GROUNDWATER IMPACTS FROM COAL COMBUSTION ASH

DISPOSAL SITES IN WISCONSIN

Written by Michael Zillmer1 and Philip Fauble2

Introduction

The State of Wisconsin’s Department of Natural Resources (WDNR) regulates both coal-powered electric 

generating plants and the corresponding ash disposal sites. These sites range from active, engineered landfills to 

closed, unlined disposal sites located in abandoned bedrock quarries, wetlands, and sand & gravel pits. The 

disposal of coal combustion by-products (CCB) in unlined sites was only an accepted practice in Wisconsin 

prior to the promulgation of administrative codes and the establishment of procedures for siting and 

constructing waste disposal facilities. Chapter NR180, Wisconsin Administrative Code for Solid Waste 

Management was promulgated in 1988. Solid waste disposal, environmental monitoring, and beneficial reuse 

are currently regulated under administrative code chapters referred to as the NR500 series (NR500-NR590). 

Groundwater quality standards for regulating solid and hazardous waste facilities are specified under Chapter 

NR140, Wis. Adm. Code. Groundwater quality is measured against the enforcement standard (ES) and the 

preventive action limit (PAL) for substances that are of public health concern. The enforcement standards are 

roughly equivalent to the federal maximum contaminant levels (MCLs). The preventive action limit is generally 

10% of the ES for all substances that have carcinogenic, mutagenic, teratogenic properties or interactive effects 

and 20% of the ES for other compounds. Enforcement standards and preventive action limits for boron became 

effective on January 1, 1999. Samples from potable drinking water wells generally are not filtered, and 

represent total values for compounds and are regulated under Safe Drinking Water Standards in Chapter 809. 

The regulatory standards for some groundwater contaminants have changed over time and while others have 

been only recently been codified. 

The primary purpose of this paper is to analyze groundwater quality data from a wide variety of Wisconsin 

CCB disposal sites and to compare and contrast these results with water quality data from the two detailed study 

sites: the WE Energies Highway 59 and Cedar Sauk landfills. The data was also examined to determine possible 

trends or similarities between different sites and among various disposal site categories. 

Wisconsin Groundwater Quality Data

1 Wisconsin Department of Natural Resources, Milwaukee Service Center

2 Wisconsin Department of Natural Resources, Madison

Groundwater Impacts from Coal Combustion Ash

Disposal Sites in Wisconsin

PUB-WA 1174 2004

Waste & Materials Management 

P .O. Box 7921

Madison, WI 53707-7921

 Groundwater Impacts from Coal Combustion Ash Disposal Sites in Wisconsin Page 1

 
To evaluate of the impact of CCB disposal sites on groundwater quality, it became necessary to identify both 

active and closed CCB monofills in Wisconsin that have active groundwater monitoring. All groundwater 

quality data for solid waste facilities that is reported to the WDNR is recorded in the Groundwater and 

Environmental Monitoring System (GEMS) database. The GEMS database is one of the largest in the nation, 

containing over 10,994,294 analytical results from 18,467 active and 4,259 inactive monitoring points.

From the 22 identified CCB monofill landfills in GEMS, 12 sites (6 active and 6 closed) were chosen based on 

size, known groundwater impacts, and the completeness of their data sets. A Monitoring Data Summary by 

Parameter report was reviewed for each of these 12 sites to determine the most impacted monitoring wells at 

each site. Four compounds were identified as the most commonly detected at levels that exceeded the State of 

Wisconsin's groundwater protection standards. These compounds include boron, sulfate, arsenic and selenium. 

Elevated levels of manganese were detected at about half the sites and there were sporadic exceedances of lead, 

chromium and mercury at several sites. Typically, 3 or 4 downgradient monitoring wells would account for the 

majority of the exceedances at each site. From there, a Summary Exceedance Report detailing all parameters 

and results was generated for the most impacted well at each site. The report listed the lowest and highest 

reported sample results and calculated the mean of all samples collected. A summary of these findings is listed 

in Table 2.

It must be acknowledged that this analysis is intended as a broad attempt to categorize groundwater quality data 

that is strongly influenced by a large number of variables, most of which are not easily quantified and not 

addressed in this study. The type and concentrations of contaminants available for release into a groundwater 

system are directly related to the coal source, the combustion method employed by the generating plant, and 

environmental conditions of the disposal site. This information is often difficult to obtain or unavailable, 

especially for older, long closed sites.

In addition, the groundwater monitoring data presented are the mean value of all available data for the most 

impacted well at the facility. Some of the wells represented are no longer in service. The location of the well 

can strongly influence the results and some of the monitoring points were actually screened through or just 

below the waste mass. Especially with regards to the older, closed sites, the mean can be skewed higher by 

older data that recorded values that have since declined, in some cases dramatically. Even given these 

constraints, some interesting results can be discerned from the groundwater quality data.

Measurable quantities of boron were recorded in at least one downgradient monitoring well at all the sites 

reviewed, including active sites that were constructed with clay liners. However, the boron concentrations 

tended to be rather low at active lined sites, with 2 sites recording mean values at concentrations below the 

Wisconsin groundwater standard (0.960 mg/l) for boron. That is in stark contrast to several closed sites that 

have mean concentrations of boron over 10 times the mean concentration of even the highest value at an active 

site. 

