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DISCUSSION

In this section, ATSDR 1) presents an overview of available groundwater quality data, 2) describes groundwater use in the area, 3) evaluates how and to what extent people may have been exposed to contaminated groundwater, and 4) explains why no apparent health hazards are likely associated with past exposures to water from private wells in the vicinity of the West/Hows Corner site.

Groundwater Quality Data

In late 1987, testing of private drinking water (residential) wells in the vicinity of the West/Hows Corner site revealed elevated levels of contaminants (primarily PCE and TCE) in 10 wells. In response to these findings, MEDEP established a monitoring program to continue testing these and other area residential wells. This program continued until 1994 when residences with affected wells were connected to a safe public water supply and stopped using their private wells. During that time period, PCE concentrations ranged from 0.6 parts per billion (ppb) to 3,880 ppb and TCE levels ranged from 0.6 ppb to 125 ppb (see Table 1) (MEDEP, 1993).

In 1996, MEDEP and the U.S. Environmental Protection Agency (EPA) resumed sampling of area residential wells when they learned that new private wells had been installed on newly developed lots as early as 1994. Data from 1996 and 1997 revealed that PCE levels in tested residential wells ranged from 0.2 ppb to 150 ppb. Only one well, however, had concentrations exceeding the state and federal drinking water standard for PCE of 5 ppb. No TCE was detected in any of the residential wells in use during these sampling events. PCE and TCE were detected in wells on vacant lots in the area at levels above drinking water standards (see Table 2). No sampling data are available for the 1994 to 1996 time frame.

In addition to residential wells in the area, "monitoring wells" (used only to evaluate groundwater conditions, not to supply drinking water) are also routinely sampled by EPA. Recent sampling of monitoring wells revealed that PCE was only detected in a few wells at concentrations ranging from 1 ppb to 20,000 ppb, with the highest concentration detected in monitoring well 2IB (MW-2IB). TCE was only detected in two samples from the same well (MW-2IB) at concentrations of 890 ppb and 2,400 ppb. In general, the highest contaminant concentrations were detected on site or in close proximity to the site.

Groundwater Use/Exposure

The Plymouth area relies on groundwater from the bedrock aquifer for its potable water supply. Prior to the institution of the Plymouth Water District public water supply in 1994, individual private wells supplied water to all businesses and residences in the vicinity of the site. After groundwater contamination was discovered in 1987, measures were taken to eliminate possible exposure to contaminated groundwater. Key information related to use of groundwater in the vicinity of the West/Hows Corner site from 1987 to the present is summarized below.

    • Alternate water supplies (bottled water) and carbon filtration systems were provided to 10 residences with contamination detected in 1987/1988.
    • Thirty-six residences began receiving public water from the Plymouth Water District from unaffected groundwater west of the site by May 1994 (EPA, 1995a). Twelve residences with potentially affected wells chose not to be connected to the public water supply and continue to use water from their private wells.
    • New residential lots and wells have been developed in the West/Hows Corner area as early as 1994 (EPA, 1997b). One of these new residences was connected to the public water supply in November 1996 after elevated levels of contaminants were detected in the private well at that location.

It is possible that groundwater supplying residential wells in the area could have been affected by disposal practices at the site shortly after operations began in the mid-1960s. No testing data are available to confirm this, however. For the purposes of this health consultation, ATSDR assumed that people may have been exposed as long as 20 years that is, from the time contaminants may have migrated to private wells (assumed to be 1968) to the time safe alternate supplies and filtration were provided (by 1988). ATSDR also evaluated more recent exposures, a 2-year period which represents the time when new wells were installed in the area (1994) until the time contamination was discovered in these wells and alternate supplies were provided (1996).

ATSDR estimated PCE and TCE levels that people may have been exposed to during both periods of time, as described below.

