ASSESSMENT OF ARSENIC ATTENUATION IN PUBLIC AND DOMESTIC SUPPLY WELLS

Earlier work by Pippin and others (2003, 2005, 2006), Reid and others (2005), Haven and others (2006), and Withers (2007), have established the occurrence of arsenic as a naturally occurring element in the groundwater systems of the North Carolina Piedmont. Temporal arsenic data has been collected for several domestic supply wells since 2000. In general, domestic supply well concentrations for total arsenic remain relatively constant over time. In contrast, data from public water supply wells in North Carolina suggests that arsenic is not of concern. Relatively few public water supply wells have arsenic concentrations that are greater than the EPA Primary Drinking Water Standard of 10 ug/L for arsenic. Historical data from public water supplies indicates that dissolved arsenic has been detected in the past for several systems and in some cases at concentrations greater than the EPA standard; however, these historical occurrences of elevated of arsenic attenuate over time. A conceptual model of the piedmont aquifer system will be presented with emphasis on these data sets and how differences in water usage and operation may explain the differences between observed arsenic attenuation in public systems compared to relatively stable arsenic concentrations in domestic systems.