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PUBLIC HEALTH ASSESSMENT

FORT DEVENS
AYER, MIDDLESEX COUNTY, MASSACHUSETTS


APPENDIX A: LIST OF COMPARISON VALUES

Comparison values represent media-specific contaminant concentrations that are used to select contaminants for further evaluation to determine the possibility of adverse public health effects. The conclusion that a contaminant exceeds the comparison value does not mean that it will cause adverse health effects.

Cancer Risk Evaluation Guides (CREGs)

CREGS are estimated contaminant concentrations that would be expected to cause no more than oneexcess cancer in a million (10-6) persons exposed over their lifetime. ATSDR's CREGs arecalculated from EPA's cancer potency factors (CPFs).

Environmental Media Evaluation Guides (EMEGs)

EMEGs are based on ATSDR minimal risk levels (MRLs) that consider body weight and ingestionrates. An EMEG is an estimate of daily human exposure to a chemical (in mg/kg/day) that is likelyto be without noncarcinogenic health effects over a specified duration of exposure to include acute,intermediate, and chronic exposures.

Maximum Contaminant Level (MCL)

The MCL is the drinking water standard established by EPA. It is the maximum permissible level ofa contaminant in water that is delivered to the free-flowing outlet. MCLs are considered protective ofpublic health over a lifetime (70 years) for individuals consuming 2 liters of water per day.

Reference Media Evaluation Guides (RMEGs)

ATSDR derives RMEGs from EPA's oral reference doses. The RMEG represents the concentrationin water or soil at which daily human exposure is unlikely to result in adverse noncarcinogenic effects.


APPENDIX B: GLOSSARY

Comparison Values:
Estimated contaminant concentrations in specific media that are not likely to cause adverse health effects, given a standard daily ingestion rate and standard body weight. The comparison values are calculated from the scientific literature available on exposure and health effects.


Concentration:
The amount of one substance dissolved or contained in a given amount of another. Forexample, sea water contains a higher concentration of salt than fresh water.


Contaminant:
Any substance or material that enters a system (the environment, human body, food, etc.) where it is not normally found.


Dose:
The amount of a substance to which a person is exposed. Dose often takes body weight into account.


Environmental Contamination:
The presence of hazardous substances in the environment. From the public healthperspective, environmental contamination is addressed when it potentially affects the health and quality of life of people living and working near the contamination.


Exposure:
Contact with a chemical by swallowing, by breathing, or by direct contact (such as through the skin or eyes). Exposure may be short term (acute) or long term (chronic).


Health Consultation:
A response to a specific question or request for information pertaining to a hazardous substance or facility (which includes waste sites). It often contains a time-critical element that necessitates a rapid response; therefore, it is a more limited response than an assessment.


Ingestion:
Swallowing (such as eating or drinking). Chemicals can get in or on food, drink, utensils, cigarettes, or hands where they can be ingested. After ingestion, chemicals can be absorbed into the blood and distributed throughout the body.


Media:
Soil, water, air, plants, animals, or any other parts of the environment that can contain contaminants.


Minimal Risk Level (MRL):
An MRL is defined as an estimate of daily human exposure to a substance that is likely to be without an appreciable risk of adverse effects (noncancer) over a specified duration of exposure. MRLs are derived when reliable and sufficient data exist to identify the target organ(s) of effect or the most sensitive health effect(s) for a specific duration via a given route of exposure. MRLs arebased on noncancer health effects only. MRLs can be derived for acute, intermediate, and chronic duration exposures by the inhalation and oral routes.


No Apparent Public Health Hazard:
This category is used for sites where human exposure to contaminated media may beoccurring, may have occurred in the past, and/or may occur in the future, but the exposure is not expected to cause any adverse health effects. This determination represents a professional judgement based on critical data available to ATSDR and that the data are judged sufficient to reach a decision. This does not necessarily imply that the available data are complete, in some cases additional data may be required to confirm or support the decision made.


Potentially Exposed:
The condition where valid information, usually analytical environmental data, indicates the presence of contaminant(s) of a public health concern in one or more environmental media contacting humans (i.e., air, drinking water, soil, food chain, surface water), and there is evidence that some of those persons have an identified route(s) of exposure (i.e., drinking contaminated water, breathing contaminated air, having contact with contaminated soil, or eating contaminated food).


Parts per Billion (ppb)/ Parts per Million (ppm):
Units commonly used to express low concentrations of contaminants. As example of each, one part per billion (ppb) of trichloroethylene (TCE) equals one drop of TCE mixed in a competition-size swimming pool and one part per million (ppm) equals one ounce oftrichloroethylene (TCE) in one million ounces of water.


Reference dose:
The value used by EPA as an estimate of daily exposure (mg/kg/day) to the general human population (including sensitive populations) that is likely to be without appreciable risk of harmful effects during a lifetime of exposure.


Risk:
In risk assessment, the probability that something will cause injury, combined with the potential severity of that injury.


Route of Exposure:
The way in which a person may contact a chemical substance. For example, drinking(ingestion) and bathing (skin contact) are two different routes of exposure to contaminants that may be found in water.


Volatile organic compounds (VOCs):
Substances containing carbon and different proportions of other elements such as hydrogen, oxygen, fluorine, chlorine, bromine, sulfur, or nitrogen; these substances easily become vapors or gases. A significant number of the VOCs are commonly used as solvents (paint thinners, lacquer thinner, degreasers, and dry cleaning fluids).


Zone II Areas of Influence:
Defined by Massachusetts Department of Environmental Protection as the area of an aquifer which contributes water to a well under the most severe pumping recharge conditions that can be realistically anticipated, as approved by the Department's Division of Water Supply.

APPENDIX C: ESTIMATES OF HUMAN EXPOSURE DOSES AND DETERMINATION OF THE POTENTIAL FOR ADVERSE HEALTH EFFECTS

Estimating Potential Exposure Levels

ATSDR estimated the human exposure doses from ingestion of drinking water from the Grove Pondwells, dermal contact with Grove Pond sediment along Pirone Park, and ingestion of fish. Derivingexposure doses requires evaluating the concentrations of the contaminants to which people may havebeen exposed and how often and how long exposure to those contaminants occurred. Together, thesefactors help influence the individual's physiological response to chemical contaminant exposure andpotential noncancer (noncarcinogenic) or cancer (carcinogenic) outcomes. In the absence ofexposure specific information, ATSDR applied several conservative exposure assumptions to definesite-specific exposures as accurately as possible for area residents.

