From Bureau of Economic Geology, The
University of Texas at Austin (www.beg.utexas.edu).
For more information, please contact the author.
Bureau Seminar, October 23, 2009
Arsenic in near-surface groundwater: patterns at petroleum-affected sites
Franz K. Hiebert, Environmental Resources Management, Inc. (ERM)
In January, 2006 the United States Environmental Protection Agency (USEPA) lowered the maximum contaminant level (MCL) for dissolved arsenic in groundwater from 0.050 mg/L to 0.010 mg/L heightening public and regulatory awareness of dissolved arsenic in groundwater. Arsenic, both naturally-occurring and of anthropogenic source, may be mobilized into shallow groundwater by inputs of biodegradable organic carbon, including petroleum hydrocarbons. Hydrocarbon impact of shallow aquifers is a common occurrence and resulting effects are well characterized. Spatial patterns of arsenic distribution are linked to geochemical zones that develop as the result of biodegradation of petroleum in near-surface groundwater.
The purpose of this work is to develop a conceptual model of arsenic occurrence at petroleum-impacted sites that serves as a basis for regulatory/technical evaluation of site-specific risk to human health and the environment.
The research team collected field data and surveyed existing data on mineralogy and groundwater chemistry from a series of sites in which a pulse of hydrocarbons were introduced as a result of industrial activity. We report on our findings regarding sources of arsenic, groundwater chemistry, mechanisms of mobilization and attenuation, and fate of arsenic under a series of conceptual models of hydrocarbon biodegradation.