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L L 1.0 INTRODUCTION LOn behalf of Marley Cooling Technologies(MCT),Dudek&Associates, Inc. (Dudek)has prepared this report, summarizing groundwater monitoring activities at the MCT facility in Stockton,California during October 2004 and January 2005 (Figure 1). This report includes an analysis of groundwater elevation data, groundwater flow, and groundwater quality data collected during the sampling events; I L At the conclusion of the January 1997 Annual Full-Scale Soil Flushing, Groundwater, and Performance Monitoring event at the MCT facility, the California Regional Water Quality Control Board (RWQCB) 6 allowed the reporting frequency to be reduced from quarterly to semi-annually. Water levels were measured quarterly during the months of January,April, July and October. Selected wells were sampled 6 during the months of April and October and the results reported semi-annually. In a letter dated July 11, 2002,the California Regional Water Quality Control Board approved a change in monitoring frequency which eliminated the April and October sampling of wells for total dissolved chromium. Groundwater elevation data will continue to be collected on a quarterly basis. The sampling of select wells for total 6 dissolved chromium and hexavalent chromium will continue on a semi-annual basis during the months of January and July. Groundwater elevation data was collected in October 2004 and January 2005 by GeoAnalytical L, Laboratories, Inc. (GeoAnalytical), of Modesto, California. Domestic and irrigation wells,all reclamation and extraction wells, and select monitoring wells were sampled for total dissolved chromium '` in January 2005 (Figure 2). Select domestic and irrigation wells and California Water Service(CWS) wells were sampled for hexavalent chromium in January 2005. The sampling schedule for January 2005 Lis summarized in Table 1. ` Groundwater samples collected in January 2005 were analyzed for total dissolved chromium using s United States Environmental Protection Agency(USEPA)Method 6010. Groundwater samples were Lalso analyzed for hexavalent chromium using USEPA Method 7199. Laboratory analyses were performed by GeoAnalytical (Appendices A and B). The detection limit of groundwater samples for total dissolved chromium was 5 micrograms per liter(ug/1), and 0.5 ug/1 for hexavalent chromium L —s LMarley Cooling Technologies 3909-09 Semi-Annual Groundivaier Monitoring Report Dudek&Associates,Inc. October 2004IJanuary 2005 -1- April 2005