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4.0 CHEMICAL QUALITY OF GROUNDWATER Interim performance monitoring, in the form of groundwater sample collection and laboratory analysis 1 fr for total dissolved chromium and hexavalent chromium,was performed for California Water Supply I Wells,domestic wells,and irrigation wells in January 2005. Select accessible monitoring wells were sampled for total dissolved chromium in January 2005 (Tables 3 and 4). The Annual Evaluation Report L addresses data gaps for analytical results in greater detail (Dudek, 2005). This interim sampling was I conducted in accordance with the RWQCB letter dated 14 August 1996(RWQCB, 1996). Original and field duplicate groundwater samples were analyzed by GeoAnalytical for total dissolved chromium using USEPA Method 6010,and hexavalent chromium using USEPA Method 7199 (Appendices A and B). The detection limit for total dissolved chromium was 5 ug/l. The detection limit for hexavalent I t6, chromium was 0.5 ug/l. The results are presented in Tables 3 and 4. Quality assurance/quality control(QA/QC)sampling in January 2005 included collection and analysis of field duplicate groundwater samples(Tables 3 and 4;Appendices A and B). Laboratory QAIQC documentation was included with analytical reports from GeoAnalytical (Appendices A and B). The QC report produced by GeoAnalytical included matrix spike and matrix spike duplicate samples of known ` concentration for both total dissolved chromium and hexavalent chromium, the relative percent difference between the matrix spike and matrix spike duplicate, and percent recovery of a laboratory j ` control sample(Appendices A and B). Based on the QC report supplied by GeoAnalytical, the relative percent difference between matrix spike and matrix spike duplicate samples ranged from 0.6%to 4.0% ` for total dissolved chromium, and 0.4%to 2.0% for hexavalent chromium. The percent recovery of the laboratory control samples ranged from 100.9%to 108%recovery for total dissolved chromium,and r 102%recovery for hexavalent chromium. No acceptable ranges for relative percent difference and percent recovery were provided in the laboratory analytical reports. r 4.1 Soil Flushing System r 4.1.1 January 2005 Groundwater samples were collected from 4 extraction wells, 8 lysimeters,and 9 monitoring tubes and analyzed for total dissolved chromium concentrations in January 2005. Three shallow zone extraction wells had detectable concentrations of total dissolved chromium at concentrations ranging from 8.9 ug/1 1 - ` Marley Cooling Technologies 3909-09 Semi-Annual Groundwater Monitoring Report Dudek&Associates,Inc. October 2004/January 2005 -13- April 2005