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11 [r <br /> . Mr Kyle Christie Project 0805-114 04 <br /> December 6, 1995 <br /> Page 2 <br /> hydrocarbons as gasoline (TPHG) concentrations have ranged from less than 10 parts per billion <br /> (ppb) to 18,000 ppb, and benzene concentrations have ranged from less than 0 3 ppb to <br /> 2,500 ppb <br /> Based on the FRP, RESNA proposed the installation of a combined SVE and AS system to <br /> remove gasoline hydrocarbons from soil and groundwater beneath the site The system <br /> consists of a 100-standard-cubic-foot-per-minute catalytic oxidizer equipped with a <br /> 7 5-horsepower vapor extraction blower <br /> In September 1994, EMCON observed the final installation of the remediation system The <br /> system consists of an air sparging-enhanced SVE system with catalytic oxidation treatment <br /> (i e , AIREX KATOX 100) In November 1994, the system was started up The system <br /> was shut down in February 1995 due to catalyst malfunction The catalyst was replaced <br /> and the system was restarted in Apnl 1995 <br /> Based on a letter from San Joaquin County Public Health Services (SJCPHS) dated August 29, <br /> 1994, the County requested an addendum to the PAR be subirutted outlining remedial <br /> alternatives and further assessment activities necessary to delineate hydrocarbons north and <br /> .� south of the site EMCON submitted three access agreement forms to the property owner north <br /> of the site and did not receive a response However, during a meeting conducted on May 16, <br /> 1995, between SJCPHS, ARCO, and EMCON, SJCPHS concluded that the additional <br /> monitoring well north of the site was not necessary at this time Because relatively low <br /> concentrations of benzene have been detected in water samples collected from monitoring: well <br /> MW-10 during the last four quarters (highest concentration of 12 ppb) and the hydraulic <br /> gradient has been consistently toward the east to southeast, it is EMCON's opinion that a <br /> monitoring well south of monitoring well MW-10 (laterally crossgradient) is not warranted at <br /> this time <br /> GROUNDWATER MONITORING: THIRD QUARTER 1995 <br /> EMCON was contracted by ARCO to conduct the field work at the site Field work included <br /> measuring depths to water and collecting groundwater samples for subjective and laboratory <br /> analyses EMCON used these data to evaluate the direction and gradient of groundwater flow <br /> beneath the site <br /> On August 28, 1995, a technician from EMCON measured depths to water and collected <br /> groundwater samples from wells MW-1 through MW-8 and MW-10 for subjective and <br /> laboratory analyses The remediation system was operational during the site visit Floating <br /> product or product sheen was not noted in samples from the wells (see Table 1) Sampling <br />. and analyses procedures are presented in Appendix A <br /> SA(\N\P1MOM05i1404ES-95\pas i <br />