Evaluating Potential Health Hazards

The estimated exposure doses are used to evaluate potential noncancer and cancer effects associatedwith chemicals of concern. ATSDR uses standard toxicity values, including ATSDR's minimal risklevels (MRLs) and EPA's reference doses (RfDs) to evaluate noncancer effects. The MRLs andRfDs are estimates of daily human exposure to a substance that are unlikely to result in adversenoncancer effects over a specified duration. To be very protective of human health, MRLs and RfDshave "uncertainty" or "safety" factors built into them. Therefore, if an estimated dose is higher thanan MRL or RfD, it does not necessarily follow that adverse health effects will occur.

To evaluate cancer effects, ATSDR sometimes uses cancer potency factors (CPFs) that define therelationship between oral exposure doses and the increased likelihood of developing cancer over alifetime. The CPFs are developed using data from animal or human studies and often requireextrapolation from high exposure doses administered in animal studies to the lower exposure levelstypical of human exposure to environmental contaminants. CPFs represent the upper-bound estimateof the probability of developing cancer at a defined level of exposure; therefore, they tend to be veryconservative (i.e., overestimate the actual risk) in order to account for a number of uncertainties inthe data used in the extrapolation.

ATSDR estimated the potential for cancer to occur using the following equation. (The estimatedexposure doses and CPF values for the contaminants of concern are incorporated into the equation):

Lifetime Cancer Risk = Estimated exposure dose (mg/kg/day) x CPF (mg/kg/day)-1

Although no risk of cancer is considered acceptable, it is impossible to achieve a zero cancer risk. Consequently, ATSDR often uses a range of 10-4 to 10-6 estimated lifetime cancer risk (or 1 new case in 10,000 to 1,000,000 exposed persons), based on conservative assumptions about exposure,to determine the likelihood of excess cancer resulting from this exposure.

In addition to estimating the likelihood of noncancer and cancer effects, ATSDR reviewed theliterature to evaluate possible health effects associated with exposure at the doses/concentrationsestimated for the pathways described below.

Estimated Exposure Doses From Ingesting Drinking Water From Grove Pond Wells

Arsenic and manganese concentrations measured in Grove Pond well water exceeded ATSDRcomparison values for drinking water, but ATSDR determined that drinking water containingeven the highest detected levels of these contaminants is unlikely to cause adverse health effects.

To determine whether exposure to these contaminants in the well water may be related to adversehealth effects, if any, ATSDR estimated exposure doses for people consuming water containing thehighest measured concentrations in the Grove Pond wells. The estimated exposure doses were thenused to evaluate potential noncancer outcomes. In estimating to what extent people might beexposed to contaminants, ATSDR used "conservative" or safe assumptions about possible humanexposure and any associated health effects. ATSDR assumed that a person drank the mostcontaminated Grove Pond well water, before it is treated or blended with Spectacle Pond well water.ATSDR also used conservative assumptions about how often people drink water and how much theydrink. These assumptions allow ATSDR to estimate the highest likely exposure dose and evaluatethe potential health effects. Although ATSDR expects that few Ayer residents, if any, were exposedto the highest levels of contamination, the "conservative" estimates are used to protect public health.

Table C-1 summarizes the estimates of exposure to arsenic and manganese in Grove Pond wellwater and the following describes the equation and assumptions used to estimate the exposure:

Estimated exposure dose equals Conc. times CF times IR times EF times ED divided by BW times AT

where:
Conc. Maximum concentration in the Grove Pond water (ppb)
CF Conversion factor to convert ppb to parts per million (1/1,000)
IR Ingestion rate: adult=2 liters per day; child=1 liter per day
EF Exposure frequency or number of exposure events per year of exposure: 7 days/week x 52 weeks/year
ED Exposure duration or the duration over which exposure occurs: adult=30 years; child=6 years
BW Body weight: adult=70 kg (154 pounds); child=10 kg (22 pounds)
AT Averaging time or the period over which cumulative exposures are averaged (6 or 30 years x 365 days/year for noncancer effects)

Assumptions for Estimating Exposure Doses

  • ATSDR assumed that an adult drank 2 liters and a child drank 1 liter of water a dayand that all drinking water came from Grove Pond wells. This assumption likelyleads to an overestimate of the actual exposure dose because well water was blendedwith Spectacle Pond well water before being distributed for consumption in homes.

  • The exposure frequency (EF), or number of exposure events per year, was assumedto be 365 days per year, based on a 7-days-a-week exposure over 52 weeks per year.This assumes that all of the water consumed over the course of each day came fromthe Grove Pond wells.

  • The duration of exposure (ED) is assumed to have occurred over a 30-year periodfor adults. This value is the 90% upper-bound limit for residency at a singleresidence (EPA, 1989). For a child, ATSDR used a 6-year exposure duration.

ATSDR's evaluation of potential arsenic and manganese exposures, the only contaminants ofconcern in drinking water are presented below.

Arsenic

Exposure to the detected levels of arsenic in Grove Pond well water is not expected to result inadverse health effects.

Arsenic was detected in the inactive Grove Ponds wells at concentrations above ATSDR'scomparison value (cancer risk evaluation guide [CREG]) but below EPA's MCL of 50 ppb. AsTable C-1 indicates, an adult who may have consumed the maximum detected concentration ofGrove Pond well water in the past would have received a dose of 0.0009 milligram per kilogram perday (mg/kg/day) of arsenic. A child's dose was estimated as 0.003 mg/kg/day. Because theestimated doses are slightly higher than the MRL and RfD of 0.0003 mg/kg/day, ATSDR reviewedthe scientific literature on arsenic to further evaluate the health significance of these estimated doses.Nonetheless, no one in Ayer is expected to have used water containing the highest levels of arsenicfor the length of time used to estimate these exposure doses. By blending well water with SpectaclePond well water, the Ayer Department of Public Works was able to reduce the arsenicconcentrations and delivered safe drinking water to consumers.

At low level exposures, arsenic compounds are detoxified in the body--that is, changed into lessharmful forms--and then excreted in the urine. At higher level exposures, our bodies capacity todetoxify arsenic may be exceeded. When this happens, blood levels of arsenic increase and adversehealth effects may occur. Saturation of our bodies detoxification mechanism may explain noncancerand cancer arsenic effects exhibiting a threshold, or a minimal effective dose that may result inhealth effects.

