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t*N" Environmental Technology Inc All laboratory analytical results including QA/QC and chain-of-custody documentation are enclosed in Appendix D. Table 3 also includes the historical data for wells MW-1 through MW-6, and new data for MW-7 and MW-8 ' The groundwater level observations (Table 3) indicated a consistent increase of groundwater levels of 9 68 (MW-7) to 10 24 (MW-5) feet during the reporting ' period (10/25/95 to 02/08/96). It should be noted that the fluctuation in groundwater level is a common occurrence in the Stockton area as reported by Applied Consultants Data, April 9, 1994 Figure 4 presents the groundwater contour map. The general groundwater flow direction is toward the west- southwest during the reporting period. During the reporting period 10/25/95 to 02/08/96, seven wells (MW-1, MW-2, ' MW-3, MW-4, MW-6, MW-7, and MW-8) showed significant decreases in TPH-g concentrations in groundwater. TPH-g concentrations in four wells (MW-2, MW-3, MW-6, and MW-8) decreased to below laboratory detection limits, and MW-5 has remained below the detection limit Benzene concentrations in ' groundwater has decreased in six wells (MW-1, MW-2, MW-4, MW-6, MW-7, and MW-8). Wells MW-3 and MW-5 showed slight increases in benzene concentrations. A TPH-g concentration contour map and a benzene ' concentration map are shown in Figures 5 and 6, respectively 6.0 SAMPLE QUALITY ASSURANCE CONTROL PLAN All soil and water samples collected by SOTA were analyzed by Del Mar Laboratory, Irvine, California Del Mar is a state certified laboratory and is contracted with UHI for laboratory services SOTA provided the appropriate chain-of-custody documentation to ensure that ' Del Mar Laboratory performed the appropriate quality assurance program The Del Mar laboratory quality assurance (QA) program encompasses all facets of activity that may have a bearing on the date, from sample integrity, to data quality, to proper verification, and finally documentation Del Mar's QA plan is modeled after the EPA 16 point Manual QAMS-004/80 The quality assurance program is an essential part of the analytical protocol ' and is used by all levels of the professional staff'to detect and correct problems in the measurement process or to demonstrate attainment of a state of statistical control. The goal of the quality assurance program is to reduce ' measurement errors and to assure that the results have a high probability of being acceptable in quality Two concepts are involved In Del Mar's plan (1) Quality Control, the mechanism established to control errors, and (2) Quality Assessment, the system used to verify that the analytical process is operating within acceptable limits 8