Groundwater contaminants

Wisconsin DNR maintains a groundwater database. Sampling is conducted for the purpose of problem assessment, at-risk monitoring and some regulatory monitoring. Many of the sampling events are focused on problem areas. The Groundwater Retrieval Network (GRN) inventories more than 10,000 wells within the basin. Sampling for specific parameters is not uniform across the basin and some watersheds have had very little sampling done.

Following are the most common categories of groundwater contaminants:

Biological hazards

Several areas within the basin have the potential for contamination due to shallow depth to fractured dolomite bedrock. Biological agents include bacteria, viruses and parasites. These agents can cause acute illness and life-threatening conditions in some people. Statewide, 23% of private well samples test positive for coliform bacteria, a non-pathogenic organism. While not harmful itself, its occurrence indicates the possible presence of dangerous pathogenic organisms.

Groundwater contamination by bacteria can occur wherever conditions are favorable, primarily shallow soils and fractured bedrock. Unabandoned wells, open to the surface, serve to directly inject surface bacteria to the aquifer. This may occur also in areas of permeable soils spread with large amounts of manure.

Contamination problems are usually worse during groundwater recharge, usually in spring or fall.

Note: the highest detection rate is in August and September. Sources of bacterial contamination include animal waste, wastewater from land disposal systems, on-site systems, sewer systems, septage and wastewater spreading and naturally occurring bacteria. Bacteriological problems affecting humans can usually be avoided if wells are constructed and located according to code. Wisconsin DNR recommends that well owners test for biological quality annually or when there is a change in water taste, color or odor.

Nitrate

Nitrate-nitrogen is the second most commonly found groundwater contaminant and frequently exceeds the state drinking water enforcement standard (ES) of 10 milligrams/liter (mg/l) for nitrate + nitrite nitrogen. (Nitrate + nitrite nitrogen will henceforth be referred to as nitrate in this section).

Consumption of water containing high concentrations of nitrate by infants under 6 months can induce methemoglobinemia or "blue baby syndrome," a condition in which hemoglobin is oxidized to a form unable to carry oxygen to body tissues. All infants under 6 months of age are at risk of nitrate poisoning, but some babies may be more sensitive than others. Serious poisonings in infants have occurred following ingestion of water containing nitrate concentrations as low as 50 mg/l, just 5 times the current standard. Fatal poisonings usually involve the ingestion of water containing 100-150 mg/l nitrate. The effects of ingesting lower concentrations are not known, but some experts believe a chronic oxygen shortage could result, which could injure an infant's nervous system. Some scientific studies have found evidence suggesting that women who drank nitrate-contaminated water during pregnancy are more likely to have babies with birth defects. Nitrate ingested by the mother may also lower the amount of oxygen available to the fetus. Nitrate is not usually harmful to adults or older children. Although scientists are unsure about the chronic health effects of nitrate, long-term ingestion of water containing high nitrate levels is not recommended.

The Department of Health and Family Services (DHFS) and Wisconsin DNR recommend that all newly constructed private wells and wells that have not been tested during the past five years be tested for nitrate. Testing is recommended for wells used by pregnant women and is essential for wells that serve infants under 6 months old. One study in humans has reported an association between increased methemoglobin levels and spontaneous abortions. Spontaneous abortions were found to possibly be related to ingestion of nitrate contaminated well water (MMWR).

Nitrate can enter groundwater from many sources, including nitrogen-based fertilizers, animal waste storage and feedlots, municipal and industrial wastewater and sludge disposal, refuse disposal areas and private sewage systems. Recent studies have shown that about 10% of private wells in the state contain nitrate above the ES. This number can be highly variable between counties, but if true, 75,000 of Wisconsin's 750,000 wells exceed the standard of 10 mg/l of nitrate.

The rate of 10% percent above the ES was confirmed by work done through the Wisconsin Geologic and Natural History Survey (WGNHS) and DHSS as a summary project using data from existing databases at the Central Wisconsin Groundwater Center (CWGWC), the U.S. Geological Survey (USGS), the Department of Agriculture, Trade and Consumer Protection (DATCP), WGNHS and Wisconsin DNR. This summary work indicated that the rate at which nitrate exceeds the ES from each of these existing agency databases ranges from 9% to 14%, depending on the dataset used. This data summary project was initiated to compare or validate the data from a U.S. Centers for Disease Control and Prevention (CDC) sampling project, which indicated a statewide rate of 6% above the ES.

