FS-28/FS-29 Proposed Plan Public Meeting
February 10, 2000
Unitarian Universalist Fellowship

Meeting Minutes

Agenda Item #1. Introduction

Ms. Larkin, the Community Involvement Coordinator for the Joint Program Office (JPO), convened the meeting at 6:24 PM. She introduced Mr. Snyder from the Air Force Center for Environmental Excellence (AFCEE), Mr. Lim of from the United States Environmental Protection Agency (EPA), Ms. Kiley from the Massachusetts Department of Environmental Protection (DEP), Mr. Aker and Mr. Karson from AFCEE, and Ms. Foster from Jacobs Engineering. Ms. Larkin then reviewed the meeting agenda and groundrules.

Mr. Karson stated that tonight the Air Force will present its preferred alternatives for the Fuel Spill 28 (FS-28) and FS-29 groundwater plumes. The 30-day public comment period for these two plumes begins tomorrow, and during the comment period, both written and oral comments on the proposed plan can be submitted to the Air Force. Mr. Karson noted that the FS-28/FS-29 Proposed Plan is available tonight, and the feasibility study report for these plumes is in the local libraries. The feasibility study includes more detailed information about everything that was considered to determine the preferred alternatives that will be discussed tonight. Mr. Karson reported that a public hearing is scheduled for March 2, 2000, and any oral or written comments made at that time will be included in the official record. He stated that a draft Record of Decision (ROD) is scheduled to be issued to the regulatory agencies for review by May 1, 2000. Mr. Karson added that all comments received during the public comment period will be taken into consideration to reach the draft decision.

Agenda Item #2. Background Information

Mr. Karson displayed a graphic of the groundwater recharge process. He explained that precipitation falls from the sky onto the ground where it quickly percolates into the sandy soil and eventually reaches the groundwater aquifer, where all the air spaces between the sand particles are saturated with water. He noted that the saturated area of sand can be 230 feet thick in vertical height. Mr. Karson noted that water within the aquifer is moving at an average flow rate of a foot and a half per day. He explained that the water is moving toward ponds, streams, and the ocean; evaporation occurs, and the cycle begins again.

Mr. Karson displayed a map of the Sagamore Lens, a large area of the aquifer that supplies drinking water to Upper Cape Cod, and noted that the numbers on the map represent height of groundwater compared to sea level. He explained that there is a mound of clean water located below the Massachusetts Military Reservation (MMR), and rainwater percolates down into the groundwater and flows perpendicular to the contour lines shown on the map. Mr. Karson then pointed to the general area in the southern portion of the base where industrial activities occurred and solvents and fuels were used.

Mr. Karson displayed a slide that depicted the creation of a groundwater plume and its flow pattern over time. He noted that the base has been in existence since the early 1920’s, and chemicals, such as solvents and fuels, have been used for decades. He then explained that a plume begins with a source area where there might have been a chemical or fuel spill, or a landfill where chemicals and fuels were used or disposed. Those materials eventually enter the sandy soil and percolate down into the water table. Mr. Karson explained that over time, those materials dissolve in the groundwater and begin to flow with the groundwater. He stated that the FS-28 and FS-29 plumes are detached, in that they no longer are connected to a source area on the base. He also noted that in some instances some of the contamination can stick to the silty or clay materials as the plume is moving through them, and remain deposited there.

Mr. Karson displayed a map of the FS-28 and FS-29 plumes and pointed out the plumes’ contours and buffer zones. He explained that buffer zones are drawn around the plume outlines in order to help make decisions about protecting public health. He pointed to the residences that have private wells, some of which are potentially threatened by the plumes. He noted that the Air Force evaluated where the plumes potentially could pose a risk and, in this case, paid for municipal water connections for those residences. Mr. Karson reported that the Air Force recently has agreed to connect the homes within the boundary of Boxberry Hill Road, Sam Turner Road, and Hatchville Road, as well as all the residences located to the west of Sam Turner Road, from the intersection of Hatchville Road to Route 151. The Air Force will be working with the Town of Falmouth to make those municipal water connections. Mr. Karson stated that the Air Force also is testing private wells and converting private wells to municipal water supply systems to ensure that people are not exposed to these plumes.

