, lead, and strontium can prove useful in differentiating CCR from other pollutant sources, including between CCR from coals of different coal basins in the U.S. For example, lead and neodymium isotopes can separate coal combustion emissions from nonpoint traffic pollution in urban settings, and strontium isotopes can help differentiate fly ash from different coal sources. Additionally, advanced statistical techniques, such as Bayesian methods, can quantify the proportion that CCR contributes to a given constituent (i.e., strontium, lead, neodymium, osmium) within an environmental sample and constrain any associated uncertainty. This allows for more quantifiably determining the presence or absence of CCR as a source within an environmental sample. Collectively, isotopic analysis and statistics can help better track where CCR solids and/or associated leachates are in the environment, and quantify their relative proportions that may be present in an environmental sample such as soil, water, and sediment.