In response to widespread flooding in the summer of 1993, the CDC sponsored a private well sampling program across the nine midwestern flood-affected states. Wisconsin DNR Water Supply staff took 636 private well samples -- at least eight in each county. Each well was analyzed for nitrates, coliform bacteria, E. coli bacteria, atrazine, radon and some for sulfates and arsenic. A GIS coverage consisting of point locations for each private well sampled was created by the Wisconsin DNR Water Resources Management Program.

The CDC study showed that concentrations of nitrate in groundwater are not uniform across the state. Some undeveloped areas have low nitrate levels, whereas up to 50% of rural wells in some agricultural areas of southern Wisconsin exceed the ES for nitrate. Statewide data compiled for the "Nitrate in Wisconsin's Groundwater: Strategies and Challenges" conference in 1994 shows the percentage of wells exceeding the ES range from 3.8% in the Bark River watershed to more than 65% in the Blackhawk Creek subwatershed. Local areas may have substantially higher percentages of wells exceeding the ES. Data from GRN indicates 24% of the wells or 379 wells sampled in the basin had nitrate levels exceeding the ES. Many of the watersheds have had less sampling done and more data is required to fully evaluate groundwater quality. Many of the differences across the basin can be related to variations in nitrogen loading and to differences in soil, geology and groundwater conditions.

Due to the concern over nitrate, the Groundwater Coordinating Council (GCC) endorsed a resolution in 1989 recommending that newly constructed water supply wells be sampled for nitrate in addition to coliform bacteria. Also, the Department of Industry, Labor and Human Relations (DILHR) continues evaluating state-of-the-art septic system designs for nitrate removal. DILHR drafted revised private system regulations that would require compliance with the groundwater standards in NR 140. In addition, DATCP has been evaluating the need for regulation of nitrogen-based fertilizers. Wisconsin DNR and DHSS produced a joint Nitrate in Drinking Water brochure (PUBL-WS-007-93REV) to address nitrate education concerns.

As is the case with any contaminant in groundwater discharging to a stream, nitrate loading from groundwater can be a significant source in surface water. A study in the Missouri Valley showed groundwater accounted for 84-95% of nitrate loading to surface water. Up to 40% of the nitrates in Chesapeake Bay are attributed to groundwater discharge (USEPA 1994). Locally, research is being conducted on this problem in the Little Plover River watershed.

Pesticides

Pesticide contamination of groundwater may result from general field use according to label directions, or from spills, misuse or improper storage and disposal. Serious concerns about pesticide contamination from runoff in Wisconsin were first raised in 1980 when aldicarb was detected in groundwater near Stevens Point. Wisconsin DNR, DATCP and other agencies responded to these concerns by implementing monitoring programs and conducting groundwater surveys.

Wisconsin DNR expanded its sampling programs in 1983 to include analysis of pesticides commonly used in Wisconsin. Since many of the pesticides are known to be carcinogenic and some to have a disrupting effect on endocrine systems, federal and state groundwater quality standards for many of these compounds were also adopted. To date, standards for more than 30 pesticides are included in Chapter NR 140, Wis. Adm. Code.

Beginning in 1985, DATCP installed about 150 monitoring wells at 50 highly susceptible sites across the state where pesticide use characteristics (e.g., specific compounds and application rates) were known. Data from these wells have been collected quarterly and are used to identify problem pesticides and field use activities that may contribute to groundwater contamination in Wisconsin. To date, the herbicide atrazine has been found at 29 of 40 monitoring sites, with the ES being exceeded at 12 sites. Alachlor (trade name Lasso) has been detected at 10 of 27 sites.

Since the late 1980s, DATCP has also initiated a number of surveys to investigate runoff-related pesticides in groundwater. In 1994, DATCP completed a groundwater survey of alachlor and its metabolite or breakdown product, ethane sulfonic acid (ESA), in southern Wisconsin. The study was funded by DATCP, Wisconsin DNR and Monsanto and was designed to determine the extent of alachlor and ESA contamination in Wisconsin private wells most at risk. The study was conducted in the following 11 counties where alachlor sales and use have been concentrated: Columbia, Dane, Dodge, Grant, Green, Jefferson, Iowa, Lafayette, Rock, Sauk and Walworth. Immunoassay test kits were sent to about 1,300 homeowners whose wells had either a previous detection of triazines or nitrates above 10 mg/l. A total of 669 samples were returned for immunoassay analysis at DATCP's Bureau of Laboratory Services.

