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Congressional District # 05


EPA ID# WID980820070
Last Updated: March, 2011

Site Description

The Master Disposal Service Landfill (MDSL) site is located at 19980 West Capitol Drive in the town of Brookfield, Waukesha County, Wisconsin. The site occupies a 40-acre parcel of land, of which 26 acres comprise a now inoperative landfill. The site is on the marshy floodplain of the headwaters of the Fox River, which flows southwest into Illinois. It is estimated that 1,416,000 cubic yards of waste, including industrial wastes such as solvents, paints, adhesives, oils, and foundry waste were disposed of at the site when the MDSL operated between 1967 and 1982. The site was partially closed in 1982, but the cover materials used at the time were derived from an onsite source with an inadequate clay content. Erosion of the cap and subsequent reexposure of waste materials became a problem.

On September 21, 1984, the site was listed on the National Priorities List (NPL). In June 1986, about 20 potentially responsible parties (PRPs) entered into a legal agreement [Administrative Order on Consent (AOC)] with the United States Environmental Protection Agency (EPA) and the Wisconsin Department of Natural Resources (WDNR) for the purpose of performing a remedial investigation and feasibility study (RI/FS). The goal of the RI/FS was to determine the impact of the site on the surrounding environment and to explore alternatives for cleaning up the site.  The PRPs are parties that the EPA has determined may be legally responsible for the site's contamination.

Site Responsibility

This site is being addressed through a combination of federal, state, and PRP actions. 

Threats and Contaminants

During the RI, samples were collected from the surface and subsurface soils, monitoring wells, residential and municipal wells, surface water, and sediment. A limited amount of air sampling was also performed. The largest class of waste at the site included foundry sands and slags, plastic wastes, and certain solvents. The groundwater and soil were found to be contaminated with volatile organic compounds (VOCs), including benzene, toluene, xylenes, and chlorinated solvents. Inorganic contaminants included cadmium, chromium, arsenic, lead, iron, manganese, and barium. A surface water ditch which drains into the site and ultimately leads into the Fox River was found to contain cadmium levels exceeding pertinent state water quality standards.

The risk assessment concluded that the chief exposure pathways at the MDSL site involved contact with the landfill waste mass and ingestion of contaminated groundwater. Accidental ingestion and direct contact with soils, as well as the inhalation of contaminated airborne dusts also posed potential health threats. The site lies on a raised plateau in the middle of a wetland that could be contaminated from site runoff. The western suburbs of Milwaukee have experienced steady to rapid growth over the past 20 years.  The formerly rural site setting is now characterized by light industrial, commercial, and residential development. The land immediately surrounding the landfill, however, is a wetland and is zoned as an environmental corridor.

Cleanup Progress

The fact that the site is situated in a wetland near the Fox River complicated the cleanup plan. The sensitive wetland environment required a stable water balance, yet containing the plume and restoring the groundwater quality required some extraction of groundwater. EPA organized the work into two operable units (OUs), the first being a source control OU (OU 1) to contain the waste mass. OU 1 prescribed the installation of a landfill gas control system, construction of a suitable landfill cap, and the construction of a groundwater extraction and treatment system to capture contaminated groundwater beneath the site. A second OU (OU 2) was deemed necessary to restore the groundwater to federal and state standards. The remedy for OU 2 was anticipated to define the groundwater cleanup goals and the restoration time frame. In January 1992, 33 companies entered into a consent decree (CD) with EPA and WDNR to perform the remedial design and remedial action (RD/RA) at the site. 

Both OUs were constructed between 1994 and 1997. The source control measures were performed first; the cap construction began in April 1994 and was completed later that year. Rough grading was performed to remove large debris; a thick compacted clay layer was installed from May to August 1994. Cover soils were then placed over the clay layer, and seeding was completed in late fall 1994. Because of the relatively steep slope on the eastern side of the MDSL, a thick high density polyethylene geomembrane was put in place. A concrete mat was placed over the geomembrane. While installation of the clay layer occurred, trenching and installation of piping for collection of landfill gases also proceeded. 

