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March 24, 1997 • Page 4 . Geophysical Investigation On June 18, 1996, a geophysical survey of the site was conducted by NorCal Geophysical Consultants, Inc (NorCal) The survey identified five "anomalies" (A through E) The anomalies were located as follows A)the waste oil tank and associated sump drain line, B) and C) two corners of the former building where utilities formerly entered the building, D)one location adjacent to the former product island and most likely associated with the former product lines, and E) one location southwest of the building located approximately where the former product lines and utility lines crossed Subsequent exploratory excavations in locations D and E revealed miscellaneous debris within two feet of the ground surface including asphalt and both clay and metal utility piping and wires Excavation to a depth of 5 feet in areas D and E did not reveal other structures Regarding locations B through E,NorCal reported that the GPR data in these areas was"typical of small isolated objects and utility lines" NorCal's report is included as Attachment C Former Gasoline UST Pit Excavation and Sampling On September 23, 1996, the former gasoline UST pit was excavated to 15 feet bgs and six samples were collected under the approximate location of each end of the former USTs Excavated material consisted of a mixture of soil and construction debris • (mostly concrete) Concentrations of 1,500 and 4,000 ppm TPH-g were reported in two samples (T-3 and T-1, respectively) collected from the southeast corner of the excavation A concentration of 8 2 ppm of TPH-g was reported in the southwest corner of the excavation TPH-g was nondetect in the other three UST pit samples Benzene was not detected in any sample On October 23, 1996,the southeast courier of the UST pit was over-excavated to between 19 and 23 feet bgs and was extended several feet laterally to the south and east Confirmation samples were collected beneath sample locations T-1 and T-3 as well as on each sidewall Concentrations of TPH-g and benzene were reported nondetect with the exception of 2,300 ppm TPH-g in sample T-8 (collected below T-1 at a depth of 23 feet bgs) The remaining impacted area is defined laterally by samples T-7, and T-9 through T-11 Soil staining and odor were observed to lessen with depth in the impacted area Vertical definition of the residual impacted soil is proposed in the work plan portion of this document The sample locations are shown on Figure 2 Sample data including sample designation, sample depth and sample results are presented in Table 1 Underground Waste Oil Storage Tank Removal One underground waste oil storage tank was removed from the site on September 23, 1996 The tank was of single-walled steel construction, and approximately 550-gallon capacity I he removed tank was in good condition, with no apparent holes or cracks 9200191 AIS]I I PUi L DOC