Triazines, a class of herbicides including atrazine and simazine, were detected in 45% of these samples. Well owners with a detection were offered free follow-up sampling and more comprehensive laboratory analysis for alachlor, ESA, nitrate and other commonly used pesticides. Follow-up analysis indicated that about 1.8% of the original 669 wells had detections of alachlor and 32% had detections of ESA. Alachlor was detected above the ES of 2.0 micrograms/liter (µg/l) in six follow-up samples, while ESA was detected above the Interim Health Advisory of 20 µg/l in two follow-up samples.

DATCP plans to conduct site investigations around wells that exceed the alachlor ES, or around those that exceed the ESA Interim Health Advisory to identify the source(s) of groundwater contamination. Information from the investigations will be used to determine what actions DATCP will take in response to alachlor and ESA contamination in groundwater.

In 1994, DATCP also completed Phase 1 of a survey designed to evaluate the effectiveness of the atrazine rule (Chapter ATCP 30, Wis. Adm. Code). This evaluation is required in ATCP 30 and will attempt to determine if a "statistically significant change" has occurred in groundwater concentrations of atrazine and its three chlorinated metabolites between Phases 1 and 2 of the survey. The focus of this evaluation is groundwater exploitable by private water supply wells.

In Phase 1, DATCP collected 289 groundwater samples statewide to establish a statistically reliable basis for comparison with samples that will be collected in 1996 for Phase 2. The private wells were chosen using a stratified-random selection process and groundwater samples were analyzed for atrazine, its breakdown products and a number of other pesticides. Phase 1 survey results indicate that between 8 and 16.4% of wells in Wisconsin contain detectable levels of atrazine and/or its metabolites, with .6% to 2.8% exceeding the ES of 3.0 µg/l. In addition, 4.2% to 9.4% of private water supply wells in Wisconsin had detections of alachlor's ESA metabolite; 50.7% to 67.8% of private wells contain nitrate, with between 6.7% and 13.1% exceeding the ES of 10 mg/l.

DATCP also collects groundwater samples from private wells that are associated with pesticide investigations. Most of these investigations are initiated based on wells exceeding the pesticide ES. DATCP investigators may take confirmation samples from those wells or from wells on adjacent property. The sample data help DATCP staff identify probable sources of pesticides in groundwater, provide background water quality information and assist in the development of regulatory actions, such as atrazine rule amendments.

In addition to runoff sources of pesticides in groundwater, a significant point source problem was identified during two surveys of groundwater quality at pesticide storage and handling facilities. The Agricultural Chemical Cleanup Program (ACCP), administered by DATCP, was created in 1993, primarily to address point source contamination at these facilities and in nearby wells. Point source contamination on farms is also handled by ACCP. To date, more than 200 cases involving soil or groundwater remediation related to spills, misuse, improper storage and other point sources have been initiated at facilities and farms. Monitoring groundwater from adjacent private wells and/or installation of monitoring wells are often associated with these cases.

GRN sample records indicate that 1,083 wells sampled in the Lower Rock River basin had detects of one or more of the major pesticides. Of the 1,636 wells sampled, 105 exceeded the preventive action limit (PAL) for some form of pesticide. Another 80 wells exceeded the ES.

Triazine screening

Triazines are a class of herbicides that include atrazine and simazine. Beginning in January 1991, the Wisconsin State Laboratory of Hygiene (SLOH) initiated a testing program for the public based on the immunoassay screening test for triazine-based compounds. This program is available to the public through a toll-free telephone number (1-800-442-4618). Since the start of this program, about 10,000 groundwater samples have been screened for triazine compounds. SLOH has expanded the immunoassay screening program to include other pesticides as requested.

Data from the SLOH program indicate that about 18% of the samples have exceeded the PAL for atrazine of .3 µg/l and about 2.2% have exceeded the ES of 3 µg/l for atrazine. These numbers are used only for reference since the test screens for compounds other than atrazine specifically and does not screen for two of the three breakdown metabolites included in the groundwater standard.

Metals

Metals in groundwater can be naturally occurring or the result of human activities. For example, iron is a common, naturally occurring metal, while cadmium and chromium are associated with metal plating operations. Other elements are often found affiliated with metals. Arsenic and lead were commonly used in pesticides on orchards. The geology of the basin does not include any major sources of naturally occurring metals and levels in groundwater are relatively low. Several localized areas have shown elevated levels of metals associated with plating and foundry operations.