The highest mean boron concentration among all sites was recorded at the Cedar Sauk Landfill (mean 101 

mg/l). This value is well above the next highest mean concentrations (69 mg/l and 30.7 mg/l, respectively) for 

either active or closed sites. The GEMS database documents that the highest recorded boron concentration in 

groundwater monitoring wells (as high as 186 mg/l) were recorded at wells W-3 and W-3A at the Cedar Sauk 

Landfill. These elevated boron concentrations were most likely influenced by the boron concentrations in the 

original coal source and the transmissivity of the disposal environment. Data from EPRI database (January 

2004) on the boron content of various coals from different regions of the country indicates that the range of 

boron content can vary considerably.

 Groundwater Impacts from Coal Combustion Ash Disposal Sites in Wisconsin Page 2
Table 1

As with boron, sulfate was detected in measurable quantities at downgradient wells at all the sites studied. 

Unlike boron, however, elevated sulfate levels were common among most sites including the active, engineered 

landfills. The mean sulfate value was above the Wisconsin enforcement standard (ES) of 250 mg/l at 10 of the 

12 sites studied. Only one site, the NSP-Woodfield Landfill, had a downgradient well that never recorded a 

value above the ES. Two active landfills had mean values at (or above) the mean values for most of the closed 

sites.

Most active sites had mean arsenic values just below the Wisconsin enforcement standard of 10 ug/l. The one 

active site that had a mean arsenic value above 10 ug/l was the Highway 32 Landfill (30 ug/l). However, the 

mean was calculated from only 2 data points, so they may not be representative of the actual arsenic 

concentrations near the landfill. The arsenic levels at other monitoring wells downgradient of the Highway 32 

Landfill were significantly lower.

The results that most stand out are the extremely elevated mean arsenic values at three of the closed sites, 

Edgewater 1-4 (364 ug/l), Nelson Dewey (197 ug/l), and Alliant-Columbia (40 ug/l). The one thing that all 

these sites have in common is that CCB waste was sluiced to the site before they closed. None of the other 

parameters studied has such a close correlation with the waste disposal method. In addition, at least one study 

site, the Highway 59 Landfill, had very low values of arsenic (mean of 3.04 ug/l) in spite of having a 

documented significant release into a transmissive subsurface environment. All this suggests that the elevated 

arsenic levels are more related to the coal source or combustion process rather than hydrogeologic conditions. 

Selenium rarely exceeds concentrations of 1 ug/l in natural surface or groundwater (Hem, 1992), so it is useful 

in determining potential releases from CCB disposal sites. Low levels of selenium were detected at all the 

study sites, with the lowest mean concentrations occurring in the active sites. However, only two sites, the 

Cedar Sauk Landfill (77 ug/l) and the Nelson Dewey Landfill (78.8 ug/l), had mean selenium values that 

exceeded the Wisconsin enforcement standard of 50 ug/l. While they had similar mean values, the Cedar Sauk 

Landfill had some of the highest selenium values (up to 730 ug/l) of any landfill in the study. Other than their 

elevated selenium levels, the two sites have little in common. This suggests that the coal source may be the

dominant factor in determining whether or not excessive selenium contamination will be a problem at any given 

site.

Site Specific Studies

To further illustrate the nature of groundwater contamination from CCB disposal sites, two landfills, the Cedar 

Sauk Ash Landfill and Highway 59 Ash Landfill, were examined in detail. WE Energies, formerly the 

Number of

Coal Median Average Std. Dev. Maximum Minimum Number of Nondetect

Type Detected Detected Data Points Values

Eastern Bituminous 25 41 43 201 0.26 60 4

Eastern Interior (Illinois Basin) Bituminous 100 113 57 214 11 47 1

Northern Great Plains Lignite 0.5 53 68 150 126 10 6

Northern Great Plains Subbituminous 29 62 99 353 22 22 3

Rocky Mountain Subbituminous 43 56 22 80 39 5 0

All data that are designated as "poor" or "unacceptable" quality in the PISCES Database were excluded from all calculations. All "unknown" quality data were included in the calculations.

Coal analyses are for "as-fired" or "as-received" coals and are presented on a dry weight basis.

Boron Concentrations in Coal, by USGS Region

Summary Statistics (mg/kg dry weight)

Source: EPRI PISCES Database (January, 2004)

Notes: The concentrations presented in the tables were calculated using one half of the detection limits for all nondetected values. Nondetected values (represented by one half the detection

limit) greater than two times the highest detected concentration were removed from the data set before statistics were applied.

 Groundwater Impacts from Coal Combustion Ash Disposal Sites in Wisconsin Page 3
Wisconsin Electric Power Company (WEPCO), operated both landfills. Both sites were located in old 

nonmetallic mine sites, neither was constructed with a liner, and both were closed by 1980. These sites were 

chosen based on their identification by the US Environmental Protection Agency (US EPA) as examples of sites 

where there was proven or potential damage involving the placement of coal combustion wastes in sand and 

gravel pits or mines (US EPA, 2000). A third Wisconsin site not included in this study, the Lemberger Landfill 

in the Town of Franklin, was also identified by the US EPA. The Lemberger Landfill accepted municipal, 

industrial waste, and power plant ash during its life. Due to the nature of the disposal methods, it was 

determined that groundwater impacts from contaminants in the municipal and industrial waste could not be 

separated from potential impacts from coal ash. Given these uncertainties, this site was determined to be 

unsuitable for any study attempting to quantify the impacts of CCB disposal on groundwater and was therefore 

not included in this report.

