Meeting Minutes

Agenda Item #1. Introduction/Background

Mr. Sobel convened the meeting at 6:37 PM and noted that this forum is sponsored by the Air Force Center for Environmental Excellence (AFCEE), the Massachusetts Department of Environmental Protection (DEP), and the United States Environmental Protection Agency (EPA). He stated that the presentations tonight will be updates on work that has been conducted since September 1997, when AFCEE, the MassDEP and the EPA made a decision on the plume response for the Ashumet Valley Plume. In addition, there will be a presentation about the work planned for this spring and summer, and about measures that might be taken to address the phosphorus in Ashumet Pond. Mr. Sobel noted that scientists from the Technical Review and Evaluation Team (TRET) and the Barnstable County Science Advisory Panel (BCSAP) are in attendance and are available to answer questions. Mr. Sobel then briefly reviewed the meeting groundrules.

Meeting Purpose/Program Summary

Mr. Smith introduced himself as the AFCEE Project Manager for the Ashumet Valley project and noted that AFCEE is currently developing a solution to the phosphorus problem. He stated that the purpose of tonight’s meeting is to look at the impact of the phosphorus components of the sewage treatment plume on Ashumet Pond. Mr. Smith explained that ponds go through a natural process of eutrophication. People can influence the process, however, by introducing nutrients, which can expedite the eutrophication. This is what AFCEE is attempting to avoid. Mr. Smith briefly reviewed the agenda (see attachment #1 that includes all slides shown in this presentation).

Mr. Smith reported that AFCEE is currently addressing the plume’s effects on the ecology of the pond. He noted that human health has been evaluated and will be revisited. He also noted that the Massachusetts Department of Public Health (MDPH) has produced fact sheets, which indicate that Ashumet Pond is safe for fishing and swimming (see attachments #2 and #3). Mr. Smith then mentioned that the local boards of health also regularly collect data on other contaminants in the pond.

Mr. Smith reported that in 1997 it was determined that the best approach to address the phosphorus was to hydraulically capture the plume and prevent it from discharging into the pond. He stated that, based on discussions with a number of nutrient specialists and review of the United States Geological Survey (USGS) data, it was determined that a pump and treat approach might not be the best method. He reported that in August 1998 a recommendation was made to change the focus from a full-scale pump and treat approach to the protection of the pond itself. Mr. Smith explained that if the pond is eutrophying, and the Air Force addresses phosphorus in the aquifer, there might not be a near-term effect on the pond. If the focus is on the pond and the symptoms within the pond, a strategy could be developed that would provide near-term benefits to the pond.

Mr. Smith stated that a summit was held in July 1998, and a number of subsequent meetings were held to discuss the findings. He reported that, based on the data, the phosphorus does not pose an imminent threat and no emergency action is required. He emphasized the importance of understanding how phosphorus is being used in the pond. Mr. Smith reported that it was determined that the current extraction, treatment, reinjection (ETR) approach is inefficient and potentially has its own detrimental effects. He explained that phosphorus is a highly sorbed contaminant – it attaches to the sands in the aquifer, which makes it difficult to remediate phosphorus in the aquifer. This was the basis for shifting the focus to stabilizing and improving the symptoms in the pond. Mr. Smith also noted that the geochemistry and pond ecology are important in developing the optimum solution, and commented that with this sensitive ecology, a full-scale action could result in mistakes and detrimental effects. Mr. Smith added that bench-scale and field-scale testing will be conducted prior to full-scale remediation system construction.

Mr. Smith stated that the focus has changed to pond health, nutrient loading, how best to curtail continued eutrophication of Ashumet Pond. He said that a phosphorus budget is needed, and stated that it is important to determine the source of the phosphorus, nitrogen, and other nutrients contributing to the pond. He explained that there may be more effective ways of lowering the phosphorus entering the pond, rather than trying to address the plume, which is likely the greatest contributor. Mr. Smith stated that there is a focus on developing detailed pond health and information to support the design. He reiterated that the strategy is shifting toward design of a system that is focused on the pond itself.

Mr. Smith listed the actions that have occurred to date: closure of the infiltration beds in 1984, closure of the Massachusetts Military Reservation (MMR) sewage treatment plant in 1995, ongoing monitoring of Ashumet Pond and of the aquifer, expanded sampling plans in 1999, and an action recommendation. He noted that as a result of closing the infiltration beds and the sewage treatment plant, the source has been reduced and ultimately the only phosphorus being introduced is the residual phosphorus in the aquifer.

Mr. Smith reported that in addition to AFCEE, Jacobs Engineering, the USGS, the Woods Hole Oceanographic Institute (WHOI), and the University of Massachusetts (UMASS) are involved in this effort. He stated that key "growing season" data are being collected to support the refined phosphorus budget, pond health, and design. In parallel to this data collection effort, pond remedial strategies are being designed. Mr. Smith explained that those strategies were developed as contingency plans in the event that the conclusions of the phosphorus summit were incorrect, and there is an emergency. He noted that these strategies might become interim or long-term solutions to the health of the pond. Mr. Smith stated that once collected, the scientific data will be presented to the public throughout this summer, and AFCEE will seek public comment on the approaches presented for the pond. Then a recommendation for action will be made, and an appropriate system will be developed.

Mr. Smith reported that the experience of the EPA, the DEP, the Canadian Lake Management Programs, and work conducted in Europe have all been utilized while considering the phosphorus problem. He also noted that EPA and MassDEP nutrient criteria and guidance have also been used. He added that nutrient specialists are reviewing the data and the treatment options.

