Fact Sheet #99-04 Landfill 1 (LF-1) Plume Remedial Action Update A fact sheet describing the progress of the remedial action for one of the groundwater plumes emanating from the MMR The purpose of this fact sheet is to describe the extraction, treatment, and reinjection (ETR) system and related actions for the cleanup of the Landfill 1 (LF-1) groundwater plume east of Route 28. The Air Force Center for Environmental Excellence (AFCEE) issued a wellfield design report for regulatory review in March, 1999. A decision was announced in December 1997 for the portion of the plume west of Route 28. Another decision announced on December 8, 1998 focused on the plume east of Route 28. Both of these decisions were made after significant public involvement. They are described in a fact sheet that was published in December 1998 (#98-21). That fact sheet is available at the main libraries in Bourne, Falmouth, Mashpee, and Sandwich, The U.S. Coast Guard library on base, and at the Installation Restoration Program (IRP) office on base. Words in italics are defined in the glossary at the end of this fact sheet. They are only italicized the first time they are used. OVERVIEW OF THE ACTIVE TREATMENT SYSTEM The wellfield design includes the following components:
The LF-1 groundwater remedial system will prevent further migration of the plume past the MMR base boundary while minimizing ecological impacts to the environment. Performance monitoring evaluation (PME) will be conducted to determine the effectiveness of the remedial system. It is anticipated that system operation will result in restoration of the aquifer between the base boundary and Route 28A in approximately 15-20 years. Goals of the system The system was designed to ensure protection of human health and the environment. The goal of the LF-1 remedial system is to reduce contaminant concentrations in the northern and southern lobes of the LF-1 plume along the base boundary while minimizing ecological and hydrological impacts. In addition to the remedial system, AFCEE has also committed to:
Components of the ETR system The remedial system consists of five extraction wells (four in the southern lobe and one in the northern lobe), a 700-gpm treatment facility, and a central infiltration gallery (see figure 1). The infiltration gallery will be situated between the northern and southern lobes of the plume along the MMR western boundary. This design will facilitate the capture of contaminated groundwater by extracting water from those zones within the plume that contain the highest concentrations of trichloroethylene (TCE), perchloroethylene (PCE), and carbon tetrachloride (CCl4). Further migration of contaminants will be significantly limited. Contaminant distribution, implementability, and ecological considerations were considered in selecting the well locations. The following paragraphs summarize the three main components of the LF-1 ETR system.
Extraction Wells Contaminated groundwater is pumped out of the aquifer through a series of extraction wells. This requires extraction wells in different locations and at different depths in order to capture the plume. Groundwater Treatment The untreated groundwater will be transported to a treatment facility near the southern extraction wells (see Fig 1). The site was selected for the following reasons:
The treatment system uses activated carbon, which will clean the groundwater to non-detect levels for contaminants. Carbon has the ability to adsorb, or grab onto, passing organic molecules and hold them on the surface of the carbon granule. When contaminated groundwater is pumped through a filter of carbon granules, most of the organic contaminants become trapped on the surface of the carbon. Eventually the carbon is saturated with contaminants and the carbon must be replaced. Used carbon is sent off-Cape to be recycled. The activated carbon system is housed in cylinders inside a treatment plant and is used to treat groundwater pumped from several extraction wells. Safety precautions, such as leak detection and containment monitoring systems, ensure that any leaks are detected and managed immediately. Infiltration Galleries After being tested, the treated water is then transported through a second set of underground pipes and pumped back into the aquifer through a series of infiltration trenches. An infiltration gallery consists of a network of trenches located several feet below the frost line with perforated distribution pipes to carry water throughout a network. The infiltration gallery design was influenced by the following criteria:
Infiltration of treated water will be through perforated horizontal pipes. The infiltration gallery will be approximately 150 feet square and located approximately 5 feet below the ground surface (see figure 2). The gallery depth of 5 feet is recommended for the following reasons:
The primary functional difference between infiltration trenches and reinjection wells is that infiltration trenches deliver water to the vadose zone, the area below ground where the water table begins, whereas reinjection wells deliver water much deeper into the aquifer. This arrangement buffers groundwater both from changes in the quantity and chemistry of the reinjected water. Trenches percolate water at a low enough velocity that sand grains would not be rearranged. The centralized infiltration gallery funnels the plume toward the northern and southern extraction wells, thus enhancing capture of contaminants. The infiltration gallery is less costly to construct and maintain than standard reinjection wells. Further, construction and long-term maintenance of the infiltration gallery would be less disruptive to the ecosystem than reinjection wells. The gallery design balances system performance, adherence to the ecological thresholds, and constructability concerns.
