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EXPOSURE INVESTIGATION
GREAT POND WEYMOUTH, NORFOLK COUNTY, MASSACHUSETTS
The Exposure Investigation for Great Pond, Weymouth, Massachusetts was prepared by the Massachusetts Department of Health under a cooperative agreement with the federal Agency for Toxic Substances and Disease Registry (ATSDR). It is in accordance with approved methodology and procedures existing at the time the public health consultation was initiated.
ATSDR. 2000. Toxicological profile for arsenic. Agency for Toxic Substances and Disease Registry, Atlanta, GA.
EPA. 1994a. Method 200.9: Determination of trace elements by stabilized temperature graphite furnace atomic absorption. U.S. Environmental Protection Agency, Office of Research and Development, Environmental Monitoring Systems Laboratory, Cincinnati, OH.
EPA. 1995. Environmental Protection Agency. Superfund Program Representative Sampling Guidance, Volume 5: Water and Sediment, Interim Final. Environmental Response Team, December, 1995.
EPA. 1996. SW-846: Test methods for evaluating solid wastes physical/chemical methods. U.S. Environmental Protection Agency, Office of Solid Waste, Washington, D.C.
Shacklette and Boerngen. 1984. Element concentrations in soils and other surficial materials of the conterminous United States. U.S. Geological Survey Professional Paper 1270.
Talbot, M. 2003. Personal communication (telephone conversation with Elaine T. Krueger, Massachusetts Department of Public Health, regarding Weymouth, April 16, 2003).
Weston Geophysical Corporation. 1998. Geophysical Investigation: Weymouth Great Pond Reservoir.
PROTOCOL FOR WATER AND SEDIMENT TESTING
INTAKE PIPE AREA
GREAT POND, SOUTH WEYMOUTH, MASSACHUSETTS
Bureau of Environmental Health Assessment
Massachusetts Department of Public Health
Boston, Massachusetts
Background
In response to community concerns and at the request of local officials and residents, the Massachusetts Department of Public Health's (MDPH) Bureau of Environmental Health Assessment (BEHA), is seeking funding from the U.S. Agency for Toxic Substances and Disease Registry (ATSDR), Exposure Investigation Branch, to conduct sampling of surface water and sediment near the intake pipe of the Great Pond Water Treatment Plant (WTP) in South Weymouth, Massachusetts. The intake pipe takes water from Great Pond and brings it into the Weymouth public water supply system. The figure depicts the approximate location of the intake, pumping station, sample locations and other details of the northeast area of Great Pond. The depth of the pond ranges from approximately 12 to 24 feet (Weston Geophysical Corporation, 1998). To supplement the water in Great Pond during periods of low precipitation, water is pumped from the South Cove of Whitman's Pond, across town, and into Great Pond in close proximity to the Great Pond pumping station (Weymouth Water Department 2002).
Community concerns about potential arsenic contamination of the reservoir's surface water and sediment were raised following the occurrence of elevated urinary arsenic levels among several South Weymouth families in late spring of 2001. A pediatrician with training in environmental medicine and working with one of the families hypothesized that the source of arsenic may be the drinking water. Because Great Pond is reported to be the primary source of drinking water for South Weymouth, residents were particularly concerned about possible sediment contamination in this reservoir that may impact the municipal drinking water supply.
Although Weymouth's water supply has been monitored for arsenic in accordance with applicable regulations, concern has been expressed that this monitoring is not frequent enough (e.g., at times 18 month gaps occurred for drinking water testing) to detect possible sporadic elevations in the levels of arsenic in the municipal supply that may occur at certain times of the year (e.g., spring and fall during turnover of Great Pond). An environmental engineer hired by one of the families suggested that if the sediment in Great Pond contained arsenic, it is possible that sediment could be stirred up during spring and fall turnover and enter the water distribution system bringing arsenic with it. It is hypothesized that such a phenomenon may result in higher levels of arsenic in the water that are not captured by the regulatory testing frequency of the water supply.