The lowest observed levels at which adverse effects, such as skin and gastrointestinal effects, havebeen reported range from 0.014 to 0.05 mg/kg/day in humans drinking arsenic-contaminated waterfor up to 45 years (Tseng et al., 1968; Tseng, 1977). Thus, the estimated exposure dose (0.0009mg/kg/day) for adults who consumed Grove Pond well water is almost 16 times lower than thelowest arsenic dose reported to cause health effects, while the exposure dose for a child (0.003mg/kg/day) is almost five times lower than that literature-based value.

Regarding possible cancer effects, note that ATSDR's CREG is simply a screening value and setvery low based on the conservative assumptions that no "threshold" exists. As mentioned above,people can tolerate certain levels of arsenic. Therefore, just because arsenic concentrations arehigher than the CREG does not mean that people drinking water at those levels from the Grove Pondwells are at increased risk of developing cancer. ATSDR reviewed the available scientific literatureto further evaluate the likelihood of cancer effects.

ATSDR looked more closely at the Taiwanese drinking water study from which scientists reportedan association between arsenic and skin cancer. In this study, the lowest exposure levels associatedwith the onset of cancer (skin) were observed in people drinking water containing 170 to 800 ppbarsenic over a 45-year exposure period (Tseng et al., 1968; Tseng, 1977). Although the studydemonstrated an association between arsenic in drinking water and skin cancer, the study failed toaccount for a number of complicating factors, including exposure to other nonwater sources ofarsenic, genetic susceptibility to arsenic, and poor nutritional status of the exposed population.Furthermore, arsenic exposure may have been underestimated in the study, possibly leading to anoverestimation of the actual risk. These uncertainties may limit the study's usefulness in evaluatingcancer risk for residents drinking water containing arsenic in Ayer. It appears from these data,however, that arsenic levels shown to cause cancer in humans drinking contaminated water aremuch higher than arsenic levels detected in Grove Pond wells. Therefore, even if exposure did occurin the Ayer area over an extended period, it is unlikely that the level of exposure would lead tocancer.

Manganese

Exposure to the detected levels of manganese in Grove Pond well water is not likely to result inadverse health effects.

The highest concentrations of manganese detected in untreated Grove Pond well water (1900 ppb) were above ATSDR's health-based comparison value. Manganese is a naturally occurring element that is essential for normal functioning of the human body. Toxicity in humans has been associated with both deficiencies and excess intakes of manganese. Determination of safe and adequate intake of manganese is difficult because there are several factors, both environmental and biological, that greatly influence an individual's response to manganese (ATSDR, 1997a).

There are many reports of human toxicity from exposure to manganese by inhalation; however,ingested manganese has rarely been associated with toxicity (ATSDR, 1997). Therefore, whenevaluating potential public health impacts most scientists focus on what is known to be a safe oralintake for the general population. The National Research Council has established "estimated safeand adequate daily dietary intakes" (ESADDIs) for manganese. The ESAADIs for manganese are0.3 to 2.0 mg/day for children less than 6 years and 2 to 5 mg/day for adolescents (more than 11years) and adults (NRC, 1989). The World Health Organization estimates an average dailyconsumption of manganese in adult diets range from 2 to 9 mg/day and an intake of 8 to 9 mg/day is"perfectly safe."

Absorption of manganese from the stomach is slow and incomplete. Only a small fraction (up to5%) of ingested manganese, either from diet or water, is absorbed into the body (ATSDR, 1997). Absorption and retention of manganese varies by individual and is influenced by diet. Highermanganese intakes are associated with diets high in whole grain cereals, nuts, leafy vegetables, andtea. Persons with a vegetarian diet or high dietary levels of calcium, phosphorus, or other metalsmay have decreased absorption of manganese from the stomach (Ellenhorn and Barceloux, 1988).

Epidemiologic studies suggest that ingesting water containing high concentrations of manganesemay be associated with neurological problems resembling Parkinson's disease (Kawamura et al.,1941; Goldsmith et al., 1990; Kondakis et al., 1989). One epidemiologic study investigated theeffects in humans of exposure to excessive amounts of manganese (28,000 ppb) in drinking water(Kawamura et al., 1941). Symptoms reported included lethargy, muscle problems, and mentaldisturbances. Most symptoms were observed in the elderly, while children appeared to beunaffected. The levels associated with these symptoms are approximately 15 times higher than themaximum manganese concentration detected in the Grove Pond wells. Results from these studiessuggest that environmental exposure to manganese may be of health concern; however, there are anumber of limitations to these studies, including uncertainty about environmental exposure levels,dietary sources of manganese, and whether exposure occurred to manganese alone or to other agentsas well, that make this conclusion uncertain.

Considerably more data are available on the adverse effects of manganese ingestion in animals. Aswith humans, neurological toxicity is the primary effect of manganese ingestion; however, only afew studies report adverse effects, including neurochemical changes in the brain, muscle weakness,and rigidity of limbs following oral administration of manganese (ATSDR, 1997). The levels ofmanganese required to produce these effects in animals are higher than estimated for personsingesting water from the Grove Pond well despite the fact that very conservative assumptions wereused to estimate the human exposure doses.

There is some concern by scientists that infants may be at increased risk of toxicity because theyretain a higher percentage of ingested manganese than adults due to greater uptake from the stomachand less ability to excrete manganese from the body. Additional concern for formula-fed infants hasbeen expressed because manganese levels may be elevated in formula and formula made withcontaminated tap water may contain higher levels of manganese than in human milk. However,there are no reports of manganese toxicity reported for infants (ATSDR, 1997). Elevated levels ofmanganese have been found in hair learning disabled children compared to normal children;however, no causal relationship was established for learning disabilities and manganese intakebecause information was lacking about how exposure occurred and whether it involved other agentssuch as lead (Collipp et al., 1983; Pihl and Parkes, 1977).

Using maximum concentrations detected in untreated well water and other conservative assumptionsabout exposure, ATSDR estimated that an adult who drank 2 liters and a child who drank 1 liter ofGrove Pond well water daily in the past might have received a dose of manganese up to 0.05mg/kg/day (3.5 mg/day) and 0.2 mg/kg/day (2 mg/day), respectively (see Table C-1). The doses fallwithin the range of concentrations generally considered to be "safe" dietary intakes and are lowerthan levels associated with adverse health effects in animal and human studies. Although there isconcern that infants may be more sensitive than adults to manganese, there is no scientific datasupporting increased toxicity from manganese in infants. More importantly, it is unlikely thatpersons were ever exposed to maximum concentrations of manganese in the Grove Pond wellbecause water from this well was blended with uncontaminated water prior to distribution tohouseholds. Also, levels of manganese in the Grove Pond well fluctuated over time and weregenerally much lower than maximum levels while the well was used for drinking water.

