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The tables in this section list the environmental contaminants of concern. This concern is based on the comparison of contaminant levels detected on or near the site with those levels to which exposure has been associated with no adverse health effects. These comparison values include calculations from Reference Doses (RfDC) and EPA's Drinking Water Life Time Health Advisories (LTHA) which are values derived from animal and human studies for which non-cancer adverse health effects were investigated. Cancer Risk Evaluation Guides (CREGs) are used for compounds which are known or suspected to be carcinogenic based on either animal or human studies. CREG levels are those for which exposure is associated with an excess cancer risk of one in a million. It is important to note that the presence of hazardous contamination levels is not indicative that actual exposure to site-related contaminants is occurring. The likelihood of hazardous exposure and the subsequent health ramifications are disclosed later in this Public Health Assessment.

The data tables in this section include the following acronyms:

    -Polynuclear Aromatic Hydrocarbons
    -Contaminant not detected
    -Comparison value for compound in specific environmental media is not available
    -ATSDR Cancer Risk Evaluation Guide
    -Media concentration calculated from EPAs reference dose (RfD)
    -EPAs drinking water Lifetime Health Advisory
    -parts per million (milligrams per kilogram soil)
    -parts per billion (micrograms per liter of water)
    -Depth Below Land Surface

A. On-Site Contamination


Results of soil monitoring conducted in 1984, 1988, and 1989 are summarized in Table 1. Polynuclear Aromatic Hydrocarbons (PAH'S) are components of creosote. The highest levels of potentially carcinogenic PAH's in soils 6 inches below land surface (BLS) were detected near the abandoned storage tank farm, upgradient from the southern edge of the pond. Elevated PAH levels were also detected in soils 0-2 feet BLS immediately east of Kettle Pond, as well as in the area near the former lagoon and in the area at the southwest edge of Hocomonco Pond. PAH contamination was initially believed to be present in subsurface soils as far down as twenty feet below land surface (BLS). Further investigation of subsurface soils near Kettle Pond revealed PAH contamination at forty-five feet BLS. Raw creosote product was detected in subsurface soils between Hocomonco Pond and Kettle Pond as far down as 140 feet BLS. The highest measured levels of subsurface soil PAH contamination were detected 2.5 feet below the former tank storage area in 1988. Napthalene, which may also be a constituent of creosote is considered to be a PAH compound and was also found in site-associated soils. Arsenic is both a naturally occurring element as well as an environmental contaminant. This element was detected in soils sampled throughout the site.


The highest levels of on-site sediment contamination were detected in 1984 from sediment sampled from the center of Kettle Pond. Creosote compounds and arsenic comprised the majority of the contamination detected. The sediment from this area was monitored again in 1988 and contaminant levels detected had decreased. Arsenic and PAH's were also detected in sediments sampled from Hocomonco Pond (Table 2). Sediment sampled from middle of the sewer drain pipe that runs through the former lagoon area also demonstrated elevated levels when monitored in 1984 (Table 3).

    Ground Water

Elevated levels of benzene, PAHs and arsenic were detected in waters monitored from a well detected at the northern edge of Kettle Pond (Table 4). No contamination was detected in soils recovered during the development of this well. There was no other significant benzene, PAH or metal contamination detected in on-site ground water.

    Surface Water

Elevated levels of benzene, PAH's and arsenic were detected at the outfall of the storm drain running from the Smith Valve Parkway through the former lagoon into Hocomonco Pond. These levels subsided when monitored in 1990 but were still among the highest levels detected in on-site surface water. PAH contamination was also detected in surface waters monitored from Hocomonco Pond at the Otis Street culvert (Table 5).


Fish caught in Hocomonco Pond were monitored for PAH contamination and the results are presented in Table 6. The data presented in this table are the results of combined (or composite) five fillet samples for each species caught. The weight or size of each individual fish caught was not stated. Carcinogenic PAHs were detected in four of the five composite samples of fish caught from Hocomonco Pond.

