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z • Since the tanks, contaminated soil and groundwater source have been removed, extremely low concentrations remain However, on the basis of observations and reported literature on soil absorption, these contaminants are interpreted as relatively immobile It is possible that some desorbtion may continue, however the dissolved plume movement situation is not interpreted to substantially change from that previous observed in Well MW-1 data A 2,000-foot well search showed that there are no pumping municipal or domestic wells in the same aquifer at locations which could intercept the site plume Site Cleanup and General Risk Discussion Usually a cleanup approach is selected using a best available technology (BAT) In this case, BAT was excavation and groundwater removal given the need for construction of the streets, hence expedited an cleanup approach was used prior to and during construction in 1993 A follow-up soil and groundwater assessment performed in March, 2000 showed that very low residual and dissolved contaminants were present (see References) Groundwater monitoring has shown that the dissolved contaminants have declined to none detected A further water quality impact beyond that discussed, is not envisioned from the existing residuals A threat to health and beneficial use is interpreted as very remote since, there is not a well used on-site, the drinking water is supplied by the City of Tracy, the source is removed, the source area is capped by asphalt pavement and monitoring data show a declining contaminant trend Conclusions and Recommendations A site interim cleanup was performed by Wright where underground storage tanks, contaminated soil and groundwater were removed in 1993 That work was performed due to an expedited construction schedule for the City road widening and realignment A soil and groundwater assessment was completed, and one groundwater monitoring well was installed at the location of highest observed contaminants with PHS EHD approval Wright sampled the monitoring well, and contaminants were not detected in the latest sampling Calculations of estimated contaminants removed and remaining show that very low concentrations remain Benzene was not present in dissolved samples and MTBE has not been detected in either assessment or quarterly monitoring work The PHS-EHD stated in their letter dated December 27, 2000 that if the groundwater monitoring results had declined or showed a none detected trend, a closure report should be prepared for the site Since those results showed contaminants were not present, Wright has prepared this site closure report using the guidance outlined in the PHS-EHD letter On the basis of the data contained herein, it is Wright's opinion that further work is not warranted, and we recommend that this site be closed Upon approval of site closure, Wright will submit permits for abandonment of the one existing monitoring well Limitations This report has been prepared specifically for the City of Tracy, for Tracy Auto Stereo site on Grant Line Road in Tracy, CA and was done according to State and local agency suggested guidance documents for these investigations The interpretations, conclusions and recommendations made herein are based on the data and analysis for the soil and water Page 6