In order to address the possibility of sporadic elevations of arsenic that may result from various environmental conditions (e.g., turnover events in Great Pond), MDPH is proposing to conduct focused sediment and surface water sampling in the pond. Samples will focus on the areas of the pond where the WTP intake is and where surface water from South Cove enters the pond, both of which are in the northeast corner of the pond. Thus, the purpose of the proposed sampling is to gather sediment and water concentration data for arsenic in that area of Great Pond closest to the WTP intake, as this area would most likely impact water quality entering into the municipal system. In addition, raw drinking water samples will be taken prior to treatment. These samples will reflect the water entering the treatment system directly from the WTP intake in Great Pond. Data gathered during this focused sampling effort can aid in better evaluating potential exposure opportunities and thus potential health impacts through consumption of drinking water. The proposed sampling is not designed to conform to requirements under regulatory programs.
Goals
The goals of the proposed sampling are to gather water and sediment data on arsenic concentrations in the northeast area of Great Pond and to gather data on arsenic concentrations in raw drinking water to evaluate opportunities for exposure to arsenic in drinking water originating from Great Pond.
Objectives
The objectives for sampling include collecting raw drinking water samples originating from the Great Pond WTP intake prior to treatment; and sediment and surface water from the WTP intake area, the location at which the water from South Cove enters Great Pond, and at two other locations farther into the pond from the WTP intake. The sampling will serve to address several questions:
What arsenic concentrations are seen in raw drinking water samples originating from the Great Pond intake and prior to treatment?
What arsenic concentrations are seen in sediment and surface water samples in proximity to the WTP intake in Great Pond?
What arsenic concentrations are seen in sediment and surface water samples in the area where water from South Cove enters Great Pond?
Are there variations in arsenic concentrations observed in surface water or sediment during lake turnover period (e.g., fall) compared to other time periods when the pond is likely to be more stratified (e.g., summer)?
Are there variations in arsenic concentrations observed in sediment and surface water during times when water from South Cove is pumping (fall and winter) and when it is not (spring and summer)?
If arsenic is present in surface water or sediment, could the levels present intermittent exposure opportunities or health concerns via drinking water to area residents?
Study Design
This section describes the key aspects of how raw drinking water from the WTP, and surface water and sediment samples from Great Pond will be collected. The study design includes descriptions of the sampling locations and the number and frequency of each type of sample.
Drinking Water Sampling. Samples of drinking water prior to water treatment will be taken over the course of one year in order to obtain a representative picture of the concentration of arsenic in the water entering the system under all conditions.
Location of Samples. Samples will be collected at the water treatment plant prior to the water undergoing any treatment. This will represent raw water drawn directly from the pond.
Frequency of Samples. One sample will be collected every other week for one year. Thus, a total of 26 samples will be collected..
Additional Sampling. At the time that each sample of raw water is collected, a sample of finished water post-treatment will be collected and stored. Thus, if any unusual result is found in the pre-treatment sample, the post-treatment sample can be analyzed to provide information on the quality of water actually being introduced into the water distribution system and provided to residents' homes.
Surface (Pond) Water Sampling. Samples of pond water will be taken at the same time sediment samples are collected in order to relate any results found in sediment samples to concentrations in the water itself in the vicinity of the sediment samples (i.e., Locations 1-4 on Figure). The fall turnover time will be determined by water specific information (e.g., temperature and weather events) gathered during the biweekly raw drinking water sampling and review of historical data for the local area. Surface water samples will be collected prior to sediment samples to avoid disturbing sediments into the water and biasing the water sample. In order to minimize disturbance, samples will be collected closest to the intake to the water treatment plant first, and then outward (or upgradient) from that location. The assumption is that surface water flows toward the WTP intake and thus taking samples from near and then farther from the WTP intake, in that order, should minimize the potential for cross-contamination of samples. Pond surface water will also be collected in the area where water from South Cove discharges into Great Pond (Location #2 - see Figure). Information from MDEP indicates that water from South Cove is usually pumped into Great Pond during the winter quarter and again during the fall quarter (MDEP 2002). Thus, samples from this area will be collected during both pumping and non-pumping periods.