Brief History – Sewage Treatment Plant (STP) Operation and Phosphorus Plume

Mr. Leblanc of the USGS, stated that the purpose of this effort is to protect Ashumet Pond from the potential threat of eutrophication by phosphorus. He noted that the major driver, and the main reason for the Air Force’s involvement, is because it is believed that the sewage plume is a major contributor of phosphorus to the pond.

Mr. Leblanc reported that the sewage plume was first mapped in 1978-1979 by the USGS as part of a study that was funded by the Massachusetts Division of Water Pollution Control. He noted that the USGS mapped the plume that emanated from the wastewater treatment plant on the basis of a number of typical constituents in sewage, such as nitrates, chloride, detergents, and phosphates. It was discovered that the Ashumet Valley sewage plume extends several miles downgradient from the disposal location in the direction of groundwater flow. He displayed a map and noted that the Ashumet Valley sewage plume is aligned in the direction of flow, down the water table slope.

Mr. Leblanc stated that it was discovered that there is a zone within that plume that contained elevated levels of phosphorus, above the detection limit of 0.01 parts per million (ppm). He noted that the zone of elevated phosphorus did not extend anywhere near as far as the rest of the sewage plume – in fact it appeared to have advanced only a couple of thousand feet away from the disposal site. He noted that, based on other studies of sewage treatment plants, it is known that the phosphorus was part of the treated sewage. The question, however, is why this zone of phosphorus was so much shorter than the rest of the plume.

Mr. Leblanc explained that the key is that phosphorus interacts strongly with the aquifer sediments. He noted that the sand in this area is brown because it is coated with iron oxides, which are a very efficient scavenger of a number of things, including phosphates. The phosphorus tends to strongly sorb to the iron oxide coatings. Mr. Leblanc stated that if sediment cores and water samples were collected from the phosphorus zone within the plume, and a phosphorus accounting was done on a gallon of the water and sand, it would indicate that within the plume itself, most of the phosphorus is "stuck" to the sediments. He displayed a slide that showed the amount of phosphorus stuck to the sediments and the amount of phosphorus, in that same volume, floating in the water. He stated that in any volume of aquifer material within that sewage plume, most of the phosphorus sitting on the sediments is not moving at all.

Mr. Leblanc used an analogy to explain how this translates into the fact that the phosphorus plume has not advanced very far. He compared the fate of this phosphorus to a group of vehicles traveling at the same speed to the same destination. He explained that the vehicles will reach the destination at different times due to time spent at rest areas, subsequently reducing the average rate of speed. He said that one could think of phosphorus spending 99% of its time in the rest area, or sorbed to the sediments. Mr. Leblanc stated that the average rate of movement of the phosphorus is significantly slowed, relative to other things such as chloride, or volatile organic compounds (VOCs). He commented that, when thinking about the fate of phosphorus in the aquifer and what might be done to remove it, it is important to remember that the phosphorus likes to stick to the sediments.

Mr. Leblanc reiterated that the plume has not advanced very far, and the bulk of the phosphorus is stored on the aquifer sediments. He noted that the key to understanding what might be done to remediate the aquifer is to consider how to deal with the large volume of phosphorus that is stored in that reservoir. He noted that in the early 1990s the USGS began to look in more detail at the phosphorus plume. He displayed a contour map that shows the phosphorus concentrations dissolved in the water and remarked that this is the "tip of the iceberg" in that there is far more phosphorus that is sorbed to the sediments. Mr. Leblanc stated that as a result of this sampling effort it was discovered that the plume has zones of higher and lower concentrations. The zone located northwest of Sandwich Road, with phosphorus concentrations as high as 6 ppm, appeared to be poised just upgradient of Ashumet Pond. Mr. Leblanc reported that there was a concern about whether the zone was a transient feature, a pulse of some sort, or an artifact of the sampling. He said that this was the picture in 1993, and it was on the basis of this map in particular, that many of the earlier decisions were made.

Mr. Leblanc reported that, since the work conducted in 1993, the USGS has been monitoring the evolution of the sewage plume, including the phosphorus. He noted that in 1993 it was known that the sewage plant would be shut off in 1995, and the USGS wanted to use this opportunity to look at how the plume would flush itself away. Subsequently, a number of sampling points were added in the old sewage beds, downgradient of the beds, and near Ashumet Pond. He reported that the USGS takes a "snapshot" of the phosphorus plume about once a year. He also noted that each "dot" shown on the slide represents well clusters or multi-level wells, where there are 15 wells in one location. These well clusters are designed to provide an understanding of the three-dimensional nature of the phosphorus plume.

Mr. Leblanc displayed a slide that showed annual maps of the phosphorus concentrations. There were maps for the years 1994 and 1995, which was prior to the shut off of the sewage treatment plant, and maps for the years 1996 through 1998. Mr. Leblanc pointed out that although there are differences in the details, the basic footprint of the phosphorus plume has not dramatically changed over the last six years. He stated that throughout the years the zones of higher concentrations have appeared to "come and go" – there has been a fair amount of temporal variability, however, the zone appears to be northwest of Sandwich Road.

Mr. Leblanc then showed water quality profiles at two sites, F-300, located along Ashumet Pond, and F-567, located in the high zone on the northwest side of Sandwich Road. He noted that F-300 has 30 sampling points in the vertical direction, and that Ashumet Pond has an altitude of 44 feet above mean sea level. Mr. Leblanc displayed a slide that showed dissolved phosphorus at the edge of the pond. He pointed out that over the five years during which measurements were taken, the concentrations have remained at a maximum of just below 2 ppm. He referred to the area along the edge of Ashumet Pond and noted that it appears that not much change in concentration of phosphorus is seen with time. A member of the audience questioned Mr. Leblanc’s statement that Ashumet Pond is 44 feet deep. Mr. Leblanc clarified that the altitude of the water’s surface is approximately 44 feet above mean sea level.

