SURFACE WATER AND GROUNDWATER CHEMISTRY OF WESTERN WISCONSIN: ESTABLISHING AN ENVIRONMENTAL BASELINE

The primary objective of this investigation is to conduct the first comprehensive analysis of surface water and groundwater chemistry throughout western Wisconsin. This analysis will establish an important environmental baseline that documents background variations in dissolved metal content in surface water and groundwater throughout the region. This investigation focuses specifically on concentrations and mobility of metals that are naturally occurring in geologic units in western Wisconsin. The study area encompasses a large portion of western Wisconsin in the northeastern upper Mississippi River watershed. This geographic area closely aligns with the distribution of silica sand mines in western Wisconsin. Establishment of baseline water chemistry in this region is needed to assess the potential impacts of silica sand mining.

Surface water samples have been collected from second, third, and fourth order streams, including the Chippewa, Red Cedar, and Eau Claire Rivers. Groundwater samples are being collected from municipal wells across the region, which permits examination of aquifers within different stratigraphic units (primarily alluvial, Mt. Simon and Wonewoc Fms.). The dissolved metal fraction has been analyzed for a wide range of elements. Analytes are significantly below, sometimes orders of magnitude below, EPA drinking water standards. Lead counts average 5 ppb (EPA std = 15ppb); arsenic values average 1 ppb (EPA std = 10 ppb); chromium values average 2 ppb (EPA std = 110 ppb). Sequential extraction analysis is being conducted on various stratigraphic units across the region to assess the regional variability and mobility of metallic elements. These analyses will constrain the natural metallic load available to the surface water and groundwater system in western Wisconsin.