ARCHIVED REPORTS_QUARTERLY MONITORING REPORT FIRST QUARTER 2007

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IQuarterly Monitoring Report Page 3 Morton-Alco&Unocal Operable Units April 27,2007 WKA No.6324.02 3.2 Site History The following information was obtained from Clayton Group Services quarterly reports and RWQCB MRP Nos. R5-2004-817 and R5-2004-818. Both the Unocal OU and Morton-Alco OU sites have been undergoing environmental investigations since 1989. These investigations included extensive subsurface investigation consisting of subsurface sampling and analysis of soil- vapor, soil, and groundwater. Laboratory tests were conducted on the samples collected in order to evaluate the occurrence and distribution of petroleum hydrocarbons,metals and metal compounds, tvolatile organic compounds (VOCs), semi-volatile organic compounds(SVOCs), and light non- aqueous phase liquids (LNAPL). Approximately fifty-three(53) groundwater-monitoring wells are currently located in the vicinity of the site. Of these 53 monitoring wells, as listed previously,three are associated with the Morton-Alco OU and eight are associated with the Unocal OU. ' 4.0 MONITORING AND SAMPLING The DTW and DTP measurements were obtained on February 5, 2007 in conjunction with groundwater monitoring and sampling activities conducted by Secor at nearby sites as required by the RWQCB. Coordinated groundwater monitoring was conducted within an 8-hour period of Secor's monitoring activities. DTW was measured from the top-of-casing of each well, either from the north side or as indicated by survey marks on the casing edge. Monitoring well construction details for the wells of interest are presented in Table 1. The groundwater monitoring well network at the site consists of eleven monitoring wells (listed previously) (Figure 2). The surveyed top-of-casing elevations for the monitoring wells are presented in Table 1. The survey data presented in Table 1 is based on a horizontal and vertical control survey conducted by Morrow Surveying Inc. of West Sacramento, California in October 2005. 4.1 Groundwater Monitoring On February 5, 2007 WKA conducted first-quarter 2007 groundwater monitoring and sampling at the site. Monitoring consisted of measuring DTW and DTP, if present, in all monitoring wells. All measurements were obtained with an electronic sounder or inter probe (IP)with a tape graduated in 1/100ths of a foot. Measurements were obtained to an accuracy of±0.01 feet.