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In a health evaluation, ATSDR considers how people might come into contact with the contaminants. This process is described in greater detail in Appendix C. ATSDR uses a sequential process of reviewing the available environmental data. If the concentration of detected chemicals in a specific media is less than the comparison value, the exposure is not of health concern and no further evaluation is required. If the concentration is greater than the comparison value, the exposure requires further public health evaluation to determine if the exposure might result in an adverse health effects. If a chemical does not have a comparison value, ATSDR reviews the scientific literature to determine if the exposures are of health concern.

Two potential exposure pathways were identified at the Rock Avenue Landfill after evaluation of the existing environmental data. These potential pathways were evaluated as to whether they represent a health concern for the public, a summary of these evaluations are presented below.

Potential Exposure Pathways
Surface Soil
Because of the lack of surface soil data, only a limited evaluation of the soil pathway is possible. Surface soil data are limited to two MIT near-surface soil samples, which are taken at a depth of 6 inches bgs. Despite the lack of data, exposure to site soils is not likely a significant concern because 1) the site is presently vegetated, which reduces the possibility of contacting surface soil contaminants; 2) the waste material is buried and not presently accessible to the public; 3) limited human activity on the site; 4) infrequent human contact with site materials; and, 5) contaminant concentrations detected in near-surface soils are not at levels thought to be associated with adverse health effects.

The potential for contacting contaminants at concentrations associated with adverse health effects is limited. It is, therefore, doubtful that exposure to surface soil either via ingestion of or dermal contact with surface soil would present a public health hazard. If soils were disturbed in the future (e.g., new construction), further evaluation of the nature and extent of subsurface contamination would be warranted.

Area residents expressed concern about contamination being blown off the site by the wind (fugitive dust) and contaminating residential gardens and causing adverse health effects from inhalation and dermal contact with the contamination. It is unlikely that area residents are experiencing adverse health effects associated with fugitive dusts or dermal contact with the contamination for some of the same reasons listed above. Specifically, 1) sampled near-surface soil has low levels of contamination; 2) the waste was disposed of at depth; and 3) the presence of surficial ground cover on the site limits the amount of dust emissions that could migrate off site. For these reasons, no public health hazards are likely associated with exposures from surface soil contaminants blowing off the site; however, these conditions represent present conditions and may not represent conditions that occurred in the past, without representative surface soil data, definitive conclusions cannot be made.

Soil Gas
Methane gas is odorless and highly explosive when mixed with air at a volume between 5% and 15% (50,000 ppm to 150,000 ppm), which is the lower and upper explosive limits of methane, respectively. The accumulation of methane gas in structures (e.g., basements, crawl spaces, utility ducts) can result in explosions and fires. Methane gas migrating underground (soil gas) can damage or kill vegetation in surrounding areas because it displaces oxygen and effectively suffocates plant roots (EPA, 1991). All vegetation requires different amounts of oxygen for healthy growth; therefore, a plant's tolerance to oxygen displacement depends on the type of plant. It should be noted that much of the site is covered with naturally growing vegetation that appears to be healthy.

Soil gas monitoring revealed the presences of elevated methane concentrations at the Rock Avenue property perimeter greater than 10% of the LEL. The presence of methane on site at concentrations ranging from non-detect to 24,550 ppm (or approximately 50% of the LEL) does not present an imminent health hazard, but the uncertainty relative to the source and the extent of methane in soil gas is of concern. Consequently, EA recommended follow-up monitoring and controls. To date, no controls or follow-up soil gas monitoring has been conducted at the Rock Avenue Landfill. Although no methane was detected on neighboring property at levels that pose a public health hazard, off-site methane data are limited to one soil gas sample. Soil gas, therefore, cannot be eliminated as a potential source of contamination that may migrate to ambient indoor air and lead to an explosion.

It is unlikely that methane explosions threaten nearby structures or residents. In fact, methane sampling in both nearby basements indicated a level of 1 ppm, which does not represent a public health hazard. Although no dangerous methane concentrations were observed in nearby residences, elevated methane concentrations were detected in soil gas at the perimeter of the site. Although no PAHs or methane levels associated with health effects were detected in air samples, available air data are limited to two indoor samples.

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