B. Off-Site Contamination


Contaminated sediment was recovered from the discharge stream that drains Hocomonco Pond through the Otis Street culvert into the Assabet River. PAH contaminated surface sediments were detected as far as 1,900 feet east of the Otis Street culvert. This contamination was also detected as far down as four feet below the bed of the stream (Table 7).

For comparative purposes, background sediment levels of PAH's were determined by sampling sediments from streams distant to the site. The highest levels of carcinogenic PAHs (14.5 ppm) detected in off-site sediment were found in that sampled from Jordan Pond in Shrewsbury approximately eight miles west of the site. It is important to note that this contamination was not related to the site. The lowest levels of PAH's (.025 ppm) were detected approximately 1,000 feet north of Hocomonco Pond in a discharge storm drain flowing northerly away from the pond.


Soils (0-2 feet BLS) contaminated with PAH's were detected near a monitoring well approximately 25 feet south of the storm drain which flows to Hocomonco Pond (Table 8).

    Ground Water

The process wells west of the Smith Valve plant as well as the observational wells and the municipal well north of the pond were monitored for environmental contamination. No hazardous levels of volatile organic compounds (VOCs), PAHs or metals were detected in waters drawn from these wells. In addition, the Massachusetts Department of Environmental Protection has routinely monitored the municipal water supplies in the Commonwealth on a biannual basis for VOC contamination since 1987. No VOC levels have been detected in the Otis Street well during this period.

C. Quality Assurance and Control

The conclusions presented in this public health assessment are based on the data reviewed. The validity of the conclusions is dependent on the quality of the data provided.

D. Physical Hazards

In addition to the risk of drowning in the two surface water bodies on the site, trespassers are at risk of injury due to falling from the steep bluff on which the tank remnants are situated. These individuals may also risk puncture wounds from the metal remnants that were observed at the site.

E. Toxic Chemical Release Inventory (TRI) Data

To identify possible facilities that could contribute to the air, surface water and soil contamination at the Hocomonco Pond site, the Toxic Chemical Release Inventory (TRI) data base was searched. TRI is developed by the USEPA from the chemical release information provided by certain industries. No on-site releases of contaminants were reported. A summary of contaminants released by off-site industries are presented in Table 9.

The closest reported emission of these contaminants is approximately two miles from the site. These releases are not likely to impact the pathways discussed in the following section.


In this section, various transport means of environmental hazards from the contamination source to human receptor populations and means of human exposure are presented. To determine whether residents are exposed to contaminants migrating from the site, environmental and human components that lead to human exposure are evaluated. This pathways analysis consists of five elements: A source of contamination, transport through an environmental medium, a point of exposure, a route of exposure, and an exposed population. Completed pathways require that these five elements exist and indicate that exposure to site-related contaminants has occurred in the past, is currently occurring, or will occur in the future. Potential pathways require that at least one of the five elements is missing but could exist at some point in time. An exposure pathway can be eliminated if at least one of the five elements is missing and will never be present. Complete exposure pathways are summarized in Table 10. The presence of a complete exposure pathway, does not, however, necessarily mean that adverse health effects will occur or have occurred in the past as a result of such exposure. Potential exposure pathways are identified in Table 11.

The extent of public health risk depends not only on the opportunity for exposure but also on the toxicity of the contaminants and the dosages to which the receptor population is exposed. These two factors are discussed in the Public Health Implications section.

A. Completed Exposure Pathways

    Sediment - past and present

In 1976, a drainage system was placed between the newly constructed Smith Valve Parkway and Hocomonco Pond. Unknowingly these pipes, which were not sealed at their joints, were run underground through the former waste lagoon operated by the wood treatment company. As a result, creosote contamination leached from soils of the former lagoon and migrated through the system that eventually drained into Hocomonco Pond. Pond sediments were contaminated with PAHs at the discharge point of the drainage system.