In accordance with the CD, the groundwater extraction system was designed in July 1996, and by 1997, a series of 11 groundwater extraction wells began discharging into a large pond on the western side of the site. Effluent from the pond was filtered through the wetlands between the site and the Fox River. Had the discharge been routed directly into the Fox River, the wetlands could have suffered a net loss of water. A construction completion report for the entire site was signed in June 1997.

On September 25, 2000, EPA completed the first five-year review for the site. The five-year review documented that the remedy protects human health and the environment, is functioning properly, and clean-up goals are being achieved. A monitoring program was implemented to track the effectiveness of the groundwater capture and treatment system. 

After a two-year evaluation of the monitoring results, EPA and WDNR approved a reduced monitoring schedule in January 2000. Based on relatively slow groundwater movement and negligible changes in the groundwater gradient, EPA and WDNR subsequently approved a probationary shutdown of the groundwater extraction system in 2003; however, groundwater contaminant monitoring continues on an annual basis. During the 6.5 years that the groundwater pumping system operated, groundwater contaminant levels declined to nondetectable levels and the surrounding wetlands have remained viable. Since 2003, benzene is the only contaminant of concern that has been detected in groundwater at levels ranging from nondetectable to 9.6 parts-per-billion (ppb). 

A second five-year review was completed in September 2005 and found that the remedy is currently protective of human health and the environment because all portions of the remedy, except for institutional controls (ICs), are functioning properly. During the review, EPA assessed the effectiveness of ICs at the site, the status of private well use downgradient of the site, and whether the probationary shutdown of the groundwater extraction and treatment system has adversely affected the protectiveness of the remedy. The five-year review indicated that an EPA decision document needed to be signed for OU 2 in order to memorialize groundwater cleanup criteria.

On July 12, 2007, EPA issued a Proposed Plan which described EPA's preferred alternative for a final groundwater cleanup remedy at the site. On September 26, 2007, at the conclusion of the public comment period, EPA issued a Record of Decision (ROD) for OU 2. The ROD documented EPA's selected cleanup plan which included the use of monitored natural attenuation (MNA) to remove the remaining low levels of benzene from the groundwater. The remedy also specifies clean-up levels for groundwater contaminants; requires regular groundwater testing; requires ICs to prevent the use of groundwater and to protect the remedy; and requires the reactivation of the on-site groundwater pumping system should pollutant levels indicate that contamination might move off-site.  

The WDNR has concurred with the selected remedy. EPA is now working with the responsible parties to ensure that the benzene levels in the groundwater do not exceed the cleanup level of 5 ppb. The most recent annual monitoring in April 2008 of the up gradient, side gradient and down gradient monitoring wells did not show detectable levels of benzene.  A June 2008 sample of a downgradient onsite piezometer (PZ-02) showed a benzene level of 7.5 ppb. These levels will continue to be tracked. 

In September 2010, EPA completed a third five-year review. The data collected during this process showed that MNA is generally effective. EPA determined that the plume capture and treatment system should neither be reactivated nor dismantled. Further EPA found that monthly monitoring of PZ-02 for benzene can be reduced to quarterly or semi-annually. EPA and WDNR also approved reduction of the landfill cap inspections from quarterly to semi-annually.

The 2010 review found that OU 1 (source control) remains protective of human health and the environment in the short term. The final groundwater remedy for OU 2 (MNA) is also protective in the short term. For the site-wide remedy to be protective in the long term and fulfill the requirements of the September 2007 ROD, effective institutional controls (ICs) to restrict land and groundwater use must be put in place. To ensure enforcement of ICs, EPA determined that a Restrictive Covenant signed between the property owner, EPA and WDNR will be necessary. EPA is currently negotiating with the property owner to achieve this goal.

Property Reuse

EPA had been working with a model aeronautics club to explore the feasibility of using the landfill cap as a flying field. This plan is no longer being pursued and no further reuse inquiries have been made.


Remedial Project Manager, U.S. EPA
sheila sullivan (sullivan.sheila@epa.gov)
(312) 886-5251

Community Involvement Coordinator, U.S. EPA
susan pastor
(312) 353-1325




Site Profile Information

This profile provides you with information on EPA's cleanup progress at this Superfund site.


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