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Limited Groundwater Investigation 11 6.0 CONCLUSIONS Groundwater was encountered at approximately 21 feet bgl at Lathrop facility and approximately 29 feet bgl at the French Camp facility. Groundwater samples collected from these zones by direct push sampling methods were found to contain dissolved Cr VI at concentrations above the PHG of 0.2 µg/L at two sample locations (LP-G2 and LP-G4) at the Lathrop facility and all five sample locations (FC-G1 through FC-G5) at French Camp facility. In most cases these concentrations were lower than the concentrations reported previously in the stockpile extracts DIWET and storm water samples from each facility (Brown and Caldwell,April 2001). The total Cr and dissolved Cr concentrations reported in the groundwater samples were greater than the PHG of 2.5 µg/L at all sample locations except for the dissolved Cr concentration at LP-G3 and LP-G5 at Lathrop and FC-G1 at French Camp. Total Cr concentrations were found to be several orders of magnitude greater than the dissolved Cr levels. In most cases, the total Cr concentrations were greater than the stockpile extracts and the storm water sample results (Brown and Caldwell, April 2001),where as the dissolved Cr concentrations were less than the storm water sample results. Additionally, the high total Cr levels observed in the grab groundwater samples (highest reported concentrations of 1,700 µg/L at French Camp and 2,100 4g/L at Lathrop) may be attributed to background concentrations of Cr associated with the suspended soil observed in the samples. Based on the data presented in this report and the reported Cr background values for San Joaquin County, Brown and Caldwell believes that the elevated levels of total Cr detected in the grab groundwater samples may be attributed to background conditions. Additionally the Cr VI levels observed in groundwater were less than that found in the extracts DIWET of the cement from each facility (Brown and Caldwell,April 2001),where as the total Cr in most cases was greater than the cement extract levels. 7.0 REFERENCES Brown and Caldwell, March 2001,Workplan for A Limited Groundwater Investigation, MonierLifetile,LLC Lathrop and French Camp Facilities, California (March 27, 2001) Brown and Caldwell, March 2001,Workplan for Stockpile Sampling, MonierLifetile,LLC Lathrop and French Camp Facilities, California (March 30, 2001) Brown and Caldwell,April 2001, Stockpile and Storm Water Sampling Report, MonierLifetile,LLC Lathrop and French Camp Facilities, California (April 27, 2001) California Department of Water Resources, September 1975, California's Groundwater, Bulletin 118. California Waste Extraction Test (WET),Title 22 of the California Code of Regulations, Division 4, Chapter 30, Subsection 66700, using deior zed water. PAw•p\jobs\20587\LP FCGW.doc—DCN I02300 June 2001