Mr. Karson displayed a graphic that showed examples of the groundwater treatments being discussed, and noted that extraction wells are used often. He explained that wells are drilled to where the plume is dissolved in groundwater. The water is pumped out of the ground to a vault, and then transported through an underground pipe to a treatment facility. Mr. Karson reported that on the base there are two large treatment facilities, which use two methods of treatment – greensand filtration and carbon filtration. He explained that greensand filtration is a pretreatment for certain areas where iron and manganese is found naturally in groundwater. Granular activated carbon (GAC) is the main method of treatment to remove contaminants such as fuel, solvents, trichloroethylene (TCE), tetrachloroethylene (PCE), and ethylene dibromide (EDB). Mr. Karson noted that GAC is similar to what is used in a fish tank to purify the water. He also noted that fuels and solvents like to adhere to carbon.

Mr. Karson explained that the treated water is returned to the environment in one of three ways. The water can be reinjected via a reinjection well, which "pushes" the water back into the aquifer. Infiltration galleries also can be used to return water to the environment. Mr. Karson noted that an infiltration gallery is located on Sandwich Road for the Ashumet Valley groundwater plume project. An infiltration gallery consists of slotted pipe that is placed underground, through which water naturally percolates back into the aquifer. The third method to return water to the environment is through surface water discharge, which is being used at the Coonamessett River and at the Quashnet River, where the treated water is purified and then discharged directly to the surface water via a bubbler.

Agenda Item #3. Question and Answer Period

A member of the audience asked how one can determine exact addresses that may be included in the town water connections. Mr. Karson replied that the actual agreement, which lists all the street addresses, has not been finalized with the Town of Falmouth. He reiterated that all properties within the boundaries of Sam Turner Road, Boxberry Hill Road, and Hatchville Road, and all residences to the west of Sam Turner Road, from Route 151 to the intersection of Hatchville Road, will be included in the agreement. Mr. Karson stated that once the agreement with the Town of Falmouth is signed, the street addresses will be identified.

A member of the audience asked if the private wells will continue to be tested, regardless of the plans to provide municipal water within the next couple of years. Mr. Karson replied that the private well testing program will continue in that area until the homes are connected. All homes within the boundary he mentioned are eligible for free water connection and for private well testing. Mr. Karson encouraged people who live in that area, whose private wells currently are not being tested, to let him know. He noted that the testing program is conducted twice a year, usually in April/May and September/October.

Mr. Dow asked if private wells could be used for watering lawns and other uses, once those residences are connected to municipal water. Mr. Karson replied that the Air Force does not have a mechanism to restrict the use of private residential wells. However, the Air Force and the Town of Falmouth do discourage that practice. He noted that people can keep their private wells in operation for whatever purposes they choose.

Ms. Larkin noted that Ms. Grillo, with the DEP, and Ms. Valiela, a Falmouth Selectman are in attendance tonight.

FS-28

Ms. Foster noted that most of the material she will present is in the FS-28/FS-29 Proposed Plan, and she displayed a list of commonly used acronyms. She stated that AFCEE is the lead agent for cleaning up the plumes, and that EDB, which was used as a gasoline additive, is the primary contaminant of concern for the FS-28 and FS-29 plumes. She explained that an FS, feasibility study, provides more detail on the proposed alternatives, and she noted that FS also can denote Fuel Spill. She further explained that an RI, remedial investigation, is the study conducted before the feasibility study. Ms. Foster noted that ETR, extraction, treatment, and reinjection, also will be mentioned tonight, and noted that infiltration is another version of ETR.

Ms. Foster displayed a SWOU area map and noted that, in addition to the FS-28 and FS-29 plumes, the SWOU contains four other plumes: FS-13, CS-21, CS-20, and CS-4. The public comment period for those four plumes ran from June 1999 to August 1999, and AFCEE currently is finalizing the ROD, which documents the selected remedy for those four plumes. Ms. Foster stated that AFCEE has committed to axial systems for CS-4, CS-20 and CS-21. The 13-extraction well treatment system at the leading edge of CS-4 will be abandoned and replaced with approximately three extraction wells, using the existing CS-4 treatment plant to the extent possible. New systems will be designed and constructed for CS-20 and CS-21, and probably will entail two new treatment plants. Ms. Foster then pointed out various points of reference, including the MMR boundary, the town line between Bourne and Falmouth, the movie theater, the golf course, Hatchville Road, the existing treatment system for FS-28, and the Ashumet Valley plume. She noted that treatment systems are in place for the Ashumet Valley, CS-10, and LF-1 plumes.