Creosote wastes were also deposited in Kettle Pond immediately southeast of Hocomonco Pond. Kettle Pond is a small shallow surface water body that is charged by ground water flowing northerly into the pond. The pond discharges to ground water to the north, east, and west. PAH-contaminated sediment was detected at the southeast edge of Hocomonco Pond, north of Kettle Pond. It is not known whether this contamination in Hocomonco Pond is attributable to northward migration of PAHs through ground water flow between the two surface water bodies. The only point where PAH contamination was detected in on-site ground water was in that sampled from a well situated immediately north of Kettle Pond. PAHs, however, have a very low water solubility and tend to adhere strongly to soil and sediments.

The possibility that surface soil runoff from Kettle Pond toward the southeastern edge of Hocomonco Pond could contribute to the contamination detected at this point has also been considered. PAH contamination was detected in surface soils upgradient to the southeastern edge of Hocomonco Pond. These levels, however, were much less than those detected at the pond's southeastern edge.

Raw creosote product was detected in monitoring wells drilled between Kettle Pond and Hocomonco pond. This contamination is classified as a dense non-aqueous phase liquid (DNAPL). Since this contamination is heavier than water, it will settle to its lowest point. It is possible that creosote deposited in Kettle Pond migrated vertically through permeable sand and gravels. This contamination might then have moved laterally along the impermeable till layers or along the bedrock surface towards bedrock depressions situated between Hocomonco Pond and Kettle Pond.

PAH contaminated sediment was detected at the Otis Street culvert and the discharge stream that drains Hocomonco Pond. The pond accepts ground water and surface water drainage from both the north and south. The pond discharges to the stream which flows easterly and eventually drains into the Assabet River. Surface water movement could possibly carry contaminated sediments from the southeastern edge toward the discharge stream.

Hocomonco Pond and some sections of the discharge stream are accessible to pedestrian traffic. Evidence of fishing activities was noted at the pond and at a point 100 feet east of discharge point, indicating the possibility that dermal contact and inadvertent ingestion of contaminated sediment may be occurring. The contaminated sediment at the Otis Street culvert discharge point is for all practical purposes, inaccessible. The area is overgrown with brush and bramble decreasing the likelihood that individuals would fish from this point. It is also not likely that exposure to contaminated sediment in Kettle Pond is occurring via ingestion since these sediments are five feet below the water surface. Dermal contact with these sediments is also possible but not likely to be regularly occurring since the pond does not appear attractive for swimming or wading purposes.

Arsenic has been detected in sediments sampled throughout the pond. It is uncertain whether it was used in the wood treatment process. Arsenic is also known to be naturally present in soils, however the arsenic levels detected in pond sediments were higher than those detected in sediments which were considered to be background. Since it is not known if arsenic was used or discharged at the site, its origin and consequent migratory mechanisms cannot currently be defined. Individuals engaged in activities at Hocomonco Pond can be exposed to arsenic via dermal contact with contaminated sediments.

The probability of further exposure to PAH-contaminated sediments will be reduced upon completion of the remedial plan selected by USEPA in 1985 and modified in 1992. Migration of PAHs via the Smith Valve Parkway drainage system was halted when, in 1990, the storm drain was relocated. New conduits that diverted the flow of runoff were placed around the existing pipeline that ran through the former lagoon. The old pipeline was sealed and will be disconnected and disposed of in an on-site landfill when other remedial measures are implemented.

These measures include the dredging of the PAH contaminated sediments that were detected at the edge of Hocomonco Pond along its southern and eastern banks. The sediments from the discharge stream will also be dredged to a point approximately 600 feet east of Otis Street culvert. These sediments will be placed in the lined landfill situated on the site. This landfill will be capped with water impermeable material upon completion of sediment dredging and burial and will also contain a leachate collection system as specified by the Resource Conservation and Recovery Act (RCRA).