Cedar Sauk Ash Landfill

Background

The Cedar Sauk Ash Landfill (WDNR License # 603) located in the Town of Cedarburg, Ozaukee County, was 

operated as a disposal site from 1969 through 1979. The fly and bottom ash was generated by the Port 

Washington Power Plant (WEPCO, 1985). During this time approximately 650,000 cubic yards of ash was 

disposed of on 25 acres of a 42-acre site. Prior to its development as a landfill, the parcel was used as a sand and 

gravel pit. The landfill was sited before Wisconsin's solid waste disposal laws were enacted so the site was not 

constructed with either a liner or a leachate collection system.

In response to approval conditions from the WDNR, WEPCO installed and began monitoring a series of 

monitoring wells in late 1978. The initial results indicated elevated levels of boron, sulfate and selenium in 

wells downgradient of the landfill. Follow-up inspections of the closed landfill in 1980 and 1981 revealed 

vegetative stress characteristic of boron toxicity in the wetland vegetation downgradient of the landfill. 

Analysis of plant tissue collected from the visibly impacted plants showed boron concentrations from between 

300 and 1,600 mg/l. Healthy plant tissue sampled in the area had boron levels between 7 and 61 mg/l 

(WEPCO, 1982). WEPCO concluded that precipitation percolating through the waste mass and a water table 

near the base of the landfill were likely the cause of these impacts and they proposed some remedial actions.

In 1983, WEPCO proposed a groundwater mitigation plan to the WDNR consisting of 3 groundwater extraction 

wells to be placed downgradient of the fill area. The water was to be pumped into Mole's Creek after flowing 

over rock-filled trench. The WDNR approved the action and the system began operating on September 7, 1984.

During the first 5 years of its operation, the extraction well system seemed to operating well and the 

contaminant levels in the downgradient monitoring wells dropped. However, by 1990 the levels of all 

contaminants began to rise again in spite of the extraction system (WEPCO, 1995). Based on groundwater 

modeling of the system, WEPCO concluded that the capture zone of the 3 extraction wells was inadequate to 

capture all groundwater contamination migrating from the landfill. To address this problem, WEPCO installed 

an engineered cap over the landfill in the summer of 1997 consisting of recompacted clay, 30-mil PVC 

geomembrane and a rooting layer with 2 feet of general fill and 6 inches of topsoil. The cap work was 

completed on October 3, 1997 and the groundwater extraction system was permanently abandoned. 

Geology and Hydrogeology

The Cedar Sauk Landfill is located in an area of hummocky end moraine and glacial outwash deposits from the 

last of the glacial advances of the Lake Michigan Lobe some 13,000 to 14,000 years before present. The 

 Groundwater Impacts from Coal Combustion Ash Disposal Sites in Wisconsin Page 4
underlying unconsolidated glacial sediments generally consist of poorly to moderately well sorted sand and 

gravel deposited on and beneath glacial ice by meltwater streams near the ice margin (WGNHS, 1997). These 

deposits and underlying tills are assigned to the Oak Creek Formation. Underlying the Wisconsonian-aged 

glacial deposits is a relatively thick deposit of Silurian dolostone of the Niagaran Series. This massive dolomitic 

limestone has a highly irregular erosional surface and contains numerous fractures and solution features. Crosssections based on borings near and beneath the landfill area show that the landfill was sited on a bedrock knob 

of Niagaran dolostone. The sand and gravel mining operation removed the unconsolidated material over the 

bedrock allowing waste to be placed directly on the fractured rock. North and east of the bedrock high, towards 

Mole's Creek, the sand and gravel outwash deposits thicken from absent to 25 feet thick beneath the landfill to 

over 50 feet thick near the creek.

There are two major aquifers present at the site: the upper sand and gravel outwash deposits and the lower, 

Niagaran dolostone (WEPCO, 1995). The sand and gravel aquifer is generally unconfined and forms the water 

table. To the east of the landfill, near Mole's Creek, the sand and gravel unit is underlain by silty clay to clayey 

silt glacial till unit. Beneath the landfill this unit is either absent due to mining or directly underlain by bedrock.

Groundwater flow in the Niagaran dolostone is primarily through an extensive network of fractures and solution 

features (including paleokarst) in the bedrock. This aquifer is considered a regional aquifer and is used by 

private water supply wells in the Town. However, beneath the landfill and elsewhere along the bedrock knob, it 

is in contact with the upper sand and gravel aquifer and the water table can occur within both units. 

