Send Letter to Editor

Wisconsin Natural Resources magazine

Wisconsin Natural Resources magazine

logo1.jpg - 18141 Bytes

April 2006

Threats to groundwater

Obvious and hidden sources of contamination

Natasha Kassulke and Laura Chern

Air pollution is water pollution, too
Fertilizer and manure storage and application
Nitrate: a widespread contaminant | Use and misuse of pesticides
Landfills | Wastewater | Onsite sewage systems
Spills and illegal dumping of industrial and commercial chemicals
Leaking underground storage tanks | Unused wells
Stormwater | Sources of natural contamination
Groundwater cleanup | Groundwater quantity – enough for all
The Great Lakes Charter | Quality is quantity

You name it – gasoline, fertilizer, paint thinner, antibiotics – if it's used or abused by humans and dissolves in water or soaks through soil, it may show up in Wisconsin's groundwater. New concerns are coming to the attention of local citizens and state government. These emerging issues include the potential for pharmaceuticals, pathogens and viruses to contaminate public or private wells.


A new area of research examines the combined effects of many contaminants that can occur in an aquifer. For example: What are the health effects of drinking water with very low levels of both pesticides and nitrate.

Activities in urban areas that pose significant threats to groundwater quality include industrial and municipal waste disposal, road salting, and petroleum and hazardous material storage.

In rural areas, different threats to groundwater quality exist; animal waste, onsite sewage systems, fertilizers and pesticides are primary pollution sources.

Air pollution is water pollution, too

Particles clouding the air from car exhaust, smokestacks and dust from city streets or farm fields can contribute to groundwater contamination. These particles of hydrocarbons, pesticides and heavy metals settle on the ground, are washed into the soil by rain, and eventually trickle into aquifers. Although a rain shower may disperse the particles from the air, the rains can carry the pollutants down into the ground as the water hits land.

Fertilizer and manure storage and application

Protecting water quality and farm profits is a balancing act that the UW-Extension's Nutrient and Pest Management Program is trying to perfect. To produce good yields, farmers need to apply nitrogen, phosphorus and other nutrients to their crops. If farmers don't account for the nutrients contained in the manure they spread on their fields, crops may be over-fertilized. Excess nitrate plants can't use will leach into the groundwater and excess phosphorus will runoff into lakes, streams and wetlands. Proper measuring of nitrogen and phosphorus in manure saves farmers the cost of purchasing extra commercial fertilizer – and also protects groundwater.

Farmers also must be careful about where and when they spread manure. Spring snowmelt or excessive rainfall can lead to fish kills and contamination of drinking water wells due to bacteria in manure that has run off from farm fields.

As subdivisions replace farm fields in rural areas, lawn replace crops. Over-use of commercial lawn fertilizer is an additional source of nitrate to groundwater.

Nitrate: a widespread contaminant

Department of Natural Resources scientists looked at nitrate contamination in groundwater and were concerned with some findings. Nitrate occurs in groundwater in every Wisconsin county; both rural and urban populations are exposed. Solving this problem means controlling all sources of nitrate to the environment.

According to a DNR survey, Wisconsin communities have spent more than 24 million dollars to bring nitrate levels down to acceptable levels in municipal wells. That cost has been spread out among 22 municipalities with a combined population of 150,000 or more.

nk5new.jpg - 10259 Bytes
Monitoring is one way to identify
groundwater threats.

© Robert Queen

On the private well side, present data indicate that more than 10 percent of the private well samples analyzed for nitrate statewide show groundwater contamination above the federal drinking water and state groundwater standard.

Infants under six months and pregnant women should not drink water with nitrate levels above 10 parts per million – the health-based federal and state standard. Mixing baby formula with high-nitrate water threatens infants under the age of six months, because their stomach acid isn't strong enough to kill certain types of bacteria capable of converting nitrate to harmful nitrite. Nitrite binds hemoglobin in the blood, preventing oxygen from getting to the rest of the body; the baby may lose its healthy color and turn blue.

Methemoglobinemia, or "blue baby syndrome" can cause suffocation. Using water with low levels of nitrate can prevent the condition. Other health effects linked to nitrate in drinking water include certain types of cancer, thyroid problems and diabetes.

Use and misuse of pesticides

All types of pesticides, (insecticides, herbicides and fungicides) have been used in Wisconsin agriculture for a long time. These pesticides can reach groundwater when spilled at storage, mixing and loading sites, or when over-applied to fields. "Empty" pesticide containers not properly disposed of are another source of trouble. Just a little spill of most pesticides can have a big impact on groundwater quality. For example, three parts per billion of atrazine (an herbicide used widely for riding corn crops of weeds) in groundwater is enough to increase the risk of cancer for those who drink the water.