Estimated Exposure Doses From Contact With Grove Pond and Plow Shop Pond Sediment

ATSDR determined that metal concentrations measured in Grove Pond and Plow Shop Pond donot indicate a public health hazard.

In evaluating whether exposure to contaminants in the sediment may be related to adverse health effects, if any, ATSDR estimated exposure doses for adults and children contacting sediment containing the highest measured contaminant levels detected at either Grove Pond and Plow Shop Pond. Because children are known to play at Pirone Park along Grove Pond, ATSDR also evaluated exposure to sediment containing the highest levels of sediment along the shoreline of Pirone Park. (9) To estimate the extent to which people might be exposed to contaminants, ATSDR used "conservative" assumptions about possible human exposure and the associated health effects. ATSDR assumed that an adult or child contacted the most contaminated found anywhere at Grove Pond or Plow Shop Pond and the most contaminated sediment at Pirone Park while wading. ATSDR also used higher values than actually expected on how often people contacted the sediment. These assumptions allow ATSDR to estimate the highest possible exposure dose and evaluate the corresponding health effects. Although ATSDR does not expect that most people at the park were exposed to the highest levels of contamination, the "conservative" estimates are used to protect public health.

ATSDR used the following equation to estimate human exposure doses for dermal contact with sediment:

Estimated exposure dose equals Conc. times CF times SA times ABS times AF times EF times ED divided by BW times AT

where:
Conc. = Maximum contaminant concentration in the sediment (ppm)
CF = Conversion factor: 10-6
SA = Skin surface area available for contact (cm2/event):
-For exposure to feet only: adult male (M) = 1,310 cm2 and child = 334 cm2 (EPA, 1995a)
ABS = Absorption factor= 1% for dermal exposure to inorganic compounds (EPA, 1995a)
AF = Skin to soil adherence factor = 0.6 mg/cm2-event (EPA, 1992)
EF = Exposure frequency, or number of exposure events per year of exposure:
1 event/day x 7 days/week x 20 weeks/year or 140 events per year
ED = Exposure duration, or the duration over which exposure occurs: adult = 30 years; child = 6 years
BW = Body weight (kg): adult = 70 kg (154 pounds); child = 10 kg (22 pounds)
AT = Averaging time, or the time period over which cumulative exposures are averaged: 30 years x 365 days/year or 6 years x 365 days/year for noncancer effects; 70 years x 365 days/year for cancer effects

Assumptions for Estimating Human Exposure Dose

  • Absorbed doses were estimated based on the amount of contaminant expected to beabsorbed into the body through the skin. The ABS-dermal values used represent thepercent of the contaminant concentration contacted that is expected to pass throughthe skin.

  • The surface skin area (SA) available for contact per exposure event was assumed tobe the 50th percentile values for feet for adult males and children (2 to 3 years ofage) (EPA, 1995a).

  • The amount of sediment adherence to skin (the adherence factor, AF) per exposureevent was assumed to be 0.6 mg/cm2, the midpoint of the range recommended byEPA for dermal exposure to soil (EPA, 1992).

  • ATSDR reviewed local climatologic data to estimate the period of seasonal activity.ATSDR used a 20-week period--or the length of time average air temperatures meetor exceed 70 degrees--to approximate this period (NOAA, 1997).

Determination of the Potential for Adverse Human Health Effects

As Table C-2 indicates, the exposure doses estimated by ATSDR for dermal contact with sedimentcontaining arsenic or cadmium by adults and children were considerably lower than the MRL orRfD. Therefore, noncancer effect associated with these metals are not expected to occur. Althoughno health-based guidelines (MRL or RfD) currently exist for either chromium or mercury(inorganic), ATSDR believes that exposure to sediment containing the detected concentrations ofthese chemicals is likewise unlikely to result in harmful effects for visitors of either pond. Estimatedexposure doses for both chromium and mercury, based on the maximum detected levels in sediment,are significantly lower than those shown to result in harmful effects in occupational and animalstudies. In fact, the estimated doses for a child are more than 2 to 3 orders of magnitude lower thanthe lowest levels linked with adverse health effects in humans exposed to either chemical (ATSDR,1997b; 1998b).

Because arsenic is classified as a carcinogen, ATSDR estimated the lifetime cancer risk from dermalcontact with sediment containing the maximum concentration of this chemical. Based on theestimated cancer risks presented in Table C-3, ATSDR does not expect that contact with sedimentcontaining arsenic will result in an increased likelihood of developing cancer.

Estimated Exposure Doses for Ingestion of Fish

ATSDR used the following equation to estimate exposure doses for ingestion of Grove Pond andPlow Shop Pond fish:

Estimated exposure dose equals Conc. times IR times FI times EF times ED divided by BW times AT

where:
Conc. = Maximum concentration in fish (mg/kg)
IR = Ingestion rate: 0.0065 kg/day (approximately one 8-ounce meal per month), average consumption of fish and shellfish from estuarine and freshwater by the general U.S. population (EPA, 1989). Because a child likely eats smaller fish meals, ATSDR assumed that a child eats a one 4-ounce meal per month.
FI = Fraction ingested from contaminant source (assumed 100%)
EF = Exposure frequency, or number of exposure events: 365 days per year
ED = Exposure duration, or the duration over which exposure occurs: adult = 30 years; child = 6 years
BW = Body weight (kg): adult = 70 kg (154 pounds); child = 10 kg (22 pounds)
AT = Averaging time, or the time period over which cumulative exposures are averaged: 30 years x 365 days/year or 6 years x 365 days/year for noncancer effects; 70 years x 365 days/year for cancer effects

Determination of Potential for Adverse Human Health Effects

Using maximum detected concentrations and other conservative assumptions about exposure, thedoses estimated for ingestion of fish containing either arsenic, cadmium, manganese, selenium, andzinc are lower or just slightly higher than the corresponding MRL or RfD (see Table C-4). Theestimated dose for a child exposed to mercury exceeds the MRL, but only by a factor of two.Conservative assumptions (e.g., maximum concentration) allow ATSDR to estimate the highestpossible exposure dose, even though ATSDR does not expect that most people were exposed to thehighest levels each time they ate fish. Based on these estimates, even when considering the highestlevels detected in fish, exposures are very unlikely to lead to noncancer effects.