It was originally planned that Kettle Pond would also be dredged after a sufficient amount of ground water was removed. As previously stated, engineering studies determined the original plan to be infeasible. USEPA currently plans to dredge the pond to approximately five feet below land surface and deposit the dredgings in the proposed on-site landfill. The remainder of the subsurface PAH contamination will be handled in two ways. The raw creosote product believed to have settled in the bedrock valley between Hocomonco Pond and Kettle Pond, will be pumped from monitoring wells situated in the area. The saturated soil in the Kettle Pond area will be treated by injection of bacteria with the capability of breaking down these compounds to a nontoxic form. Nutrients and oxygen will be injected hydraulically upgradient to the contamination to aid in the process. It is uncertain, however, whether this innovative remedial technique can completely degrade subsurface PAHs to acceptable levels. If, after sufficient time has elapsed, bioremediation has been shown to be ineffective, these subsurface soils will be flushed with detergents and the contaminated waters generated in this process will be treated with activated charcoal.

In summary, the sediment exposure pathway is considered to be complete since PAHs have migrated from disposal areas such as the lagoon and possibly Kettle Pond to sediments in Hocomonco Pond and its discharge stream. Individuals who fish in Hocomonco Pond and its discharge stream constitute a population who are exposed to PAHs and arsenic via dermal contact with, and inadvertent ingestion of, contaminated sediments. This exposure is occurring in Hocomonco Pond at its southeastern edge and at the discharge point of the underground drainage system that once ran through the lagoon. Exposure to contaminated sediments is also occurring at the discharge stream approximately 100 feet east of the Otis street culvert. The dredging planned by EPA and MDEP will mitigate future exposure to these sediments.

    Biota-Past and Present

PAHs were detected in fish caught in Hocomonco Pond and fishing has been observed at the pond. The biota pathway is therefore considered to be complete and human exposure to PAHs is probably occurring via ingestion of contaminated fish. PAHs detected in sediments sampled from Hocomonco Pond are able to migrate through the food chain. These compounds ultimately accumulate in fish due to their high carbon content and fat-soluble properties. Removal of highly contaminated sediment from the pond may, in time, serve to reduce the PAH levels in fish. The time needed to achieve this end can not be currently determined. Future monitoring of aquatic organisms can enable health and environmental officials to determine whether removal of pond sediment contaminated with PAH's has enhanced their quality.

    Surface Water

Human exposure to contaminants detected in the surface waters of Hocomonco Pond is occurring via dermal contact. Swimming activities have been reported by local citizens but have not been observed by state or federal environmental officials. Individuals swimming in pond waters may be therefore exposed to surface water contaminants via ingestion or dermal contact. PAHs have varying water solubilities. Those large PAHs (those of high molecular weight), which are associated with increased risk of cancer development, have very low water solubilities and tend to adhere strongly to sediment and soils. Given these properties, only very low levels of heavy PAH compounds were detected in site surface waters. Those compounds of lower molecular weight such as napthalene which are not believed to be carcinogenic are relatively water soluble.

Benzene, which was detected in surface waters at the terminus of the Smith Valve Parkway storm drain, is relatively water soluble. Since benzene was only detected in this one area, it is likely that it is quickly diluted to non-detectible levels. Exposure to benzene in other areas of the pond is therefore not likely. While no surface water treatment is planned, it is possible that contamination levels in the site surface waters will subside following removal of contaminated sediments.

B. Potential Exposure Pathways

    Surface Soil - Past, Present and Future

Exposure to the elevated surface soil PAH contamination that was detected near the abandoned tank farm is remotely possible since the site is readily accessible to older children and adults. This pathway is considered potential and not complete since it is not likely that dermal contact through the feet will occur in this area. Ingestion of this contamination, however, could possibly occur through inadvertent hand-to-mouth activity. The possibility of deliberate ingestion of these soils is extremely remote since it is unlikely that young children who may exhibit this type of activity could wander onto the site. As previously stated, the site is one quarter of a mile from the nearest residence. In addition, vehicular traffic on the roads near the site is moderately heavy, and the probability of observing unattended young children between one and six years of age near these thoroughfares is remote.

    Air - Future

The chemical hazards detected on the site generally do not volatilize. Fire in the wooded area that surrounds the pond, however, could release those contaminants detected near the tank farm. Those individuals living in residences downwind could possibly be exposed to the vapors at this time. Risk of this occurrence will be reduced in the future since EPA plans to remove these soil contaminants and deposit them in the on-site landfill.