Mr. Leblanc reported that along the shore of the pond there has not been much change in phosphorus concentration, however, site F-567 indicates that the phosphorus has a couple of unexplainable peaks. He stated that an attempt is being made to understand why, geochemically, there has been a lot of variation in phosphorus concentrations, with time and why there is not a definite pattern. He noted that more water samples are being collected, geochemical modeling is being conducted, and core samples are being collected. He summarized that not much change is seen near the pond, a lot of the geochemical changes are occurring upgradient of Sandwich Road, and those high concentrations have never been seen in sampling sites downgradient of Sandwich Road.

Mr. Leblanc reported that monitoring of the aquifer will continue, and he mentioned that the USGS collected samples yesterday and today. He displayed a map that showed the sampling points. Mr. Leblanc reported that with AFCEE’s assistance, the USGS is adding more sites to better understand the phosphorus distribution along "this" side of the plume. He identified the location of two new well clusters, and stated that the USGS has proposed some additional sampling points between Sandwich Road and Ashumet Pond. Mr. Leblanc said that the USGS continues to "check the pulse" of the phosphorus plume to see whether or not it is correct that concentrations are not changing dramatically downgradient of Ashumet Pond, and that zones of higher concentrations seem to come and go, but not propagate. He also noted that the results from this 1999 sampling effort will be available within a few months.

Background

Mr. Citterman, with the Ecological Studies Program at Jacobs Engineering, introduced himself. He displayed a conceptual model for Ashumet Pond and noted that a unique feature of Ashumet Pond, and many other ponds on Cape Cod, is that they have very few surface water inputs. He stated that approximately 75% of the water flowing through Ashumet Pond is groundwater, and explained that groundwater enters on the upgradient side of the pond and recharges on the downgradient side. He noted that elevated levels of phosphorus are entering the pond along with the water, and leaving the pond through the downgradient side. This creates some unique issues in terms of trying to understand how the pond works. Mr. Citterman explained that most of the models were developed for ponds that have a surface flow in, and a river outflow – those models do not work very well when dealing with Ashumet Pond.

Mr. Citterman reported that AFCEE is working to get a better understanding of what is going on with phosphorus by developing a phosphorus budget, to quantify all of the phosphorus inputs to the pond. The inputs include: the sewage plume, the groundwater coming in that is not impacted by the sewage plume, septic systems, and the cranberry bog north of the pond. He said that an attempt is also being made to determine what is leaving the pond, and what is occurring in the pond as far as phosphorus recycling. He explained that phosphorus gets into the ground through the groundwater, and becomes incorporated into organisms. When the organisms die, they degrade "microbaly," and as a result, a lot of the phosphorus can be released back into the pond. Mr. Citterman stated that an attempt is being made to prevent huge phosphorus blooms that normally occur in a eutrophic pond. He then explained that a eutrophic pond is one that is enriched in nutrients and has a lot of production going on, which will cause large blooms. The plankton die and decompose, and the decomposers use oxygen, causing the ponds to go anoxic, which can lead to fish kills.

Mr. Citterman explained that in the fall through the late spring, Ashumet pond is isothermal – the pond is in a continual state of mixing and nutrients are fairly uniform throughout the pond. In the summer months, however, the air becomes warmer and the pond will thermally stratify – the upper waters are warm and the deeper waters are cold, which will keep the waters separate. He also explained that the surface waters are in contact with the atmosphere, in a state of mixing, and there is always oxygen going into them. This would be where most of the growth is occurring – the lower waters are essentially cut off from the atmospheric input. In ponds that have high productivity, this will result in the microbes using the oxygen in the lower portions of the pond. The oxygen cannot be replaced at the same rate in which it is being utilized, and the pond becomes anoxic.

Mr. Citterman stated that the Ecological Studies Program has been looking at Ashumet Pond, the study pond. He defined study ponds as ponds that are directly impacted by a plume. He also defined reference ponds as those being investigated to provide a means of comparison, to determine whether what is occurring at Ashumet Pond, is localized in the pond, or whether it is occurring regionally.

Mr. Citterman noted that Ashumet Pond and Johns Pond are both study ponds, and Mashpee Pond and Peters Pond are reference ponds. He noted that Mashpee Pond is similar to Ashumet Pond in terms of the amount of development – it is a larger pond, however, and has a slightly different shaped basin. Mr. Citterman noted that Peters Pond has less development and less productivity than Ashumet Pond, but is still a viable reference pond.

Mr. Citterman displayed a map that showed the Ecological Studies Program’s sampling locations, which have been sampled since the summer of 1996, and continue to be sampled. He noted that the locations north of Ashumet Pond, in the abandoned cranberry bog, have been added to the Ecological Studies Program. He also reported that samples have been collected since March, and sampling will continue in May, June, August, September, and November, in order to characterize the phosphorus input to Ashumet Pond from the abandoned cranberry bog.

Mr. Citterman reported that the Ecological Studies Program is routinely collecting the following types of parameters: chemical, physicochemical, and biological. He explained that the physicochemical parameters include the nutrients that are important when considering the health of the pond, and developing a phosphorus budget. Mr. Citterman reported that to date the Ecological Studies Program has collected more than 500 water samples, more than 50 sediment samples, 140 phytoplankton samples, 90 zooplankton samples, and more than 50 benthic macroinvertebrate samples. As a result of the work conducted, it has been determined that Ashumet Pond is at the mesotrophic state, a similar trophic state as Johns Pond and Mashpee Pond, as measured by Secchi Depth, chlorophyll a, phosphorus, phytoplankton specieation, and enumeration.

