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QUARTERLY GROUNDWATER MONITORING PROGRAM EAST BAY MUNICIPAL UTILITY DISTRICT FIRST QUARTER 1993 1 ' 1.0 INTRODUCTION The 1993 groundwater monitoring program at the East Bay Municipal District (EBMUD) Stockton Center (Figure 1) consists of monitoring groundwater elevation in all seven wells on the site and sampling four wells for analysis of total petroleum hydrocarbons as gasoline (TPH-G) The purpose of the monitoring program is to acquire additional data on the distribution and concentrations of petroleum hydrocarbon compounds in groundwater beneath ' the site The scope of this monitoring program was agreed upon by EBMUD and the San Joaquin County Public Health Services Environmental Health Division (EHD) in a meeting between EBMUD and EHD on January 19, 1993 ' This report summarizes the sampling methods utilized and presents the field and analytical results for the first quarter 1993 groundwater monitoring event ' 2.0 GROUNDWATER MONITORING SUMMARY The groundwater monitoring and sampling work was conducted on March 2, 1993 Groundwater elevation measurements were collected in all seven wells prior to collecting groundwater samples from wells MW-1, MW-2, MW-5 and MW-7 One quality control sample, labelled MW-8, was collected as a blind duplicate of primary sample MW-1 in order to evaluate laboratory reproducibility Monitor well locations are shown on Figure 2 and a detailed description of field activities is presented in Appendix A 2.1 Physical Parameters Summary Groundwater elevation was measured to determine the groundwater flow direction and gradient ' beneath the site Figure 3 presents groundwater elevation contours which indicates that the groundwater flow is toward the northeast and east Groundwater physical parameters of temperature, pH, and electrical conductivity were recorded during the purge of each well ' sampled These data are presented in Table 1 2.2 Chemical Analysis Summary ' Groundwater samples were collected for analysis of TPH-G from wells MW-1, MW-2, MW-5 and MW-7 The analytical results are summarized in Table 2 and the complete analytical report is presented in Appendix B All wells sampled contained no detectable hydrocarbons except for ' MW-1, which contained 2,700 µg/L of TPH-G The blind duplicate of MW-1, labelled MW-8, contained 3,200 µg/L TPH-G which indicates reasonable comparability between the primary and duplicate sample To provide a means of reviewing groundwater quality historical trends on the site, Table 3 presents previous groundwater analytical results together with the current results For this chart, all previously reported results have been converted to yg/L to eliminate inconsistency in units Comparison of the current analytical results with results of two previous sampling rounds indicates that the TPH-G concentration in March 1993 compares closely with the concentration found in the well in July 1992 The 3,200,000 µg/L TPH-G concentration shown for October ' 1992 appears to be anomalous ' ST1,1RMNI LIMLILII4TT WP 1 04/07193