    Ground Water - Future

No known use of on-site groundwater is currently ongoing nor is any planned for the future. If left unremediated, exposure to those compounds detected could occur if a well was drilled for drinking purposes in the area north of Kettle Pond. During the remedial process, these waters will be pumped and filtered through activated carbon. This process will continue until target clean-up levels for PAHs and benzene levels have been achieved.

The Smith Valve Company operated two process wells west of the site. Since there was no contamination detected in these waters, no exposure to site-related compounds is occurring during the operation of these wells.

Ground water in the area of the pond has been determined to flow toward the pond. Regional hydrogeological studies have indicated that ground water flows from the south toward the pond. A municipal well is situated approximately 1,000 feet north of the pond's northern edge. While it is not known whether this well is situated in the same aquifer that charges Hocomonco Pond, it is believed to be hydraulically upgradient to the pond and at current usage rates, the pond is not within the well's zone of influence (TRC, 1984). This could change if the wells production rate were to increase. Monitoring of waters drawn from this well for VOC, PAH and metals (especially arsenic) will ensure that exposure to site-related contaminants will not occur. Monitoring conducted by both state and federal agencies has shown that no exposure to hazardous compounds via ingestion of these well waters is currently occurring.


In this section, the potential health risks posed to the public as a result of possible exposure to site contaminants are evaluated. In addition, available health data pertinent to the site are presented. The possible impact of environmental exposure on disease rates is discussed in this section. Finally, citizen concerns specifically voiced to public health officials are addressed.

A. Toxicological Evaluation

    Carcinogenic PAHs

Carcinogenic PAH's are compounds to which exposure is suspected by the scientific community to be associated with an increased risk of cancer development. These compounds include benzo(a)pyrene, benzo(a)anthracene, benzo(b)fluoranthene, benzo(k)fluoranthene, dibenzo(a,h)anthracene and indeno(1,2,3-cd) pyrene. These compounds have been characterized as to their carcinogenicity with varying degrees of extensiveness. Benzo(a)pyrene is best understood with respect to cancer risk. Rarely is an individual exposed to one type of PAH. For this reason, no conclusive human evidence currently exists associating exposure to particular PAHs with increased risk of cancer development. Animal studies conducted under controlled conditions have provided the majority of the evidence for characterizing these compounds' carcinogenic properties. As previously stated, benzo(a)pyrene is that compound whose carcinogenic effects are best studied. As a result, until further evidence is presented to the contrary, the remaining carcinogenic PAH's are assumed to be as potent carcinogens as benzo(a)pyrene. Given the uncertainty of these data it is possible that future evidence may be presented which may change those exposure levels which are currently considered to pose no significant increase in cancer risk.

The majority of the animal studies conducted have demonstrated an increased risk of stomach cancer development upon ingestion of these compounds. Based on these animal studies, it is possible that those individuals consuming contaminated fish from pond waters may be at risk of stomach cancer development. Mice who were administered high PAH levels through the skin demonstrated an elevated risk of skin cancer development. Exposure to contaminated sediments via skin contact may, therefore, pose an increased risk of skin cancer development.

It is important to note that estimates of cancer risk are largely dependent on the nature and frequency of exposure to site-related contaminants. Some sediments where elevated PAH levels were detected are readily accessible while others are not. It is not likely that even the accessible areas will be accessed regularly throughout an entire year thus diminishing the risk of exposure and cancer development. This scenario could change in time depending on future land usage. Exposure to known PAH levels detected on or near the site do not pose a significant non-cancer risk. The extent of inhalation exposure that would occur if the PAHs at the site volatilized during a fire can not currently be determined. In addition, it is not known what, if any, health effects would result from short term exposure to air containing PAHs detected at the site.