Groundwater within both the sand and gravel aquifer and the Niagaran bedrock flows from the west to the east 

and southeast. Mole's Creek is considered a groundwater discharge point for shallow groundwater that flows 

from the landfill area. Groundwater table elevations within the shallow, unconfined sand and gravel aquifer 

range from 808 feet above mean sea level (MSL) at the southwest corner of the fill area to 779 along Mole's

Creek. There are no strong vertical gradients at any of the nested monitoring wells, although wells west and 

within the fill area tend to have slight downward gradients and wells to the east trend to have slightly upward 

vertical gradients.

Groundwater Quality

The Cedar Sauk Landfill has had an extensive groundwater monitoring system in place since 1978. As might 

be expected, most of the contamination is concentrated in the sand and gravel aquifer that discharges into 

Mole's Creek. The most common elevated parameters include boron, sulfate and selenium.

The highest levels of both dissolved boron and sulfate were recorded at monitoring wells W-3 and W-3A. 

These nested wells were located within the waste mass and both wells were screened in ash. The data from 

these two wells is of limited usefulness because they were only sampled from August of 1979 until June of 

1983, while the site was closed but inadequately capped. During this limited period, boron levels ranged from 

11 to 186 mg/l in well W-3A and sulfate ranged from 520 to 1923 mg/l in well W-3. Both these levels are well 

above the Wisconsin enforcement standard (ES) of 0.96 mg/l for boron and 250 mg/l for sulfate. While 

consistently elevated, the levels could vary considerably even from one month to the next. There were even 

some distinct seasonal trends over the four years of sampling. This pattern suggests that mobilization of both 

sulfate and boron were related to periodic inputs of precipitation infiltrating through the ash (WEPCO, 1995).

A detailed review of all groundwater quality data from the site indicated that monitoring well W-4 was the best 

candidate to represent groundwater impacts from the landfill. W-4 is an active well that has groundwater 

quality data stretching from August of 1979 to the present. It is located on the eastern edge of the fill area and 

is screened in the shallow sand and gravel unit. The data indicates that is has been significantly impacted by 

disposal practices. In fact, the highest levels of selenium, up to 730 ug/l, recorded at the site were from well W-

 Groundwater Impacts from Coal Combustion Ash Disposal Sites in Wisconsin Page 5
4. The groundwater quality trends from this well are also very similar to general water quality trends found in 

other downgradient wells. 

The pH values from well W-4 were very consistent and only varied between pH 6.7 to 7.6, with a mean value of 

pH 7.07, essentially neutral. This is in contrast to the leachate results from wells W-3 and W-3A, where the 

results were slightly alkaline with pH values between 6.8 and 8.7 with a mean of pH 7.8. These results mirror 

the results of the larger study presented in this paper, again suggesting that the buffering capacity of even sandy 

soils at the site were adequate to neutralize the low-level alkalinity in the leachate.

Boron concentrations were consistently elevated at well W-4 with levels between 6 and 140 mg/l, well above 

the ES of 0.96 mg/l. What is most remarkable about these concentrations is the way they responded to site 

activity. The boron levels steadily climbed as the site was being filled up to its final grades, going as high as 

112 mg/l. However, when the site was finally closed and the relief well system was activated in 1984, the 

boron levels dropped dramatically from 52 mg/l to 6.8 mg/l in the space of 3 months. The levels fluctuated, but 

stayed relatively low until they began creeping back up starting in 1993. The exact cause of this upward trend in 

spite of the continued operation of the relief well extraction system was evaluated (WEPCO, 1995), but an exact 

cause was not determined. It was suggested that the well system was no longer effectively capturing most of the 

contamination coming from the landfill.

The boron concentrations reached their peak in August of 1997, when the relief well system was shut down and 

the new geomembrane cap was being installed. However, after 1997, the boron levels dropped rapidly and 

dramatically, from a high of 140 mg/l to a low of 14 mg/l in 2003. This drop was mirrored by the sulfate levels, 

which decreased from 1070 mg/l in 1997 to 262 mg/l in 2003. Clearly, reducing infiltration through the waste 

mass by installing a geomembrane cover has effectively reduced contaminant concentrations downgradient of 

the landfill.

While the boron and sulfate at well W-4 reacted in similar ways to the remedial measures at the landfill, 

selenium levels reacted a bit differently. While selenium levels in W-4 were generally elevated, with levels as 

high as 980 ug/l, before the site was closed, the selenium concentrations dropped sharply after the site was 

closed and the relief well system was operational in 1984. Within 3 months (September, 1984 to December, 

1984, the same period mentioned with the boron and sulfate results), the selenium levels dropped from 240 ug/l 

to 12 ug/l and they never recovered. These results suggest that selenium does not stay in solution as readily 

than either sulfate or boron.

Highway 59 Ash Landfill

Background

The Highway 59 Ash Landfill (License number 918) is located southeast of intersection of state trunk highways 

59 (Arcadian Avenue) and 164 in the Town of Waukesha, in Waukesha County. The landfill was sited in a 

former sand and gravel quarry, which had ceased operation in 1940. The quarry was operated into a hillside, 

and had a 1.5 acres pond that was approximately ten feet deep and covered 1.5 acres. Coal ash disposal occurred 

at the site from 1969 to 1978. The facility was originally licensed in 1970, and covered approximately 30 acres. 