Mr. Citterman stated that many of the ponds on Cape Cod, which go through a normal evolution of eutrophication. He explained that the ponds start out as pristine, low in organic material and nutrients. As they evolve, nutrient levels increase, productivity increases, and the ponds eventually evolve to a wetland. He noted that this naturally occurring process could take thousands of years to occur. Mr. Citterman explained that cultural eutrophication is an acceleration of that naturally occurring process, which is caused by human activities. He said that the development seen on Cape Cod accelerates the eutrophication of many of the ponds. He noted that the development that is occurring is putting pressure on surface water bodies, and the Commonwealth of Massachusetts developed its Title V Septic requirement in attempt to alleviate some of those problems.

Mr. Citterman reported that the health of Ashumet Pond appears to be stable over the last five years and the pond does not seem to be in imminent danger of going eutrophic at this time. He noted that AFCEE feels that it is very important to develop a refined phosphorus budget in order to provide a better understanding of the health of the pond and to identify the best way to treat the pond, should the decision be made to do so.

Questions and Answers

Mr. Dow referred to the bottom water in Ashumet Pond, which goes anoxic during the summer, thereby releasing a lot of the phosphorus stored in the sediments. He asked how that phosphorus source would be addressed in the phosphorus budget. Mr. Citterman replied by explaining that internal recycling is not important for the phosphorus budget, but it is important when looking at productivity. He stated that the phosphorus in the sediments has already been accounted for by the inputs of the phosphorus budget.

Mr. Dow commented that the phosphorus might not be in a steady state in recycling, rather it might be a net source. He noted that studies in Europe have found that the bottom sediments are a net source of phosphorus and not just recycled in the pond. Mr. Citterman stated that it is important to remember that Ashumet Pond has two basins – the northern basin, which is deeper and larger, is cone shaped. He said that in the summer, when the pond goes anoxic, the depth of anoxia is at least 30 feet, and the average depth of the pond is about 27 feet. He noted that there is a small area of the pond that is anoxic and that the majority of the sediments in the pond are primarily sand. The depositional areas are in the deep hole and in the southern portion of the pond.

Mr. Citterman also noted that Mr. Blunt will discuss an aggressive sampling program that is designed to characterize the phosphorus in the sediments. He mentioned that the Ecological Studies Program has attempted to do this through nine sampling locations, however, it is not believed that these are accurate enough to characterize the phosphorus in the sediment. Mr. Smith added that, to address that question, the sampling program includes a lot of core sampling and grab sampling throughout the pond and in the deep water. He commented that regeneration could be significant and could present an opportunity to control the phosphorus and develop some benefits for the pond on a near-term basis.

Mr. Baker, a Mashpee resident, asked if it is correct that some of the phosphorus that enters the pond also leaves the pond in the groundwater. He also referred to the VOCs that appear to be travelling either through or under Ashumet Pond to Johns Pond, would the phosphorus leaving Ashumet Pond would potentially head in the direction of Johns Pond. He then asked Mr. Leblanc to discuss the anoxic zone in more detail, specifically, whether it changes size or shape, and what causes it.

Mr. Smith replied that the concentrations of phosphorus in the groundwater are not going to be great. He explained that typically, from a eutrophication perspective, the assumption is that all the phosphorus that enters a pond stays in that pond. In this system, some of the phosphorus is going out the other side in a dissolved form – part of this investigation is to determine how significant that is. He said that there is also the potential that the phosphorus is sorbing on the aquifer as it goes out the other side. Mr. Smith stated that although this is being addressed, there is the potential that the phosphorus will move through the system toward Johns Pond. He noted that the phosphorus moves very slowly – it gets off, sorbs, re-dissolves, gets off, sorbs, and so forth. Mr. Smith stated that the phosphorus is in the system and potentially will continue on through the aquifer. He noted that an attempt is being made to answer questions pertaining to the concentration of phosphorus and impacts it could have on the pond.

Mr. Smith asked Mr. Baker to clarify his second question. Mr. Baker asked if the anoxic zone located northwest of Sandwich Road changes or if it is permanent. He noted that he has been told that in sorbing to iron oxides, anoxic conditions can be a problem. Mr. Leblanc displayed a map and explained that the light gray indicates the total extent of phosphorus contamination. The darker gray indicates the anoxic zone, where there are not only elevated levels of phosphorus, but no dissolved oxygen in the groundwater. He explained that the anoxic zone is formed because of the degradation of organic material that is in the treated sewage. The USGS’s field data and geochemical modeling indicate that the anoxic zone advances very slowly and there is no evidence of it changing size or shape. Mr. Leblanc said that now that the sewage treatment plant has been shut off, eventually that zone should dissipate away completely. Mr. Baker asked if the anoxic zone advances. Mr. Leblanc replied that it does advance, however, it has done so very slowly.