Ms. Foster stated that the FS-28 and FS-29 plumes are disconnected and their sources are unknown. She again noted that EDB is a gasoline additive, and said that the source release mechanism for these plumes is believed to be fuel spills on the base – possibly multiple fuel spills, in multiple areas, at multiple times. She said that compared to EDB, the other components of gasoline are relatively easily degraded by naturally occurring microbes in the groundwater, and do not travel in the groundwater as quickly. Ms. Foster stated that EDB is very soluble, and, compared to those other compounds, is not very degradable. The other compounds probably degraded a long time ago. Ms. Foster reported that FS-29 also contains carbon tetrachloride (CCl₄), which is an industrial degreasing agent that was used on the base to clean avionics, electronics, and communications equipment.

Ms. Foster reported that the trailing edge of the FS-28 plume is intermingled with the leading edge of the CS-4 plume. In 1992, during design and construction of the treatment system for CS-4, EDB was detected in a monitoring well. Subsequent investigations, until the summer of 1996 when AFCEE became involved, determined that the plume had migrated underneath Coonamessett Pond and underneath the Coonamessett water supply well (CWSW). Ms. Foster noted that there is approximately 100 feet of clean water between that well screen and the plume, but as a precaution, AFCEE installed a treatment system on this well, which has been operating since that time. Ms. Foster noted that the pretreated water from this well is sampled on a monthly basis by the Air Force, and on a more frequent basis by the Town of Falmouth. There have been no measurable concentrations of EDB in that well.

Ms. Foster reported that the Air Force’s additional investigation in 1996 found that the further south the samples were taken, the higher the concentrations of EDB detected. In the fall of 1996 the Air Force discovered that the leading edge of the FS-28 plume was discharging into the surface waters of the Coonamessett River and associated cranberry bogs. As an immediate response to that discovery, AFCEE started supplying bottled water to residents overlying the plume, and connected a total of 175 homes to municipal water. In the fall of 1997, AFCEE installed extraction well 1 (EW-1), which for the first year was pumped at a rate of 700 gallons per minute (gpm). The water was treated on site in the treatment building, and the treated water was discharged directly to the Coonamessett River.

Ms. Foster reported that in 1997 the Coonamessett River surface waters contained measurable concentrations of EDB, almost all the way south to Route 28. Several cranberry growers and other agricultural users utilized this water for irrigation and flooding of crops. Therefore, AFCEE installed nine irrigation wells in clean areas that could be used for those purposes, rather than the EDB contaminated surface waters. Ms. Foster also reported that in 1999, the extraction, treatment and discharge system was expanded by the installation of a shallow groundwater extraction system. The system includes 204 shallow well-points, which are 13-foot steel mini-wells that are connected together. Currently 86 of the 204 shallow well-points are being used, and specific well-points are connected to a vacuum system. Ms. Foster referred to a deep well and pointed to an area where EDB is upwelling. She stated that 300 gpm is being pumped from the shallow well-point system, and 400 gpm from the well treating and discharging the water directly to the surface water.

Ms. Foster stated that under Superfund cleanup authority, the Air Force implemented the shallow well system, the deep well, the water supply well, the municipal connections, and the bog separation project, in order to prevent any immediate risks to human health. Concurrently, the Air Force conducted a remedial investigation, which led to the feasibility study, which led to the proposed plan that is being presented tonight.

Ms. Foster reported that the entire plume was investigated as part of the remedial investigation, and it was found that the highest concentrations of EDB were in the lower part of the plume. She also noted that contamination was detected in a portion of the river, although the pond was clean. A risk analysis was conducted, and it was determined that since there was EDB contamination in the river, there would be unacceptable cancer risks to anyone wading or working in the water, eating fish caught in the river, or, in the future, drinking water from the plume.

