Groundwater Protection

Groundwater protection is vital to states like Wisconsin, where two-thirds of the people draw their drinking water from underground aquifers. Unfortunately, these waters face several threats:

1. Excessive Withdrawals --- In several areas, groundwater levels have dropped drastically because high-capacity wells are pumping too much water and the aquifers aren't being given enough time to recharge naturally. In urban areas, recharge is difficult because much of the land surface is covered with pavement and roofs, causing rainwater and snowmelt to flow away rather than seep into the ground. In Wisconsin, our regulation of groundwater quantity is extremely weak and has resulted in major concerns when large water withdrawals are attempted, such as a recent proposal by Perrier for a bottled water plant. Despite fears that Perrier would damage local spring-fed streams and private wells, the Wisconsin DNR did not have the authority to stop the project. Perrier left because of public opposition, but still owns property in a sensitive area and is likely to try again. Our groundwater law loopholes must be closed and a groundwater conservation plan enacted.

2. Toxic Contamination --- In some localities, our groundwater becomes contaminated because of insufficient topsoil layers to filter rainwater as it trickles down to recharge the groundwater. Livestock manure, human sewage sludge, fertilizers and pesticides can also seep down into groundwater supplies.
In some areas of northeast Wisconsin, contaminated surface runoff can directly enter underground water supplies through fractured rock outcroppings (see below), sink holes, quarries and abandoned wells. To make matters worse, large areas of northeast Wisconsin suffer from naturally high levels of toxic minerals and contaminants - such as arsenic, lead, fluoride, iron and radium - in certain layers of the underground aquifer. When these toxic layers are drilled through or pumped, the contaminants can spread into clean aquifer layers resulting in wider groundwater contamination problems.

karst diagram

https://wgnhs.wisc.edu/water-environment/karst-sinkholes/

Fractured Limestone in Northeast Wisconsin

Open most basic groundwater textbooks and you'll find hydrogeology discussed in terms of porous media, with aquifers composed of well-sorted sand, and groundwater moving through pores between sand grains. In the dolomite terrain of northeastern Wisconsin, however, the story is much different. Over much of Wisconsin's Door Peninsula, fractured dolomite is exposed at or near the land surface. Rain or snow falling on this landscape enters the groundwater system through an interconnected network of vertical and horizontal bedrock fractures. Once in the aquifer, the water flows laterally, through horizontal fractures, until it discharges to local lakes, springs or streams or is captured by water-supply wells.

In such systems, rapid groundwater movement and minimal contaminant attenuation are common, and so the land-use practices in the areas where the water originates — often called the capture zones or contributing areas — highly influence the quality of groundwater produced by local wells.

water pump

Determining these capture zones and understanding how groundwater moves from recharge to local wells are critical to protecting groundwater in karst topography. The Wisconsin Geological and Natural History Survey (WGNHS) has carried out a series of field-based, hydrogeological research investigations with the goal of improving our understanding of fluid movement in fractured carbonate rocks throughout Wisconsin. The other aim of this research is to find the best methods for protecting groundwater and making sure contaminants are not carried to the wells that supply drinking water. Undertaking wellhead-protection studies in fractured-rock settings is a challenging endeavor, yet it is in these very vulnerable settings that wellhead-protection programs are most essential.

The focus of our work is the Silurian dolomite aquifer of Door County, in northeastern Wisconsin. A rocky peninsula between Lake Michigan and Green Bay, Door County has rugged shorelines, mild climate, abundant natural resources and a small-town feel that together have made it one of the most popular tourist destinations in the Midwestern United States.

Approximately two-thirds of the people living in Wisconsin get their drinking water from groundwater, but groundwater quality problems have plagued the county for many years. Beginning in October 2000 and ending in May 2001, the Department of Agriculture, Trade and Consumer Protection (DATCP) and the University of Wisconsin-Extension collected and tested 336 samples from rural private drinking water wells to determine the impact of agricultural pesticides on groundwater resources. DATCP analyzed the samples for commonly used herbicides. Results from the study showed over 35 percent of wells tested contained detectable levels of herbicides or their metabolites (compounds created when herbicides and other chemicals deteriorate in soils). Other groundwater contaminants include agricultural chemicals, pesticide residues from cherry and apple orchards, and petroleum and other non-aqueous phase liquids such as gasoline and solvents.

