2009-05-19_REVISION - M1977416 (29)

Home Browse Search

• AT = Carcinogenic Averaging Time (period over which exposure resulting incarcinogenic effects is averaged - years) EF = Exposure Frequency (days/year) SF. = Oral Carcinogenic Potency Slope (mg/kg-day)- 1 CF = Conversion Factor (kg/mg) Nco = Number of COCs with an Oral Carcinogenic Potency Slope (unitless) MN = Number of Media IRS = Age Adjusted Soil Ingestion Rate (mg-yr/kg-day) SF, = Inhalation Carcinogenic Potency Slope (mg/kg-day)-1 Nci = Number of COCs with an Inhalation Carcinogenic Potency Slope (unitless) IR = Inhalation Rate (m3/hr) • Default Exposure Parameters: BLM default values for several of the input parameters identified below were provided by Karl L. Ford, Ph.D. (BLM National Science and Technology Center) in a January 6, 2009 telephone conversation and email correspondence (CDM 2009). * 30 years for adult exposure and 6 years for child exposure. As discussed above, the camper scenario is the most conservative BLM exposure scenario that is also appropriate for current and future site conditions. Key RMC Input BLM Receptors Parameter Camper ATV Driver Worker Surveyor EF (days/year) 14 5 40 5 ED ears 30/6* 30 30 30 IR (mg/ da 114 114 114 114 IHR m3/hour 1.28 3.9 2.5 2.5 ET hr/ day) 24 4 8 8 Mn 5 1 1 1 Relative Bioavailability(RBA): As discussed above, site-specific bioavailability can be a key factor in developing appropriate RMC for the Site. Relative bioavailability (RBA) is measured using an in vitro test, referred to as the Relative Bioavailability Leaching Procedure (RBLP) or in vitro bioaccessibility assay (IVBA). This test has been developed by EPA Region 8 and the University of Colorado. The IVBA test measures the fraction of lead or arsenic solubilized from a soil sample under simulated gastrointestinal conditions. For the Site, only the arsenic results will be pertinent. The in vitro test uses a warm (38C) weak acid solution, into which the contaminant is introduced. After a prescribed time period, the solution is analyzed for arsenic. The mass of arsenic found in the filtered extract is compared to the mass introduced into the test. The fraction liberated into the aqueous phase is defined as the bioaccessable fraction of arsenic in that media or the relative bioavailability (RBA); typical RBA values for arsenic in soil are between 0.5 and 0.8. Additional information regarding the IVBA test method is available at the following website: http: / / www.colorado.edu / geolsci/ legs/ invitrol.html. 0