Mr. Leblanc stated that there is interplay between the iron oxides and the phosphorus. Even in the anoxic zone, where there is no dissolved oxygen and there is high iron dissolved in the water, there is still plenty of iron oxide present, and the phosphorus is sorbing strongly there as well. He said that even though there is an anoxic zone, as far as phosphorus transport is concerned, it does not play that big of a role. Mr. Baker asked if the oxides are ferric or ferrous. Mr. Leblanc replied that the oxides on the sediment are ferric iron (FE3). He explained that when the iron gets reduced in the anoxic zone, it becomes ferrous iron, and is soluble in the water. He also noted that, in that zone, there is enough ferric iron left on the sediments that is sorbing the phosphorus. Eventually, over decades, as the anoxic zone dissipates, the iron will re-precipitate back out as iron oxide on the sediments, taking some of the phosphorus with it – this will only happen in the anoxic zone, and it might take years to happen.

Dr. Feigenbaum asked if it is correct that the pond is not in trouble now, in terms of phosphorus. Mr. Leblanc replied that at the edge of the lake, an increase in phosphorus concentrations has not been seen over the last seven years – the concentrations detected in the groundwater at the pond are similar to those detected in 1978/1979. He mentioned that the data at that time was very sparse. Dr. Feigenbaum stated that this could indicate an equilibrium situation between the pond, the sediment, and the groundwater. He commented that since the phosphorus is holding constant while other things are changing, there must be some equilibrium phenomenon occurring that is holding it constant.

Mr. Leblanc replied that there are a number of hypotheses for which the USGS is attempting to provide evidence. One hypothesis is that the concentration of phosphorus in the groundwater is strongly dependent on the pH of the water and on the amount of other particles that are competing with the phosphorus for those sorption sites. The phosphorus concentration changes that are seen in the water seem to be closely related to minor fluctuations in pH. Mr. Leblanc explained that the bulk of the phosphorus, under both high and low concentrations, is on the sediments and a tiny amount that comes on or off will double the concentration. He commented that the amount is not viewed as "tiny," but it is a tiny fluctuation in terms of the percentage of phosphorus in the water. He also remarked that there are a number of hypotheses about what is causing the small changes in pH, some of which relate to the loading history of the beds, and to the regional changes in groundwater flow directions. He stated that a lot of those variations seen at that one site occur right on the boundary of the plume, as clean water sweeps back and forth across the boundary. It is believed that this is a localized effect, right along the boundary of the plume where those sampling sites are located, which is why a site was drilled today right along the boundary. Mr. Leblanc noted that those changes are not seen elsewhere, and this has not yet been explained.

Dr. Feigenbaum noted that the changes in the high concentration area are not at the boundary of the plume. Mr. Leblanc clarified that this is incorrect. He noted that this site is the last site going from west to east, before going to sites where there is no phosphorus. Dr. Feigenbaum commented that he thought the high concentration area was in the center. Mr. Leblanc displayed a map, identified the area that was "in the plume" and "out of the plume," noted that there are no data points in between, and explained that this was why a sampling point was added "here." He stated that the USGS believes that the high concentrations detected were on the last sampling points before going outside of the plume.

Dr. Feigenbaum asked if it is thought that there is water entering the plume, from outside the plume, that is changing the pH. Mr. Leblanc replied that this is believed to be the case. He also explained that as the water table fluctuates seasonally, and flow directions change seasonally, there are pH changes along that boundary, which cause the phosphorus concentrations to come and go – this does not represent a "pulse" of water that is going to move. He added that one could not take the high spot and track it down to see the rise. He noted that this is why sampling points are being added along that boundary. Dr. Feigenbaum commented that the pond would only become in danger if a higher concentration slug like the one that appears to be there, is moving. He stated that the chemical effect that is changing that needs to be determined.

Mr. Leblanc stated that it is a chemical effect caused by the flow changes. He pointed to site F-567, and stated that two sites will be added "here" and "here," and additional sites are being proposed "here" in order to address this question. Dr. Feigenbaum asked why, if the flow were laminar, there would be mixing from the sides. Mr. Leblanc explained that the flow is not constant in direction – as groundwater levels fluctuate because of seasonal changes and long-term changes in recharge, the flow directions in this part of the plume change by as much as 15°F. He stated that it is thought that there are times when the flow cuts across the average boundary of the plume, and there are times when the flow parallels the plume. He reiterated that it is a hypothesis that there are times when fresh water from alongside the plume moves in temporarily and causes some of these pH changes. Mr. Leblanc stated that when a correlation is done between phosphorus concentrations, pH, and specific conductants, they are definitely related. He commented that it is interesting that the highest phosphorus concentrations are always associated with the otherwise cleanest water. He explained that the clean water causes phosphorus to come "off the sponge," resulting in a spike in phosphorus concentrations when there is nothing else there.

Dr. Feigenbaum asked if it is thought that the CS-10 plume is also "wiggling around." Mr. Leblanc replied that all the plumes, along their boundary, probably "wiggle around" to some degree. He added that this area tends to have the greatest flow direction changes because of the influences of the ponds. Dr. Feigenbaum commented that he is looking forward to the remainder of the USGS’s study.

Agenda Item #2. Data Collection Plans

Mr. Smith reported that the data collection effort will begin this summer. He stated that this is significantly greater than what is being done with the Ecological Program, and the key is to refine the phosphorus budget, to develop more detailed information about pond health, and to develop information that will support design of active remedial schemes. Mr. Smith then introduced Mr. John Blunt from Jacobs Engineering, and noted that Mr. Blunt will discuss the sampling effort and preliminary information about the various approaches for on-pond treatment. He also mentioned that more detailed information will be provided as the approaches are developed.

Agenda Item #3. Pond Remediation Approaches

Mr. Blunt displayed a slide and identified the hinge line, which moves back and forth as the water table fluctuates in the pond. He explained that on one side of the hinge line the groundwater is primarily discharging to the pond and on the other side the pond is recharging into the groundwater. Mr. Blunt stated that in order to determine the phosphorus budget, there needs to be an understanding of the phosphorus that is entering the pond and where the phosphorus is leaving the pond.

