Landfill-1 Public Meeting Meeting Minutes
Agenda Item #1. Welcome and Introductions Mr. Snyder convened the meeting at 6:40 PM, welcomed the attendees, and briefly reviewed the proposed agenda. Agenda Item #2. Design and Construction Status Mr. Hoda stated that the final decision on Landfill 1 (LF-1) is to install focused extraction treatment reinjection (ETR) systems in both the southern and northern lobes of the plume. He noted that the concept of a focused ETR system was requested by the community. He also reported that monitored natural attenuation (MNA) will be used in the central portion of the plume and explained that the nitrogen is active in this location and therefore, the plume will remediate itself. He added that the natural attenuation process will be closely monitored and expanded if deemed necessary. Mr. Hoda reported that the ETR system will consist of four extraction wells in the southern lobe and one extraction well in the northern lobe. He stated that an infiltration gallery will be installed in the center of the plume. He also noted that the Air Force Center for Environmental Excellence (AFCEE) is committed to comprehensive monitoring to ensure that the plume is behaving as predicted. Mr. Hoda reported that the LF-1 decision also includes municipal water connections to potentially impacted residents, the replacement of Bourne wells 2 and 5, and a remedial systems performance review. Mr. Hoda then reported that construction has already begun at LF-1 and the system startup date is September 15, 1999. Agenda Item #3. Modeling Mr. Goydas reported that the following field activities were performed over the course of the last year: the installation of additional groundwater wells, the collection of groundwater screening samples, the sampling of existing wells, and additional aquifer pumping tests. He noted that the field activities were performed to support groundwater modeling, which is considered one of the major design tools. Mr. Goydas also reported that a contaminant fate and transport model was developed, which was based on the data collection results. This model will help to predict what the plume will do in the future, thereby aiding in the refinement of the design alternative. Mr. Goydas then reviewed the well field design components, which include five extraction wells, all of which are located along the base boundary. He noted that the treated water will be reintroduced into the aquifer through a centralized infiltration gallery. He stated that there will be four extraction wells in the southern lobe and one in the northern lobe. Mr. Goydas explained that these locations were chosen because most of the zones of higher contamination are located in the central to south-central portions of the plume; because the properties of the aquifer are more complex as it migrates to the south; and because groundwater flow predictions suggest that the southern portion of the plume is where the most attention will need to be focused. Mr. Goydas reviewed the features of the final design and noted that, based on model predictions, the aquifer will be restored in approximately 20 years. He noted that monitoring is one of the primary tools used to determine whether the model predictions are accurate. Mr. Goydas then showed several design animation scenarios, which indicate how the plume is predicted to behave in the future. Agenda Item #4. Public Comment – Questions and Answers Mr. Denny referred to the design animation presented by Mr. Goydas and asked if the lighter color represents a higher concentration. Mr. Goydas explained that the animation represents only one horizon at a time. He then pointed out the highest concentration, represented in dark blue, and the next highest concentration, represented in light blue. He noted that the darker blue is below the maximum contaminant level (MCL.) Mr. Goydas explained that the animation presented a 2-dimensional surface, and although the area of the impacted water may get larger over time because the plume is moving and expanding, the concentrations are well below the MCLs. Mr. Seaver commented that the animation made it appear that the plume is going backward toward the source. Mr. Goydas said that although it appears that the plume is migrating backward, this is not the case. He explained that a progression of contaminants, from shallow to deep, and then a subtle drawback, would be indicated if all the layers were shown. He stated that the animation depicted the current conditions for this particular horizon, layer 19. He further explained that over time, contaminants that are upgradient will migrate down into the model layer. He commented that it appears that the zone increases, but, in fact, the concentrations are decreasing. Mr. Seaver referred to the map of the plume area and asked when the 5 parts per billion (ppb) contour would pass the Bourne schools. Mr. Goydas replied that tetrachloroethylene (PCE), trichloroethylene (TCE), and carbon tertrachloride (CCl4) have a different history in the plume. Generally, however, the flushing rate into Buzzards Bay is a 10 to 15 year time frame. Mr. Seaver commented that concentrations at monitoring well 18 are already below MCLs. Mr. Goydas remarked that the concentrations near the source are still high and, therefore, they drive the restoration time frame. Mr. York commented that this is the first time that he has seen the reinjection gallery so "decoupled" from the extraction. He asked how the location of the reinjection gallery affects the flushing of the extraction wells downgradient. Mr. Goydas noted that although the infiltration gallery has, in the past, been placed immediately downgradient of the extraction well, there are benefits to changing the location. He explained that an infiltration gallery in the interior portion of the plume helps to manipulate the water table to drive contaminants toward the northern well and drive them to the southern wells, which creates a mound in the center. Mr. Goydas further explained that there will always be water migration to Buzzards Bay behind the extraction well because pumping is not occurring at a high enough rate to change the gradient. He stated that groundwater flow is moving relatively rapidly, so the zone at which contaminants are pulled