Possible Exposures from 1968 to 1988

Because no sampling data are available for this time period, ATSDR reviewed and evaluated the available data collected from 1987 through 1993 to derive an estimate of possible earlier exposures. As mentioned previously, PCE was detected at elevated concentrations in several residential wells in close proximity to the site. Wells were sampled multiple times. As indicated in Table 1, PCE concentrations ranged from not detected up to 3,880 ppb. PCE levels varied over time. The highest hit of 3,880 ppb detected in one well (in 1992) was much higher than other measurements of PCE in this and other wells. Most samples contained concentrations below the drinking water standard for PCE of 5 ppb. PCE was detected sporadically at concentrations up to 1,000-1,800 ppb in a few other wells.

ATSDR averaged the PCE levels detected in the most contaminated well to estimate levels to which some area residents may have been exposed over time. ATSDR believes that this average concentration (equal to 760 ppb PCE) represents a reasonable and conservative estimate of exposures during this time period. ATSDR also evaluated the possible effects of being exposed to the highest concentration (3,880 ppb PCE) over a short period of time.

Possible Exposures from 1994 to 1996

Again, because no data are available for this two-year period, ATSDR evaluated the levels of PCE and TCE found in 1996 in newly installed wells and assumed that people could have been exposed to PCE at levels up to 150 ppb, the highest PCE level detected in wells being used during this time period. It is uncertain, however, whether exposure to higher PCE levels ever existed, because the one well with the 150 ppb detection was sampled only once. As mentioned earlier, no TCE was detected in the residential wells in use during this time period.

Possible Exposures from 1994 - 1996

Again, because no data are available for this two-year period, ATSDR evaluated the levels of PCE and TCE found in 1996 in newly installed wells and assumed that people could have been exposed to PCE at levels up to 150 ppb, the highest PCE level detected in wells being used during this time period. It is uncertain, however, whether exposure to higher PCE levels ever existed, because the one well with the 150 ppb detection was sampled only once. As mentioned earlier, no TCE was detected in the residential wells in use during this time period.

Note that although contaminants were detected at levels above state and federal drinking water standards between 1988 and 1994, no one was believed to be using water from affected wells at that time. Bottled water and filters were provided to affected residences. Because the wells on residential wells are below drinking water standards, no current unacceptable exposures to contaminants are believed to exist.

Toxicologic Evaluation

Note of Explanation

This section of the health consultation focuses on estimating how much PCE and TCE people might have been exposed to daily and how that estimated dosage compares to doses that may produce health effects in the community. Because many uncertainties exist when making these estimations (e.g., lack of well water data or knowledge of how long people were exposed), ATSDR tends to use what are called "conservative" assumptions about possible exposures and associated health effects. To make a conservative estimate, ATSDR usually assumes a person is exposed to the most contaminated well water reasonably possible. This allows ATSDR to determine the highest possible level of exposure and the corresponding health effects. Although ATSDR does not expect that most people in the West/Hows Corner area were exposed to the highest (most conservative) levels of contamination, the conservative estimates are used to protect public health.

While the relative toxicity of a chemical is important, the response of the human body to a chemical exposure is also determined by several additional factors, including the concentration (how much), the duration of exposure (how long), and the route of exposure (breathing, drinking, or skin contact). The probability that exposure-related adverse health outcomes will actually occur does not depend solely on concentrations in the water. Instead, the combination of all of the factors helps ATSDR to evaluate how individuals may be affected by chemical exposures.

Based on available scientific data, much of which ATSDR has collected in its toxicological profiles, ATSDR has determined concentrations of chemicals that can reasonably (and conservatively) be regarded as harmless, assuming default conditions of exposure. The resulting comparison values (see Appendix B) and health guidelines generally include safety factors believed to be sufficient to ensure protection of sensitive populations. The values are used to screen contaminant concentrations at a site, and to select so-called "contaminants of concern" that warrant closer scrutiny by agency health assessors and toxicologists. A "contaminant of concern" is defined as any substance that is detected in air, water, or soil at concentrations that exceed one or more of ATSDR's comparison values.

