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Case Closure Report Former Tosco(Unocal) SS No 5421, Stockton,California July 8, 1998 Stockpile and sludge sampling were performed in accordance with the State of California LUFT manual, local agency guidelines and disposal facility requirements Groundwater Contamination Delineation Based on the analytical results of all of the groundwater samples collected and evaluated to date, the extent of the petroleum hydrocarbon impacted groundwater is well defined The analytical results of groundwater samples collected from the four monitoring wells have been reported as non detected for TPHg, BTEX, and MtBE for a mimmum of 24 months Recent groundwater sampling requested by SJCPHS have reported all oxygenates in groundwater as non detected Historically, the groundwater data has primarily been non detect for all analytes except for some isolated low detectable concentrations At the request of SJCPHS, additional groundwater samples were collected from the down-gradient well MW-2 in June 1998 These results were also reported as non detected for TPHg, BTEX, MtBE and the five additional oxygenates Drinking Water Standards and Impact on Beneficial Uses Groundwater samples were all reported as non detect, and are below the established Drinking Water Standards set by the State of California A water well survey was • conducted from the area surrounding the former Tosco (Unocal) site in order to identify existing water wells within a 114-mile radius of the site Based on the analytical results of the soil and groundwater samples collected and analyzed from the former Tosco (Unocal) site to date, and based on the distance ( approximately 1,350 feet east and down-gradient of the site), of a municipal well from the subject site, it is unlikely that any petroleum hydrocarbon would emanate from the site and impact the municipal well The current residual petroleum hydrocarbons do not pose a threat to human health or the environment The primary and secondary sources have been removed, and the land use of the subject site has changed (no longer dispensing fuels) Natural attenuation of the residual petroleum hydrocarbons are expected to continue to degrade overtime Conclusions After a review and evaluation of all of the site data available and data presented in this report, GR has arrived at the following conclusions • The primary and secondary sources have been removed, and the subject property no longer dispenses petroleum products • • An approximate total of 3,180 cubic yards of impacted soil has been removed from the site 14016203 13