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29 September 1995 .; AGE-NC Project No 95-0139 Page 2 of 7 is our understanding that the monitoring wells were sampled in June 1988, January 1990 and September 1990 During each sampling, hydrocarbons were detected in MW-1, north of the tank cavity It is uncertain if any additional field work was performed between September 1990 and February 1993 A quarterly monitoring program was initiated by GeoAudit in February 1993 Since 1988,the depth to ground water at the site has fluctuated from 8 5 to 12 feet Ground water flow direction has remained between N 8' W to N 28° W This flow direction is consistent with regional trends I2 4 SOIL EXCAVATION In January,1990, additional hydrocarbon-impacted soils were removed to a depth of 14 feet from the former tank cavity Ground water was encountered during excavation procedures and the excavation had to be dewatered The water was placed in an 5,000-gallon above ground tank and stored on-site Between March and May 1990, all of the previously excavated soil was returned to the excavation, bringing the surface of the excavation to 7 feet below grade Subsequently, additional soil was _ imported and used to backfill the excavation to surface grade The water stored on-site in the above ' • ground tank was released to,the area of the former excavation The backfilling and discharge of _ purged ground water were done without notification of the PHS-EHD, and therefore, no official documentation was available ' n f the PHS-EHD the former tank cava was overexcavated in August 1993 At the requirement o y � The excavation was widened to approximately 40 feet by 50 feet and deepened to a depth of ' approxunately 14 feet Approximately 1,000'cubic yards of soil were removed from the excavation Of the soil removed, 700 cubic yards were placed into"contaminated" stockpiles and 300 cubic yards ' were placed into "clean' stockpiles Ground water was encountered in the excavation at a,depth of approximately 12 feet Total petroleum hydrocarbons quantified as gasoline and diesel (TPH-g and TPH-d) were detected in the north wall of the excavation at concentrations of 350 and 160 ppm, respectively Petroleum hydrocarbons were also detected in the east wall of the excavation On 7 and 8 September 1993, under the direction of the PHS-EHD, the "clean" stockpiles were used to partially backfill the excavation The soil was placed into the excavation and compacted using a ' loader/backhoe On 31 December 1993, the excavation was backfilled to surface grade with pea gravel Backfilling of the excavation was performed by Stokley Construction of Tracy, California