The CCB wastes were derived from eastern bituminous coal fly ash and bottom ash from their Valley Power 

Plant. Approximately 500,000 cubic yards of solid waste (Class F ash) were deposited in this landfill. The ash 

has pozzolanic properties but is not self-cementitious (Ladwig, 1989). Waste thickness ranged from less than 

10 ft in the southern one-half of the site to more than 40 ft in the northern one-half. Approximately 8,000 cubic 

yards of ash was deposited below the water table in the pond on the northern portion of the site, and 30,000 

yards in the southern portion of the site behind an earthen dike constructed on clay till. 

 Groundwater Impacts from Coal Combustion Ash Disposal Sites in Wisconsin Page 6
Numerous active private water supply wells are located around the landfill with the exception of the southern 

side where railroad & utility corridors and low marshy terrain limited construction. Most private wells in the 

area serve family residences, but there are a few two-family buildings and businesses with wells. Immediately 

west of the ash landfill is an old abandoned unlicensed (Pre-regulation) municipal waste dump operated by the 

City of Waukesha in the 1950’s and 1960’s. An old abandoned foundry sand waste disposal site lies directly 

west of the City’s waste site. Monitoring data from these two sites were used to refine the groundwater flow 

patterns in the area and evaluate the migration of the CCB contaminant plume.

Geology & Hydrogeology

The geological setting of this site is generally similar to the Cedar Sauk site. There are unconsolidated glacial 

deposits below the site that range from 90-150 feet in thickness. These deposits were subdivided into four units: 

an upper sand and gravel unit (suitable as an aquifer), a sandy glacial-till (diamicton) unit, a silty clay unit, and 

a lower sand and gravel unit (also suitable as an aquifer). The lower sand & gravel unit is in direct contact with 

the weathered bedrock north of the site. The underlying bedrock is also Silurian Dolomite, which serves as the 

primary aquifer for the City of Waukesha and many Town of Waukesha. The CCB ash landfill is located 

upgradient of both of the two other disposal sites mentioned above. The thorough evaluation of the limits of fill 

and the careful placement of monitoring wells between the ash landfill and the other nearby sites made the task 

of evaluating the water quality impacts complex but possible. 

The groundwater monitoring around the landfill was initiated 1970’s. WEPCO initiated a hydrological 

investigation in 1988, which included the installation of 13 additional monitoring wells and piezometers and the 

sampling of four private water supply wells adjacent to the site. A report to the Department in 1989 indicated 

elevated concentrations of sulfate and boron in private water supply wells to the west of the site. There were no 

NR140 water quality standards for boron at the time of the investigation in 1989. Subsequent groundwater 

monitoring consisted of sampling 20 monitoring wells and private water supply wells on a regular basis. 

Groundwater Evaluation

The time vs. concentration (TvC) plots for various monitoring wells and private drinking water supply wells 

show a variety of interesting trends. There is a decrease in sulfate levels for shallow wells near the landfill, but 

boron levels are increasing. This appears to document the continued migration of the high mobility of boron 

ions. The data for this site showed a close correlation between the occurrence of boron and high levels of 

sulfate. Molybdenum occurred in the CCB leachate in the low ug/l range. Although it does not have a NR140 

standard, it served as a marker for leachate contamination from this site. This distinction was essential for 

discriminating between leachate contamination from CCB materials, and background levels of sulfate and/or the 

potential commingling of leachate plumes from the other two waste sites. 

The highest levels of both boron and sulfate in monitoring wells were recorded in monitoring well nest W-8, 

which was located in native materials downgradient and in close proximity to the ash disposed of in the former 

quarry pond. The sulfate levels are usually three orders of magnitude higher than the boron, but some plots 

show sulfate concentrations decreasing while the boron have climbed (In Figures 1 & 2: Well W-8A in black, 

W-8B in blue, and W-8C in red).

The monitoring wells and shallow piezometers are screened in the sand and gravel units. The sand & gravel 

units southeast, southwest, west, and northwest of the ash site show contamination above enforcement standards 

 Groundwater Impacts from Coal Combustion Ash Disposal Sites in Wisconsin Page 7
for sulfate and boron. Nine piezometers were completed in the bedrock in order to evaluate deeper groundwater 

impacts. The migration of CCB contaminates into the deep aquifer may have been hastened by a private water 

supply well (WJAC) near the western edge of the ash fill. The business operating the well may have been 

pumping it on a regular basis to wash the numerous cars on their sales lot. This well was the first impacted 

private well near the landfill. The concentration of sulfates made the water undrinkable and bottled water was 

supplied up until the time the well was abandoned and the facility placed on city water. 

Elevated concentrations of sulfate and boron have been detected in deeper bedrock piezometers primarily 

northwest of the site. This information confirms that there is northwestern component to the contamination 

plume, which was not identified in the early stages of the off-site investigation. This component of flow may 

have been influenced by the installation of a higher capacity water supply well for a large retail store northnorthwest of the landfill. This bedrock well has since been abandoned and the building connected to municipal 

water. 

