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Gem€ni Petro ra hic Investigations SITE HISTORY A preliminary site appraisal and assessment was performed on 14 April 1989 by Convenant Environmental (Mr.Craig Wright). During the assessment,three underground storage tanks were identified(two diesel 5,000 and 10,000 gallons;and one 1,000 gallon gasoline tank). The 1,000 gallon leaded gasoline tank was removed In April of 1989 with additional excavations of the former tank pit during January of 1990. During the Initial excavation of the tank,Jeff Miller,of Western Meter,Stockton collected two samples from each end of the tank and submitted the samples under chain-of-custody protocol to California Water Labs of Modesto. Laboratory analysis of soil samples taken below the e,,cavated gasoline tank indicated the presence of TPF#-G(up to 200 ppm)and aromatic hydrocarbon(STX&E)ranging from N.D.to 5.6 ppm(predominately xylene). Total Lead was also analyzed with results within natural sell abundance levels. Addltlonat excavation and sampling of the pit was performed on 23 May 1989 by Troy Williams, Universal Engineering and transported under chaln-of-custody protocol to Precision Analytical Laboratory In Richmond. Laboratory analysis Indicated TPH-G concentrations of 124 ppm. Soil samples were collected from all excavations and stockpiles(10 cu. yds.)on 10 January 1990 by George Reed, Universal Engineering,and analyzed by Precision Analytical of Richmond, indicated the presence of TPH-G (N.D. to 90 ppm), TPM-D (N.D. to 190 ppm) and aromatic hydrocarbons from N.D. -0.7 ppm. Diesel contamination was suspected to be derived from the excavation equipment since diesel was not store In the tank. Sol[removed from the gasollne excavation was stockpiled and aerated until N.D.values were obtained. In June 1989,two diesel tanks(5,000 and 10,000 gallons)were - removed,sampled by George Reed,Universal Engineering,and transported under chain-of-custody protocol to Groundwater Technology Laboratory In Concord. Laboratory analysis of soil samples taken below the excavated diesel tanks Indicated no soil contamination for TPH-D. The excavations were backfilled and re-surface with concrete In June 1990. SITE DESCRIPTION SITE GEOLOGY Based on a review of geological data obtained from California Division of Mines and Geology publications and other Investigations In the vicinity,the site Is underlain by very gently dipping Quaternary fluvial sediments _ consisting of sand, silt and clay. The topographic Is slightly Irregular with generally a southwest slope. Underlying the Quaternary sediments are Mid-Tertlary to recant sediments of continental crigin, with Pre-Cretaceous to Mld-tertiary sediments of marine origin stratigraphically below the continental deposits SITE HYDROLOGIC CONDITIONS Site hydrologic condition can be partially Inferred as data Is available from an Initial investigation performed at 4648 East Waterloo Road In 1988. At this site,groundwater was not encounter at 20 feet,maximum depth of soil borings. This concurs with the observation that since 1986 the groundwater level has lowered to 80 feet below this site and adjacent areas. The nearest surface water is the Stockton Diversion Canal approximately 1 mile southwest of the site. The canal Is unlined and flows to the northeast.Groundwater dlrectlon is variable __- _ranging_frpm- southwest to south-south-east.-_Mean-seasonal_precipitatlon for the site-Is from 10-15_Inches according to the National Weather Service. 2