Beginning in October 2000 and ending in May 2001, the Department of Agriculture, Trade and Consumer Protection (DATCP) 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 show that over 35 percent of wells tested contained detectable levels of herbicides or their metabolites (compounds created when herbicides and other chemicals deteriorate in soils).

Protecting groundwater from pesticide contamination while maintaining farm profitability isn't easy – too much pesticide and the environment suffers; too little and crop yield goes down. Integrated pest management, or IPM, is a pest control strategy that uses all appropriate control methods (chemical and nonchemical) to keep pest populations below economically damaging levels while minimizing harm to the environment. Here's how it works: farmers "scout" their fields for weeds and pests. After identifying what is present, the farmer purchases and applies the minimum amount of herbicides and insecticides only in the areas where weeds and bugs are a problem. Farmers using IPM find they spend less on pesticides. It's a bargain for the environment, too.


Thanks to recycling efforts since 1995, each year we divert about 40 percent of the Wisconsin generated solid waste from Wisconsin's landfills. The wastes we can't divert are disposed of in properly sited, designed, constructed and maintained landfills, which prevent leachate (the foul liquid that forms when water percolates through solid waste) from polluting groundwater. There are 72 highly engineered licensed landfills accepting solid waste in Wisconsin that do a good job of protecting groundwater.

We weren't always so fortunate. In the early 1970s about 2,000 dumps were identified by DNR. Those located near navigable waters, within floodplains, wetlands or critical habitat were ordered closed. Remaining landfills posing a threat to the environment due to hydrogeologic setting or poor operation were required to monitor groundwater and surface water. The monitoring data indicated that some landfills and open dumps were causing groundwater pollution.

Based on the data, and current state and federal regulations, all landfills are now required to have a composite liner system (a plastic membrane on top of four feet of compacted clay) and a leachate collection system to keep liquid waste out of the groundwater. Municipal dumps that did not meet design standards were closed prior to 1993.


Wastewater, generated by municipalities, industries and farms may be treated or stored in ponds or lagoons. Many small communities operate lagoon systems for treating sanitary sewage through bacterial degradation of organic material in the wastewater. A manure lagoon on a dairy farm can hold waste until conditions are right for field application.

Lagoons are sealed with compacted clay or plastic liners. Nevertheless, burrowing animals or soil movement can cause leaks. Routine inspections and maintenance are necessary to keep lagoons operating properly and to prevent contamination of groundwater. Some industries dispose of their wastewater by applying it to farm fields or to land specifically operated as a disposal system. Most municipalities and some industries also apply sludge produced in their treatment systems to cropland as a nutrient and soil conditioner. The waste is applied according to how much water, solids and nutrients soil and crops can absorb. If the system isn't managed properly, and too much waste and water are applied to the land, or if the operator fails to adjust the amount applied to account for rainfall, groundwater and wells can be contaminated or the material may run off to surface waters.

Onsite sewage systems

There are more than 750,000 private onsite sewage systems (private onsite wastewater treatment systems) in Wisconsin – serving approximately 30 percent of all households in the state. Most of these systems are located in unincorporated areas. Here's how onsite sewage systems work: wastewater flows from the house to a settling tank where solids settle out. The liquid continues out to an absorption field consisting of a series of perforated pipes that drain away from the house. The liquid is then absorbed into the soil. Bacteria in the settling tank break down solid waste, leaving a sludge that needs to be removed periodically by a licensed septage hauler or "honey wagon."

When systems don't work properly, bacteria, nitrate, viruses, detergents, household chemicals and chloride may contaminate groundwater, nearby wells, and surface water. Even properly installed systems may pollute groundwater if they are not located, used, and maintained correctly.

Spills and illegal dumping of industrial and commercial chemicals

When paint thinners, degreasers, pesticides, dry cleaning chemicals, used oil, fertilizers, manure and a host of other hazardous materials trickle into the groundwater, they create a potential danger to the public and the environment.

Accidents happen – over 1,000 spills of toxic or hazardous materials are reported each year in Wisconsin. Volatile organic compounds (VOCs) such as petroleum products account for many of the spills in the state. Topping the list is diesel fuel. Other substances, such as pesticides, paint, and ammonia, make up the rest. Most spills occur at industrial facilities or during transport of hazardous substances. Response efforts focus on containing and removing the hazardous material to a proper disposal facility. This protects groundwater and surface waters.

An undetermined number of spills go unreported, their presence a secret until area wells become polluted. Although there are strict regulations governing transport, storage and disposal of toxic and hazardous wastes, illegal dumping continues. Problems from past practices that occurred before regulations were in place surface periodically.

