Letter to the Editor: Introduction to Earth Science

How about an abbreviated course in Introduction to Earth Science 101?

Groundwater and surface water quality are common subjects lately, and for good reason. It is important because those living in Door and Kewaunee Counties drink water that comes from the ground, unlike Green Bay that uses water from Lake Michigan.

Where does groundwater come from and what happens to it underground? Wisconsin receives about 30 inches of rain and snow annually. Depending upon the type of soul a third runs off, a third evaporates, and a third soaks into the ground to the shallow aquifer. If the soils are sandy, more water infiltrates than if the soils are clay.

Water moves downward inches/year in clay soils and tens to hundreds of feet annually in sandy soils. Gravity moves water down until enough saturates the voids creating an aquifer. The aquifer can be in sandy and gravely soils or the fractured bedrock. In many cases, the sand/gravel aquifer lies immediately on the bedrock creating a single aquifer.

The bedrock underlying the two counties is crisscrossed with vertical fractures and layers of rocks. The fractures and layers range from microscopic cracks to large gaps. Once groundwater soaks through the soils it will move quickly through these cracks to the aquifer. Physical and chemical processes can remove some contaminants while water moves through soil and bedrock. Dilution only reduces the concentrations of contaminants.

Much has been made of the “karst” features in the area. Karst by definition refers to sinkholes and caves of which there are few in either county. The issue is that bedrock is permeable because of the numerous cracks and fractures in the bedrock. There are two elements that control the movement of surface water to groundwater: soil type and vertical fractures. The depth to bedrock is not as critical to protect groundwater as is the soil type overlying the aquifer. Five feet of clay overlying bedrock will be more protective of groundwater quality as would tens of feet of gravel.

In the 1960-70s the Soil Conservation Service prepared detailed soil maps that identified soil types and subsurface characteristics. This mapping presents areas of shallow soils, bedrock exposures, and other physical features. The data contained on the maps is a simple and effective source of information to identify sensitive areas.

In summary: we all use groundwater, groundwater moves through soil to the aquifer. Contaminants, nutrients, and pathogens move through soil and enter the aquifer that people use for drinking water. There was enough information 40 years ago to use to prevent groundwater contamination from landfills, septic tanks, manure spreading, etc. We do not need new studies, instead just match land use to the capacity of soils to “clean-up” contaminants. Proper management can take place immediately if anyone is really interested in preventing contamination of our groundwater.

The test for this abbreviated introductory Earth Science course is True/False. Uncontaminated groundwater is critical to the quality of life in Door and Kewaunee Counties. TRUE__ FALSE__.

The next abbreviated course will be on surface water.

Michael Dovichi

Algoma, Wis.