Fact Sheet #99-06 Landfill 1 (LF-1) Source and Plume Update Facts sheet providing updated information on the Landfill-1 source area, groundwater plume and cleanup. The purpose of this fact sheet is to provide updated information to the public regarding the Landfill 1 (LF-1) groundwater plume emanating from the Massachusetts Military Reservation (MMR). This information is provided by the Air Force Center for Environmental Excellence (AFCEE) which manages the groundwater plume cleanup program at the MMR with input from the U.S. Environmental Protection Agency (EPA) and the Massachusetts Department of Environmental Protection (DEP). In addition to this fact sheet, we encourage you to read other fact sheets such as Landfill 1 (LF-1) Groundwater Plume, Monitoring and Sampling, Landfill 1 (LF-1) Plume Response Decision, Landfill 1 (LF-1) Plume Remedial Action Update, and Groundwater Treatment Technologies, which provide background information about the LF-1 groundwater plume. 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. Plume Background The source of the LF-1 groundwater plume was the primary MMR landfill, which is located near the center of the MMR. From 1941 to 1989, disposal of solid waste occurred in this area. Disposal of wastes was discontinued at the landfill in 1990. The LF-1 groundwater plume was generated when rainwater soaked through wastes in sections of the landfill, known as "cells." The rainwater carried the contaminants into the underlying groundwater as it flowed through the landfill. The primary contaminants of the LF-1 groundwater plume are trichloroethylene (TCE), perchloroethylene (PCE), and carbon tetrachloride (CCl4). Each of these contaminants has a maximum contaminant level (MCL), referred to as federal drinking water standards, of 5 micrograms per liter (ug/L). Concentrations equal to or above these drinking water standards define the boundaries of the plume. The primary contaminants are chlorinated solvents previously used at the MMR for cleaning purposes. Several other volatile organic compounds (VOCs) also have been detected, but below their associated MCLs. The plume is approximately 17,300 feet long, a maximum of 5,500 feet wide, and averages 35 feet thick with a maximum thickness of 125 feet. In general, the plume is 150-300 feet below ground and 50-200 feet below the water table along most of its length. Groundwater sampling collected during the past year has been used to redefine the boundary of the LF-1 plume. Figure 1 depicts the LF-1 plume. Groundwater near the LF-1 plume flows primarily westward toward Buzzards Bay.
The western end of the plume continues to be identified as dividing into northern and southern lobes as it migrates west of the MMR boundary. Data acquired during the last year indicate that each primary plume contaminant represents a discrete zone of affected groundwater (essentially small plumes within the overall LF-1 plume area). These discrete zones are smaller in extent than the overall LF-1 plume. Source Area Cleanup The cells of the landfill that caused contamination were "capped" in 1995. Capping the landfill eliminated the infiltration of rainwater thereby reducing the movement of contaminants from the landfill to the groundwater. The cap covers about 60 acres of the 100-acre former landfill site. The landfill cap consists of several layers, including a geo-synthetic clay liner, a geo-membrane, sand, and vegetation to prevent erosion. Please refer to Figure 2 for a diagram of the cross-section of the capped landfill.