Volatile organic compounds (VOCs)

VOCs, which vaporize readily under normal ambient temperatures and pressures, are present in gasoline, diesel fuel, industrial solvents and many other common products such as paints, paint thinners, drain cleaners, air fresheners, spot and stain removers. Many VOCs are suspected carcinogens when exposure is long-term. In the short term, high concentrations of VOCs can cause nausea, dizziness, tremors or other health problems. Within the basin, Groundwater Retrieval Network (GRN) records indicate that 218 of the 592 wells sampled have detected one or more VOC, 169 of these wells had exceeded the preventive action limit (PAL) and 80 wells exceeded the enforcement standard (ES).

Sources of VOCs include landfills, underground storage tanks and hazardous substance spills. Wisconsin DNR's Emergency and Remedial Response Section conducts problem assessment and at-risk monitoring at state Environmental Repair Fund sites, abandoned facilities, CERCLA (Superfund) sites, leaking underground storage tank (LUST) sites and spill sites. Wisconsin DNR has sampled thousands of wells for VOCs. More than 60 different VOCs have been found in Wisconsin groundwater. Trichloroethylene is found most often.

Wisconsin has 101 active licensed solid waste landfills, of which 99 are required to undergo groundwater monitoring. Two studies conducted over four years revealed that of 51 landfills, including engineered and unengineered industrial and municipal landfills, 27 (53%) had VOC-contaminated groundwater.

Of the 26 unengineered municipal solid waste landfills included in the two studies, however, VOC contamination occurred in groundwater at 21 (81%) of the 26 wells. While 20 different VOCs were detected overall, 1,1-dichloroethane was the most commonly occurring VOC at all landfills.

Two Wisconsin DNR publications, Volatile Organic Compounds in Groundwater and Leachate at Wisconsin Landfills (1988) and VOC Contamination at Selected Landfills - Sampling Results and Policy Implications (1989) describe the research findings. In a follow-up VOC study conducted from July 1992 through June 1994, Wisconsin DNR reviewed historical data and sampled groundwater at 11 closed, unengineered landfills and at six older, engineered landfills. VOC levels have decreased at all but two of the unengineered landfills, although at many of the sites VOC levels do not show a continued decline and the level of contamination remains high at several sites. There was no VOC contamination attributable to leachate migration at any of the six older, engineered landfills.

Wisconsin requires underground storage tanks to be registered with DILHR if their capacity is 60 gallons or more. This registration program identified 151,865 tanks statewide as of October 1993. Of these, 69,157 are regulated by the federal underground storage tank program. By July 1994, about 37,450 federally regulated underground storage tanks were removed. About 3,940 underground storage tank cleanups have been completed to date. There are about 7,800 currently active cleanups. Of the active sites, 1,029 are in a long-term monitoring phase that precedes site close-out.

The contaminants most commonly associated with leaking underground storage tanks (LUSTs) are components of gasoline and diesel fuel including benzene, toluene, ethylbenzene and xylene (i.e. BTEX compounds). There are more than 3,000 LUST sites that exceed BTEX groundwater standards. About 285 private water supply wells have been affected by contamination from LUST sites.

Another VOC source is hazardous waste storage and handling facilities. The Wisconsin DNR Hazardous Waste Section is investigating or remediating 28 of these contamination sites. Statewide, 140 sites have been identified as subject to corrective action authorities. Not all of these sites will undergo the corrective action process, due to minimal contamination at the site or to jurisdiction under other regulatory authorities.

VOC-containing petroleum products comprise 65% of all reported spills in Wisconsin. Section 144.76, Wis. Stats, the Hazardous Substance Spill Law requires those who spill hazardous substances to report spills and to take immediate actions necessary to restore the environment. The number of spills reported per year has increased from 360 during 1978 to around 1,400 in 1993. Groundwater monitoring is performed when necessary to delineate the contamination extent.

"Natural" groundwater quality

Natural groundwater quality within the state's major aquifers tends to be fairly uniform (Born 1987). Calcium bicarbonate and calcium magnesium bicarbonate are the predominant basin water types (Kammerer). The many exceptions to this uniformity are due to variations in geologic environments. Undesirable, but naturally occurring constituents commonly found in Wisconsin groundwater include radioactive compounds, iron and chloride. High levels of manganese, arsenic and sulfates are less commonly found and more localized in extent.

