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Human Health Risk Assessment Former Mobil Oil Bulk Plant 04-343 500 East Grant Line Road Tracy, California Beginning July 23, 1990, clean, imported fill material was delivered �,o the site for backfilling of the open excavation. The backfill material was compacted in accordance with Section 70 of filling required an approximate total volume of 7,300 cubic the Uniform Building Code. Back yards of imported fill. Field density testing and inspections were conducted throughout the duration of the backfilling operation. A relative compaction of 90 percent was used to establish acceptable field densities of the backfill material. Backfilling of the excavated area was performed in seven lifts. The first lift was 2 feet thick to isolate wate, interference in the open ' excavation; subsequent lifts were 12 to 14 inches thick. Each lift was compacted and tested in accordance with ASTM methods to conform to the building standards established in Section 70 ' of the Uniform Building Code (Alton Geoscience, 1990). 1.2.7.2 Ground Water Remediation Activities Manual pumpouts for interim remediation of ground water began in March 1992 for Monitoring ' Well AW-3 and in April 1992 for AW-9. As of March 1993, a to ,J of 11,195 gallons of ground water had been removed from AW-3 and AW-9. As a result of interim remediation of ground water, a total of 2,410 and 3,005 gallons of ground water has been recovered from AW-3 and AW-9, respectively. In addition, approximately 5,780 gallons of ground water were recovered from AW-9 during the aquifer pump tests performed April 13 through 16, 1993. ' Recovered ground water was properly disposed of at Liquid Waite Management, Inc., McKittrick, California, by Balch Petroleum, Inc., Milpitas, California. Interim remediation is conducted in accordance with San Joaquin County Public Health Servict;s (SJCPHS) guidelines. ' 1.3 EVALUATION OF REMEDIAL ALTERNATIVES FOR SOIL AND GROUND WATER 1.3.1 Background ' Remediation is an affirmative, purposeful activity designed to diminish the measurable presence of chemicals in a specific medium. The general objective of any remedial action is to reduce ' the toxicity, mobility, or volume of contaminated materials. Remediation activities conducted to date (i.e., excavation of 6,100 cubic yards of hydrocarbon-affected soil) have been effective in diminishine the volume of petroleum hvdrocarbonc in coil Althmah it mAv ha dim6rnhla tn i- 30-0136-11 ' 1-11