Location of Samples: Surface water samples will be taken in the water column at each of the four sediment sample locations (see discussion of sediment sample locations below). A surface water sample will be taken at one foot below the surface and one foot above the bottom of the pond.
Frequency and Time of Testing: Surface water samples will be collected twice: (1) during fall turnover and (2) during the summer when the pond is most likely to be experiencing stratification. Supplemental water from South Cove of Whitman's Pond is generally pumped to Great Pond during the first (winter) and fourth (fall) quarters of the year and generally not pumped during the second (spring) and third (summer) quarters of the year (MDEP 2002). Thus collecting samples from summer and fall turnover will provide information for a number of different environmental and pumping conditions (MDEP 2002). In addition, the U.S. Geological Survey (USGS) commented that a likely mechanism for seasonal variations in water-column arsenic concentrations would be arsenic release from sediments in oxygen-depleted bottom water during summer followed by mixing of this water higher into the water column during fall mixing. Oxygenation of the entire water column following mixing would reduce water column arsenic concentrations. A total of 16 surface water samples will be collected (i.e., two samples from each of four locations taken two times during the year). In addition, for each of the two sampling events and for quality control purposes, duplicate samples of surface water will be taken for each of the two sampling depths at the WTP intake location.
Additional Measurements: At the time of collection of each surface water sample, additional surface water measurements that will be taken using a Horiba machine, including temperature, pH, dissolved oxygen, conductivity, and turbidity. Depth measurements from the surface to the pond bottom will be made by the boat depth finder and a measuring rope. The overall pond water level will be noted. Air temperature and wind direction will also be recorded. Locations will be verified with a Global Positioning System (GPS).
Sediment Sampling: Sediment samples will be taken at selected locations in Great Pond (Locations #1-4 on Figure). Sediment sampling will be targeted to those areas of the pond most closely associated with the intake area in the WTP or with areas that might affect the intake water, and to areas that would be expected to represent where arsenic concentrations are likely to be highest.
Location of Samples: Sediment samples will be collected at the following locations (see Figure): (1) the intake to the WTP (at the shoreline, as there is no pipe that extends into the pond); (2) the location at which water from South Cove enters Great Pond (i.e., at the shoreline approximately 150-200 yards to the west of the WTP); (3) at the deepest part of this northeastern corner of the pond; and (4) in an area that is approximately 250-300 yards south of the WTP intake and between the intake and a partially enclosed cove adjacent to Lakeview Cemetery. In addition, for quality control purposes, a duplicate sample will be collected for the sample taken in the WTP intake area (Location #1). The samples to be taken from the WTP intake area will provide information on arsenic concentrations adjacent to the intake prior to water entering the pipe. The sample from the South Cove discharge area will provide information on possible arsenic concentrations that may be related to water originating from South Cove (Location #2). The scientific literature indicates that sediment samples taken from deeper locations in water bodies generally are more likely to contain higher concentrations of compounds (EPA 1995). Thus, the deep location farther into Great Pond (Location #3) was chosen to represent an area where the highest concentration of arsenic would likely be detected in sediment in this area of the pond. The figure depicts approximate contours of the pond bottom (Weston Geophysical Corporation 1998). The sampling location between the WTP intake and Lakeview Cemetery will provide information that may address community concerns that this cemetery (due to possible historical use of embalming fluid containing arsenic) may have impacted water quality in Great Pond (Location #4).
Frequency and Depth of Samples: Sediment samples will be collected two times at the same time and under the same conditions as described in the surface water sampling section above. During the two sampling events (summer, fall turnover), a total of 16 sediment samples will be collected, along with two duplicate samples taken at Location #1. At all locations, the sediment samples will be collected from the top six inches of sediment.
Methods
Raw drinking water samples will be collected in accordance with USEPA guidance (EPA 1994a) (see MDPH protocol, Appendix B). The surface water and sediment samples will be collected consistent with USEPA guidance (e.g., EPA 1994b, 1994c, 1994d) (see attached MDPH protocols).
