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DISCUSSION

The sampling results discussed in this consultation were taken from the available investigations of the property, and are not adjusted for limitations or bias in the sampling programs. The Tables presented in this consultation include maximum and median concentrations in the samples collected. Health discussions are based on the maximum concentrations reported and long-term, frequent exposure scenarios, reasonably conservative assumptions.

During the BFRA field work in December 1997, the MDEQ collected 5 surface soil samples from the lawn behind the building on the property. None of these samples contained any chemical at concentrations above the MDEQ Generic Clean-Up Criteria for Industrial, Commercial, or Residential Use (Table 1) (2, 3, 4).

During the BFRA field work in December 1997, the MDEQ collected 32 subsurface soil samples (ranging in depth from 4 feet to 17 feet) from 18 borings on the property. They collected single samples from 4 locations on the north end of the property and 2 samples at different depths from each of 14 locations around the building, the former underground storage tanks, the gas pump islands, and other locations on the property. The arsenic concentration in one sample collected at a depth of 5 to 7 feet behind the building equaled the MDEQ Residential Use Criteria (Table 2) (2, 4). This concentration was within the range found in background soils in Michigan (5). The benzene concentration in one subsurface soil sample, collected adjacent to the pump islands at a depth of 8 to 12 feet, exceeded the MDEQ Generic Soil Inhalation Criteria for Residential or Industrial Use (6). No one visiting the property would be exposed to the subsurface soil unless the property is excavated. MDEQ and MDCH do not know of any plans for an excavation on the property. The surface in the area where the high benzene concentration was found is paved with asphalt, which would likely prevent benzene vapors from migrating to the surface.

During the BFRA field work in December 1997, the MDEQ collected groundwater samples from 6 temporary monitoring wells on the property, four in the area where the station's underground storage tanks were, one between the gas pump islands, and one in the southeast corner of the property. Water from all of the wells contained benzene, ethylbenzene, manganese, and toluene concentrations above the MDEQ/U.S. EPA drinking water standards (Table 3) (2). Some of the samples also contained concentrations of acetone, arsenic, bis(2-ethylhexyl)phthalate, lead, 4-methylphenol, naphthalene, or xylenes above the MDEQ/U.S. EPA drinking water standards (4). The benzene concentration in water from two of the wells also exceeded MDEQ Generic Contact Criteria for Utility Workers. The benzene concentration in all the samples exceeded MDEQ screening criteria concerning volatilization to indoor air in residential or commercial/industrial use (7). The highest concentrations were generally in water from a well on the east side of the tanks or the one in the southeast corner of the property. Benzene, ethylbenzene, toluene, and xylenes are common constituents of gasoline, and tetraethyl lead was long used as an anti-knock additive in gasoline used for motor fuel.

The Caro Municipal Water system supplies water to the entire area around the property. The system gets water from 5 wells around the village. The closest municipal wells to the property are approximately 0.75 miles away, one to the west and two to the east.

The property is not fenced and is freely accessible. MDCH and MDEQ staff observed a child's toy on the property. At the time MDCH personnel visited the property in December 1997, one window in the building was broken, but the window had been boarded up. The building was generally in good shape. There were peeling paint and fallen suspended ceiling tiles inside the building.

There are no records of private wells in the immediate vicinity of the property. The building on the property has no basement, though at least one nearby residence does. Seepage of contaminated groundwater into a basement might result in human exposure to the contaminants. The contaminated groundwater on the property was found at approximately 17 feet below the surface, deeper than typical residential basements. However, volatile contaminants in the groundwater might volatilize and migrate through the soil to basements above the contamination plume. The concentration in the air in such a basement would be much lower than that in air that would be in contact with the water, due to dispersion and diffusion in the migration, but there is not enough information available to estimate the concentrations. There is no information available on sampling of air from basements near the Old Total Gas Station - Caro property. The MDEQ only collected groundwater samples from the property, and the samples collected nearest the property boundaries contained very high concentrations of contaminants, so the areal extent of the contaminant plume has not been determined.

The groundwater sampled on the property during the BFRA was found at approximately 17 feet below the surface. The MDEQ issues general advice that wells used for drinking water supplies should be no shallower than 25 feet unless there is a confining layer present to prevent surface contamination from entering the drinking water. There are no known producing wells on the property, and with the municipal water system readily available, no one is likely to drill a well or use the groundwater on the property for household uses or for their primary drinking water source. The following toxicological discussion addresses the potential health impact from household use of the groundwater, a very conservative assumption in the light of the current and probable future use of the property.

The maximum concentration of manganese in the shallow groundwater on the property was comparable to that in the drinking water in a town in Greece whose elderly residents showed higher rates of various minor neurological effects than did those in a neighboring town where the manganese concentration was lower (8). Exposure to manganese has not been observed to be related to cancer rates (9).

No one is likely to ingest as much, on a body-weight basis, of any of the other chemicals present from the groundwater on the property as has been observed to cause adverse health effects in epidemiologic or laboratory studies. The U.S. EPA has classified arsenic and benzene as proven human carcinogens (U.S. EPA Class A) and bis(2-ethylhexyl)phthalate and lead as probable human carcinogens (U.S. EPA Class B2). Lifetime consumption of the shallow groundwater from the property might result in a high increased risk of contracting cancer due to the arsenic and benzene present. The bis(2-ethylhexyl)phthalate in the water is not likely to result in any apparent increased risk of contracting cancer. There is not sufficient information available to evaluate the increased cancer risk from exposure to lead (10, 11, 12, 13, 14, 15, 16, 17, 18, 19).

The concentration of benzene in the air in a shower using water from the property might exceed the concentrations at which people exposed to benzene in their employment experienced irritation of the skin and mucous membranes, anemia, reduced white blood cell counts, and other changes in the blood after short-term exposures (less than 2 weeks), and increased incidence of leukemia after long-term exposures (over 1 year). Lifetime exposure to air containing this concentration of benzene might result in a very high increased risk of contracting cancer(10, 20).

Based on the model used in Reference 6, the benzene concentration in the air in an excavation on the property might attain the levels at which workers exposed for years experienced decreased numbers of white blood cells and increased rates of leukemia. Lifetime exposure to air containing this concentration of benzene might result in a high increased risk of contracting cancer (10).

The concentration of toluene in the air in a shower using water from the property might exceed the concentrations breathed by people who showed headaches, dizziness, decreased dexterity, and other minor neurological effects after a 6-hour exposure(11, 20).

The concentration of xylenes in the air in a shower using water from the property might exceed the concentrations breathed by workers who reported irritation of the nose, eyes, and throat, reduced appetite, and various subjective minor neurological symptoms after working for some years with xylenes (12, 20).


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