Ms. Foster noted that out of the remedial investigation came two remedial action objectives, which apply to both the FS-28 and FS-29 plumes. One remedial action objective is to prevent or reduce residential exposure to contaminants of concern. At FS-28, the contaminant of concern is EDB in the surface water and in the groundwater. Ms. Foster noted that the risk assessment concluded that the waders and fish consumers could be harmed by exposure; however, once the feasibility study phase was reached and the interim actions were completed, the shallow well-point system and the deep extraction well, working together, had eliminated the risks to surface water. Monthly testing at 27 locations, since May 1999, has shown no detections of EDB in the river. Ms. Foster stated that the Air Force believes that the actions it already has taken have successfully eliminated the surface water risks successfully, and municipal connections have removed the groundwater risk. She did note, however, that there is a potential for risk in the future, should a private well be installed for residential household use. Ms. Foster reiterated that the primary goal of the remedial action is to prevent or reduce residential exposure to contaminants of concern. She stated that the second goal is to restore the aquifer to its beneficial uses within a reasonable time.

Ms. Foster reported that the feasibility study evaluated seven remedial alternatives, four of which were retained for detailed analysis, and are presented in the proposed plan. The first alternative, which is no remedial action with long-term monitoring, is required by the Superfund process for comparison purposes.

Ms. Foster reported that Alternative 3 involves continuing the operation of the shallow well-points and the deep extraction well system. She explained that there is a naturally converging flow field that will bring the whole plume to the capture area. She also noted that a small portion of the plume, which is downgradient of the capture zone, would not be captured. The concentrations in that portion of the plume, although above drinking water standards, are relatively low, and that piece represents approximately 0.3% by mass, of the entire plume. Groundwater modeling indicates that this portion of the plume will continue to migrate and degrade, and eventually discharge into the Coonamessett River farther downstream. The Air Force believes that when that portion of the plume does discharge to the river, it will be nondetectable.

Ms. Foster reported that Alternative 3 also includes maintenance of the CWSW. In addition to municipal water connections, institutional controls also protect residents from exposure. Ms. Foster defined institutional controls as non-engineering measures to protect human health; an example of an institutional control is deed restrictions. In this case, institutional controls include the residential well sampling program and Falmouth’s bylaws, which were passed in September 1999, to prevent the drilling of news wells for residential or irrigation purposes, over plumes. Ms. Foster noted that long-term monitoring would continue for each of the remedial alternatives. She stated that Alternative 3 would restore the plume within 18 years. She also noted that Alternative 3 meets the first remedial objective of preventing exposure, but it does not go as far as it could in terms of meeting the second remedial objective, to clean the aquifer as quickly as possible.

Ms. Foster reported that Alternative 6 attempts to reduce the restoration time by simultaneously capturing the southern portion of the plume with the existing system, and aggressively addressing the northern portion of the plume, which would require the construction of an additional treatment system. She stated that modeling has determined that a successful scenario would entail approximately five extraction wells pumping at a rate of 600 gpm. The water would be treated near those extraction wells and discharged in three reinjection wells. Ms. Foster noted that the well layout shown on the map is conceptual, and further design and analysis is needed to determine exact well locations. She stated that AFCEE did not select Alternative 6 as its preferred alternative, primarily because of public input received from the Lochstead Estates community.

Ms. Foster reported that Alternative 7 is a variation of the same goal to cut aquifer restoration time by cutting the plume in half and simultaneously capturing the northern and southern portions of the plume. Modeling of this alternative determined that a successful scenario would include three extraction wells pumping at a rate of 600 gpm. She pointed out the location of the Souza Conservation Area, where two of the extraction wells would be installed, and noted that the third well might be installed on private property. Ms. Foster reported that when this system was modeled, it reduced the aquifer restoration time from 18 years to 9 years.

Ms. Foster also reported that a potential problem with Alternative 7 is that reinjection might not work as a viable method of returning the treated water to the aquifer. She noted that the CWSW currently is pumping at a rate of 500 gpm. She then identified a low flow area of the Coonamessett River, which is controlled by a weir, and said that during low water table periods, the river can run dry. It was dry for several months this fall. Ms. Foster explained that the combined drawdown effects of the 500-gpm CWSW and the 600-gpm extraction wells probably would cause adverse impacts to the Coonamessett River, unless the treated water was discharged to the pond, to the river, or a combination of both.