Groundwater Monitoring As part of the overall LF-1 plume response program, comprehensive long-term environmental and ecological monitoring plans were developed. These plans ensure that the overall remedy for LF-1 protects human health and the environment. Further, they also provide valuable data to determine the effectiveness of the ETR system and monitored natural attenuation (MNA). Extensive monitoring will enable AFCEE and the regulatory agencies to determine what effect the remedy is having on the LF-1 plume. Analysis of the monitoring will help to guide future actions, such as long-term operation of the ETR system. The following summarizes the proposed monitoring plan:
LF-1 Plume Configuration Groundwater sampling and analytical data collected during the LF-1 data-gap investigation has been used to redefine the boundary of the LF-1 plume (see figure 1). This boundary is defined by the area encompassing all exceedences of the maximum contaminant levels (MCLs) or drinking water standards for TCE, PCE and CCl4. The maximum contaminant level allowed under federal and state safe drinking water standards is 5 parts per billion (ppb) for TCE and PCE and CCl4. Two areas of the plume have changed: the eastern boundary where the plume exits the source area (Landfill-1), and the southern boundary where new monitoring wells were established in 1998. Closure and capping of LF-1 was completed in December 1995. Landfill leachate entering the groundwater has been reduced by eliminating water percolation by precipitation (rain and snow). This successful reduction in leachate is indicated by the decreased constituent concentrations in groundwater samples collected over the last three years at the eastern edge portions of the plume, those nearest the capped areas of the landfill. The southern edge of the plume is better defined in the vicinity of the base boundary. Two monitoring wells were installed along the previously known edge of the plume to refine the plume boundary. Data from these wells indicate that the plume has not advanced as far south as these wells. This has allowed for a redrawing of the plume boundary further north than previously determined. The western end of the plume continues to be identified as dividing into northern and southern lobes as it migrates west of the base boundary. This division has been previously explained by AFCEE as the result of natural degradation of the volatile organic compounds (VOCs). This division was still apparent after the data-gap investigation results were evaluated. Contaminant Distribution Data acquired during the LF-1 data-gap investigation indicates that each plume constituent (e.g., TCE, PCE, CCl4) represents a discrete zone of affected groundwater (essentially small plumes within the overall LF-1 plume footprint). These discreet zones are smaller in extent than the overall LF-1 plume. Data indicates that a TCE zone extends throughout the northern lobe, from the western toe to the eastern edge near to the capped LF-1. A second TCE zone extends the entire length of the southern lobe from the western toe to the eastern edge near the capped LF-1, where the two TCE zones merge near the source area. Except for the eastern 4,000 to 5,000 feet of the LF-1 plume, the two TCE zones are separate and distinguishable based on the available data. Also present within the southern lobe of the LF-1 plume is an identifiable PCE zone. The PCE zone extends from the western toe of the LF-1 plume to the eastern edge near the capped LF-1. This PCE zone is generally coincident with the TCE zone in the southern lobe of the LF-1 plume. Areas in which CCl4 are present in concentrations above the MCL are sporadic but they generally coincide with the southern lobe of the plume that has TCE and PCE concentrations above drinking water standards. The samples that exceeded the MCL were found in the wells along the base boundary and toward LF-1 (eastward). Next Steps
Glossary carbon tetrachloride (CCl4)—a man-made liquid that was used widely in refrigerant coolants and aerosol cans. It was also used as a degreaser. extraction, treatment, and reinjection (ETR)—a system that extracts groundwater, treats it to reduce or eliminate contaminants, and reinjects the treated water into the aquifer. groundwater plume—a body of groundwater containing contaminants that exceed federal and state drinking water levels or other risk-based levels at multiple test well locations. Contaminated water can result when fuels, solvents, or other contaminants are spilled or released on the ground. When these materials filter through the sandy Cape Cod soil, they encounter groundwater, or the water table, where the soil is saturated with water. As the groundwater moves, the contaminants are carried with it, creating a groundwater plume. maximum contaminant levels (MCLs)—the maximum concentration of a given contaminant allowed in drinking water under state and federal regulations. monitored natural attenuation (MNA)—the remedial strategy of allowing natural processes to reduce contaminant concentrations to acceptable levels. perchloroethylene (PCE)—also referred to as tetrachloroethylene; a man-made solvent commonly used for degreasing metal and dry-cleaning clothes. performance monitoring evaluation (PME)— monitors: [1] the down-gradient portion of the plume to ensure proper groundwater chemistry; [2] ensures that the contaminants are being captured by the ETR system; [3] ensures that the treated water does not significantly impact the groundwater (i.e. raising the water table in the vicinity of the infiltration trenches). sentry well—a monitoring well, located upgradient of a public water supply well, that it used to watch for possible contamination. trichloroethylene (TCE)—a solvent used to dissolve or disperse another substance such as oil; often used in degreasing metal. vadose zone—the area below ground where the water table begins. It is called a zone because groundwater levels fluctuate through various seasons. volatile organic compounds (VOCs)—organic chemical compounds that evaporate readily to the atmosphere. For More Information Doug
Karson, Community Involvement Specialist Jim Murphy, Community Relations Coordinator Ellie Grillo, Community Involvement Coordinator
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