ARCHIVED REPORTS_2008_2 - Laserfiche WebLink

Home Browse Search

' 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. As previously noted, exceedences for sulfate and bicarbonate are reported by Sanitas software under these circumstances, but are apparently not valid based on evaluation of historic data. ' Additional data from new background well MW-4 will provide new tolerance limits for all parameters, including sulfate 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. The following "exceedences" are therefore considered invalid and do not indicate water quality impact from landfill activities. Monitoring data shows that all constituents were within interwell tolerance limits except for: ' • Well MW-1: Bicarbonate was recorded at 130 mg/L in first semester exceeded the tolerance limit of 110 mg/1. ' • Well MW-2R: Bicarbonate was recorded at 150 mg/L in first semester exceeded the tolerance limit of 110 mg/l. ' • Well MW-3: Bicarbonate was recorded at 130 mg/L in second semester exceeded the tolerance limit of 110 mg/L. • Well MW-4: Sulfate was recorded at 9.88 mg/L and 9.6 mg/l in the first and second ' semesters, respectively, exceeded the tolerance limit of 8.9 mg/l and 8.8 mg/1 respectively. Bicarbonate was recorded at 150 mg/L and 130 mg/l in first and second semesters, respectively, exceeded the tolerance limit of 110 mg/L. • Well MW-5: Sulfate was recorded at 9.93 mg/L and 9.99 mg/L in the first and second semesters, respectively,exceeded the tolerance limit of 8.9 mg/L and 8.8 mg/L respectively. Bicarbonate was recorded at 130 mg/L during the first and second semesters exceeded the tolerance limit of 110 mg/L. It also should be noted that sulfate concentrations in the Foothill Landfill wells (approximately 10 mg/L or less) are far below the secondary maximum contaminant level (MCL) of 250 mg/L, indicating good water quality. There is no MCL for bicarbonate alkalinity. VOCs ' Two VOCs (1,1-Dichloroethene and Acetone) were reported in samples collected from well MW-2R on July 29, 2008, but were not reported in this well when re-sampled on August 28, 2008; therefore, the first reports were erroneous, probably due to laboratory contamination. Other than those false positives, VOCs were not detected in any wells during the first and second semester 2008 sampling events, and have not been confirmed in any well since October 2001. Foothill Sanitary Landfill j 1 Department of Public Works/Solid Waste 2'd Semester and Annual 2008 Groundwater Monitoring County of San Joaquin—January 31,2009