Arsenic contamination lacks one-size-fits-...(ipal water supply wells but it is primar...)

"Large areas of Outagamie and Winnebago counties have high arsenic levels in one of the shallower aquifers," Gotkowitz says. "Upwards of 10,000 private homes are affected by having arsenic above the standard [acceptable level]."

Wells are routinely disinfected with chlorine bleach to control pathogenic and other bacteria. However, such treatment raises questions in regions with arsenic problems.

While bleach should kill off arsenic-producing bacteria, it also creates a high-oxygen environment that some worry could enhance release of additional arsenic from the rocks.

Gotkowitz and UW-Madison geologists Eric Roden and Evgenya Shelobolina evaluated the impact of chlorination on bacteria and arsenic levels in Wisconsin wells.

The results were presented at the American Geophysical Union meeting in San Francisco today (Dec. 10).

In wells with arsenic levels only moderately above the accepted standard, the scientists found that the presence of iron-reducing bacteria was associated with higher arsenic concentrations. Disinfection of these wells with chlorine adequately removed bacteria and reduced arsenic levels in the short term.

In addition, chlorination did not increase arsenic release from the surrounding rocks, showing that oxidation of the rocks is not an important source of arsenic here.

Similar effects were seen in areas with a relatively high water table, where aquifers are exposed to less oxygen.

The results suggest that disinfection is an effective way to control pathogenic bacteria and may also limit arsenic release in wells under these conditions.

"It's not like there's going to be an easy solution, but there are some basic indicators," Gotkowitz says. Under low-oxygen conditions or where water levels are high, "you might want t
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