ARCHIVED REPORTS_2011_3 - Laserfiche WebLink

Home Browse Search

VOCs Two VOCs (Trichloroethene, and 1,1-Dichloroethene) at concentrations below 2 ppb were reported in samples collected from well MW-3 during the lst and 2nd semester 2011 sampling events. These detections will continue to be scrutinized in the future. As previously described,the County suspects that this new detection of VOCs at MW-3 is related to the placement of a gas-tight HDPE membrane over Module"I" refuse. VOCs were not detected in any other well during 2011. Collection of LFG was improved in the second quarter 2011 by installing a replacement well GX-2A and increasing the size of collection pipes that serve wells GX-7 and-9. The County continues to be concerned that installation of impermeable liner over refuse decreases the potential venting of LFG in spite of the presence of a LFG collection system. Sealing the refuse from the air can increase the potential for contamination of groundwater by LFG entering the soil beneath the landfill. Surface Water Surface water samples were last taken from the creek flowing along the eastern property boundary during the first semester 2011. The results of analyses of the upstream and downstream samples were similar, showing that the surface water contribution to the stream did not degrade the quality of the stream. In fact,the downstream sample had a lower concentration in both total dissolved solids and electrical conductivity than the upstream sample,possibly indicating that the surface water from the landfill contributes less to the stream than upstream surface water. Surface water was not flowing in the second semester due to lack of rain. Note that the creek receives contribution from the ground surface and several smaller creeks on the neighbor's properties east of the creek, and that these surfaces and the creek itself are subject to cattle grazing(and defecation). Surface water from these adjacent properties also enters the stream, and is included in the samples taken. HISTORICAL TIME SERIES PLOTS AND STIFF DIAGRAMS Constituents not detected are plotted at a value of half their respective detection limits in the Historical Time Series Plots (Appendix F). Outliers were included in the plots as directed by RWQCB staff. Stiff diagrams are submitted annually with the second semester and annual report. The stiff diagrams submitted for the first and second semesters indicate a calcium-bicarbonate water type since these ions have the highest concentrations in the six wells (Appendix F). The water type is similar in all wells as indicated by similarity in concentrations of the various constituents and the similarity in diagram shapes. This similarity indicates that the groundwater is not impacted as it moves under the landfill. The shapes of the diagrams between the first and second semesters are also very similar indicating that the general groundwater quality has not changed throughout the year, which is also an indication of no impact from the landfill. PROGRESS OF EVAPOTRANSPIRATION COVER The purpose of the evapotranspiration cover is to capture rain water during the wet months, allowing the vegetation growing on that cover to remove the water from the soil during the dry months,restoring the ® storage capacity of the soil for the next rainy season. Providing storage for rainwater each year prevents the percolation of water into the refuse. The intention of this closure method is to minimize water percolating Foothill Sanitary Landfill 12 Department of Public Works/Solid Waste 2"d Semester and Annual 2011 Groundwater Monitoring County of San Joaquin—January 31,2012