Groundwater near the former landfill is monitored regularly and continues to show very low levels of contamination. Groundwater samples collected from monitoring wells near the LF-1 site indicate that capping the landfill has been effective in reducing the amount of contaminants moving into the groundwater. Recent groundwater results have shown that wells located immediately downgradient of the cap continually have shown lower contaminant concentrations since groundwater monitoring began at the landfill site in 1989. Ongoing monitoring over the next 30 years will help AFCEE determine the effectiveness of the cap, movement of the groundwater plume and levels of contaminants. Plume Cleanup In December 1997, a decision was agreed upon by AFCEE, EPA and MassDEP for the portion of the LF-1 groundwater plume located west of the MMR boundary. Extensive involvement of the nearby community helped to create this decision which was supported by those members of the community who participated in meetings and submitted written or verbal comments about the options for cleaning up this part of the plume. The 1997 decision called for the implementation of monitored natural attenuation (MNA) for a portion of the plume, but not the sole remedy. MNA refers to the cleanup strategy of allowing natural processes to reduce contaminant concentrations together with active monitoring. Natural attenuation involves physical, chemical, and biological processes that act to reduce the mass, toxicity, and mobility of subsurface contamination. Use of MNA as a specific treatment method is not a "do nothing" approach because it involves active monitoring to evaluate contaminant reduction rates. MNA was chosen for the western portion of the LF-1 plume because of two primary concerns. The community expressed concerns regarding the highly dense residential population in the area where a potential treatment system would be constructed. Secondly, MNA was selected for this portion of the plume due to the unproductive nature of portions of the aquifer west of State Route 28A. Much of this area of groundwater is considered unproductive as a source of drinking water due to its relative closeness to the of the interface between fresh and salt water. In December 1998, a decision was agreed upon by AFCEE, EPA and the MassDEP for the portion of the LF-1 groundwater plume located east of the MMR boundary. This decision also was made with considerable input from local residents regarding the chosen methods for cleaning up this portion of the plume. The 1998 decision for the eastern portion of the LF-1 groundwater plume implements a probationary plan, subject to review and revision after 3 years of operation. It consists of two primary approaches: extraction, treatment and reinjection by infiltration (ETR) and MNA. The ETR system consists of five extraction wells (four in the southern lobe and one in the northern lobe), a carbon treatment facility, and an infiltration gallery area (see Figure 1). This design will facilitate the capture of contaminated groundwater by extracting water from those zones within the plume that contain the highest concentrations of TCE, PCE, and CCl4. Further migration of contaminants will be reduced significantly. Contaminant distribution, ability to implement the remedy, and ecological considerations were considered in selecting the extraction well locations. The system was started August 26, 1999, 21 days ahead of the enforceable milestone of September 15, 1999. Monitoring Comprehensive long-term environmental and ecological monitoring plans were developed as part of the overall LF-1 plume decision made in December 1998. These plans include, but are not limited to, sampling of groundwater, surface water, sediments, and landfill gas. The primary objectives of these sampling plans include protecting human health, studying the ecological impacts of groundwater contamination and groundwater cleanup work, and evaluating the effectiveness of the ETR system and changes in the plume concentrations and location. These plans outline data to be collected that will ensure the selected cleanup methods achieve cleanup goals and protect human health and the environment. Analyses of the monitoring data will help guide future actions, such as long-term operation of the ETR system. The following information summarizes the comprehensive monitoring plan. Landfill Closure Monitoring: Monitoring the former MMR landfill includes numerous activities such as groundwater sampling, gas sampling and inspections of the cap. This inspection work includes monitoring the cap’s physical performance, surface materials, and amount of settling. Continued sampling of groundwater monitoring wells will enable engineers to evaluate the performance of the landfill cap and changes in contaminant concentrations near the landfill over time. Landfill gases are monitored primarily to ensure that flammable gases are not present. The most recent results available are for monitoring work completed in May 1999. None of the primary contaminants¾ TCE, PCE, or CCl4¾ was detected above the associated drinking water standards. Methane was detected in three of twelve locations sampled, but not at concentrations high enough to be a concern. Bourne Public Water Supply Well Monitoring: Three monitoring wells, located upgradient of the Bourne water supply wells #2 and #5, are sampled monthly to ensure that LF-1 plume constituents are not threatening these public wells. Three additional wells also are sampled, but on a quarterly