Much of Door County's charm, and its groundwater problems, are directly related to its unique geology — a combination of Paleozoic bedrock and Pleistocene modifications. Silurian-age dolomites form the backbone of the peninsula and dip gently eastward into the Michigan Basin. In the Late Pleistocene, continental glaciers covered the area, and, when they retreated, left behind a fascinating landscape.

On the western side of the county the Silurian escarpment forms high cliffs along the Green Bay shoreline; only a few miles to the east the land meets Lake Michigan with sandy beaches and diverse wetlands. In between, in the uplands of the county, the glaciers removed most of the soil, so that in most places the bedrock is less than two meters below the surface and in many places it is exposed at the land surface. The dolomite contains both near-horizontal and vertical fractures. These fractures are extensive, and the vertical fractures are easily visible from the air, particularly under alfalfa fields in dry weather. The combination of thin soils and fractured rock makes groundwater in the county extremely vulnerable to contamination.

Over the past 20 years, Wisconsin Geological and Natural History Society (WGNHS) has carried out a number of scientific studies of the hydrogeology of Door County at the request of, and with substantial funding from, local, state and even national regulatory agencies. Each of these studies has involved the collection and analysis of new field data and has included extensive cooperation with local landowners, citizens' groups and decision makers. Each project builds on previous work and has led to a broader understanding of fractured-rock hydrogeology that WGNHS scientists have shared in national and international venues. For example, Maureen Muldoon, from the University of Wisconsin-Oshkosh, carried out detailed groundwater monitoring and tracer experiments in an active dolomite quarry, producing some of the most detailed data on dolomite hydrogeology ever collected.

A Fast Trip to Well Water

In 2000, Mark A. Borchardt conducted a study to find a connection between contamination of groundwater and human enteric viruses. It was found that since 1981, data has shown that approximately half of all water-borne disease outbreaks were associated with contaminated groundwater in Wisconsin. The objective of the present study was to estimate the incidence of viruses in Wisconsin household wells located near septage land sites or in rural subdivisions served by septic systems. Fifty wells divided in seven hydrogeologic districts were sampled four times over a year, once each season. Reverse transcriptase PCR (RT-PCR), followed by Southern hybridization, was used to detect enteroviruses, rotavirus, hepatitis A virus (HAV), and Norwalk-like viruses (NLVs). In addition, cell culture was used to detect culturable enteroviruses. Companion water samples were collected for total coliforms, Escherichia coli, fecal enterococci, F-specific RNA coliphages, nitrate, and chloride analyses.

Among the 50 wells, four (8%) were positive for viruses by RT-PCR. Three wells were positive for HAV, and the fourth well was positive for both rotavirus and NLV in one sample and an enterovirus in another sample. Contamination was transient, since none of the wells was virus positive for two sequential samples. As seen on the map below, two sites were tested positive in Sturgeon Bay in Door County. This is because the peninsula has shallow topsoil underlain with extensively fractured dolomite, allowing contaminants to easily reach groundwater and travel far distances. The wells in the Door County peninsula are among the most vulnerable in the state for virus contamination, based upon the hydrogeologic features of this region. This study is the first in the United States to systematically monitor private household wells for virus contamination and, combined with data for public wells, provides further insight on the extent of groundwater contamination with human enteric viruses.

Armed with the technical understanding that municipal well water is coming from several kilometers away and from outside the city limits, the city, water utility and county officials are working together to develop a wellhead-protection plan that will identify and perhaps reduce potential contaminant sources at the land surface in the contributing areas for the city wells.

map

 

Links to More Groundwater Information

http://dnr.wi.gov/topic/groundwater/

http://wi.water.usgs.gov/gwcomp/find/dane/index_full.html

http://aem.asm.org/content/69/2/1172.full.pdf+html

© Clean Water Action Council

P.O. Box 9144

Green Bay, WI 54308

(920) 421-8885


Office location:
A307 MAC Hall, UW-Green Bay
2420 Nicolet Drive
Green Bay, WI 54311

contact@cleanwateractioncouncil.org