The method of analysis for raw drinking water and surface water is EPA method 200.9, with a detection limit of 2 ug/L (or 2 ppb) (EPA 1994a). The method of analysis for sediment samples is EPA SW 846, with a detection limit of 1 mg/kg (or 1 ppm) (EPA 1996). A laboratory certified by MDEP for analysis of drinking water will perform the chemical analyses.
QA/QC Procedures
Field sampling methods will be checked by collecting an equipment rinsate blank from the sediment sampling equipment in pre-cleaned sample containers provided by the contract laboratory. This test will measure the quality of decontamination procedures for the sediment sampling equipment and the container pre-cleaning process. The equipment blank will be analyzed for chemical parameters. In addition, variability of concentrations in the media and consistency in sampling methods will be checked by performing duplicate analyses of one sediment sample and one water sample from each of two depths at Location #1 for chemical parameters.
Laboratory performance will be evaluated according to QA/QC procedures prescribed for each individual analytical method. A QA/QC report will accompany the analytical results for the chemical analyses.
Interpretation
MDPH, under its cooperative agreement with the ATSDR, will provide a health consultation on the results of this sampling program. The health consultation will review the sediment and water data and their implications for opportunities for exposure to arsenic via the Weymouth water supply. These opportunities for exposure will be evaluated in light of available health effects information as well as what the scientific literature indicates is typical background levels of arsenic in sediment or soil (e.g., from ATSDR toxicological profiles for arsenic). For example, ATSDR reports that background concentrations in soils range from about 1 to 40 parts per million (ppm), with a mean value of about 5 ppm (ATSDR 2000). The U.S. Geological Survey (USGS) reports that average background arsenic concentration in eastern US soils was about 7.4 ppm, with a range from less than 0.1 ppm to 73 ppm (Shacklette and Boerngen 1984). The Massachusetts Department of Environmental Protection reports that background concentrations in Massachusetts soils ranged from less than one to 99 ppm, with an average of 8.2 ppm (MDEP 1995). The current Maximum Contaminant Level (MCL) for arsenic in public drinking water supplies is 10 ppb. (EPA 2001).
References
ATSDR. 2000. Toxicological profile for arsenic. Agency for Toxic Substances and Disease Registry, Atlanta, GA.
EPA. 1994a. Method 200.9: Determination of trace elements by stabilized temperature graphite furnace atomic absorption. U.S. Environmental Protection Agency, Office of Research and Development, Environmental Monitoring Systems Laboratory, Cincinnati, OH.
EPA. 1994b. Environmental Protection Agency. Environmental Response Team. Surface Water Sampling. SOP #: 2013, November 17, 1994.
EPA. 1994c. Environmental Protection Agency. Environmental Response Team. Sediment Sampling. SOP #: 2016, November 17, 1994.
EPA. 1995. Environmental Protection Agency. Superfund Program Representative Sampling Guidance, Volume 5: Water and Sediment, Interim Final. Environmental Response Team, December, 1995.
EPA. 1996. SW-846: Test methods for evaluating solid wastes physical/chemical methods. U.S. Environmental Protection Agency, Office of Solid Waste, Washington, D.C.
EPA. 2001. Environmental Protection Agency 40 CFR 745. Lead; Final Identification of Dangerous Levels of Lead; Final Rule
MDEP. 1995. Guidance for disposal site risk characterization. Massachusetts Department of Environmental Protection, Bureau of Waste Site Cleanup and Office of Research and Standards. Boston, MA.
MDEP. 2002. Letter to Weymouth Water Division from Bureau of Resource Protection, Massachusetts Department of Environmental Protection, Boston, MA. January 28, 2002.
Shacklette and Boerngen. 1984. Element concentrations in soils and other surficial materials of the conterminous United States. U.S. Geological Survey Professional Paper 1270.
Weston Geophysical Corporation. 1998. Geophysical Investigation: Weymouth Great Pond Reservoir.
Weymouth Water Department. 2002. Personal communication with James Leary.