The threat to groundwater from these toxic products is real. That's why state and federal resources are devoted to finding these sites and cleaning them up. Many programs exist to clean up sites, from the federal Superfund program to address the worst sites in the nation, to the state cleanup program that includes spill response, leaking underground storage tanks, the state Superfund program, and a focus on cleaning up "brownfields" (properties that have been abandoned or are underutilized because of actual or perceived contamination).

Leaking underground storage tanks

People in the environmental cleanup business call them LUSTs; for all of us, it spells trouble. Over the years, many old leaking underground storage tanks that used to hold gasoline, diesel and fuel oil have slowly corroded and released their contents into the soil and groundwater. About 18,000 of Wisconsin's older tank systems have leaked as rust and other factors took a toll on the tanks and dispensing lines. Even small leaks caused significant groundwater contamination; it takes only a little gasoline in water to make it undrinkable. Property owners and their environmental consultants have cleaned up contamination at over 16,000 sites during the past 20 years. New regulations require existing tank systems to be upgraded. This will help prevent future problems.

Unused wells

What happens to the old well can determine how the new well functions. If old wells are not properly filled with such impermeable materials as cement or bentonite clay they provide a direct channel for pollutants from the surface to groundwater and other nearby wells. Thousands of old wells that are no longer used, but still open at the soil surface threaten Wisconsin's groundwater. Whenever you see an old windmill in the country, it's likely there's an unused well underneath. Licensed well drillers and pump installers are routinely hired to properly abandoned or fill old wells.

Drainage wells draw water off a section of wet ground by piercing a clay layer, and allowing surface water to run directly into groundwater. Drainage wells have been prohibited in Wisconsin since 1936, but they do turn up occasionally.


When development occurs, recharge to groundwater can be short-circuited. Rainfall, instead of infiltrating, runs off pavement and collects in lakes rivers and streams. Stream levels become more variable or "flashy," floods and channel erosion are more common, and groundwater recharge decreases. To put the hydrologic cycle to rights and preserve stream banks from washing out, Wisconsin requires that new developments infiltrate most of the stormwater falling on their site.

Because stormwater from roofs, driveways, parking lots and streets contains contaminants such as gasoline, metals, and bacteria it must be cleaned up or pretreated before it is put back in the ground using engineered stormwater infiltration devices.

Sources of natural contamination

Minerals found naturally in soils and rocks dissolve in groundwater, giving it a particular taste, odor or color. Some elements, such as calcium and magnesium, are beneficial to health. Radium, radon gas, uranium, arsenic, barium, fluoride, lead, zinc, iron, manganese and sulfur are undesirable ingredients found in Wisconsin groundwater. The levels of the contaminants depend on their concentrations in the aquifer and the amount of time the water has been in contact with them. Radioactive contaminants expose those drinking the water to risk of cancer. Public water systems are required to test groundwater for radioactivity. Recent sampling has detected radionuclides in some Wisconsin groundwater. Gross alpha activity and radium also have been found in Wisconsin water supplies. The EPA has drinking water standards for radium and radon.

Most natural contaminants aren't harmful, the problem is aesthetic rather than safety. Iron and manganese are found throughout the state. They stain plumbing and laundry, and can give drinking water an unpleasant taste and odor.

Excess fluoride, sulfur, lead and arsenic are less common and more localized. Changes in the aquifer system, such as declining water levels, can cause chemical reactions that release the contaminants into the groundwater. In northeastern and western Wisconsin declining water levels have caused the release of arsenic and heavy metals. Arsenic is a known carcinogen and has been found at very high levels (up to 15,000 parts per billion). Special well construction requirements have proven effective at avoiding the problem, but add greatly to the cost of getting a water supply. In some parts of Wisconsin the groundwater is naturally acidic and can corrode pipes and plumbing, leading to elevated levels of lead and copper in drinking water. Well owners should test their water periodically to assure the water quality is acceptable.

Groundwater cleanup

Groundwater contamination can be linked to land use. What goes on the ground can seep through the soil and turn up in drinking water, lakes, rivers, streams and wetlands. Tracking down and stopping sources of pollution is a lengthy and expensive process. It's usually impossible to completely remove all traces of a pollutant. Conducting a partial cleanup of an aquifer to a usable condition can cost a substantial amount of money.

Who pays the enormous cost of groundwater cleanup? The owner or facility operator causing the pollution should shoulder the cost. But what happens when the owner is bankrupt, out of business or dead? Taxpayers must step in. Federal and state money is used for cleaning up sites and enforcing laws governing waste disposal and hazardous material spills.

