§ 5.11. Groundwater

Groundwater is a limited resource, and both its quality and quantity are important factors. These factors are primarily influenced by local geology and local land use. Precipitation percolates through the soil and bedrock where it eventually reaches a saturated zone known as an aquifer. It is from these aquifers that private wells are used to draw their water.

Groundwater in Clark County is generally abundant and of good quality. Three primary aquifers are present in the county: the sand and gravel aquifer, the sandstone aquifer, and the crystalline rock aquifer. The sand and gravel aquifer is present throughout most of the county at approximately 20 to 50 feet below the ground surface. This aquifer is easily accessible, but it is also the most easily contaminated. The sandstone aquifer is a deep aquifer and is found in the western and southeastern portions of Clark Count. Groundwater is abundant in the sandstone aquifer and is generally less susceptible to contamination. The crystalline rock aquifer is also a deep aquifer and is found in the northern and northeastern portions of the county, as well as along the course of the Black River throughout the county. The crystalline rock aquifer yields low to moderate amounts of water, but is generally less susceptible to contamination.

Groundwater contamination is most likely to occur where fractured bedrock is near the ground surface, or where only a thin layer of soil separates the ground surface from the water table. According to a WDNR map, Groundwater Contamination Susceptibility in Wisconsin, 1989, Clark County is moderately susceptible to groundwater contamination. Potential sources of groundwater contamination include:

• Chemical storage

• Landspreading of animal, sewage, and industrial waste

• Road salt usage and storage

• Animal feedlots

• Use and spillage of fertilizers and pesticides

• Accidental spills

• Septic tanks and drainfields

• Underground storage tanks

• Underground pipelines and sewers

• Landfills

• Mines, pits, and quarries

Wellhead Protection

The goal of wellhead protection is to prevent potential contaminants from reaching the wells that supply municipal water systems. This is accomplished by monitoring and controlling potential pollution sources within the land area that recharges those wells.

Wellhead protection planning is administered by the WDNR as required by the U.S. Environmental Protection Agency (EPA) and the 1986 amendments to the Federal Safe Drinking Water Act. Wellhead planning is encouraged for all communities, but is required when any new municipal well is proposed.

The general process of community-level wellhead protection planning includes:

1. Forming a planning committee.

2. Delineating the wellhead protection area.

3. Inventorying potential groundwater contamination sources.

4. Managing the wellhead protection area.

The City of Greenwood maintains wellhead protection plans for nine of the city's 12 wells.