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HISTORICAL TIME SERIES PLOTS 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. 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. Early rains of November 2009 allowed the germination of annual seeds and revitalization of perennial grass roots. Much growth of grasses, as well as other species, such as Purple Vetch, was apparent in the spring of 2010 (Photos 1 and 2). The County's consultant with the California Department of Agriculture suggested that the perennial grasses could be selectively encouraged by grazing after those seeds had been dropped by the plants. To enhance perennial grasses, and to control the potential for grass fire,the landfill surface (including the ET closure areas)was grazed by sheep in May and early June 2010 (Photo 3). Purple Vetch and other species palatable to the sheep were quickly removed, as were much of the annual grasses(Photos 4 and 5). It was interesting to note that the sheep avoided the stalks of the Purple Needlegrass. Active perennial plants were more easily observed after grazing(Photo 6). It is likely that removal or trampling of the dry stalks of the annual grasses allows more sunlight to reach the perennial plants, which may increase evapotranspiration. Sheep feces add fertilizer. Depending on the growth of the ET cover over the winter of 2010/2011,the County contemplates grazing in the early spring of 2011, when the annual grasses have developed seed pods, but before the perennial species are developed. Foothill Sanitary Landfill 13 Department of Public Works/Solid Waste 1s`Semester 2010 Groundwater Monitoring County of San Joaquin—July 21,2010