ARCHIVED REPORTS_SECOND SEMIANNUAL 2002 GROUNDWATER MONITORING

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GEOMATRIX the Guidelines' low risk criteria. The Guidelines acknowledge that petroleum hydrocarbons may be left in place as long as compliance with Water Quality Objectives (WQOs) is achieved within a reasonable time period. Site data indicate that WQOs will be achieved at that site via natural attenuation(NA). Subsequently, Geomatrix evaluated several remedial technologies (Geomatrix, 2000b) as requested by the RWQCB (RWQCB, 2000), and NA was identified as the most technically and economically feasible remediation alternative for the site. Based on this evaluation and ' additional information provided to the RWQCB (Geomatrix, 2001), the RWQCB (RWQCB, 2002)requested that ChevronTexaco continue to assess the progress of NA at the ' site by conducting semiannual groundwater monitoring in accordance with the revised MRP (RWQCB, 1998) and measuring NA parameters. ' 2.0 GROUNDWATER MONITORING AND SAMPLING The field activities for the second semiannual 2002 groundwater monitoring event (July-December) were conducted on November 26, 2002. In accordance with the MRP and its revisions, five groundwater monitoring wells (MW-5, MW-6, MW-7, MW-8, and MW-12) were included in this monitoring event. The field procedures, analytical methods, and laboratory analytical results are described in the following sections. ' 2.1 FIELD AND ANALYTICAL METHODS The depth to water was measured in the groundwater monitoring wells using an Interface probe. The pH, temperature, and electrical conductivity (collectively referred to as field ' parameters) of the groundwater from each well were measured using hand-held meters during well purging. The monitoring equipment was calibrated and/or checked in the field prior to ' use. To obtain representative groundwater samples, the wells were purged using an electric submersible pump until the field parameters stabilized (a minimum of three consecutive readings with values within 10 percent for each parameter) and a minimum of four casing volumes of water was removed. The wells subsequently were sampled using disposable bailers after purging was completed. The sampling equipment was decontaminated before purging and sampling each well. The ' purge water and rinsate from equipment decontamination procedures were stored temporarily . on site in labeled and sealed 55-gallon drums. The drums subsequently were removed for ' I:\PROJECIVOOOs\2463\DOCUMENM463 12-02 tpt.dw 2