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URS Mr. Ross Atkinson Regional Water Quality Control Board—Central Valley Region May 20,2011 Page 8 of 10 • Lead -Lead was not detected on a consistent basis within the groundwater samples collected from any of the monitoring wells. Lead was detected in 8 of 18 events for MW-1, 12 of 18 events for MW-2, and 10 of 18 events for MW-3. However, lead was only detected above the reporting limit of<0.01 mg/L on three occasions (4Q07, 4Q08,and 2Q09). A trend in the lead data could not be established with any certainty. For the 4Q07 and the 4Q08 events, the lead results within all of the monitoring wells exceeded the MCL of 0.015 mg/L, and for the 2Q09 event,the lead concentration exceeded the MCL in MW-2. For the 2Q09 event, lead was detected within MW-2 at 0.0154 mg/L, MWA at 0.0106 mg/L, and MW-3 at 0.0114 mg/L. • There is uncertainty as to the validity of the lead data for the 4Q08 event because it was observed that during the 4Q08 event,two other metals (aluminum and iron)were found to be at the highest concentration for the entire monitoring program to date. This was the only time that aluminum was found to be above the report limit and for iron,the concentration of 26.2 mg/L was more than 2 times the next highest reported concentration of 11.2 mg/L. • The highest lead concentration found in the groundwater samples at the DDRW Sharpe site was 0.427 mg/L. This concentration was considered to be within background concentration. The highest concentration found at the World Enterprises site was 0.0823 mg/L (MW-2 during 4Q08). However, there is uncertainty as to the validity of this value. The next highest concentration found at the World Enterprises site was 0.0354 mg/L(MW-2 during 4Q07). Should the highest lead concentration be disregarded due to its uncertainty to its validity,the remaining lead results would be considered within the background concentration for the area when compared to the DDRW Sharpe site. • Manganese -The highest average manganese concentration was found in MW-1 at 4.01 mg/L. The lowest average manganese concentration was found in MW-3, and for the past eight quarters the concentration was below the reporting limit of the analysis of<0.01 mg/L. The average manganese concentration was found in MW-2 at 3.52 mg/L. The concentration within MW-I and MW-2 exceed the SMCL of 0.050 mg/L, as does the constituents of TDS and iron; 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 • Nickel -The highest average nickel concentration was found in MW-2 at 0.171 mg/L. The lowest average concentration was found in MW-3, and for the past 9 quarters and 14 of 16 quarters, the concentration was below the reporting limit of the analysis of<0.010 mg/L. The average nickel concentration in MW-1 was 0.0101 mg/L. Although the nickel concentration within the former landfill is greater than the up-gradient and down-gradient monitoring wells, it is less than the MCL of 0.10 mg/L; therefore, it could be supplied to the public by the community water systems based on only this constituent. Of the eight constituents identified by RWQCB, aluminum, arsenic, and lead are within background concentration of the area. TDS, iron, and manganese were found to be above the SMCL. Although TDS, iron, and manganese were found to be above SMCLs, these constituents are not considered to present a risk to human health. SMCLs are established only as guidelines to assist public water systems in managing their drinking water for aesthetic considerations, such as taste, color, and odor. In addition, the background concentration of TDS was found to be above the SMCL. Hence, should this groundwater be utilized for drinking water, treatment of this groundwater is needed before it can be supplied to the H:\Wprocess\25532\WorldEiitei-prise\Closttrc\05201 l.doc