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ANNUAL SUMMARY Groundwater General Water Quality Parameters The following is based on use of data from crossgradient well MW-1 as if it were upgradient of the landfill. As previously noted, although exceedences for sodium and bicarbonate are reported by Sanitas software they are not valid indication of impact from landfill activities.. Additional monitoring data from new background well MW-4 will provide new tolerance limits for all parameters,including sodium and bicarbonate. Until sufficient data from MW-4 is available for that analysis, conclusions regarding possible groundwater impacts will be based on review of the data and exceedences to concentration limits based on data from MW-1 will be considered provisional. The following annual compliance review was prepared for each well: • Well MW-1: Groundwater samples were unable to be obtained during the second semester 2009 sampling events due to low water levels. Therefore, the reliance on MW-1 as an indicator of background water quality conditions could lead to false impressions of landfill impact. • Well MW-2R: No General water quality parameters were exceeded during either the 1St or 2°d semester 2009 sampling events. • Well MW-3: Chloride was recorded at 9.73 mg/L in the first semester which slightly exceeded the tolerance limit of 9.7 mg/L. Bicarbonate was recorded at 140 mg/L in the first semester which exceeded the tolerance limit of 130 mg/L. Sodium was recorded at 17 mg/L in the second semester which slightly exceeded the tolerance limit of 16 mg/L. However, these provisional exceedences may be false, as MW-1 as could not be sampled during this monitoring period and insufficient data exists for MW-4 to develop a more appropriate chloride, sodium, and bicarbonate concentration limits. The MCL for chloride was not exceeded. These Chloride and sodium concentrations represent good water quality. • Well MW-4: Bicarbonate was recorded at 140 mg/L in the first semester, 3`d and 4th quarters,respectively, exceeded the tolerance limit of 130 mg/L. However, MW-4 is hydraulically upgradient from the landfill and concentration limits calculated at side gradient well MW-1 would not apply to this well. • Well MW-5: Sulfate was recorded at 10.93 mg/L in the first semester which exceeded the tolerance limit of 9.7 mg/L. However, this provisional exceedence may be false, as insufficient data exists for MW-4 to develop a more appropriate sulfate concentration limit. The MCL for sulfate was not exceeded. These sulfate concentrations represent good water quality. It also should be noted that there are no MCLs for sodium or bicarbonate alkalinity. Foothill Sanitary Landfill 13 Department of Public Works/Solid Waste 2nd Semester and Annual 2009 Groundwater Monitoring County of San Joaquin—January 31,2010