Remediation

WEPCO retained Natural Resources Technology, Inc. and Science & Technology Management, Inc. to evaluate 

various remedial action alternatives. An environmental contamination assessment (ECA) report was submitted 

in 1995. Between 1995 and 1998, WEPCO submitted additional reports assessing the degree and extent of the 

contamination from the landfill. In 1999 WEPCO submitted a remediation plan that included removal of the 

saturated ash from the northern portion of the site and replacement of ash above the seasonal high groundwater 

elevation (excess ash was reburned in their Pleasant Prairie Power Plant). It has been noted that several samples 

of leachate from the on-site basin constructed for dewatering the ash showed molybdenum values two orders of 

magnitude higher than other samples. 

The majority of landfill area was recapped with a synthetic geomembrane. Although ash fill covers about 26 

acres, only 19 acres were recapped due to presence of buildings and other structures; some of the remaining ash 

landfill was covered by asphalt and is being used for parking. The cover design consists of 3-inches of existing 

cover fill, a 4-inch sand bedding layer, a 30-mil PVC geomembrane, a geocomposite drainage layer (consisting 

of geotextile and geonet), 2-feet of general fill, and 6-inches of topsoil.

As part of the remediation plan, WE Energies paid for the abandonment of contaminated private water supply 

wells and the connection to municipal water from the City of Waukesha. The restoration of clean water to the 

affected citizens was only possible through the cooperation of the local Town and City of Waukesha officials. 

WE Energies supplied bottled water to residents with affected wells after contamination was detected. Longterm environmental sampling of the monitoring network which consists of wells and piezometers as well as 

numerous private water supply wells. The WDNR conditionally approved the remedial option selected by 

WEPCO. The Remedial Design Report was submitted on May 1999. 

WE Energies made a case for not excavating the 30,000 cubic yards of saturated ash along the southern portion 

of this landfill. WDNR recommended the removal of these materials since they seemed to represent an 

additional source of leachate generation. The WDNR included additional environmental sampling of private 

water supply wells as a condition of approving the remedial action plan. The monitoring frequency for 

downgradient water wells is currently being increased in response to movement of the plume of CCB 

contaminants. 

 Groundwater Impacts from Coal Combustion Ash Disposal Sites in Wisconsin Page 8
FIGURE 1

FIGURE 2

 Groundwater Impacts from Coal Combustion Ash Disposal Sites in Wisconsin Page 9
Conclusions

As mentioned earlier, this study was a simplified attempt to extract some meaningful conclusions out of a very 

large amount of groundwater monitoring data. The results can be considered fairly conservative because the 

means were calculated based on the most contaminated well at the site using all historical data without regard to 

the well's placement (including those located in the waste mass itself) or status. While much of the analysis was 

inconclusive, several general trends can be discerned.

First of all, it appears that the engineered, recompacted clay liners at the active sites evaluated are effective at 

limiting groundwater contaminate releases. They are by no means perfect and there were measurable 

groundwater impacts in at least one monitoring well downgradient of each landfill. However, the contaminant 

levels were, in most cases, an order of magnitude lower when compared with the results from the closed, 

unlined landfills. This is especially true with regards to arsenic and boron concentrations. 

A review of groundwater quality data at both active and closed disposal sites in Wisconsin indicates that boron, 

sulfate, arsenic and selenium are generally the best indicators of water quality impacts from CCB disposal. 

Manganese was also indicative of groundwater impacts, but there weren't enough sample results to adequately 

characterize the connection. Of all the parameters studied, boron seemed to the best indicator of groundwater 

impacts. Arsenic was only useful at sites that sluiced their waste or used certain coals that were high in arsenic. 

Arsenic was also only found in appreciable amounts at wells that were screened within the waste or fairly close 

to the waste fill limits and may be documenting an ion halo effect. Further out, arsenic likely undergoes a 

geochemical interaction with the groundwater, complexes with iron hydroxides or organics and is therefore no 

longer chemically available to go into solution (Hem, 1992). 

The data certainly suggests a strong connection between the practice of sluicing CCB waste and strongly 

elevated levels of certain compounds, including heavy metals and arsenic, in the leachate and groundwater. 

This problem is confined to older, closed sites, as sluicing CCB waste has not been practiced in Wisconsin since 

the mid-1980's. 

In fact, the volumes of CCB waste disposed in Wisconsin has dropped dramatically as the power utilities have 

switched to dry handling and have aggressively pursued beneficial reuse options for their CCB wastes. In fact, 

as of 2003, WE Energies now reuses more CCB waste than they produce. This is due to a WE Energies project 

at their Pleasant Prairie Landfill where they are mining an old site, reburning the ash, and beneficially reusing 

the subsequent ash. Most ash is beneficially reused in concrete as an additive or as fill in construction projects. 

As for the site specific studies, it should be noted that the results at Cedar Sauk and Highway 59 Ash Landfills 

were the result of a very specific set of circumstances that should not be extrapolated to any specific site or use 

except in a very general sense. Each disposal site was unique with respect to the geologic environment and the 

type and nature of the CCB waste. All of these factors combined to determine the degree and extent of 

contamination at each site, including the type of contaminant found.