When it comes to groundwater, prevention is the best strategy. This means looking at the many ways we pollute groundwater and finding methods to keep those pollutants at bay. Landfills and wastewater lagoons need to be sited, designed and operated to prevent infiltration to groundwater. Pesticides must be applied according to need and label instructions, and fertilizers and manure should be applied in carefully calibrated amounts to enhance crops without damaging the environment. With vigilance and care, we can protect our buried treasure.

Groundwater quantity – enough for all

With 1.2 million billion gallons of groundwater, the Mississippi River and two Great Lakes, there is no other state that comes close to having the water resources we have in Wisconsin. Yet Wisconsin has a growing thirst for groundwater. There are areas in the state where streams aren't running and springs aren't flowing because the groundwater that feeds them is being pumped dry. In a growing number of places we are pumping groundwater faster than it can be replenished.

In the past century, groundwater has been drawn down several hundred feet around Waukesha and Brown counties. In water-rich Dane County, groundwater levels have dropped 60 feet and are expected to drop more as the population continues to grow. These long-term drops in groundwater levels affect fish, wildlife and people from farmers to factory owners. Local scarcity sometimes pits communities against one another and the natural resources we all enjoy.

When a proposed water bottling plant in Adams County was opposed by citizen groups in 1999, the interest of policymakers and the public in water quantity issues bubbled to the surface. It became clear that state laws didn't address the effect of high-capacity wells on nearby springs, wetlands or trout streams. The Big Springs case made people much more aware of the connection between groundwater, surface water and human activities.

The Great Lakes Charter

The Great Lakes constitute the largest volume of unfrozen fresh surface water in the world – about 5,440 cubic miles. There has been a great push in recent years to protect these waters. Much of the effort has been focused on updating the Great Lakes Charter, an agreement signed in 1985 by the eight Great Lakes governors and the premiers of Ontario and Quebec outlining principles for managing Great Lakes water resources.

A 1998 proposal to export bulk quantities of Lake Superior water to Asia raised concerns that existing agreements were inadequate to protect these waters. It spurred action in 2000-2001 to develop an annex to the charter, which would strengthen it by establishing clear procedures for deciding whether to approve any proposed withdrawal of Great Lakes waters.

On December 13, 2005 the eight states and two Canadian provinces in the Great Lakes announced the Great Lakes Water Management Strategy, also called Annex 2001. The agreement to manage water quantity in the Great Lakes basin and, with just a few limited exceptions, ban diversions of Great Lakes basin water, is the first multi-jurisdictional agreement of this magnitude in the world. All 10 governments have agreed to collectively manage water usage according to the shared goals expressed in this agreement. The fundamental principle is that the most significant fresh water resource in the Western Hemisphere must be treated as one ecosystem. Procedures also address pumping from wells outside the basin that alter groundwater flow and capture groundwater originating within the basin.

The United States Geological Survey is exploring the connection between groundwater and the Great Lakes in southeastern Wisconsin.

The distribution and the amount of water pumped from shallow and deep rock formations in southeastern Wisconsin has changed significantly over time. Groundwater that once flowed toward Lake Michigan is now intercepted by pumping and diverted west, where it is discharged after use to surface waters flowing into the Mississippi River Basin. This may reduce inflows to the Great Lakes.

Ground water is important to ecosystems in the Great Lakes Region because it is, in effect, a large, subsurface reservoir from which water is released slowly to provide a reliable minimum level of water flow to streams, lakes, and wetlands that feed into the Great Lakes. Groundwater discharge to streams generally provides good quality water that, which promotes habitat for aquatic animals and sustains aquatic plants during periods of low precipitation.

Quality is quantity

It isn't just the amount of water that is at stake but the quality too. In southeastern Wisconsin, the resulting drop in the groundwater level means water is now drawn from deeper rock layers that have naturally occurring radium. The concentration of radium in drinking water is high, and the water must be treated to protect the health of citizens. The cost of treatment is borne by the ratepayers.

We're beginning to realize that stewardship of groundwater has to be more than just keeping it clean. We have to conserve. The Groundwater Protection Act, passed in 2003, attempts to control well location and pumping rates to protect trout streams and other sensitive surface water bodies in the state. Regional efforts to assess and manage drinking water supplies are underway in southeastern Wisconsin, where use has resulted in the most severe drop in groundwater levels.

Our great-grandparents may have used hand pumps and buckets but they knew how deep their wells were and they thought about how to protect their drinking water. Today, community wells are located far from our homes and we take it for granted that water will pour out of the tap when we turn it on. It's time to ask ourselves, can we have it all – green lawns, swimming pools and quality springs, streams and drinking water?