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Mr Kyle Christie Project 0805-114 04 • January 29, 1996 Page 2 hydrocarbons have been detected in all groundwater monitoring wells Total petroleum hydrocarbons as gasoline(TPHG) concentrations have ranged from less than 10 parts per billion (ppb) to 18,000 ppb, and benzene concentrations have ranged from less than 0 3 ppb to 2,500 ppb Based on the FRP, RESNA proposed the installation of a combined SVE and AS system to remove gasoline hydrocarbons from soil and groundwater beneath the site The system consists of a 100-standard-cubic-foot-per-minute catalytic oxidizer equipped with a 7 5-horsepower vapor extraction blower In September 1994, EMCON observed the final Installation of the remediation system The system consists of an au sparging-enhanced SVE system with catalytic oxidation treatment (i e , AIREX KATOX 100) In November 1994, the system was started up The system was shut down in February 1995 due to catalyst malfunction The catalyst was replaced and the system was restarted in April 1995 Based on a letter from San Joaquin County Public Health Services (SJCPHS) dated August 29, 1994, the SJCPHS requested an addendum to the PAR be submitted outlining remedial . alternatives and further assessment activities necessary to delineate hydrocarbons north and south of the site EMCON submitted three access agreement forms to the property owner north of the site and did not receive a response However, during a meeting conducted on May 16, 1995, between SJCPHS, ARCO, and EMCON, SJCPHS concluded that the additional monitoring well north of the site was not necessary at this time Because relatively low concentrations of benzene have been detected in water samples collected from monitoring well MW-10 during the last four quarters (highest concentration of 12 ppb) and the hydraulic gradient has been consistently toward the east to southeast, it is EMCON's opinion that a monitoring well south of monitoring well MW-10 (laterally crossgradient) is not warranted at this time In August 1995, EMCON observed the drilling of four soil bonngs (B-26 through B-29), which were converted to air sparge wells AS-3 and AS-4 and vapor extraction wells VW-11 and VW-12 Bon-ng locations are shown on Figure 2 Borings B-28 and B-29 are located adjacent to existing borings from which soil samples were collected for laboratory analysis, therefore, soil samples were not collected from these borings Results of laboratory analyses of soil samples collected from bonngs B-26 and B-27 indicated that TPHG concentrations ranged from below laboratory detection limits to 7,700 parts per million (ppm), and benzene concentrations ranged from below laboratory detection limits to 8 4 ppm On August 29, 1995, EMCON connected the new vapor extraction and sparge wells to the remediation system • EMCON has been operating an SVE system at the site in combination with an AS system to remediate petroleum hydrocarbon-impacted soil and groundwater since November 1994 SAONTJ"805\080511404GS-95,pas I