back to the well is very close to the extraction wells. He noted that the water behind the well is filled in 3-dimensionally with water from the south side of the plume, from the infiltration gallery, and from the top of the well screens. He also noted that the long term Operation & Maintenance (O&M) cost and the capital cost are additional benefits of the infiltration gallery. Mr. Goydas stated that the ecological thresholds have been met. Mr. Fisher asked how it is determined which layer would be pumped. Mr. Goydas replied that several methods are used. He said that cross-sections of the plume provide an understanding of where the plume is moving, and the 3-dimensional model indicates the location of the screens. He stated that the layer that will be pumped is determined by a 3-dimensional assessment of field data, model interpretation, and a hydrodynamic assessment. Mr. Seaver stated that it appears that the source of CCl4 is not the landfill. He inquired about the possible source of the CCl4. Mr. Goydas pointed out the location of the western lobe of Chemical Spill 10 (CS-10). He noted that it is possible that the CCl4 may not be from LF-1, but rather from the vicinity of CS-10 because of the groundwater mound at the Massachusetts Military Reservation (MMR) and the manner in which water radiates off that mound. He pointed out that there is a clear break of clean water between CS-10 and LF-1. Agenda Item #5. Monitoring and Sampling Mr. Hoda stated that monitoring will be a key element of the remedial decision to ensure that the remedial alternative is operating as expected, and also to understand how the entire plume is behaving to prevent any "surprises." He added that the landfill cap is also a big factor in all of the decisions. Mr. Hoda reviewed the LF-1 monitoring plan which includes the monitoring of the performance of the ETR system, of MNA, and the landfill cap. He stated that there is a lot of biodegradation occurring upgradient of the ETR system, which will be monitored to predict how the ETR system will perform in the future. Mr. Hoda noted that the residential wells will be sampled twice a year. When those wells are connected to the municipal water supply, however, that monitoring will stop. Mr. Hoda then explained that a number of sampling events were under different programs – all the programs are being put under one tasking, however, so that AFCEE can more efficiently report to the public. He then reviewed the LF-1 comprehensive monitoring plan. He noted that approximately 400 samples will be collected a year. In addition, a performance monitoring program is due in May 1999. He noted that there have been many questions about the contamination that will seep into Red Brook and Squeteague Harbors. Mr. Hoda reported that AFCEE has committed to an investigation there. Because of many uncertainties, however, the United States Geologic Survey (USGS), the expert in groundwater investigation, will also do an investigation. He reported that AFCEE will first conduct a hydrogeological study of where this fresh water may be upwelling in the harbors. Based on the results of that investigation, a determination will be made regarding what kind of monitoring plan is needed. Mr. Hoda displayed several maps indicating the latest sampling results for TCE, PCE, and CCL4. He noted that PCE is mostly in the southern lobe of the plume; the highest concentration detected was 5 ppb. Agenda Item #6. Public Comment – Questions and Answers Ms. Provost referred to the 102 residential wells and asked whether it made sense to phase out the monitoring of those wells after municipal water is provided. Mr. Hoda replied that the wells may not be in the correct location or at the proper depth to provide the needed data. Mr. Samson asked if Bourne wells 2 and 5 are going to be monitored rather than shut down. Mr. Hoda replied that AFCEE is providing the Bourne Water District with the funding to develop alternative municipal water supply for Bourne wells 2 and 5, and until those new wells are on line, monitoring will continue. Mr. York referred to the seeps around the town line in Squeteague Harbor and noted that there are a couple of wells there that he did not think had been sampled yet. He then pointed to two places on the map and asked if they were wells or seeps. Mr. Hoda replied that those locations were sampled as part of the Engineering Evaluation/Cost Analysis (EE/CA) program, and added that he would share the data with Mr. York. Mr. Seaver asked why the plume followed, exactly, the boundary of North Falmouth. Mr. Hoda replied that this could be due to an artifact of the data, or could be attributed to the lack of data, or the hydrogeology in the area. Mr. Goydas stated that some of the predicted animations show that the plume will probably migrate across the town line, but based on the current distribution of data, that would be the extent of the plume, based on the MCL. He noted that several factors drive the plume configuration – the regional mound, which is the controlling factor on where groundwater moves, the stratigraphy; and the discharge locations. He stated that Red Brook Harbor and Squeteague Harbor do play a role in controlling a sink for groundwater, so the plume is migrating toward those surface water bodies. Mr. Goydas added that he could not say that the plume will not cross the boundary, but based on the current data set, it just happens to fall on line with the town boundary. Mr. Seaver asked if there were any CCl4 hits above the MCL. Mr. Hoda replied that there were no detects above the MCL at the wells that were sampled, but this does not necessarily mean that there are not contaminants above the MCL. Ms. Provost stated that she is concerned about the affect of the plume on the marine life in the bay, in particular, on the shellfish. Mr. Hoda stated that AFCEE is working with the USGS on that matter. Mr. Samson inquired about potential health risks if the plume gets into the drinking water. Mr. Hoda referred him to the fact sheets. He also said that the level of contamination is not high enough to show immediate impact to health. Agenda Item #7. Adjourn Mr. Miller thanked everyone for attending and adjourned the meeting at 7:35 PM.
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