Study of Well Construction Guidance for Arsenic Contamination in Northeast Wisconsin

Background/Need: Naturally occurring arsenic in groundwater at levels above the Drinking Water Standard (DWS = 50 ug/L) in East Central Wisconsin has resulted in the identification of an Arsenic 7 Advisory Area (AAA). In a relatively large geographic area covering several counties, a guidance document is in place that recommends 80 feet of casing extending through the upper portion of the Ordovician St. Peter Sandstone Formation.

Objectives: The objectives of the study were threefold: 1) to evaluate if the Wisconsin Department of Natural Resources (WDNR) recommendations for well construction within the AAA provide adequate protection from the presence of arsenic in drinking water above the drinking water standard, 2) to determine if arsenic concentrations increase over time, and 3) to examine if, when faced with a contaminated well, it is best to replace it with a new one or to reconstruct the existing well with a liner sealing off the arsenic bearing zone.