Because arsenic is classified as a human carcinogen, ATSDR estimated the lifetime cancer riskassociated with consumption of fish containing the highest detected concentration of arsenic andusing very conservative assumptions about exposure. The cancer risk was approximately 8 x 10-5, or8 new cancer cases in 100,000 exposed persons (see Table C-5). Therefore, ATSDR does not expectthat ingestion of fish containing arsenic will result in an increased likelihood of developing cancer.

Sources:

Agency for Toxic Substances and Disease Registry (ATSDR). 1997a. Agency for Toxic Substancesand Disease Registry. U.S. Department of Health and Human Services. Toxicological Profile forManganese. September 1997 (Update-Draft).

ATSDR. 1997a. Agency for Toxic Substances and Disease Registry. U.S. Department of Health andHuman Services. Toxicological Profile for Mercury. August 1997 (Update).

ATSDR. 1998a. Agency for Toxic Substances and Disease Registry. U.S. Department of Health andHuman Services. Toxicological Profile for Arsenic. April 1998 (Update).

ATSDR. 1998b. Agency for Toxic Substances and Disease Registry. U.S. Department of Healthand Human Services. Toxicological Profile for Chromium. August 1998 (Update).

Collipp, P.J., Chen, S.Y, and Maitinsky, S. 1983. Manganese in infant formulas and learningdisability. Ann. Nutr. Metab. 27:488-494.

Ellenhorn M. J. and D.G. Barceloux. 1988. Medical toxicology: Diagnosis and treatment of humanpoisoning. New York, NY:Elsevier, 1047-1048.

Environmental Protection Agency (EPA). 1989. Risk assessment guidance for Superfund. Volume1. Human health evaluation manual (part A). U.S. Environmental Protection Agency. EPA/540/1-89-001. December 1989.

EPA. 1992. Dermal Exposure Assessment: Principles and Applications. Office of Health andEnvironmental Assessment. INTERIM Report. 1992.

EPA. 1995a. Assessing Dermal Exposure. Region III Technical Guidance Manual Risk Assessment.Office of Superfund Programs. December 1995.

EPA. 1995b. Exposure Factors Handbook-Final Report. Office of Health and EnvironmentalAssessment. 1995.

Goldsmith J., Herishanu, Y., Ababanel J., et al. 1990. Clustering of Parkinson's disease points toenvironmental etiology. Arch. Environ. Health. 44:88-94 (As cited in ATSDR's toxicologicalprofile for manganese).

IRIS. 199. EPA's Integrated Risk Information System. National Library of Medicine.

Kawamura, R. Ikuta, H., Fukuzum1, S. et al. 1941. Intoxication by manganese in well water.Kitasato Arch Exp Med. 18:145-171. (As cited in IRIS, 1997).

Kondakis, X.G., Makris, N., Leotsinidis, M., et al. 1989. Possible health effects of high manganeseconcentrations in drinking water. Arch. Environ. Health. 44:175-178. (As cited in ATSDR, 1997).

Marcus, W.L. and A.S. Rispin. 1988. Threshold carcinogenicity using arsenic as an example. In:Advances in Modern Toxicology. Vol. XV. Risk Assessment and Risk Management of Industrialand Environmental Chemicals. Princeton Scientific Publishing, Co.1988.

NOAA. 1997. National Oceanic and Atmospheric Administration. Monthly summary of localclimatological data. National Climatic Data Center. Asheville, NC.

NRC. 1989. Recommended dietary allowances. Washington, DC: National Research Council.Tenth Edition, 231-235.

Stohrer, G. 1991. Arsenic: Opportunity for risk assessment. Archives of Toxicology. Vol. 65. 1991.

Tseng, W.P., Chu, H.M., How, S.W., et al. 1968. Prevalence of skin cancer in an endemic are ofchronic arsenicism in Taiwan. J. Natl Cancer Inst. 40:452-462 (As cited in ATSDR toxicologicalprofile for arsenic).

Tseng, W.P. 1977. Effects and dose-response relationship of skin cancer and blackfoot disease witharsenic. Environ Health Perspect. 19:109-119 (As cited in ATSDR toxicological profile for arsenic).

TABLE C-1.

Estimated Exposure Doses--Noncancer Effects Ingestion of Grove Pond Well Water in the Past 1
Contaminant Maximum Detected Contaminant Concentration (ppb) Estimated Exposure Dose (mg/kg/day)2 Health Guideline Chronic Oral (mg/kg/day) Basis for Health Guideline
Adult Child
Arsenic 30 0.0009 0.003 0.0003 MRL/RfD
Manganese 1,900 0.05 0.2 0.07 ATSDR Interim Guideline

1 ATSDR estimated past exposure doses assuming that an individual was exposed to the highest concentration of manganese and arsenic in Grove Pond well water in thepast. No one is likely to be exposed to these concentrations today because regular sampling of well water, together with effective treatment, now ensures that the levels ofthese metals are greatly reduced in water distributed to Ayer residents.

2

Conc. = Maximum contaminant concentration in the private well (ppb)
CF = Conversion factor to convert ppb to ppm (1/1000)
IR = Ingestion rate: adult = 2 liters per day; child = 1 liter per day
EF = Exposure frequency or the number of exposure events (1 event x 7 days x 52 weeks or 365 days per year)
ED = Exposure duration or the duration over which exposure occurs: adults = 30 years; child = 6 years
BW = Body weight: adult = 70 kg (154 pounds); child = 10 kg (22 pounds)
AT = Average time or the period over which cumulative exposures are averaged (6 or 30 years x 365 days)

Key: ppb = parts per billion; mg/kg/day=milligrams contaminant per kilogram body weight per day; MRL = Minimal Risk Level; RfD= Reference Dose.

TABLE C-2.

Estimated Exposure Doses--Noncancer Effects Dermal Contact with Grove Pond and Plow Shop Pond Sediment
Contaminant Grove Pond/Plow Shop Pond Pirone Park Health Guideline Chronic Oral (mg/kg/day) Basis for Health Guideline
Maximum Detected Contaminant Conc.
(ppm)
Adult Estimated Exposure Dose (mg/kg/day) Child Estimated Exposure Dose (mg/kg/day) Maximum Detected Contaminant Conc.
(ppm)
Adult Estimated Exposure Dose (mg/kg/day) Child Estimated Exposure Dose (mg/kg/day)
Arsenic 3,200 0.00001 0.0003 110 0.000005 0.000009 0.0003 MRL/RfD
Cadmium 110 0.000005 0.000009 23.3 0.000001 0.000002 0.0002 MRL
Chromium 49,800 0.002 0.004 2,680 0.0001 0.0002 no value  
Mercury 250 0.00001 0.00002 2.18 0.00000009 0.0000002 no value  

1 No MRL or RfD currently exists for inorganic mercury, the form most likely present in sediment.

Key: ppb=parts per billion; mg/kg/day=milligrams contaminant per kilogram body weight per day; MRL=minimal risk level; RfD=reference dose; ma = not available.