Ms. Foster displayed a summary of the restoration times for the FS-28 alternatives. She stated that Alternative 7, AFCEE’s preferred alternative, reduces restoration time by half. She emphasized that this is a preliminary proposed plan and no final decisions will be made until after public comment is received. She also noted that property access is critical to the implementation of this alternative. Additional data will need to be collected in order to design and construct a system, and in such a sensitive area, property access would be crucial.

FS-29

Ms. Foster reported that compared to its vast knowledge of the FS-28 plume, the Air Force has little information on the FS-29 plume. There are approximately 100 monitoring wells screened in the footprint of the FS-28 plume, and approximately 31 wells define the outside extent of the FS-28 plume. Conversely, the FS-29 plume was discovered during the remedial investigation in 1998, and there are approximately 10 monitoring wells in the plume.

Ms. Foster identified various reference points on the map, including Route 151, Cloverfield Way, the CS-21 plume, and Ballymeade. She stated that the FS-29 plume, which contains EDB and CCl₄, is comprised of two lobes, separated vertically by approximately 50 to 80 feet of clean water. She noted that the concentrations detected in the FS-29 plume are lower than those detected in the FS-28 plume, and reported that the highest concentrations of EDB detected in the FS-28 plume were 18 parts per billion (ppb), which is significantly higher than the 0.02 ppb drinking water standard. The highest concentrations of EDB detected in the FS-29 plume were approximately 0.1 ppb, and the highest detection of CCl₄ was 9.5 ppb, which is higher than the 5 ppb drinking water standard. The estimated total mass of the FS-29 plume is approximately 5.6 ounces, and the total mass of EDB in the FS-28 plume is approximately 25 pounds. Ms. Foster stated that although there is still much to learn about the FS-29 plume, in general, it is not as concentrated and does not contain as much mass as the FS-28 plume.

Ms. Foster reported that the Air Force has proposed an axial treatment system for CS-21, and it is fortunate that the system will capture approximately 23% of the FS-29 plume due to its close proximity. She also noted that the remedial investigation determined that all residences in the area, including those in Ballymeade, are connected to municipal water, so there is no immediate risk. A monitoring well was installed next to a proposed public water supply well site, and it tested clean for contaminants of concern. Irrigation wells in Ballymeade also were sampled, and tested clean. Ms. Foster stated that although there is no current risk to human health from the FS-29 plume, the concentrations detected are high enough that possible future exposure could pose unacceptable cancer risk.

Ms. Foster reported that the remedial action objectives for the FS-29 plume are the same as those for the FS-28 plume, except that at this site the contaminants of concern are EDB and CCl₄ and, unlike FS-28, there are no surface water bodies. She stated that seven remedial alternatives for the FS-29 plume were screened during the feasibility study, four of which were retained for detailed analysis and are included in the proposed plan. Alternative 1, a no action alternative, was required for comparison purposes. Alternative 2 is an institutional and engineering controls alternative, which, in this case means that AFCEE would install well head treatment on a water supply well, if it were threatened by this plume. In this case, institutional controls refer to Falmouth’s bylaws.

Ms. Foster stated that Alternatives 3 and 7 build on Alternative 2, which includes long-term monitoring. She noted that the two alternatives for active treatment include either capturing the entire plume or capturing the central portion. She displayed a map of the conceptual well layout for Alternative 3, and noted that this alternative was not modeled with the conceptual well locations. Preliminary modeling did indicate, however, that with an approximate 600 gpm system, two wells would be required to contain most of the FS-29 plume. Ms. Foster stated that 23% of the plume mass would be captured by the proposed CS-21 treatment system in all of the proposed alternatives.

Ms. Foster stated that Alternative 7, AFCEE’s preferred alternative, would capture the central portion of the FS-29 plume, but would not capture the leading edge of the plume. She then pointed to the portion of the plume that would be restored in six years with a 600-gpm system, and the portion that would be restored in ten years. She noted that this restoration time would be an improvement over the no-action alternative, which would restore the plume in 13 to 17 years.