It must be emphasized, however, that ATSDR's comparison values and health guidelines and other comparisons values, such as drinking water standards, are not thresholds of toxicity. While concentrations at or below the relevant comparison value may reasonably be considered safe, it does not necessarily follow that any concentration that exceeds a comparison value would be expected to produce adverse health effects in the community. Conservative, health-based standards and guidelines are derived to enable health professionals to recognize and resolve potential public health problems before that potential is realized. While the levels of PCE detected in residential and monitoring wells exceeded EPA's MCL, for example, it is important to understand that MCLs are developed to protect individuals who may be exposed over a lifetime (70 years). The purpose of this consultation is to evaluate whether exposures to detected contaminant levels, under site-specific conditions, are expected to affect the health of residents in the vicinity of the West/Hows Corner site.

The primary "contaminants of concern" detected in private wells sampled to date are PCE and TCE. All other contaminants detected were at levels below ATSDR comparison values. Because the 1996 PHA concluded that TCE did not present a past public health hazard and no TCE was detected during recent sampling events in private wells that were used between 1994 and 1996, the focus of this toxicological evaluation is on PCE. Several of the studies, however, reviewed and presented in this report contained information on both PCE and TCE because PCE and TCE are commonly found together in contaminated water supplies.

Based on likely, site-specific considerations, and using conservative assumptions about how often people drink and how much they drink, ATSDR estimated the dose of PCE to which people might have received (short and long-term) from using the contaminated water. These estimates allow ATSDR to evaluate the likelihood, if any, that PCE in private wells are associated with adverse health effects.

ATSDR assumed that residents obtained all their daily fluids from their private wells. This is likely a conservative assumption because individuals tend to get some of their liquid requirements from sources such as milk, juice, soda, and a variety of foods. Furthermore, in many cases, some of the daily requirements for fluids are obtained outside of the home such as at work or school. Adults were assumed to drink 2 liters (approximately 2 quarts) of tap water each day and to weigh (on average for male and female) 70 kilograms (kg) (about 150 pounds). Children were assumed to drink 1 liter (about a quart) of tap water each day and to weigh 16 kg (about 35 pounds). For the more recent exposures (1994 to 1996), ATSDR also evaluated exposures to children who may have been exposed to vapors released through the use of vaporizers. A description of the calculations and assumptions used in estimating exposures is presented in Appendix C.

ATSDR's conclusions for each of the time periods evaluated is summarized below. ATSDR reviewed the scientific literature and evaluated potential cancer (carcinogenic) and noncancer (noncarcinogenic) health effects associated with exposure to PCE-contaminated drinking water at the detected levels or estimated doses. Most of the health effects information on PCE are from experimental animal studies or epidemiologic studies looking at worker exposures. Available human health studies are largely inconclusive about the effects of low-level exposure to PCE. Additional information on PCE toxicity is presented in Appendix D.

1968 to 1988

No illnesses related to exposures to groundwater are likely because no one is thought to have been consistently (for 20 years) using contaminated well water at levels associated with health hazards.

Cancer Effects: It is unlikely that human exposures to PCE at the levels detected in private wells will lead to the increase of cancer incidence in the area. The link between PCE exposure and cancer in humans is uncertain, however. Studies looking at occupational and drinking water exposures have been largely inconclusive. PCE has been shown, however, to cause cancer in laboratory animals (rodents) at high doses and therefore may be carcinogenic to humans. A direct comparison of exposure doses for animals and humans may not be entirely appropriate, because 1) high doses are needed to induce cancer in rodents, 2) the mechanism by which cancer may be induced is different in animals compared to people, and 3) PCE was not given to test animals via drinking water. Such a comparison, however, can provide us with a relative sense of the potential for cancer effects. ATSDR estimated doses of 0.02 and 0.05 mg/kg/day for adults and children, respectively, exposed to the average PCE concentration found in the most contaminated private well (see Table 3 and Appendix C). These doses are approximately 8,000 times lower than the levels reported to cause cancer in animals, strongly suggesting that cancer effects are unlikely to be experienced as a result of exposure to drinking water during this time period.