Hardness

The quality or chemical composition of groundwater largely depends upon the composition and physical properties of the rocks and materials through which the water moves and on the duration of the contact. Generally, the deeper the water penetrates into the ground, the more minerals it is likely to pick up. In Wisconsin, the chemistry of groundwater results from the water's interaction with the unconsolidated materials and the rock formations that contain large amounts of calcium and magnesium carbonates. This makes the groundwater fairly high in calcium-magnesium carbonate. Groundwater that exhibits this characteristic is said to be "hard," having dissolved solids greater than 200 milligrams/liter (mg/l). This is a natural phenomenon of groundwater and poses no adverse health effects, although excessively hard water can corrode pipes and reduce the cleaning ability of detergents and soaps. As a result, water softening is required or at least recommended for many uses. Water throughout most of the basin is classified as very hard (more than 180 mg/l calcium carbonate). Slightly harder water can be found to the northeast due to more dolomite bedrock and in the glacial deposits.

Iron

About 30 percent of Wisconsin wells exceed the standard for iron of 0.3 µg/l. Iron concentrations above recommended limits are objectionable because of taste and discoloration but have no adverse effects on human health. Problems with iron in groundwater cannot be predicted because of random distribution and conditions under which it can occur. Iron concentrations range from 0 to almost 7,000 mg/l in the state. Levels within the basin are variable but are generally low.

Iron tends to vary seasonally and is greatly affected by the oxidation state of the iron and water chemistry. Naturally-occurring iron (and sulfate) bacteria are often associated with iron, manganese and sulfur. These bacteria may form a slime around well screens, causing decreased well yields. They also contribute to the staining of plumbing fixtures and odor problems. Brochures about iron and sulfur bacteria and controlling the problem are available from the Wisconsin DNR Bureau of Drinking Water and Groundwater.

Manganese

Manganese and iron in small amounts are essential to plants and animals. Higher concentrations may cause staining of plumbing fixtures. The distribution of manganese is similar to that of iron. Levels range between 30 and 45 mg/l in the basin.

Radioactivity

Naturally occurring radioactive substances in groundwater -- including uranium, radium and radon -- is a concern in Wisconsin. The state has initiated programs to test groundwater for radioactivity. Recent sampling has identified radionuclides in north-central Wisconsin groundwater. High levels of radium have also been found in eastern Wisconsin water supplies. These detections are associated with wells drawing from the deeper sandstone aquifer. Elevated levels have not been found in the silurian or sand and gravel aquifers. Studies are examining the occurrence and extent of these naturally occurring contaminants. The Wisconsin DNR Bureau of Drinking Water and Groundwater has published a brochure about radon and provides guidance on sampling and management of the problem.

Two recent studies have examined radon in private wells. The first, discussed earlier as the CDC Private Well Survey, sampled wells in a grid pattern across the state at 10-mile intervals.

The second radon study is being conducted by the Department of Health and Family Services (DHFS) and the Wisconsin Environmental Health Association (WEHA). This study involves selecting wells drawing water from specific geological formations. The state's formations are being mapped by WGNHS using a geographic information system. The data layer is called the Primary Bedrock Aquifer coverage. This mapping scheme will be used to select approximately 1,000 wells for radon sampling.

Sulfate

Sulfate is the most common form of sulfur in groundwater. Under reducing conditions, which are often mediated by biologic activity, hydrogen sulfide is produced. Sulfate can have a laxative effect on persons not accustomed to it. It is also reported to reduce milk production in cows. Levels generally increase from west to east in the basin ranging from about 15 to 60 milligrams per liter, with levels elevated to more than 30 mg/l from Janesville south.

Chloride

Sources of chloride include weathering of minerals, animal wastes and road salt used for de-icing. Since human activity and animal wastes are the primary sources it is often used as an indicator of contamination. Levels within the basin are low and increase slightly to the north. Concentrations range from just below 10 milligrams per liter to just over 10 mg/l. Higher levels can be found in eastern Dane, southern Rock and Northern Waukesha counties. The secondary drinking water standard for chloride is 250 mg/l.

Fluoride

Fluoride concentrations are low throughout the state. Fluoride is beneficial in preventing tooth decay. The recommended amount for addition to water supplies in Wisconsin is 1-1.2 mg/l. Concentrations in the basin are less than 0.5 mg/l.

For more information on groundwater, visit the Wisconsin DNR - Drinking Water Program.