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i GROUNDWATER MONITORING AND SAMPLING REPORT =' BP Oil Company Service Station No. 11195 16500 South Interstate 5 Lathrop, California Project No. 10-151-06-002 February 16, 1998 INTRODUCTION This report presents the results and findings of the January 15, 1998 groundwater monitoring and sampling conducted by Alisto Engineering Group at BP Oil Company Service Station No. 11195, 16500 South Interstate 5, Lathrop, California. A site vicinity map is shown on Figure 1. FIELD PROCEDURES Field activities were performed in accordance with the procedures and guidelines of San Joaquin County Public Health Services and the California Regional Water Quality Control Board, Central Valley Region. f` Before purging and sampling, the groundwater level in each well was measured from a permanent mark on top of the casing to the nearest 0.01 foot using an electronic sounder. The depth to groundwater and top of casing elevation data were used to calculate the groundwater elevation in each well in reference to mean sea level. The survey data.and groundwater elevation measurements collected to date are presented in Table 1. Before sample collection, each well was purged of 3 casing volumes while recording field readings of pH, temperature, electrical conductivity, and dissolved oxygen. Groundwater samples were collected for laboratory analysis by lowering a bottom-fill, disposable bailer to just below the water level in the well. The samples were transferred from the bailer into laboratory-supplied containers. The water sampling field survey forms are presented in Appendix A. SAMPLING AND ANALYTICAL RESULTS The results of monitoring and laboratory analysis of the groundwater samples for this and previous quarters are summarized in'Table 1. The potentiometric groundwater elevations as calculated from the results of this monitoring event are shown on Figure 2. Groundwater elevations ranged from 3.72 to 3.78 foot above mean sea level, therefore groundwater gradient contours were not prepared. The results of groundwater analysis are shown on Figure 3. The laboratory report and chain of custody record are presented in Appendix B.