TABLE C-3.

Estimated Exposure Doses--Cancer Effects Dermal Contact with Grove Pond and Plow Shop Pond Sediment
Location Maximum Detected Contaminant Concentration (ppm) Estimated Exposure Dose - Cancer
(mg/kg/day)
CPF Lifetime Cancer Risk 1
Arsenic - at Pirone Park 110 0.000002 1.5 3 x 10-6
Arsenic - highest detected concentration in either pond 3,200 0.00006 1.5 9 x 10--6

1 Lifetime Cancer Risk = estimated dose (cancer) x CPF.

Key: CPF = cancer potency factor; ppb=parts per billion; mg/kg/day=milligrams contaminant per kilogram body weight per day.

TABLE C-4.

Estimated Exposure Doses--Noncancer Effects Ingestion of Fish
Contaminant Maximum Detected Contaminant Concentration (ppm) Estimated Exposure Dose (mg/kg/day) Health Guideline Chronic Oral
(mg/kg/day)
Basis for Health Guideline
Adult Child
Arsenic 1.3 0.0001 0.00041 0.0003 MRL/RfD
Cadmium 0.88 0.00008 0.00031 0.0002 MRL
Manganese 94.7 0.009 0.03 0.14 RfD
Mercury 4 0.0004 0.0011 0.00052 MRL
Selenium 0.67 0.00006 0.0004 0.005 MRL
Zinc 29.6 0.003 0.02 0.3 MRL

1 Because of the conservative assumptions used in estimating the exposure doses, the slightly higher values do not indicate a health concern.

2 The MRL for methylmercury is currently under review.

Key: ppm=parts per million; mg/kg/day=milligrams contaminant per kilogram body weight per day; MRL=minimal risk level; RfD=reference dose.

TABLE C-5.

Estimated Exposure Doses--Cancer Effects Ingestion of Fish
Contaminant Maximum Detected Contaminant Concentration (ppm) Estimated Exposure Dose - Cancer
(mg/kg/day)
CPF Lifetime Cancer Risk 1
Arsenic 1.3 0.00005 1.5 8 x 10--5

1 Lifetime Cancer Risk = estimated dose (cancer) x CPF.

Key: CPF = cancer potency factor; ppb=parts per billion; mg/kg/day=milligrams contaminant per kilogram body weight per day.


APPENDIX D: RESPONSES TO PUBLIC COMMENTS

The Agency for Toxic Substances and Disease Registry (ATSDR) received the following commentsand questions from community members regarding the draft public health assessment (PHA) for theFort Devens site. Each comment is followed by a response from ATSDR. To facilitate the response,similar comments were grouped when possible. For comments that question the validity ofstatements made in the PHA, ATSDR verified or corrected the statements.

ATSDR issued a draft PHA for public comment on June 3, 1999, and organized communitymeetings during the public comment period, June 3, 1999, to September 13, 1999. Prior to thepublic comment period, ATSDR solicited community health concerns and received public commentson two health consultations that evaluated drinking water, sediment, and fish contamination in thecommunities adjacent to the Fort Devens site.

Groundwater/Drinking Water Comments
1. Comment: Past arsenic levels in Ayer drinking water were close to the current maximum contamination level (MCL). There is concern that the MCL for arsenic is not protective enough. ATSDR should reassess past exposure to arsenic in drinking water in light of current information on health effects of arsenic exposure.
  Response:

Because of lack of demonstrated need, the absence of extensive regulatory requirements, and limitations in analytical methods, limited historical water quality data exist prior to 1993 when the Ayer Grove Pond wells were closed. Available data suggest that concentrations in the Grove Pond wells measured below 20 parts per billion (ppb), with the exception of a few detects around 30 ppb. The arsenic concentrations neither fluctuated greatly nor exceeded U.S. Environmental Protection Agency's (EPA) current MCL of 50 ppb. Since 1978, Grove Pond well water has been blended with water from Spectacle Pond wells prior to being distributed to customers. This process would have greatly diluted arsenic concentrations in water.

Even though the reported concentrations never exceeded EPA's current MCL, ATSDR further evaluated the potential health consequences of drinking Grove Pond well water containing arsenic. This evaluation is described in the "Evaluation of the Groundwater Exposure Pathways" section of the PHA. As described, ATSDR conservatively assumed that an individual drank water containing the highest detected level of arsenic (30 ppb) over a 30-year time span. This would account for any exposure to arsenic through drinking water that might have occurred before blending and treatment began. ATSDR compared the estimated doses (based on a conservative hypothetical exposure scenario) to doses in animal and epidemiologic studies shown to result in adverse health effects. On the basis of this evaluation, ATSDR found that people who drank water originating from the Grove Pond wells were not likely to develop arsenic-related health effects.

Also of note, at EPA's request, a special subcommittee of the National Research Council (NRC) has reviewed the arsenic toxicity data base and evaluated the scientific basis of EPA's risk assessment for arsenic in drinking water (NRC, 1999). The subcommittee concluded that there is sufficient evidence to suggest that arsenic (at levels of several hundred parts per billion) causes adverse health effects, including cancer--but those levels are much higher than the levels found in the Ayer Grove Pond wells. Scientists are still studying the likelihood of health effects, if any, from low level exposure to arsenic in drinking water. Sufficient evidence exists, however, to suggest that arsenic is tolerated at low doses similar to those estimated for the Grove Ponds wells.