Mr. Blunt stated that the primary objectives of the Ashumet Pond investigations will be to develop a refined phosphorus budget, to improve and develop a baseline for the pond health and the ecology, and to obtain data to support evaluation of in-pond remedial actions. He said that in order to accomplish those objectives, there needs to be a significant data gathering event, which will occur this summer and into the fall. Mr. Blunt reported that this sampling activity will consist of the following three phases: drilling and related sampling activities, limited nutrient and phosphorus sedimentation studies, and ecological and related water column sampling activities.

Mr. Blunt reported that two new well clusters have been installed near the CS-10 reinjection wells in order to monitor for impacts on the phosphorus mobility in the plume. He stated that AFCEE will be sampling up to 50 additional monitoring wells around the perimeter of the pond, many of which will be in the "impact area" of the plume. He reported that the USGS will be installing a new multi-level well and will continue sampling activities to characterize the phosphorus in the plume. The USGS will also perform geochemical modeling of phosphorus to constrain its possible mobility over time in the plume. He displayed a map of the Ashumet Valley plume and identified the area of elevated phosphorus and a footprint of where the plume might be discharging to the Fisherman’s Cove area. He then identified the wells that will be sampled during this investigation.

Mr. Blunt reported that sediment grab samples are being collected from the surface sediments of the pond in order to determine the phosphorus distribution in the sediments. He also reported that groundwater screening beneath the pond will be conducted to determine how much plume phosphorus is entering the pond, and how much is sorbing to the sediments. Mr. Blunt stated that cores through the bottom of the pond, which will be taken at approximately 22 locations, will determine the vertical distribution of phosphorus in the sediments and into the aquifer underneath the pond. He stated that 11 of the 22 locations will be converted to monitoring well clusters in order to monitor the phosphorus that is entering and leaving the pond over time. Mr. Blunt also reported that water level and phosphorus concentration transects will also be conducted. He displayed a map of the grab-sampling grid and explained that sediment samples will be analyzed for phosphorus, total nitrogen, iron, and manganese, in order to provide a map of the chemical constituents in the pond bottom. He then displayed a map and identified the core locations, the 22 monitoring well locations, the transects, and the monitoring well clusters. He noted that of the cores that will be taken, three are concentrated in the deep hole, which address Mr. Dow’s question. He stated that the potential for the deep hole to regenerate phosphorus will be considered. Mr. Blunt explained that transects measure water level differences in the aquifer in an attempt to identify high-flow zones where a lot of the water from the pond is recharging back to the aquifer. Based on the profiles, a determination will be made regarding well locations. Mr. Blunt added that phosphorus data will be collected during the drilling activities.

Mr. Blunt reported that UMASS/WHOI will test samples from Ashumet Pond using three different laboratory approaches in parallel, to determine whether phosphorus is the limiting nutrient for Ashumet Pond. He also reported that UMASS/WHOI will collect up to ten diver-collected sediment cores to determine the rate at which phosphorus is accumulating in the pond sediments.

Mr. Blunt stated that AFCEE will continue to collect surface water samples during March, May, June, August, September, and November 1999. He also reported that UMASS/WHOI will conduct high-frequency sampling of the water column, every two weeks, from May to October 1999. The samples will be analyzed for temperature, oxygen, nutrients, and phytoplankton. Mr. Blunt displayed a map that shows the standard ecological sampling locations.

Mr. Blunt summarized that sediment grab sampling will be conducted during May and June, on-pond phosphorus drilling/coring/water sampling activities will be conducted during June and July, and periodic ecological sampling and water column profiling will extend into the fall.

Mr. Blunt reported that drilling will be performed using the direct-push method, the fastest and quietest method available. He stated that the work hours will be limited to 8:00 AM to 6:00 PM, Monday through Friday and 8:00 AM to 4:30 PM on Saturday. No work will be conducted on Sunday. Mr. Blunt reported that caution signs will be posted at pond access areas during drilling activities. He also noted that work will not be conducted during peak holiday times.

Mr. Blunt stated that one of the main uses of the data collection this summer will be to guide the evaluation of potential in-pond remedial approaches for the pond. He also reported that three general categories are being addressed: phosphorus inactivation methods, biomanipulation, and phosphorus removal.

Mr. Blunt then explained that phosphorus inactivation is a way to remove the phosphorus from the water column, where it is available for the algae, and to then isolate it in the sediments in a form that is not bioavailable. He stated that although the phosphorus may accumulate in the sediments, it will be "locked up" and not available to the algae. He further explained that this method promotes the transfer of phosphorus from the water column to the sediments. He noted that trapping the phosphorus in the sediments might be temporary with some phosphorus inactivation methods, such as alum treatments, and may require repetition. Mr. Blunt stated that some approaches might harm aquatic organisms or cause sediment/phosphorus re-suspension. Alum treatments can cause fish kills if not done properly.

Mr. Blunt reported that the biomanipulation approach modifies the food web in the pond in order to reduce the algae abundance in the pond by increasing the number of microscopic animals that eat algae. He explained that game fish would be introduced, and they would eat the smaller fish that eat the microscopic animals that eat the algae, thereby reducing the total mass of algae in the pond. He commented that this approach is quite complex to implement, and therefore, it is not a favored approach.

