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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 2010. 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. 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. Surface water from these properties also enter 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 VEGETATION 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, increasing the storage capacity of the soil for the next rainy season. A key component of this method is the vegetation established. Perennial plants, such as purple needle grass and California Brome, grow deep roots that can gather moisture from deep within the closure soil layer and are much preferred. In contrast, annual species, such as rye grass,produce shallow roots. In contrast, annual grasses produce a significant quantity of seed,but do not establish deep roots. The evapotranspirative (ET) cover was established in December 2008 when the soil of much of the top deck area was amended, fertilized and reseeded. Growth in the spring of 2009 was ® successful. Weeds were pulled in early May 2009 to reduce intrusion of wind-blown seeds into the preferred species. In June 2009, growth was between three and four feet high. Foothill Sanitary Landfill 14 Department of Public Works/Solid Waste 2"d Semester and Annual 2010 Groundwater Monitoring County of San Joaquin—January 31,2011