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i <br /> L 4.0 CHEMICAL QUALITY OF GROUNDWATER <br /> LInterim performance monitoring, in the form of groundwater sample collection and laboratory analysis <br /> for total dissolved chromium and hexavalent chromium,was performed for California Water Supply I <br /> Wells,domestic wells, and irrigation wells in January 2005. Select accessible monitoring wells were <br /> sampled for total dissolved chromium in January 2005 (Tables 3 and 4). The Annual Evaluation Report <br /> t addresses data gaps for analytical results in greater detail (Dudek,2005). This interim sampling was <br /> conducted in accordance with the RWQCB letter dated 14 August 1996(RWQCB, 1996). Original and J <br /> field duplicate groundwater samples were analyzed by GeoAnalytical for total dissolved chromium using 1 <br /> USEPA Method 6010, and hexavalent chromium using USEPA Method 7199 (Appendices A and B). <br /> L The detection limit for total dissolved chromium was 5 ug/l. The detection limit for hexavalent J <br /> chromium was 0.5 ug/1. The results are presented in Tables 3 and 4. <br /> Quality assurance/quality control (QA/QC)sampling in January 2005 included collection and analysis of <br /> field duplicate groundwater samples(Tables 3 and 4;Appendices A and B). Laboratory QA/QC <br /> L documentation was included with analytical reports from GeoAnalytical (Appendices A and B). The QC <br /> report produced by GeoAnalytical included matrix spike and matrix spike duplicate samples of known <br /> concentration for both total dissolved chromium and hexavalent chromium,the relative percent <br /> difference between the matrix spike and matrix spike duplicate, and percent recovery of a laboratory <br /> L, control sample (Appendices A and B). Based on the QC report supplied by GeoAnalytical, the relative <br /> percent difference between matrix spike and matrix spike duplicate samples ranged from 0.6%to 4.0% <br /> `. for total dissolved chromium, and 0.4%to 2.0% for hexavalent chromium. The percent recovery of the <br /> laboratory control samples ranged from 100.9%to 108%recovery for total dissolved chromium, and <br /> L102%recovery for hexavalent chromium. No acceptable ranges for relative percent difference and <br /> percent recovery were provided in the laboratory analytical reports. <br /> i <br /> t_ <br /> 4.1 Soil Flushing System <br /> 4.1.1 January 2005 <br /> Groundwater samples were collected from 4 extraction wells, 8 lysimeters, and 9 monitoring tubes and <br /> analyzed for total dissolved chromium concentrations in January 2005. Three shallow zone extraction <br /> wells had detectable concentrations of total dissolved chromium at concentrations ranging from 8.9 u9/1 <br /> 3909-09 <br /> Marley Cooling Technologies Dudek&Associates,Inc. <br /> 4 Semi-Annual Groundwater Monitoring Report <br /> { <' -13- April 2005 <br /> - October 2004/January 2005 <br /> ii <br />