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Stantec .�..- No Further Action Request Report Chevron and ARCO Commingled Plume No. CP0034 April 10, 2012 screened and the thickness (25 to 60 ft) of clay deposits between shallow and deeper aquifers, it is unlikely that petroleum hydrocarbons would impact the water in those wells. Inhalation of volatile hydrocarbons from impacted soil and groundwater to ambient air would be comparably insignificant relative to contributions from normal service station operations. SVE systems were operated at both the Chevron and ARCO facilities. The SVE systems were shut down due to rising groundwater levels and low influent concentrations at the Chevron facility and low influent concentrations at the ARCO station. The inhalation of volatile hydrocarbons to indoor air is unlikely given the limited extent of volatile hydrocarbons remaining in the soil beneath the site following post-remediation. f3.2. GROUNDWATER CLOSURE CONDITIONS Best available, cost effective technology has been implemented at the site. Excavation and removal of former USTs, dispenser pumps, and product piping has been conducted at both the Chevron and ARCO facilities. An AS/SVE system operated at the Chevron property from April/September 1997 through February 1998. The SVE system was deactivated due to high groundwater levels in February 1998. Upon shutdown of the SVE system, the system extracted approximately 70 lbs of GRO from the soil and groundwater beneath the site. A GWE system was operated at the ARCO property intermittently from 1984 to 1996 and removed approximately 3,980 lbs of GRO. Additionally, an AS/SVE system operated at the ARCO property from January/May 1995 through March 2001. The SVE system was shutdown on March 1, 2001, due to low influent concentrations. Prior to shutdown, the SVE system removed approximately 4,897 lbs of GRO, 61.3 lbs of benzene, and 4.5 lbs of MTBE. Any residual petroleum hydrocarbons remaining in the soil will naturally attenuate over time through microbial and chemical degradation. Chemical concentrations in groundwater are projected to meet water quality objectives through natural processes within a reasonable period of time, i.e., prior to any potential future beneficial use of groundwater. Groundwater monitoring and sampling has been conducted at the Chevron Facility since March 1989 and at the ARCO facility since August 1988. Petroleum concentrations have decreased to below laboratory MRLs or water quality objectives in all wells with the exception of Chevron wells MW-2R and MW-5R and ARCO well E-10. However, trend analysis shows that concentrations in these wells are decreasing and will meet water quality objectives in MW-2R and MW-5R within a year and in E-10 within approximately twelve years. The site consists of two operating gasoline service stations on asphalt/concrete paved lots with no plan to change the use of the site in the foreseeable future, and since there are no municipal 94275 NFAR 2012.doc 14