ARSENIC IN KENTUCKY’S GROUNDWATER AND PUBLIC WATER SUPPLIES

Arsenic has been a topic of significant public debate in recent months. Environmental and public health interest groups have pushed to lower the MCL for arsenic in drinking water because studies indicate human health issues, including various forms of cancer and numerous cardiovascular and neurological effects, are a concern at considerably lower levels than the existing MCL of 0.050 mg/L. Public water system (PWS) advocates argue the the inability to treat drinking water to proposed levels and associated costs outstrip the reduced risk gained by a lower MCL. EPA recently promulgated a final rule establishing the MCL at 0.010 mg/L. The KDOW has been sampling groundwater and finished PWS water in order to determine the impact of this new MCL on PWSs and to assess private groundwater sources.

The most prominent source of arsenic in Kentucky’s aquifers results from the oxidation of arsenopyrite; incorporated in iron hydroxides. Reduction of these iron oxides is believed to be the most common vehicle for the occurrence of arsenic in groundwater. Elevated levels of arsenic in groundwater occur when arsenic is released to groundwater when these iron hydroxides are reduced.

Statistical analyses were performed on 1249 ambient groundwater sample results for total arsenic from 240 sites and 5490 finished water sample results from 687 public water system sites. Results from 10 ambient sites and 100 public water systems exceeded the MCL one or more times. We anticipate only a few PWSs, whose results consistently exceeded 0.010 mg/L, will have arsenic compliance problems. Other systems with occasional excursions above 0.010 mg/L may bear additional costs resulting from additional monitoring requirements.

Ambient groundwater quality in Kentucky with respect to arsenic is good. Data indicate that aquifers most likely impacted by arsenic are alluvial, and redox conditions play a role in the presence of arsenic in groundwater. A proliferation of metal-reducing bacteria in and around wells may produce locally reduced conditions. Additionally, vacillation in the groundwater table may cause fluctuations in the redox interface and result in elevated arsenic in groundwater. Therefore, proper well maintenance and rehabilitation, and proper aquifer management (via pumping rates) may play a key role in lower arsenic concentrations.