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LM extent of contaminant migration. All excavated materials were transported to the City of Stockton -- Municipal Service Center where they were placed on asphalt and covered by 6 mil plastic sheeting. +.. Analytical results of confirmation soil samples collected from the excavation floor and sidewalls (Table 1) indicated hydrocarbon impacted soils remained in place along the northern wall of the excavation and under the concrete encased high voltage electrical lines which transversed the excavation. Subsequent to excavation and soil sample collection, the open excavation was backfilled with clean engineered sand under the requirements set forth by the City of Stockton Public Works Department. The limits of the excavation are shown on Figure 3. The PHS/EHD requested additional subsurface investigation be performed to define the extent of residual soil contamination at the site. 3.2.2 November 1993 Additional Soil Characterization On November 16, 1993, RESNA advanced three hand augured borings (SB1, SB2, SB3) in the northern vicinity of the leak location as depicted on Figure 3. Two soil borings (SBI, SB2) were �. located within the existing concrete walkway and one boring (SB3) was located within the concrete floor of the prisoner bay entrance. Analytical results of soil boring samples indicate a zone of impacted soils remain between approximately 3 and 8 feet below grade directly beneath the sidewalk and ` building of the police facility. 3.2.3 December 1993 Tank Removal and March 1994 Soil Sampling On December 17, 1993 the underground storage tanks and associated product lines and dispensers were removed by Falcon Energy under the direction of Ms. Pam Violett of PHS/EHD, Soil samples .. were collected by Epigene International Consulting Geologists for analyses of benzene, toluene, ethylbenzene, xylenes (BTEX), total petroleum hydrocarbons as gasoline (TPHg), total petroleum hydrocarbons as diesel (TPHd), ethylene dibronvde, and total lead as appropriate. Analytical results indicated that no significant residual hydrocarbons were detected from beneath the tanks, dispenser, or product lines, with the exception of an apparent leak during the removal of product lines near one of the tanks_ The soil impacted as a result of the leak was apparently removed at the time of the spill. Due to questionable delivery times of samples to the laboratory, confirmation samples were collected by Epigene International on March 21, 1994. Results of the March 21, 1994 samples indicated a minor release of gasoline hydrocarbons may have occurred in fill material south of the sidewalk along the former product lines. Analytical results of soil samples collected by Epigene International are summarized in Table 3. Sample locations reported by Epigene International are shown on Figure 3 (RESNA, June 1994). 3_3 Groundwater Monitoring and Sampling L. Five rounds of groundwater sampling have been conducted at the site since October 1989. MW-1 was r monitored and sampled on March 8, 1996. The sample was analyzed for methyl t-butyl ether(MTBE) 4 wA94368`reports\=wi1.dm - 3 4 SMTH