2. Comment: ATSDR should work with EPA and local governments in providing information to private well owners in this region that their wells may contain naturally-occurring arsenic at potentially unsafe levels and that well testing and treatment systems are available for individual home owners.
  Response: Arsenic is a natural component of the earth's crust and releases to water by natural weathering processes, so it is not unusual to find arsenic in groundwater. Private well users can obtain current information about naturally occurring, or background, groundwater concentrations for their town from the Massachusetts Department of Environmental Protection (MADEP), Division of Water Supply, at 508 792-7653. If you are concerned about the quality of your private drinking water, you can arrange to have your well water tested by one of a number of reputable testing laboratories. (In general, there is no free testing services for Massachusetts private well owners.) The MADEP can provide you with a list of MADEP certified laboratories by calling the MADEP's Wall Experiment Station at 978-682-5237. MADEP can also provide you with guidance on choosing a treatment system that will reduce arsenic concentrations in drinking water.
3. Comment: Have private wells in the area around Fort Devens been sampled for a spectrum of contaminants that may have migrated from Fort Devens property?
  Response:

The Army, with state and EPA oversight, has closely monitored contaminated groundwater through several rounds of sampling of strategically placed groundwater wells. Over the course of these investigations, no contaminants associated with the Fort Devens site have been found beyond the western, eastern, and southern boundaries of the site. No additional monitoring of private wells located beyond these site boundaries has been done or is deemed necessary because groundwater contamination has been shown to be fully contained within these boundaries.

Some contamination has been detected in groundwater migrating north of and upgradient to Area of Concern (AOC) 50. Contamination has also been detected on private industrial property, the Merrimack Warehouse, beyond the Fort Devens northern boundary. Because the warehouse relies on public water, no exposures to contaminated groundwater have occurred at this property. Through extensive routine monitoring, no contamination has been detected beyond the railroad tracks north of the warehouse nor has contamination reached areas where private residences are located. The Army, state, and EPA continue to closely monitor this area of contamination.

Grove Pond and Plow Shop Pond Comments
4. Comment: ATSDR states that there is no likelihood of harmful exposures associated with using the ponds or consuming fish from the ponds. If so, why does ATSDR continue to support an advisory at Grove Pond and Plow Shop Pond?
  Response: ATSDR continues to support the advisory as a precautionary measure to raise public awareness of contaminants in sediment and in fish. The advisory at Grove Pond and Plow Shop Pond was initially issued based on concerns about elevated contaminant concentrations in sediment in the ponds. There were also concerns that contaminant concentrations might be elevated in pond fish. During the course of the PHA process, ATSDR evaluated surface water, sediment, and fish tissue analytical data (which have become available since the issuance of the advisory) from a public health perspective. Based on the evaluation, ATSDR considers the potential for past harmful exposures to be low, even though elevated concentrations of certain contaminants were measured in the sediment and in fish. Because contamination continues to be detected in pond sediment and because fish may continue to uptake certain contaminants, ATSDR believes that people who follow the advisory are taking the appropriate precautions to help reduce their chances of exposure to contaminants. In the future if the contaminant levels decline, ATSDR can work with the other agencies to further evaluate the necessity of retaining the advisory.
5. Comment: Why did ATSDR use the Food and Drug Administration (FDA) guideline for mercury in fish as a chronic health guideline?
  Response: ATSDR used the FDA action level of 1 part per million (ppm) as a screening value to determine the elevated mercury levels in fish required further evaluation. The FDA promulgated the 1 ppm action level for commercial fish; however, many state health departments use the FDA action level as a basis for issuing freshwater fish consumption advisories. We want to emphasize that the FDA action level was used strictly for screening and that the value was not used in lieu of a chronic health guideline. Because the mercury concentrations in certain fish exceeded the screening value of 1 ppm, ATSDR further evaluated the possible chronic or long-term health consequences of consuming fish containing mercury at the highest detected levels. ATSDR describes its evaluation process (which included developing an exposure dose, comparing the dose to ATSDR's new minimal risk level (MRL) for methylmercury, and reviewing the current toxicologic literature) in the "Evaluation of the Food Chain Pathway" section of the PHA.(10) On the basis of this evaluation, ATSDR concluded that fish consumers were not likely to develop any harmful health effects associated with mercury.
6. Comment: ATSDR's analysis finds no public health hazard with contacting pond sediment, assuming exposure to Pirone Park sediment occurs for 140 days per year. Is there risk associated with other types of exposures, such as contact to higher levels of sediment contamination over a shorter time?
  Response:

ATSDR evaluated exposure to the maximum detected levels of contaminants in Pirone Park sediment in response to community concern about exposures occurring in this public area. Since its initial assessment, ATSDR conservatively evaluated exposure to the highest contaminant levels detected in the pond (which are located primarily at the cove near the former tannery). ATSDR added this evaluation to the "Evaluation of Surface Water/Sediment Pathway" section of the PHA. ATSDR found that even under this worst-case hypothetical scenario, an individual was not likely to experience harmful effects associated with the contaminants in sediment.

The reader should be aware that the Massachusetts Department of Environmental Protection (MADEP) recently completed another round of sediment sampling at Grove Pond. The location of the samples were selected with the assistance of community members. The preliminary results suggest that the highest contaminant levels are situated at the surface of the sediment and that the contaminants do not appear to be contributing to elevated surface water concentrations. When the final results of the sampling become available, ATSDR will review these data and, if necessary, modify its conclusions in the PHA and recommend appropriate actions as needed to protect public health.

