Fact Sheet #98-21
December 1998
Landfill 1 (LF-1) Plume Response Decision
A fact sheet providing information about the selected
cleanup alternative for one of the groundwater plumes emanating from the MMR
The purpose of this fact sheet is to describe the total
remedy selected by the Air Force Center for Environmental Excellence (AFCEE) to address
the Landfill 1 (LF-1) groundwater plume emanating from the Massachusetts Military
Reservation. A decision was announced in December 1997 for the portion of the plume west
of Route 28 and is summarized on page 4 of this fact sheet. The decision announced on
December 8, 1998 focuses on the plume east of Route 28.
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 DECISION
In December 1997, a decision was agreed to by the Air Force Center for Environmental
Excellence (AFCEE), the United States Environmental Protection Agency (EPA), and the
Massachusetts Department of Environmental Protection (DEP) for the western
portion of the LF-1 groundwater plume (west of Route 28). The decision called for the
implementation of monitored natural attenuation (MNA). MNA was chosen for the western
portion of the LF-1 plume because of concerns regarding: [1] population density and
impacts of construction and [2] unproductive nature (i.e. relative closeness to the
surface of the salt/freshwater interface) of the aquifer west of Route 28.
On December 8, 1998, AFCEE and the EPA reached an
agreement on the eastern portion of the LF-1 plume (east of Route 28). This
agreement calls for the design, installation and monitoring of focused extraction,
treatment and reinjection (ETR) systems for the northern and southern lobes of the
LF-1 plume and monitored natural attenuation for the center portion and plume fringes (see
Figure 1). The ETR system has been commonly referred to as "Alternative 3E".
A detailed description of the ETR system and MNA are included within this fact sheet.
"Alternative 3E" was discussed with other
alternatives during the public comment period from August 12 to October 10, 1997 and
outlined in the Supplement to the Focused Feasibility Study for Landfill 1 (LF-1), dated
October 1998.
Other actions that are part of the December 1998 decision
include:
- Developing both a comprehensive long-term monitoring plan,
and an operation and maintenance plan to measure the effectiveness of the ETR system and
MNA.
- Providing public water connections for any remaining
residences on private wells located within the present or potential path of the LF-1
plume, including Scraggy Neck.
- Replacing Bourne public water supply wells #2 and #5 in
1999.
- Working with the regulatory agencies to review the
performance of the remedial alternative over the next 3 to 5 years, and modifying it, if
necessary.
CONCEPTUAL LAYOUT OF THE SELECTED ALTERNATIVE
COMPONENTS OF THE DECISION
The decision for the eastern portion of the LF-1 plume consists of two
primary approaches: extraction, treatment, and reinjection (ETR) and monitored natural
attenuation (MNA). A third important component of the decision is monitoring, which will
be used by AFCEE, EPA and the MassDEP to determine the effectiveness of this remedy.
Extraction, Treatment, and Reinjection
Conceptually, "Alternative 3E" will consist of two ETR systems constructed near
the MMR base boundary, one in the northern lobe and one in the southern lobe of the plume
(see Figure 1). The ETR systems will consist of approximately 4 to 6 extraction wells that
draw contaminated water out of the ground; a treatment plant, where the water will be
treated; and reinjection wells that return clean water to the aquifer.
Monitored Natural Attenuation
Monitored natural attenuation refers to the strategy of allowing natural processes to
reduce contaminant concentrations to acceptable levels together with active monitoring.
Natural attenuation involves physical, chemical and biological processes which act to
reduce the mass, toxicity, and mobility of subsurface contamination.
There are several different physical, chemical, and
biological processes that comprise monitored natural attenuation. These include:
- biodegradation—breakdown of contaminants by
microorganisms in the environment, sometimes forming non-harmful byproducts like carbon
dioxide and water
- chemical stabilization—reduction in contaminant
mobility caused by chemical processes
- dispersion—the process of mixing that occurs
when fluid flows through a porous medium
- sorption—attachment of compounds to geologic
materials by physical or chemical attraction
- volatilization—transfer of a chemical from
liquid to vapor; evaporation
Natural attenuation, by definition, occurs naturally.
However, use of monitored natural attenuation as a specific treatment method is not a
"do nothing" approach. It involves sampling, active monitoring, modeling and
evaluating contaminant reduction rates.
Monitoring
As part of the decision, comprehensive long-term environmental and ecological monitoring
plans that ensure the protection of human health and the environment will be developed and
implemented. These plans will also provide valuable data to determine the effectiveness of
the ETR system and 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:
- Monitoring residential wells, within the present or
potential path of the LF-1 plume, to ensure that no plume constituents are present in
private water supplies. This will continue until those remaining homes on private wells
are connected to public water supplies.
- Monitoring the Bourne water supply sentry wells to
ensure that LF-1 plume constituents are not threatening Bourne public water supply wells
#2 and #5.
- Sampling monitoring wells west of Route 28 to support the
decision to allow MNA to continue.
- Conducting a study to locate the offshore discharge of
freshwater to help determine where the LF-1 plume is discharging in the marine
environment.
- Monitoring the ecological impact, if any, of the LF-1 plume
to help determine to what extent the ecology may have been affected. This includes, but is
not limited to, the sampling of Red Brook and Squeteague Harbors.
- Continued sampling of groundwater (LF-1 Post Closure)
monitoring wells to monitor the performance of the landfill cap and changes in the
landfill over time.
