Congressional District # 05
MASTER DISPOSAL SERVICE LANDFILLEPA ID# WID980820070
Last Updated: April, 2013
The Master Disposal Service Landfill (MDSL) Superfund 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 the now inoperative landfill. The site is on a raised plateau in the middle of the marshy floodplain of the headwaters of the Fox River, which flows southwest into Illinois. It is estimated that 1.4 million 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 on-site source with an inadequate clay content. Erosion of the cap and subsequent re-exposure of waste materials then become a problem.
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 area light industrial, commercial, and residential development. Land immediately surrounding the landfill, however, is a wetland and is zoned as an environmental corridor.
EPA placed the MDSL site on the National Priorities List (NPL) in September 1984.
Site ResponsibilityThe MDSL site is being addressed through potentially responsible party (PRP) actions under state and federal oversight.
Threats and Contaminants
The largest class of waste at the MDSL site includes foundry sands and slags, plastic wastes, and certain solvents. Groundwater and soil are contaminated with volatile organic compounds (VOCs), including benzene, toluene, xylenes, and chlorinated solvents. Inorganic contaminants include cadmium, chromium, arsenic, lead, iron, manganese, and barium. A surface water ditch that drains to the site and ultimately leads into the Fox River was found to contain cadmium at levels exceeding the state water quality standard.
The chief exposure pathways at the site included direct contact with the landfill waste mass, ingestion of contaminated groundwater, ingestion and direct contact with contaminated soil, and the inhalation of contaminated airborne dust. Each of these potential exposure pathways can cause carcinogenic (cancer-causing) or noncarcinogenic health effects to human receptors.
In June 1986, about 20 potentially responsible parties (PRPs) entered into a legal agreement [Administrative Order on Consent (AOC)] with EPA and the Wisconsin Department of Natural Resources (WDNR) for the purpose of performing a remedial investigation and feasibility study (RI/FS) at the MDSL site. The goal of the RI/FS was to determine the nature and extent of contamination, evaluate actual or potential health risks associated with exposure to site contaminants, and to evaluate potential remedial alternatives for cleaning up the site.
The fact that the MDSL 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 OU cleanup actions 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 and then a 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, a 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 (FYR) for the site. The FYR report 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 continued 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 consistently detected in shallow groundwater at one downgradient monitoring location (called "PZ-02"). Monthly monitoring has been performed at this location since 2004.
A second FYR report was completed in September 2005 and EPA 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 site ICs, the status of private well use downgradient of the site, and whether the probationary shutdown of the groundwater extraction and treatment system had adversely affected the protectiveness of the remedy. The FYR report indicated that an EPA decision document needed to be issued 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 track the cleanup of 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 concurred with the selected remedy. EPA has been working with the responsible parties to ensure that the benzene levels in the groundwater do not exceed the cleanup level of 5 ppb. Monthly monitoring of PZ-02 since June 2004 has shown benzene ranging from 0.41 ppb to a high of 14.2 ppb. These levels will continue to be tracked.
In September 2010, EPA completed the third FYR report at the site. The data collected during the FYR 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 semi-annually since benzene concentrations are relatively low and stable. The most recent data showed 9.1 ppb benzene in PZ-02 and no benzene in the deeper aquifer. EPA and WDNR also approved reduction of the landfill cap inspections from quarterly to semi-annually.
The 2010 FYR report found that OU 1 (source control) is 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. In October 2012, EPA approved the removal of additional groundwater parameters from the groundwater monitoring program because they hadn't been detected for several years.
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.
EPA will complete the fourth FYR at the site in 2015.
Property ReuseNo recent property re-use inquiries have been made. Property reuse can be explored after the Restrictive Covenant has been put in place.
ContactsRemedial Project Manager, U.S. EPA
sheila sullivan (email@example.com)
Community Involvement Coordinator, U.S. EPA
AliasesMASTER DSPL SERVICE LDFL