7. Comment: Exposures from skin contact with mercury and chromium in pond sediments were not quantified in Table C-2.
  Response: We want to reassure the reader that ATSDR evaluated the long-term health consequence of skin contact or dermal exposure to these metals found in sediment. As with other metals exceeding comparison values (CVs), ATSDR evaluated dermal exposure to mercury (as inorganic mercury in sediment) and chromium at the concentrations found in pond sediment. As you will note, Table C-2 presents the estimated exposure doses for mercury and chromium. Because a chronic health guideline does not exist for either mercury or chromium, ATSDR could not compare the estimated dose to a guideline (or include a guideline in the table). In the absence of a chronic guideline, ATSDR compared the estimated doses (for both a child and an adult) to the lowest observed adverse effect level reported in occupational and animal studies for mercury (inorganic) and chromium. As noted on page C-8 of the PHA, the estimated exposure doses are more than 2 to 3 times lower than the lowest levels linked with adverse health effects in humans. On the basis of this finding, ATSDR concludes that contact with sediment is unlikely to cause harmful effects.
8. Comment: What might happen if the town of Ayer's Park and Recreation Department pursues its proposal to pump untreated water from Grove Pond onto the fields at Pirone Park for irrigation purposes?
  Response: Monitoring data for surface water samples collected to date suggest that only very low levels of contaminants (such as metals) exist in the untreated water of Grove Pond. With such low concentrations present in the surface water, we would not expect to see any appreciable accumulation of contaminants on the ground surface or in soil irrigated with this water. Furthermore, in the event accumulation occurred, grass or other vegetative cover in the areas to be irrigated would minimize direct contact with surface soils containing any potentially accumulated contaminants (such as metals). Based on these factors, ATSDR does not expect any harmful exposure to result from using Grove Pond water for irrigation.
9. Comment: I am concerned about exposure to chemicals in non-public areas of Grove Pond and Plow Shop Pond, specifically in or near the tannery cove area in the northwest corner of Grove Pond. Did ATSDR consider non-public areas of the Grove Pond shoreline in its evaluation of the sediment contamination?
  Response: In its initial evaluation, ATSDR evaluated potential exposure to contaminant levels measured in sediment at Pirone Park in response to community concern (People of Ayer Concerned About the Environment [PACE]) about children wading along the shore in this public area. As noted in the PHA, wading along the shoreline of the park is safe for children. There is evidence that non-public areas of the pond are accessible, though use of these areas is likely infrequent and brief (such as trespasser access). In addressing exposure in non-public areas, ATSDR evaluated hazards associated with the highest detected levels of contaminants found in sediment near the former tannery. As noted in Comment/Response 6, no harmful exposures are expected even for people who choose to wade along non-public areas of the pond.
Other Comments
10. Comment: How can ATSDR make the determination that air inside the former Devens Elementary School posed no health hazard without contacting former pupils and teachers?
  Response: ATSDR did not contact former occupants of the school because our evaluation suggests that no harmful exposures likely occurred in the past. In assessing health threats, ATSDR first examines the possible exposure pathways related to a site. If through this initial screening process ATSDR determines that a completed exposure pathway to environmental contaminants poses a potential public health hazard, ATSDR may contact potentially exposed individuals to gather health outcome data. In its evaluation of possible exposures at the school, ATSDR relied on the sampling data (collected after the release) that exist for air inside the school, along with information gathered from other sources. The other information included discussions with EPA and MADEP about site conditions that existed at the time of the release, information on the contaminants associated with the release, and information on how these contaminants react in the environment. Together, this information suggests that former occupants of the school were not likely to have been exposed to harmful levels of airborne contaminants. For more information, please see the "Evaluation of the Indoor Air Pathway" section of the PHA.
11. Comment: Some soil affected by the fuel leak still remains beneath the school. Can the contaminants in soil release into the indoor air of the school and cause health problems for future students and teachers?
  Response: Most of the soil (3,500 cubic yards) affected by the fuel oil release was removed in January 1998. A small amount of the affected soil remains beneath the school because removal of this soil could threaten the structural integrity of the school building. It is important to note that the remaining soil is neither accessible or expected to contribute to poor air quality inside the school. Sampling conducted in March 1998 found no evidence of harmful levels of airborne contaminants associated with the release. Before the school is reopened (September 2000), MassDevelopment will replace the oil-based heating system with a gas heating system and renovate the school's ventilation system.Therefore, there is no reason to suspect that air quality inside the school will pose a health concern for future occupants of the school.
12. Comment: ATSDR's evaluation process does not address the possibility of harmful effects of exposure to combined chemicals.
  Response: As a screening level evaluation, ATSDR compared contaminant concentrations detected in soil, groundwater, and surface water to media-specific CVs. ATSDR found most contaminants detected in completed or potential exposure pathways were at levels below CVs. These conservative CVs are generally 10 to 1,000 times lower than the levels known to result in adverse health effects, which is what makes them conservative screening values. If the individual contaminants detected at the site are present at levels far below those that result in health effects, ATSDR considers the combined exposure to all of the contaminants unlikely to pose a public health hazard.
13. Comment: I believe the town of Ayer population was too low for the unexpected increase in cancer cases to be observable above the background cancer incidence. ATSDR should reassess whether the Massachusetts Department of Public Health (MDPH) cancer data prove that there was no risk from drinking water containing arsenic in the past.
  Response:

It is true that we are more likely to observe fewer cancer cases in a smaller community like Ayer (over a short period of time) than we are for a larger community. However, statistically significant increases in cancer rates can be observed in large and small communities alike. In its evaluation of cancer rates in Ayer, MDPH looked at the incidence of cancer in the community over a long period of time (1982-1992) and compared this rate to what is expected based on age-adjusted rates for the state as a whole. The benefit of this approach is that we are more likely to see infrequently occurring cancers that might not be noted in small communities over a short period of time. Therefore, communities that might not be expected to have an increase in cancer cases in any given year can still be evaluated and meaningful results can be obtained. It should be noted that this type of evaluation does not allow for an analysis of whether exposures are associated with, or contribute to, excess levels of cancer in the area.

It is important to note that contaminants only pose a health concern if ingested, inhaled, or contacted at levels shown to cause adverse health effects. As noted, ATSDR reviewed environmental and toxicologic data to determined whether harmful exposures associated with Fort Devens have occurred or could occur in the future. Based on its evaluation, ATSDR found that Ayer residents likely experienced exposures that were much lower than those shown to cause adverse effects or increase their likelihood of cancer.

14. Comment: The North Post Waste Water Treatment Plant is out of compliance with its water pollution permit. Does this pose a public health hazard?
  Response: Operation of the North Post Waste Water Treatment Plant (WWTP) has not posed, nor is it posing, a public health hazard. The WWTP system was designed in the 1940s to remove solids from municipal waste and dispose of fluids via a rapid filtration bed, which allows treated water to recharge to the groundwater. Although Fort Devens did not hold a National Pollutant Discharge Elimination System permit under the Clean Water Act for the system, the WWTP was overseen by MADEP. According to MADEP, the system has never been out of compliance nor has it adversely affected the underlying groundwater. During basewide environmental investigations at Fort Devens, the three components of the system, WWTP, the infiltration beds, and the sludge drying beds, were evaluated for potential harmful releases to the environment. Based on these investigations, neither MADEP or EPA found evidence to suggest that past or present operations of or releases from the WWTP caused significant environmental contamination or posed a threat to human health. MADEP has issued a permit for an upgraded treatment system, which will include new technology for the treatment of fluids and renovated portions of the existing system. The design is about 90% complete and construction will begin following MADEP's approval of the final plan.



9. ATSDR initially evaluated exposure to sediment containing the highest levels of contaminants detected along the Grove Pond shoreline of Pirone Park. In response to comments received during the public comment period for the draft public health assessment (June 3, 1999), ATSDR has additionally assessed contact with the highest level of contaminants detected at either Grove Pond or Plow Shop Pond.
10. ATSDR has recently set a chronic MRL for methylmercury of 0.0003 mg/kg/day. The discussion in our PHA about methlymercury in fish has been modified slightly to reflect the new MRL, but our conclusions about exposure have not changed.



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