Another factor that should be considered, especially at the Cedar Sauk Landfill, was that the most contaminated 

monitoring wells were located and screened in waste. In effect, they were measuring leachate quality, not 

groundwater. This is hardly unique to Cedar Sauk, as the statewide study revealed several other old sites where 

the highest contamination was from wells that were constructed within the waste mass as generally 

recommended by the US EPA at the time of the installation of the wells. It is also significant that some of the 

highest contamination levels were detected before the sites were closed and capped. These early results 

certainly can skew the mean values higher.

 Groundwater Impacts from Coal Combustion Ash Disposal Sites in Wisconsin Page 10
The documented impacts to groundwater quality at both sites were also exacerbated by the geology of the 

disposal sites, which included fractured bedrock and highly transmissive outwash sands and gravels with little 

attenuation capacity. Inadequate capping of the waste masses until recently also allowed precipitation to 

infiltrate through the waste mass and pick up contaminants that was then transmitted to the groundwater. 

However, it is important to note that, under current rules, the siting and facility design of either of these landfills 

would not be acceptable if they were still operating. The State of Wisconsin has very vigorous design and 

monitoring standards for the very reason that many areas of the State contain high-quality shallow groundwater 

that is used and valued by its citizens. 

It should also be noted that the remedial measures installed by WE Energies at both these sites have been 

effective at dramatically reducing groundwater impacts. The Cedar Sauk Landfill remediation project shows 

that proper capping of a CCB landfill is highly effective at reducing negative impacts to groundwater quality. 

Water quality at the Highway 59 site has improved, but several plumes are still migrating through both the sand 

& gravel and bedrock aquifers. The size and extent of the contamination makes off-site groundwater extraction 

difficult when balanced against the decreasingly available water resources for the City of Waukesha.

Acknowledgments

The authors wish to acknowledge WE Energies and EPRI for data on boron values for coal ash analyses.

References

U.S. Environmental Protection Agency. 2000. Regulatory Determination on Wastes from the Combustion of 

Fossil Fuels. 65 FR 32214.

Wisconsin Electric Power Company (WEPCO). 1995. Cedar Sauk Ash Landfill License #603: Groundwater 

Mitigation Biennial Report (1993-1995). March 24, 1995. 20 p.

WEPCO, 1985. First Annual Report, Cedar Sauk Ash Landfill Site. 18 p.

WEPCO, 1999. Remedial Design Report Highway 59 Ash Landfill. 

Kammerer, P.A., Jr. 1995. Ground-Water Flow and Quality in Wisconsin's Shallow Aquifer System. USGS 

Water-Resources Investigations Report 90-4171. 42 p.

Hem, J. D., 1992, Study and Interpretation of the Chemical Characteristics of Natural Water. USGS WaterSupply Paper 2254. 263 p.

Gotkowitz, M. B., Simo, J. A., and Schreiber, M., 2003, Geologic and geochemical controls on arsenic in 

groundwater in northeastern Wisconsin: Final report.

Eaton, T. T., Bradbury, K. R., 1998, Evaluation of the confining properties of the Maquoketa Formation in the 

SEWRPC region of Southeastern Wisconsin. ii + 34 p.

Muldoon, M., 1999, Data from slug tests in the Silurian dolomite using a short-interval straddle-packer 

assemblage, 23 p. + 1 CD-ROM.

 Groundwater Impacts from Coal Combustion Ash Disposal Sites in Wisconsin Page 11
Eaton, T.T., Bradbury, K. R., and Evans, T.J., 1999, Characterization of the hydrostratigraphy of the deep 

sandstone aquifer in southeastern Wisconsin. 30 p. + 15 color p. + 1 CD-ROM.

Muldoon, M. A., Stocks, D. L., Simo, J. A., 1999, Stratigraphic controls on distribution of hydraulic 

conductivity in carbonate aquifers. iv + 61 p. 

Gotkowitz, M., 2002, Report on the Preliminary Investigation of Arsenic in Groundwater near Lake Geneva, 

Wisconsin. 19 p + 5 color pages. 

Eaton, T.T., Bradbury, K. R., Wang, H. F., 2001, Verification and Characterization of a Fracture Network 

within the Maquoketa Shale Confining Unit, Southeastern Wisconsin. 35 p.

Feinstein, D. T., Eaton, T.T., Krohelski, J. T., Hart, D.J., and Bradbury, K. R., 2004, Simulation of regional 

groundwater flow in southeastern Wisconsin.

Cherry, D.S., Curry, R.J., Soucek, D.J., 2000, Review of the Global Adverse Environmental Impacts to Ground 

Water and Aquatic Ecosystems from Coal Combustion Wastes. 55 p.

Cherkauer, D.S., 1980, The Effect of Flyash Disposal on a Shallow Ground-water System. 7 p., Ground Water, 

Vol. 18, No. 6, November-December. 

Evangelou, V. P., 2000, Coal Ash Properties and Potential Impact on Water Quality, 17 p.

Mickelson, D., and Syverson, K., 1997. Quaternary Geology of Ozaukee and Washington Counties, Wisconsin. 

WGNHS Bulletin 91. 56 p.

