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URS Mr. Ross Atkinson Regional Water Quality Control Board—Central Valley Region May 20,2011 Page 7 of 10 collected during the quarterly monitoring results and from the San Joaquin County Public Works Department website. Based on this information,MW-1 is typically located down-gradient of the former landfill and MW-3 is typically located up-gradient of the former landfill. Because MW-3 is typically up-gradient from the site,the results from this well were considered to be background for this report. • TDS -The highest average TDS concentration was found in MW-2 at 2,270 mg/L. The lowest average concentration was found in MW-3 at 1,080 mg/L. The average concentration found in MW-1 was 1,320 mg/L. TDS concentrations within all of the monitoring wells were found to be above the SMCL. Because these TDS concentrations would exceed the upper level of the SMCL of 1,000 mg/L within all areas of the site including the background area,treatment of groundwater is needed before it can be supplied to the public by community water systems. This constituent is not considered to be a health hazard. • Aluminum -Aluminum was not detected on a consistent basis within the groundwater samples collected from any of the monitoring wells. Should the former landfill material be a source of aluminum,the highest aluminum concentration is expected to be found within the monitoring well located within the former landfill, MW-2. However, the highest concentration was not found in MW-2. It was found in MW-3, located up-gradient from the former landfill at a concentration of 1.44 mg/L. Based on the above information, the aluminum detected at the site is within the background concentration at the site. • Arsenic - Should the former landfill material be a source of arsenic,the highest arsenic concentration is expected to be found within the monitoring well located within the former landfill, MW-2. However,the highest concentration was not found in MW-2. It was found in MW-1, located down-gradient from the former landfill at a concentration of 0.0358 mg/L. • Based on the report by Saracino-Kirby, Inc. (2000)and the DDRW Sharpe groundwater results, arsenic detected at the site is within the background concentration of the area. • Barium -The highest average barium concentration was found in MW-2 at 1.165 mg/L. The lowest average barium concentration found in MW-3 at 0.132 mg/L. The average barium concentration found in MW-1 was 0.552 mg/L. Although barium found at the site could cause additional impairment of groundwater, impairment is not likely to increase because the contaminant area has been limited in area and has not changed(i.e.,the contaminant area is relatively stable). Although the barium concentration within the groundwater of the former landfill exceeds the MCL of 1 mg/L, it does not exceed the MCL in the monitoring well located down-gradient of the former landfill which indicates that barium in groundwater is confined to the former landfill area. • Iron -The highest average iron concentration was found in MW-2 at 4.22 mg/L. The lowest concentration was found in MW-3, and for the past 9 quarters and 17 of 18 quarters, the concentration was below the reporting limit of the analysis of<0.01 mg/L. The average iron concentration within MW-1 was 0.898 mg/L. The concentration within MW-1 and MW-2 exceeds the SMCL of 0.300 mg/L, as does the constituent TDS;therefore,treatment of groundwater is needed before it can be supplied to the public by community water systems. This constituent is not considered to be a health hazard. 1-1:AWprocess\25532\WorldEnterpriseAClosureA05201 Ldoc