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Ms. Lori Duncan, R.E.H.S. April 1, 2011 Page 4 of 6 RISC4 is a Windows-based software program that can be applied to estimate the potential for carcinogenic and non-carcinogenic impacts to human health. RISC 4 is able to calculate risks associated with several constituents of concern(COCs) via multiple exposure pathways. The software program utilizes vadose zone, saturated zone and air fate and transport models to estimate receptor point constituent concentrations. The HRA will include an evaluation of risks associated with the following exposure pathways: • On-site ingestion of surface soil; • On-site dermal contact with surface soil; • On-site inhalation of indoor air; • Off-site ingestion of groundwater via the nearest drinking water well; • Off-site dermal contact with groundwater via the nearest water well, Ramage Environmental will adjust ICI C;4=default chemical parameters as needed to comply with the California Office of Environmental Health Hazard Assessment(OEHHA) Toxicity Criteria Database. The Johnson and Ettinger model, which is included in the RISC4 program, will be applied to predict levels of COCs in indoor air used.upon site specific parameters and COC concentrations detected in soil vapor. ISC4 utilizes a one- dimensional flow, three-dimensional dispersion, dissolved phase contaminant transport model that accounts for adsorption and degradation, Rarnage Environmental will complete two separate RISC4 model runs. In the first model run,Ramage Enviromnental will evaluate potential risks to an on-site adult worker, adult resident and,child resident via exposure to CC Cs in indoor air and shallow soil. In the second model run, Ramage Environmental will evaluate potential risks to an off-site adult resident and child resident via exposure to groundwater from the nearest drinking water well. Risks to both adult and child receptors will be evaluated assuming reasonable maximum exposure(RME) levels. A cumulative carcinogenic risk and hazard index will be calculated for on-site receptors to account for potential risks from all potential exposure pathways. Ramage Environmental will consider a cumulative carcinogenic risk of one in one million and hazard index of one as acceptable target risk levels. The data set to be used in the HHRA will consist of analytical results from the proposed soil vapor samples, and the concentrations of petroleum compounds in soil and groundwater from previous investigations. Ramage Environmental will consider all detected analytes in the HHRA. used.on the cumulative soil and groundwater analytical results from the site, TPH- as-diesel, 'FPH-as-jet fuel, TPH-as-gasoline, BTEX, MTBE, DIPE, TBA, and 1,2-DCA will be included as COCs in the HHRA. Since the RISC4 chemical database does not in Total Petroleum Hydrocarbons,the concentrations will be divided into aliphatic and aromatic carbon fractions according to the draft report, Developing Petroleum Hydrocarbon Cleanup Levels, issued by the Washington State Department of Ecology on August 15, 2001.