Ladwig, K., 1989, Report on Groundwater Conditions at Wisconsin Electric Highway 59 Landfill, Facility 918, 

Waukesha, Wisconsin. 47 p. (plus appendix) 

Spencer, L., Drake, L., 1987, Hydrogeology of Alkaline Fly Ash Landfill in Eastern Iowa. Ground Water 

Journal, Vol. 25, No. 5 Sept.-Oct. 1987, 8 p.

 Groundwater Impacts from Coal Combustion Ash Disposal Sites in Wisconsin Page 12
Table 2

Parameter Boron

(mg/l)2

Sulfate

(mg/l)

Arsenic

(ug/l)3

Selenium

(ug/l)

Other

Compounds Status

Facility name

Alliant - Columbia 

Landfill

Lic# 2325

Range

0.18-4.3

Mean

3.2

Range

210-870

Mean

457

Range

5-170

Mean

40

Range

0.5-7

Mean

1.86

Lead -

10-140ug/l

Manganese -

320-830 ug/l

Closed

Sluice Site

WP&L - Rock 

River Landfill

Lic# 0728

Range

1.3-3.7

Mean

2.2

Range

53-900

Mean

322

Range

7-11

Mean

9

Range

1-5

Mean

3

Active

WP&L - Nelson 

Dewey Landfill

Lic# 2525

Range

2.3-28.4

Mean

9.23

Range

75-2100

Mean

1144

Range

5.5-800

Mean

197

Range

10-320

Mean

78.8

Manganese -

720-1200ug/l

Chromium -

45-68 ug/l

Closed 

Sluice Site

WEPCO - Pleasant 

Prairie Landfill

Lic# 2786

Range

1.7-3.6

Mean

2.8

Range

1120-1340

Mean

1215

No Data

Range

3.1-11

Mean

5.65

Mercury -

0.3-1.6 ug/l Closed

Being Mined

WEPCO - Hwy. 32 

Landfill

Lic# 2801

Range

0.5-3.7

Mean

0.85

Range

87-1100

Mean

447

Range

25-35

Mean

30

Range

0.9-4

Mean

2.4

Active

WP&L –

Edgewater 1-4 

Landfill

Lic# 2524

Range

29-120

Mean

69

Range

640-2600

Mean

1661

Range

150-540

Mean

364

Range

1-8.4

Mean

4.7

Closed

Sluice Site

NSP – Woodfield 

Landfill

Lic# 3233

Range

0.17-0.24

Mean

0.24

Range

40-96

Mean

63

Range

7-11

Mean

9.5

Range

0.5-8

Mean

3

Lead -

28-38 ug/l

Manganese -

380-510 ug/l

Active

Dairyland –

Belvidere Landfill

Lic# 2927

Range

1.4-9.1

Mean

5.25

Range

750-2000

Mean

1403

No Data

Range

2.9-30

Mean

18

Active

WPSC - Weston #3 

Landfill

Lic# 2879

Range

0.22-2.68

Mean

1.02

Range

51-791

Mean

210

Range

6.7-16.7

Mean

10.7

Range-91.4

Mean

23

Lead -

0-9.7 ug/l

Manganese -

460-1620 ug/l

Closed

WE Energies -

Cedar Sauk 

Landfill

Lic# 0603

Range

11-186

Mean

101

Range

520-1923

Mean

1397

No Data

Range

1-730

Mean

77

Closed

WE Energies -

Caledonia

Landfill

Lic# 3232

Range

0.2-9.3

Mean

4.37

Range

260-430

Mean

311.6

Range

1-17

Mean

5.26

Range

0.6-5

Mean

1.6

Manganese -

10-110 ug/l Active

WE Energies -

Highway 59 

Landfill

Lic# 0918

Range

15-50

Mean

30.7

Range

836-1170

Mean

1034

Range

2-5

Mean

3.04

Range

0.002-20

Mean

7.84

Manganese -

490-670 ug/l Closed

1 - Values represent the range and mean of all detects listed in the GEMS database for the most impacted groundwater monitoring 

well for each specific parameter at the facility.

2 - Milligrams per Liter (mg/L) or parts per million (ppm).

3 - Micrograms per Liter (ug/L) or parts per billion (ppb).

Contact 608/266-2111 or DNRWasteMaterials@Wisconsin.gov for further information.

 Groundwater Impacts from Coal Combustion Ash Disposal Sites in Wisconsin Page 13
Disclaimers: This document is intended solely as guidance and does not include any mandatory requirements except where requirements found in 

statute or administrative rule are referenced. This guidance does not establish or affect legal rights or obligations and is not finally determinative of 

any of the issues addressed. This guidance does not create any rights enforceable by any party in litigation with the State of Wisconsin or the 

Department of Natural Resources. Any regulatory decisions made by the Department of Natural Resources in any manner addressed by this guidance 

will be made by applying the governing statutes and administrative rules to the relevant facts.

The Wisconsin Department of Natural Resources provides equal opportunity in its employment, programs, services and functions under an 

Affirmative Action Plan. If you have any questions, please write to Equal Opportunity Office, Department of Interior, Washington, D.C. 20240. 

This publication is available in alternative format (large print, Braille, audio tape, etc.) upon request. Please call 608/266-2111 for more information.

 Groundwater Impacts from Coal Combustion Ash Disposal Sites in Wisconsin Page 14