Ms. Foster stated that the Air Force has proposed that, regardless of which alternative is selected, additional information on the FS-29 plume needs to be collected. She reiterated that ten wells were installed in the FS-29 plume during the remedial investigation, and noted that there is private land near the leading edge of the plume. Ms. Foster also pointed to the Crane Conservation Area, and noted that the area where the Air Force would be working is privately owned. She then pointed to another area, and noted that last year an additional golf course was planned there, but currently that area is slated for homes. Ms. Foster stated that there are private homes in this area, and property access is crucial to the implementation of this alternative.

Ms. Foster then reported that because of the rough terrain there, it would be difficult to drill wells in this area. She noted that it also will be difficult to collect the additional data that is needed, and would even be more problematic for ETR. She reiterated that property access is crucial to the successful implementation of this alternative.

Ms. Foster displayed a slide titled "FS-29 Alternative Summary," said that the figures shown are preliminary, and again stated that AFCEE prefers Alternative 7. She defined present worth costs as the amount of money needed to implement the alternative, if invested today or over the lifetime of the alternative, so there is some correlation to the expected lifetime of the alternative.

Ms. Foster displayed a cross-section of the FS-29 plume and pointed to the portion that would be uncaptured by the preferred alternative. She stated that, based on current modeling, the Air Force does not believe that the uncaptured portion of the plume would continue to migrate downgradient. She explained that the concentrations are dilute enough that the uncaptured portion of the plume is expected to degrade in place, and she noted that long-term monitoring would be conducted.

Mr. Karson reported that comments about the proposed plan can be submitted by mail, fax, or e-mail, or the MMR web page. He stated that verbal comments can be made during the public hearing. Those comments will be transcribed verbatim and will become part of the official record. Mr. Karson reported that the comment period begins February 11, 2000 and runs until March 11, 2000. He stated that AFCEE will meet with the EPA and the MassDEP to review all the comments received during the public comment period. Those comments will be considered before the final decision is being made. Mr. Karson noted that all comments, and responses to those comments, will be included in a Responsiveness Summary. Anyone who submits a comment during the comment period will receive a copy of the Responsiveness Summary.

Agenda Item #5. Question and Answer Period

Ms. Aulisio asked if cancer rate studies have been conducted in this area. Mr. Karson replied that several studies have been conducted by both the Massachusetts Department of Public Health (MDPH) and the Agency for Toxic Substances and Disease Registry (ATSDR), which is the federal public health agency. He encouraged Ms. Aulisio to discuss this with the personnel from the Environmental Public Health Center on the base, whose employees are experts on the studies conducted to date. He noted that the purpose of the Public Health Center on the base is to provide information to the community about the various cancer issues on Upper Cape Cod. Mr. Karson offered to provide Ms. Laseo with the point of contact for that center.

Mr. Dow asked if the FS-29 plume contains thallium at levels above EPA action levels. Ms. Foster replied that she does not believe so, and could look into a definitive answer.

Mr. Dow remarked that because the FS-29 plume contains CCl₄ and EDB, in his opinion, it is more than a fuel spill plume. He said that after reviewing the information available tonight, it seems to him that the EDB is higher in one of the lobes, relative to the CCl₄, and the opposite is true in the other lobe. He then asked if the Air Force can calculate back the amount of EDB to determine how much fuel was spilled. He also asked which contaminant is the dominant source, considering that the EDB and CCl₄ are intermingled and one comes from a chemical spill source and the other from a fuel spill source.

Ms. Foster replied that she has investigated the distribution of CCl₄ throughout the SWOU and MMR area, and has found that there are other areas where CCl₄ occurs. She reported that the highest concentrations of CCl₄ are in the southern lobe of LF-1, and the second highest concentrations are in the FS-29 plume. There are low concentrations, below the maximum contaminant level (MCL), just outside of the FS-28 plume. Ms. Foster stated that whether the FS-29 plume is from one or two sources is unknown. She noted that there is a diverging flow field in this area, and said that contaminants released upgradient could have traveled anywhere. Ms. Foster referred to LF-1, which is traveling west, and said that the current thinking is that neither LF-1 nor CS-10 originated from single sources. She reported that particle tracking has been conducted as part of the model calibration, and it was determined that it is possible that CCl₄, coming generally from the same place as LF-1, might have diverged – some of it could have gone to LF-1 and some of it could have gone into FS-29. Ms. Foster also said that the chemical properties are similar, and explained that EDB should have traveled faster, so 20 to 30 years ago, it may have been "back here." She added that there also are silt stringers in this area, which cause plumes to diverge. Ms. Foster said that with the contamination located three miles downgradient, it is difficult to determine the release mechanism.