Noncancer Effects: Exposures to detected levels of PCE are unlikely to be associated with noncancer effects. The PCE levels that were likely encountered at West/Hows Corner were at or below the short-term (acute) health-based guidelines developed by ATSDR (minimal risk levels [MRLs]) and only slightly higher than the long-term (chronic) health-based guidelines (EPA's reference dose [RfD]).

Although the chronic health guideline is slightly exceeded, the guideline is based on exposure levels in animal studies at which no adverse effects have been seen (14 mg/kg/day) and has an uncertainty or "safety" factor of 1,000 built into it. The lowest dose that has been shown to cause adverse effects in animals drinking contaminated water was approximately 400 mg/kg/day, which is 8,000 times higher than estimated doses for West/Hows Corner area residents. Furthermore, no one was likely consistently using groundwater with the highest levels of contamination for 20 years, although no historic data are available to confirm this. Only 12 of the approximately 180 groundwater samples collected in the West/Hows Corner area between 1987 and 1993 had PCE concentrations that were greater than the level used in this analysis (760 ppb). Therefore, the likelihood of adverse health effects from drinking the well water with the detected levels of PCE would be negligible.

1994 to 1996

No acute or chronic adverse health effects are likely associated with using contaminated groundwater during this period (including drinking and possible inhalation exposures associated with the use of vaporizers). The overall low concentrations of PCE reported in the residential wells and the short time that exposure occurred greatly reduces the possibility of any adverse health effects.

Cancer Effects: The predicted exposure doses for individuals exposed to the highest level of PCE in private wells at the West/Hows Corner are 0.004 mg/kg/day and 0.009 mg/kg/day for adults and children, respectively (see Table 3 and Appendix C). These doses are considerably lower (approximately 100,000 times lower) than doses reported to cause cancer in laboratory animals. This strongly suggests that human exposures to PCE at the levels detected in private wells are not likely to lead to the development of cancer. (See previous discussion on cancer effects and Appendix D for an explanation of possible limitations in evaluating cancer effects.)

Noncancer Effects (drinking water exposures: Estimated doses of PCE are below available health-based guideline values. While available health studies are largely inconclusive about the effects of low-level human exposures to PCE, ATSDR concludes that noncancer health effects are unlikely to occur among those who may have consumed contaminated drinking water at the West/Hows Corner site during this 2-year time period. In addition, it should emphasized that most residents likely experienced exposures much lower than the maximum level on which this analysis was based. As described previously, only one sample (the 150 ppb maximum used in this analysis) revealed PCE at levels above the drinking water standard of 5 ppb.

Noncancer Effects (Inhalation Exposures): PCE is considered a volatile compound (i.e., PCE has a tendency to migrate from water into air). PCE could volatilize from tap water during cooking, showering/bathing, or other household uses and end up in indoor air. ATSDR does not expect exposures resulting from volatilization of PCE in water to be of any greater concern than drinking the water. One resident expressed specific concern regarding potential health effects associated with using private well water in vaporizers. ATSDR, therefore, examined this issue more closely. Because no measured air data were available, ATSDR estimated indoor air concentrations using a very conservative model which served as a worst case screening tool for evaluating possible exposures. A description of the model and the assumptions used are presented in Appendix C.

ATSDR estimated the concentration of PCE in air when using vaporizers for 8 hours to be 0.005 ppm (see Table 4). This estimate does not account for air that is introduced into a room via other parts of the house or from the outside (that could further dilute the air). The estimated indoor air levels are lower than ATSDR's acute MRL of 0.2 ppm and the chronic (long-term) MRL of 0.04 ppm for air, so no short- or long-term health effects are likely associated with inhalation of PCE-contaminated water vapors possibly released from home vaporizers. For comparison purposes, PCE measured in indoor air with no known PCE sources in one study was 0.0003 ppm (Aggazzoti et al., 1994). Levels of PCE found in closets where newly dry-cleaned products were placed ranged from 0.074 ppm to 0.428 ppm (Tichenor et al., 1990). Thus, the levels of potential exposure from dry cleaning is likely to be higher than those from volatilization from the water.