Mr. Blunt reported that two primary phosphorus removal methods are being considered, hypolimnetic withdrawal, and sediment removal. He noted that hypolimnetic withdrawal has been used effectively in the United States and Europe. He referred to the time in the late summer, when the deep water stratifies and goes anoxic, and the phosphorus levels increase. He said that if that water can be pumped out when it has high levels of phosphorus, the loading of phosphorus in the pond can be reduced by taking out a relatively small volume of water. Mr. Blunt then described sediment removal as the removal of phosphorus-rich sediment hydraulic dredging or mechanical dredging, which thereby reduces the phosphorus contributed to the water column.

Mr. Blunt reiterated that the objectives of this program are to refine the phosphorus budget, acquire a better understanding of the pond health and ecology, and to recommend remedial options, or a combination of options, which can be used to improve the health of the pond, if necessary.

Questions and Answers

Mr. Coleman asked what removing a "small volume" of water meant in relation to Ashumet Pond, and where would that water be dumped. Mr. Blunt replied that a small volume might be anywhere from one to ten million gallons, which is a "drop in the bucket" for Ashumet Pond. He stated that if that amount of water were withdrawn from the pond, assuming no water enters the pond, the pond would drop less than two-tenths of a foot. He said that water that is removed could be taken to the wastewater treatment plant on the base where there is an effluent line that goes to the Cape Cod Canal. Another option would be to give the water to a Golf Course, or other commercial entity that does a lot of watering. Mr. Blunt emphasized that there is nothing wrong with the water, it just has elevated levels of phosphorus. Mr. Coleman asked how the phosphorus would be removed. Mr. Blunt replied that the phosphorus would not be taken out of the water, rather the water, containing the phosphorus, would be pumped. He said that the water itself would either be given to someone for use, watering a golf course for example, or it would be discharged along with the wastewater effluent.

Mr. Smith added that various options are being considered to address the phosphorus. He stated that going to the effluent line is an option, as is the possible re-use of the water on golf courses. He explained that the treatment mechanism in re-using the water on a golf course, would be the growing grass, which will utilize the phosphorus. He stated that although this is a "drop in the bucket" for Ashumet Pond, there is a concern with removing the water from the aquifer for consumptive use. If the water is used on a golf course and is treated by the grass, would not affect the aquifer’s overall water budget.

Mr. Bowman commented that the presentations were excellent. He then referred to the map of the areas of investigation on Ashumet Pond (see attachment #4) and commented that the phosphorus forms a circle around the pond, which could be due to the Coriolis effect. He commented that when sampling, one might assume that there is input from the eastern side of the pond, when in fact, the Coriolis effect could be responsible for the input. Mr. Bowman noted that the two areas of investigation are the area where the phosphorus is entering and the southern portion of the pond. He recommended that more samples be taken in the center of the pond and near the point. Mr. Bowman also noted that the wind conditions on the pond are a factor. He explained that when a Nor’easter storm occurs, a fresh water input from the rain would come down through the cranberry bog and potentially flush the sediments, so there could be a significant increase in the northern part of the pond. This could be blown to the southern part of the pond with a Nor’easter. He stated that the wind conditions need to be considered both before and after the sampling, which may help to explain some, if any, problems that arise.

Mr. Orlando noted that it is known where the phosphorus is coming into Fisherman’s Cove, and asked why the water would not be treated in-pond at that point. Mr. Blunt replied that the concentrations in the water at Fisherman’s Cove are very low. He stated that the key issue is that the total mass of phosphorus getting into the pond, not so much the concentration at any one point. Mr. Blunt explained that the water at Fisherman’s Cove is shallow, and there is a lot of wind-driven mixing – as soon as the water coming from the plume enters the pond, it is mixed with pond water that is very low in phosphorus. He explained that the phosphorus is eventually distributed around the pond and may end up accumulating down in the deeper hole, which is actually a better place for treatment. He stated that the concentration of the phosphorus in the deep hole in the late summer/early fall is much higher than that seen in the pond water at Fisherman’s Cove. Mr. Blunt also remarked that the phosphorus concentrations in the groundwater going to the pond are higher. He explained that the reservoir of phosphorus on the sediment is so high that it could be inefficient to pump the groundwater to extract the phosphorus – it would be like removing the foam off of a beer. Mr. Blunt stated that if the hypolimnetic situation develops, the deeper hole would be the best place because the phosphorus would be concentrated in the pond, and the secondary effects of possibly causing more phosphorus to desorb on the sediment, would not have to be addressed. Mr. Blunt stated that a key issue is that as the plume comes into the pond it is mixing over at Fisherman’s Cove with clean water. He explained that, therefore, the concentrations immediately decrease and it would be very inefficient to address the phosphorus in-pond. He stated that huge amounts of water would have to be pumped in order to remove the same amount of phosphorus.

Mr. Orlando asked if the phosphorus could be stopped before it enters the pond. Mr. Blunt replied that this is theoretically possible, and will be considered.

Mr. Dow stated that studies have been done of the uptake of heavy metals into the liver of flounder. The studies have found that the levels of heavy metals are much higher on Georges Bank, where there are sandy sediments, than the levels in Boston Harbor, where there are silty sediments, but very high levels of heavy metals compared to what occurs in the sandy sediments of Georges Bank. He noted that Mr. Leblanc had mentioned that, even though some of the areas in the aquifer where there are sandy sediments, in spite of all the anoxic conditions, there still is a lot of phosphorus bound to those sandy sediments. Mr. Dow commented that he thinks there is a possibility that, since most of the bottom is sandy sediments that may have much lower levels of phosphorus bound to them, there is probably a lot less iron there. When those areas becomes hypoxic or anoxic, more phosphorus is generated in the deep areas of the pond where there are siltier sediments. He added that he would not discount the sandy sediments because it is a matter of the binding, and how the anoxia and hypoxia affects the release of the phosphorus to the binding. Mr. Blunt assured Mr. Dow that assumptions that would cause something to be missed are not being made, and his concern would not be discounted. He stated that he believes there is enough coverage between the grab sampling and the coring to identify the types of areas Mr. Dow mentioned.