basis. Analytical results from samples collected during the months of April through July 1999 did not identify any contaminants above the drinking water standards. Residential Well Monitoring: Monitoring of residential wells located within the present or potential path of the LF-1 plume has been conducted since August 1996 to ensure that no plume constituents are present in private water supplies. Seventy-seven residential wells were sampled during the Spring of 1999, with most wells being located in the Scraggy Neck area of Bourne. Results of this sampling event did not identify any samples containing plume contaminants above a drinking water standard. This is consistent with data collected since the program began. This sampling work will continue until the potentially effected homes with private wells are connected to public water supplies. Ecological Monitoring: Monitoring the potential ecological impact of the LF-1 plume will help determine to what extent the ecology may have been affected. This type of monitoring has been broken into two phases. The first phase helps identify the current state of the ecosystem prior to the startup of the ETR system in August 1999. This data was collected on a quarterly basis during 1998 and 1999. The data collected for this part of the monitoring is in the process of being evaluated to understand the ecosystem potentially affected by the LF-1 plume. The results of this evaluation are expected to be available during the Winter of 2000. The second part of the ecological monitoring program will start after the ETR system is operating and will identify impacts to the ecosystem from extracting contaminated groundwater or from adding treated water through the infiltration gallery. Any impacts identified will be minimized or eliminated The ecological monitoring work also includes the sampling of Red Brook and Squeteague Harbors to locate the area of offshore freshwater discharge. This may help to determine if and where the LF-1 plume may be discharging to the marine environment. The preliminary data collected does not definitively identify the freshwater discharge location. Therefore, the location of the LF-1 plume discharge point has not been identified to date. Monitoring Natural Attenuation: Monitoring Natural Attenuation (MNA) work includes sampling both the western and eastern portions of the LF-1 groundwater plume. The results of this sampling effort may help to support the decision to allow MNA to continue as a component of the overall cleanup solution. Wells are scheduled to be sampled on a semi-annual basis. The first data for the western portion of the LF-1 plume was collected in July 1999. However, previous data has been collected from wells in this area while ongoing investigations of the landfill plume were conducted. In general, recent analytical data collected from within the plume boundary are consistent with those results reported the previous time each of these wells was sampled. As this monitoring program continues, additional data will allow for a better comparison of concentration changes through time. Performance Monitoring Evaluation: Performance monitoring evaluation (PME) wells will be sampled to evaluate the chemical, hydraulic and ecological impact, if any, of the groundwater extraction, treatment and infiltration systems. Data from the PME wells also will be used to evaluate system performance, and to determine whether changes to system operation are warranted. Data also will be used to evaluate the effectiveness of natural attenuation in the center and fringes of the LF-1 plume. To date, EPA and MassDEP have not approved the comprehensive long-term environmental and ecological monitoring plan. Next Steps AFCEE, EPA and MassDEP will continue the public involvement effort to ensure that the public is kept informed and has an opportunity to provide input on the ongoing remedial actions with the LF-1 plume. Residents are encouraged to attend citizen team and public meetings, become involved with the LF-1 plume cleanup and sign up on the site mailing list to receive updates. Glossary carbon tetrachloride (CCl4): a man-made liquid that was used widely in refrigerant coolants and aerosol cans. It also was used as a degreaser. chlorinated solvents: liquids used to dissolve or disperse another substance such as oil. downgradient: the area toward which groundwater flows. extraction, treatment and reinjection (ETR): a system that extracts groundwater, treats it to remove contaminants, and reinjects or infiltrates 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. As the groundwater moves, the contaminants are carried with it, creating a groundwater plume. lobe: a separate portion of a main body of a groundwater plume. monitored natural attenuation (MNA): long-term performance monitoring of groundwater and/or surface water conducted to ensure that natural attenuation (breakdown of contaminants through natural physical, chemical, and biological processes) is restoring groundwater quality as expected. monitoring well: a well from which water level and water quality data is collected. perchloroethylene (PCE): also referred to as tetrachloroethylene; a man-made solvent commonly used for metal degreasing and in dry-cleaning clothes. trichloroethylene (TCE): a solvent used to dissolve or disperse another substance such as oil; often used in metal degreasing. volatile organic compounds (VOCs): carbon 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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