The estimated indoor air concentrations are more than 5,000 times lower than the Threshold Limit Value (TLV) of 25 ppm considered safe by the American Conference of Governmental Industrial Hygienists for workers exposed 8 hours per day, 40 hours per week (ACGIH, 1996). In epidemiologic studies, workers exposed to levels of PCE in air higher than the occupational health guideline of 25 ppm experienced symptoms including irritation to mucous membranes and the respiratory tract. Liver and central nervous system effects (e.g, dizziness, mood changes, inebriation, and ultimately unconsciousness at high enough doses) were also observed (ATSDR, 1997).

Because predicted indoor air concentrations are significantly lower than concentrations shown to result in health effects in humans, ATSDR concludes that no adverse health effects would be expected as a result of exposure to water vapors generated from household use of water containing 150 ppb PCE for a 2-year exposure period.

ATSDR also considered the potential for combined exposure to drinking water, contaminated air, and dermal exposures during bathing. Studies suggest that skin contact with chemicals like PCE during bathing result in doses approximately equal to those from inhalation exposures (Weisel et al., 1996; Jo et al., 1990). Based on available data, even considering combined exposure and conservative assumptions, the levels of exposure are very unlikely to lead to either acute or long-term adverse health effects.

 

ATSDR Child Health Initiative

As a part of its child health initiative, ATSDR considered the special interests of children possibly exposed to contaminated groundwater in the vicinity of the West/Hows Corner site. ATSDR recognizes that infants and children may be more sensitive to exposures than adults in communities faced with contamination of their water, soil, air, or food. This sensitivity is a result of the following factors: Children are smaller, sometimes resulting in higher doses of chemical exposure per body weight. Also, children are shorter than adults, which means they may breathe vapors or dust that are closer to the ground. Furthermore, the developing body systems of children can sustain permanent damage if toxic exposures occur during critical growth stages.

ATSDR considered drinking water and exposures via other household uses of groundwater. ATSDR estimated child doses as well as adult doses. As discussed in previous sections, it is highly unlikely that children were exposed to high enough levels of PCE in drinking water over long enough periods of time to result in adverse health effects.

CONCLUSIONS

Based on a review of available data and discussions with local, state, and federal environmental and health officials, ATSDR concludes the following:

  • No apparent public health hazards are associated with drinking water and/or breathing indoor air vapors associated with other uses of the water from private wells containing up to 150 ppb PCE between 1994 and 1996.
  • Higher levels of PCE and TCE have been recently detected in private wells located on vacant lots and in monitoring wells on and near the site. If people were to occupy the vacant lots and use water from those wells without filters they would likely be exposed to elevated levels of PCE and TCE in the future.

RECOMMENDATIONS

While no adverse health effects are anticipated from using PCE-contaminated private well water examined to date, concentrations could increase in the near future possibly causing illness and disease in people drinking the water over a longer period of time. ATSDR believes that there are enough uncertainties in the available health literature for PCE and TCE to warrant precaution. The recommendations listed below identify actions that ATSDR believes are prudent to reduce further any potential health hazards that might be associated with groundwater contamination in the West/Hows Corner Site area.

    • Residents should continue to take precautions to limit their exposure to groundwater in private wells possibly containing elevated levels of PCE and TCE. These precautions include using carbon filters and changing them regularly or switching to an alternative water supply.
    • Because contaminated groundwater could migrate to previously non-impacted wells and because vacant lots may be used in the future, monitoring of private wells in the West/Hows Corner site area should continue, including the sampling of new wells before use.

By advocating the use of safety precautions when using private well water, ATSDR is following prudent public health policy to prevent illness and disease. ATSDR will review additional drinking water data, as needed, and review and revise the findings of this health consultation if appropriate.



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