CHARACTERIZING GROUNDWATER SUSCEPTIBILITY TO CONTAMINATION IN BURNETT COUNTY, WISCONSIN

The Wisconsin Geological and Natural History Survey (WGNHS) routinely characterizes groundwater resources at the county scale in Wisconsin. The WGNHS completed a groundwater resource inventory in Burnett County, Wisconsin, in the early 1990’s; however, as the county is currently experiencing changes in land use and an increase in agricultural activity, the Burnett County Board has contracted the WGNHS to update the original groundwater resource inventory. Project deliverables include 1:100,000-scale maps of Quaternary geology and groundwater susceptibility to contamination from near-surface sources. Groundwater susceptibility maps indicate the relative ability for water to move from the land surface to the water table on a scale from low to high and are developed using ranked inputs of mean annual groundwater recharge, depth to water, depth to bedrock, and characteristics of the surficial sediments. Preliminary results for groundwater recharge estimated by the soil-water-balance method indicate an average of 7 inches/year from 2012-2022, with the highest mean annual recharge in high-elevation areas with sandy soils and low runoff potentials. The depth to bedrock map indicates shallow depth to bedrock along the St. Croix River on the county’s western border, and at multiple locations in the southern part of the county. It is anticipated that the groundwater susceptibility map will show the most vulnerability in areas with coarse-grained surficial sediments (sand and gravel), shallow depth to bedrock, shallow depth to water, and high mean annual recharge rates. The results of this inventory will help guide long-term groundwater management strategies at the county level to protect areas most vulnerable to land use change, and will be used to educate the public about the impact of geology and land use on groundwater quality.