MEDICAL GEOLOGY, ANOMALOUS HEALTH DISTRIBUTIONS, AND GEOLOGIC CONTROL OF TRANSPORT MECHANISMS—A CASE STUDY OF ARSENIC IN NORTHWEST ARKANSAS

Within the past decade, anomalous illnesses and health problems have been reported within the Prairie Grove area, northwest Arkansas. Insofar as many of the illnesses, including several types of cancers and skin diseases, are consistent with environmental arsenic poisoning, a recent study was undertaken to characterize the hydrogeology, geochemistry, flow, and water quality of that area, with the intention of assessing sources of arsenic, and the role that geology might play as a controller of transport mechanisms from the various sources.

Potential sources of arsenic include organic-rich shales and several anthropogenic sources, most notably poultry waste containing organic arsenic that is spread on surrounding pasture lands as a nutrient-rich fertilizer. Possible transport mechanisms include solute transport by flowing ground water, and particulate transport by wind currents.

By characterizing dissolved major-element and trace-constituent water quality from 39 wells, springs, streams, and other water sources, the dominant water-quality processes acting on ground water in this setting appear to be dissolution, mixing, advection, dispersion and ion exchange. The unique conditions of pH and related geochemistry are unfavorable for ground-water transport in the study area, with the result that levels of arsenic and other redox-mediated parameters are small, well below the maximum concentration levels established by the U.S. Environmental Protection Agency for drinking water supplies. Transport of particulates by wind currents, however, is consistent with elevated arsenic concentrations collected during environmental sampling from nearby homes, and the unique topography of the study area is consistent with the unique distribution pattern of illnesses.