Mr. Baker commented that he surmised from the presentation that Ashumet Pond was compared to both Mashpee Pond and Peters Pond, and that it was concluded that they are all the same and there is no real problem. He added that the presentation also indicates that a budget needs to be developed, and there are techniques that can, if needed, be implemented. He then noted that he has fished the ponds in this area of Cape Cod for more than 40 years, including Peters Pond, Mashpee/Wakeby Pond, Ashumet Pond, and Johns Pond, to name a few. He said that he sees a difference in Ashumet Pond compared to the other ponds. He explained that although he does not have any scientific data, it is his humble opinion that Ashumet Pond is degraded. Mr. Baker then remarked that if the answer of this assembled multitude is that there is no problem with Ashumet Pond, it could rest assured that "you all" will be the subject of his personal attack.

Mr. Snyder stated that typically, in all of the ecological programs, AFCEE uses references ponds. He noted that there has been news about other surface water bodies having poor health. He also stated that in rough categorizations of pond health, there are three stages of trophic status and there is quite a range within those three stages. Mr. Snyder reported that the reference ponds and Ashumet Pond are in mesotrophic status, and explained that the ponds can be in mesotrophic status, show signs of eutrophication, and still be healthy. He said that AFCEE is hoping to address Ashumet Pond – if there are problems with other surface water bodies in this area, AFCEE wants the preferred remedy to be a useable technology, both in terms of developing an understanding of the problem and the technique to fix it. He commented that whatever is decided, he hopes to get some export to other ponds that may need some help down the road. Mr. Snyder stated that AFCEE will continue to try to do something to improve the condition of Ashumet Pond. Mr. Baker asked if Mr. Snyder is implying that Ashumet Pond is "sick" and AFCEE is going to fix it. Mr. Snyder replied that this is correct, and added that AFCEE recognizes that phosphorus loading is not normal to most ponds and it is a concern. He also mentioned that the symptoms at Ashumet Pond are not as bad as would be expected considering the amount of phosphorus going in.

Mr. Bowman asked when AFCEE would actively begin removing the phosphorus. Mr. Smith replied that the intensive data collection effort during the "growing season" has already begun and, in parallel, a document is being developed that explains the various alternatives. He stated that by the end of this season AFCEE will make a recommendation about what action should take place and implement that action in the next growing season. Mr. Smith also commented that he believes the hypolimnetic withdrawal approach is promising. He explained that the advantage of this approach is that it operates over a period of a few weeks to a month, when the pond has developed its anoxic condition. The method is in place, and is turned on when needed. He added that hypolimnetic withdrawal will remove as much phosphorus as the plume is contributing, or enough phosphorus that the condition of the pond will improve. He reiterated that there will be an intensive data collection effort this summer followed by recommendations for action. He also mentioned that AFCEE needs to meet with the regulators and determine how that process will develop – the details of when the preferred action will take place are forthcoming.

Mr. Orlando asked if the only treatment to be studied here is in-pond. He then inquired about the reactive wall and/or other types of treatments, and where they might fit in. Mr. Smith replied that the geochemical aspects of the plume are continuing to be investigated. He noted that the USGS is focused on what is going on geochemically – this is the key to an aquifer approach, whether it is a pump and treat approach or a reactive wall. He stated that the reactive wall looks promising and is being considered. He also noted that a pilot system is in-place at CS-10, with a data set that provides an analogue for how a reactive wall operates in the aquifer. Mr. Smith stated that it is important to remember the geochemical effects of the reactive wall on the aquifer, and what it might be doing to the pond if placed in close proximity. He stated that an aquifer approach has not been dismissed. He also explained that the Air Force is looking at an aquifer approach from a modeling perspective, with the intent of understanding the mobility of the plume. In the meantime, the focus will be on the symptoms, on developing an approach to at least stabilize the situation in the pond while continuing to consider potentially long-term aquifer approaches. Mr. Smith commented that it has been determined that there is not a viable "silver bullet" to remove the phosphorus from the aquifer, otherwise that route would be taken. He said that if that were the case there would not be as much of a concern about what is going on in the pond.

Ms. Valiela commented that a lot of boring and sampling will be done in an area where the CS-10 plume might be present. She asked if there will be split samples that will also be checked for VOCs. She also then asked how this effort is integrated with the effort to define the leading edge of CS-10. Mr. Blunt replied that there will be two, coordinated efforts. He stated that during the drilling and the screening of the water, samples will also be taken for VOCs.

Mr. Smith reported that additional well clusters have been installed along the edge of the phosphorus plume. He stated that key elements of the CS-10 decision are that a system be designed to capture CS-10 at Sandwich Road, and that there not be an adverse affect on the USGS site or the Ashumet Phosphorus plume. He noted that these installations serve a dual purpose – the phosphorus plume can continue to be monitored, and there can be assurance that the reinjection at CS-10 is not having an adverse affect, so adjustments there can be made if needed.

Mr. Snyder added that the efforts are coordinated, however, the leading edge investigation will include sampling for VOCs.

Agenda Item #4. Adjourn

Mr. Sobel thanked everyone for attending and adjourned the meeting at 8:29 PM.