- Performance monitoring evaluation (PME) wells will be
sampled to evaluate the chemical, hydraulic and ecological impact, if any, of the
groundwater extraction, treatment and reinjection systems.
- Data from the PME wells also will be used to evaluate the
ETR system performance, and to determine whether changes to system operation are
warranted. Data also will be used to evaluate the effectiveness of MNA in the center and
fringes of the LF-1 plume.
BACKGROUND
In late summer and fall of 1997, a public decision-making process called the
"Decision Criteria Process" (DCM) was implemented for the LF-1 groundwater
plume. The process used a matrix with decision criteria, which helped highlight the
tradeoffs associated with different cleanup alternatives for the plume. The decision
criteria focused on protection of human health and the environment, regulatory
requirements, effectiveness of treatment technologies, costs, and community acceptance.
On December 12, 1997, AFCEE, EPA, and MassDEP reached a
final agreement for the western portion of the LF-1 plume. AFCEE committed
to perform the following:
- It was agreed among these parties that, for the western
portion of the plume (west of Route 28), monitored natural attenuation (MNA) would be
implemented. Long-term performance monitor-ing of groundwater and surface water would be
used to ensure that MNA was a viable alternative.
- For the eastern portion of the plume (east of
Route 28), AFCEE would proceed with a multi-pronged approach:
- Proceed with design of an extraction, treatment, and
reinjection (ETR) system.
- Evaluate the appropriateness of using MNA.
- Begin to evaluate the extent of any natural resource
injuries that may have resulted from the plume contaminants.
To meet the conditions agreed to, AFCEE proceeded with
actions necessary for the design of the ETR system, such as data gap analysis.
In July 1998, AFCEE released a document called a
"Landfill 1 Proposed Response Document" that analyzed several remedial
alternatives for the LF-1 plume. Results of this analysis determined that there are
several "lines of evidence" to indicate that MNA is already occurring in the western
portion of the LF-1 plume. These lines of evidence include decreased concentrations of the
original contaminants, increased concentrations of the breakdown products, and anticipated
levels of other degradation byproducts, such as methane and carbon dioxide. AFCEE also
completed a Preassessment Screen Summary (PAS), as an appendix to the LF-1 Proposed
Response Document. The PAS assessed any possible injury to natural resources from the LF-1
plume contamination. Further, AFCEE completed the Focused Feasibility Study (FFS) for
Landfill 1, as a second appendix to the LF-1 Proposed Response Document. The FFS
presented information needed to select the most technically and economically feasible
remedy for the LF-1 plume. The FFS compared no action, MNA, and two ETR systems,
previously presented during the December 1997 decision criteria process.
In October 1998, the Supplement to the Focused Feasibility
Study for Landfill 1 (LF-1) was released. It provided an evaluation of additional
remedial alternatives for the cleanup of the LF-1 plume. It recommended MNA.
Based on both of these documents, and throughout the public
comment period, AFCEE presented MNA as its preferred alternative. However, the regulatory
agencies did not concur with the report findings. AFCEE then agreed to implement
"Alternative 3E" as the best remedy for the LF-1 groundwater plume.
NEXT STEPS
- The draft-long-term monitoring plan was released in December
1998 for regulator review and comment.
- Engineering design of the ETR systems will continue. The
draft well field design report will be available on March 18, 1999, in accordance with the
enforceable milestone. The well field design report will present the best location(s) for
the ETR system. A modeling report will be issued later in April 1999 that describes all of
the modeling activities that led to the design of the ETR system.
- The enforceable milestone for full-scale system startup is
September 15, 1999.
- AFCEE, EPA, and MassDEP encourage residents to attend
citizen advisory team meetings, become informed and involved with the LF-1 cleanup, and
sign up for the site mailing list to receive updates.
- The public will be notified before any construction
activities begin and during key construction activities. Drilling activities are scheduled
to in March 1999.
GLOSSARY AND ACRONYMS USED IN
THIS FACT SHEET
aquifer—an underground geological formation containing usable amounts of
groundwater that can supply wells and springs.
data gap analysis—a study or series of studies
to provide additional details regarding aquifer character-istics and contaminant
distribution. The studies may consist of literature reviews or collection of new data.
downgradient—the direction toward which
ground-water flows.
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.
monitored natural attenuation (MNA)—the
remedial strategy of allowing natural processes to reduce contaminant concentrations to
acceptable levels.
performance monitoring evaluation (PME)—a
monitoring well used to monitor either groundwater elevations or chemical constituents.
sentry well—a monitoring well, located
upgradient of a public water supply well, that it used to watch for possible
contamination.
volatile organic compounds (VOCs)—organic
chemical compounds that evaporate readily to the atmosphere.
For More Information
Doug Karson, Community Involvement Specialist
HQ AFCEE/MMR
322 East Inner Road
Otis ANGB Base, MA 02542-5028
Phone: (508) 968-4678 x 2 Fax: (508) 968-4673
e-mail: doug.karson@mmr.brooks.af.mil
Jim Murphy, Community Relations Coordinator
USEPA Region I, One Congress St
Suite 1100 (RAA)
Boston, MA 02114-2023
Phone: (617) 918-1028 Fax: (617) 918-1029
e-mail: murphy.jim@epa.gov
Ellie Grillo, Community Involvement Coordinator
MassDEP
20 Riverside Drive
Lakeville, MA 02346
Phone: (508) 946-2866 Fax: (508) 947-6557
e-mail: ellie.grillo@state.ma.us
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