Human studies have indicated that individuals exposed to arsenic via ingestion are at increased risk of skin lesion development. If untreated, skin tumors may result. Although elevated levels of arsenic have been detected in sediments monitored from Hocomonco Pond, it is unlikely that sufficient amounts could be ingested to cause development of these symptoms.


Individuals with glucose 6-phosphate dehydrogenase (G6PD) deficiency (an inherited trait), are susceptible to adverse health effects resulting from napthalene exposure. When exposed to napthalene, the walls of red blood cells weaken and eventually burst. Hemolytic anemia then ensues. Normally G6PD produces molecules that protect red blood cells from the hemolytic effects of compounds such as napthalene. This deficiency is found in about 15% of black men in the United States. According to the 1980 census, no blacks are known to live in the area near the site. A sparse number of people reside in the area surrounding the site and the probability that susceptible individuals could be exposed to napthalene contaminated sediment via ingestion is low. It is therefore unlikely that exposure to this compound via ingestion presents a significant health hazard.


Benzene contaminated ground water is not currently being used for any purpose at or near the site. If this water were available in the future, those individuals ingesting these waters on a regular basis would be at increased risk of leukemia development. It is important to note, however, that there are currently no known plans for future use of these waters.

Benzene has also been detected in surface waters sampled from Hocomonco Pond. No non-cancer adverse health effects have been associated with incidental ingestion of benzene levels detected in these waters. Animal studies have demonstrated an association between regular ingestion of benzene levels such as those detected in Hocomonco Pond surface waters over the course of a lifetime with increased risk of cancer development. It is important to note, however, that it is extremely unlikely that exposure of this frequency is occurring.

B. Health Outcome Data Evaluation

Data from the Massachusetts Cancer Registry were reviewed for the most recent period available (1982 - 1988). The observed number of incident cancer cases in Westborough were compared with those that would be expected based on the statewide cancer incidence experience. Comparisons were made in cancers for specific anatomical sites that would be of concern based on PAH exposure scenarios associated with the site. These included both cancers of the skin and stomach.

Skin cancer, (with the exception of malignant melanoma), is not diagnosed in the hospital setting. Since only hospitals report to the MCR, skin cancer in its entirety is not registered by the Commonwealth. For purposes of this health assessment, the incidence of malignant melanoma was analyzed for the town of Westborough. These data are presented in Table 12. Melanoma incidence occurred at essentially the rate expected based upon the statewide experience. An analysis of stomach cancer revealed that eight cases of stomach cancer among residents of Westborough were diagnosed between 1982 and 1988. These data are also presented in Table 12. Based on the age distribution for the Commonwealth, eight stomach cases were expected in Westborough during this time period.

The geographic distribution of cases was also reviewed to determine whether cancer cases were concentrated in the area of Hocomonco Pond. Cases of both stomach and skin cancer were evenly distributed throughout the town of Westborough.

C. Community Health Concerns

We have addressed each of the community health concerns as follows:

What are the health concerns associated with swimming and fishing in Hocomonco Pond?

Based on current toxicological data, those individuals who come in contact with contaminated sediment in the pond may be at increased risk of skin cancer development and individuals consuming PAH-contaminated fish may be at increased risk of stomach cancer development. There are, however, uncertainties with respect to the actual cancer hazards associated with such actions. The potency of sediment and fish contaminants which are suspected of causing cancer, has yet to be firmly established. Secondly, the risk of any cancer development increases with frequency of exposure to carcinogenic compounds. As a result, individuals should reduce the opportunity for exposure by heeding the postings around the site and not swim or fish in the restricted waters.

Will nuisance odors be generated from the site during the proposed bioremedial process?

It is anticipated that no odors will emanate from the site during bioremediation if the process is conducted under aerobic (in the presence of oxygen) conditions. EPA intends to inject oxygen into the impacted subsurface soils in order to ensure that aerobic degradation is occurring.

On August 12, 1993, this Public Health Assessment was released for public review and commentary. Comments and concerns expressed during the comment period ending on September 11, 1993 are addressed in the Responsiveness Summary in Appendix 4 of this document.

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