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1 ' skewing the calculations, as is the case with the laboratory data The operational measurements • of the UVB system showed that at had reached the asymptotic stage of operation The UVB ' system was therefore shut down as referenced in ETIC's letter dated 29 October 2000 (ETIC 2000b) and approved by the SJCEHD in a letter received in December 2000 (Appendix A) ' 2.8 RISK EVALUATION In October 2001 a nsk-based corrective action (RBCA) analysis based on the American Society ' for Testing and Materials (ASTM) guidelines was performed (ETIC 2001) The RBCA analysis focused on evaluating potential health risks associated with human exposure to residual hydrocarbons beneath the site at both on- and offsite locations To support the RBCA analysis, ' shallow soil vapor sampling was performed on 28 December 2000 at eight onsite locations (SB 1- SB8) The results of this sampling indicated the presence of hydrocarbons at residual levels in ' soil vapor beneath the site Based on the analytical results of the soil vapor sampling, a RBCA analysis was performed to assess potential health risks associated with residual levels of hydrocarbons present beneath the site Available soil, groundwater, and soil vapor data were evaluated and used together with conservative assumptions adopted by ASTM (1995) for a Tier I RBCA analysis This analysis included evaluation of potential nsks to both on- and offsite receptors such as residents at the Chateau Hospital adjacent to the site The RBCA analysis included an evaluation of indirect exposure via inhalation of volatiles from all potential subsurface sources (e g , soil, groundwater, and LPH) using soil vapor data Specifically, maximum onsite soil vapor data were 10 conservatively used to evaluate nsks to both on- and offsite receptors Direct exposure to hydrocarbons in soils beneath the site was also evaluated for both daily site workers and ' potential future construction workers The results of the RBCA analysis indicated (1) The nsk associated with commercial/industrial exposure to detected levels of hydrocarbons in surface soils is protective of target levels adopted by the U S Environmental Protection Agency (USEPA), (2) the nsk associated with commercial/andustnal and residential exposure to detected levels of hydrocarbons and MTBE in soil vapor beneath the site as protective of target nsk levels adopted by the USEPA, (3) the construction worker exposure nsk associated with a single historical benzene concentration in a soil sample exceeds the USEPA-defined target risk range, and therefore an appropriate health and safety plan should be developed, ensuring protection of future construction workers at the site A well survey was also performed to identify wells within a 1-mile radius of the site (ETIC 2001) Based on the well search, there are no wells pumping water from a shallow or deeper water bearing zone within one mile of the site in the downgradient direction The only active I well identified (Sta 49) is 512 feet deep, is screened from 170 feet, and is located upgradaent and approximately 1,900 feet from the site, such that it as not likely to be impacted by hydrocarbons in groundwater beneath the site G IR ccftk739421MASTERIWnWM3031Wptx dm 8