Mr. Dow noted that he is concerned that there may be a component of the chemical spill that is downgradient from the leading edge. He asked if studies have been conducted on the other side of Route 28 to elucidate that possibility. Ms. Foster replied that of the solvents, CCl₄ would be one of the most rapidly moving, with almost no retardation. She said that she cannot think of anything else from a chemical spill that would have moved faster and farther downgradient from CCl₄. Ms. Foster reported that wells have been drilled downgradient of the FS-29 plume and nothing has been found. Mr. Karson asked if those wells were located along Route 28. Ms. Foster pointed on the map to the locations of those monitoring wells and noted that one of the wells is located along Route 28.

Mr. Burns, a Falmouth resident, commented that, in his opinion, based on the information that has been provided, the justification to spend $10 million to clean up the FS-29 plume, is weak. He explained that it has been said that the mass concentration of EDB is 5.6 ounces, and 20% of that will be addressed with the treatment for the CS-21 plume, which leaves 4 ounces, "a small jar" of EDB. Mr. Burns noted that the groundwater in the area of the FS-29 plume is 100 to 200 feet deep. Because of a lack of ponds, lakes, and rivers, there is no opportunity for that groundwater to migrate to the surface, and also there are no health hazards. Therefore, the justification to spend $10 million to clean up that particular plume seems to be missing. Mr. Burnes asked for a more detailed explanation from the Air Force, the EPA and the DEP, of the justification to spend that amount of money.

Mr. Karson replied that the remedial action objective for both the FS-28 and FS-29 plumes is to protect public health. He then acknowledged that the FS-29 plume is very deep, that residences in that area are connected to municipal water, and that there are no current or projected future exposures expected from the FS-29 plume. Mr. Karson explained that for the FS-29 plume, most of the weight is on the second objective, which is to restore the aquifer in a timely fashion. He stated that the FS-29 plume could be monitored and allowed to naturally attenuate, but the current goal is to try to understand the plume and to expedite the restoration of the aquifer in that area, which currently is not useable because of the presence of that groundwater contamination. He stated that the Air Force is hoping to better define the plume, conduct additional investigation of the area, and gather new information to have more concrete decision-making tools, in terms of what might be appropriate.

Mr. Lim, with the EPA, stated that as the process proceeds with the FS-28/FS-29 Proposed Plan and the ROD, an opportunity remains for the Air Force and the regulatory agencies to change course. He explained that after the ROD is signed, the Air Force will be collecting additional data. If the information that is found supports the cleanup, the cleanup will occur; if the information that is found indicates that the plume is smaller or that active remediation is not necessary, there is an opportunity in the process to change that decision for cleanup. Mr. Lim reiterated that even after the ROD is signed, there still is an opportunity to change what is done for a particular plume.

Ms. Kiley, with the DEP, said that Mr. Karson provided a good summary of the remedial objectives. She referred to the slide that showed the number of years to restore the aquifer and the present worth of each alternative, and noted that although Alternative 7 shows ten years to restore the aquifer, that timeframe includes restoring the portion of the plume that wound not have any active treatment. Therefore, it actually would be approximately six years to restore the central portion of the plume, which is much quicker than the restoration time of 13 to 17 years for Alternative 2 and eight years for Alternative 3. Ms. Kiley explained that the central portion of the plume has the potential to affect the proposed water supply site, so the alternatives were geared toward making the aquifer useable as soon as possible. She also said that the additional data gap work will be critical to determining next steps.

