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Steven Sasson -7- February 5, 1996 i RfDG = Oral reference dose, mg/kg-day (6 mg/kg-day) RfD, = Inhalation reference dose, mg/kg-day' (6 mg/kg-day) ABS = Absorption fraction, dimensionlessz (0 15) The hazard index for the soil route of exposure was 0 006 The hazard index for the air route of exposure was 0 009 The total hazard index (adding the hazard indices for the air and the soil routes of exposure) was 0 015 This value is well below the departure level of 1 Therefore, the presence of hydraulic fluid at the levels encountered are not expected to pose a significant threat to human health It is important to reiterate that this is an extremely conservative assessment First, the soil pathway of exposure is most likely non-existent due to the location of the residual hydraulic fluid in the soil Second, the concentration of volatile compounds in the air is based on benzene Benzene is more volatile than hydraulic fluid, therefore, a higher concentration in air was estimated for benzene than what is actually the case for hydraulic fluid. Third, this assessment assumed that the property was being used by children for residential purposes The property is actually a commercial center Therefore, exposures are expected to be a lot lower than those represented by a residential scenario 2.2 Ground Water Assessment • When evaluating the impacts of releases of chemicals to the environment, it is necessary to assess the potential for adverse effects on both human health and the environment The effects on the environment can be assessed by examining the potential impact of chemicals on ground water At this site, there was a possibility that hydraulic fluid in the soli could migrate to ground water To assess this possibility, the SICPHS requested that a quarterly ground water monitoring program be implemented Three monitoring wells were installed and monitored in December of 1994 Ground water samples were collected two additional times from the same three wells in October and December of 1995 by The ground water samples collected from the three monitoring wells were analyzed for TPH calibrated as hydraulic fluid in accordance with Modified USEPA Method 8015 (GTI 1995a,b) The laboratory analytical results did not detect TPH as hydraulic fluid in the samples analyzed from any of the sampling events The absence of TPH in the ground water is an indication that no hydraulic fluid has migrated from the soil to the ground water Since most of the hydraulic fluid was removed from the soil, it is not likely that there will be any future impact to ground water. It is possible, using the same equations presented in the PEA Guidance Manual (DTSC 1994) to calculate a safe concentration of hydraulic fluid in the ground water This number would give an ' The oral reference dose was used for the inhalation reference dose This assumes equal absorption by the oral and inhalation routes 2 In the absence of an absorption fraction for hydraulic fluid, that for organic chemicals, 0 15,as suggested by the PEA guidance manual(I)TSC 1994) was used