Mr. Dow referred to the portion of FS-29 that contains EDB, and asked if the levels detected were above 0.02 ppb. Ms. Foster replied that plumes are defined by MCL exceedances, and the plume outline is based on EDB levels greater than 0.02 ppb, or CCl₄ levels greater than 5 ppb. She noted that if the two compounds were outlined separately, the plume outlines would look different. She identified a well on the map that does not contain EDB, and explained that the plume outline is drawn beneath that well because it contains CCl₄. Mr. Dow questioned whether the EDB in the portion of the plume that would be allowed to naturally attenuate is above the action level. He said that EDB does not seem to degrade in a reasonably timely fashion, and he does not understand the justification of allowing that portion of the plume to naturally attenuate. He said that while he understands that the CCl₄ could naturally attenuate, it is not clear to him that this would happen with the EDB.

Ms. Foster replied that, considering the initial concentrations, there are several different ways to look at natural processes that would degrade or disperse EDB. She stated that EDB in gasoline was used in concentrations of approximately 100 to 200 parts per million (ppm), which equates to 100,000 ppb. The EDB dissolved into the groundwater at its solubility limit, which is much higher than the concentration that was in gasoline. Therefore, the initial concentrations at the point of release were probably 100,000 to 200,000 ppb, and concentrations now being detected are 0.1 ppb. Ms. Foster asked the group to keep in mind the location of the fuel spill and how it reached its present location, and she explained that as the water that contained EDB advected downgradient, the source disappeared, the remainder of the fuels were degraded by natural processes, and the EDB, which is more soluble, continued to travel downgradient.

Ms. Foster noted that the EDB also was affected by other processes. She explained that as EDB travels downgradient, it can sorb onto the carbon on the sand, and then desorb, which tends to stretch out the plume. She said that the heterogeneity of the aquifer, as the water goes around the individual sand grains in the aquifer, tends to cause dispersion. All these factors serve to dilute a plume; therefore a plume in 1998 would not have the same concentrations that it had when it was released in 1935 or 1945. Ms. Foster explained that plumes also spread, so what originally was a small contaminated area on the water table now has spread vertically. Now there are different lobes of the FS-29 plume, which are 20 to 50 feet thick and 1000 feet wide. As those lobes spread out, the mass separates and becomes diluted. Ms. Foster stated that at a certain point, unless a plume intercepts extraction wells and discharges to a water body, it will become more dilute as it moves downgradient. Plumes will continue to advance only if there is more mass coming from behind, in which case there is the rate of dilution. She reported that the modeling indicates that the FS-29 plume – particularly the leading edge of that plume – has reached the point where the natural processes that serve to dilute the concentration are actually greater than the momentum of the mass that is flowing down to replace it. The MCL exceedances in the fate and transport modeling show the FS-29 plume shrinking. Ms. Foster mentioned that there will be a low concentration fringe, which may extend farther and may not be detectable. She noted that the leading edge of the FS-29 plume is 0.03 ppb.

Ms. Aulisio asked if the sources of these plumes include underground pipelines with fuels, fuel dumping, or buried fuel tanks. Mr. Karson replied that all of those things, in the past, have contributed to the fuel-related contamination. The exact sources are unknown for these plumes because they are disconnected. Although the sources are unknown, soil and groundwater investigations are conducted where fuel dumping activities most likely occurred. Investigations were conducted in the main industrial area, where there were motor pools and where fuels and solvents were used. Mr. Karson reported that in some cases the soil has been found to be contaminated with solvents and fuels. Those soils either have been cleaned up or will be cleaned up beginning later this year.

Mr. Burns asked if anaerobic degradation of EDB has been investigated. Ms. Foster replied that literature searches have been conducted, and bench-scale tests that support some chemical breakdown of EDB have been found. She stated that such breakdown has not been proven in the field here, primarily for technical reasons. She explained that the breakdown products of EDB are nondectable by the Air Force’s current best analytical methods. The Air Force has pushed the limit on the analytical method for EDB, because EDB is so toxic, to 0.005 ppb, a very low level.

Mr. Dow inquired about the Joint Process Action Team’s (JPAT) preferred alternative for the FS-29 plume. Mr. Karson replied that the next JPAT meeting is scheduled for February 23, 2000, at 5:30 PM in Building 330, and a discussion to develop the JPAT’s citizen members preferred alternatives for the FS-28 and FS-29 plumes will be a major agenda item.

Agenda Item #6. Adjourn

Ms. Larkin adjourned the meeting at 7:35 PM.