ARCHIVED REPORTS_2009_24 - Laserfiche WebLink

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2.0 SITE LOCATION AND CLOSURE The FSL is located at 9999 South Austin Road in Manteca, California and is a combination of two previously existing landfills, the Forward Landfill and the Austin Road Landfill. The facility is owned by Forward Landfill, Inc. and includes 567 acres,though only 388 acres have 1 been landfilled. The Stage 1 partial final closure area includes the northern slopes of the landfall; an environment that should represent the lowest ET microclimate on the site. The monolithic cover constructed over Stage 1 consists of a minimum 4-foot thick soil layer placed over the existing interim cover and/or waste, as necessary to meet final design grades. The soils used to construct ' the alternative final cover consisted of clayey silt derived from an on-site borrow source (Vector Engineering, Inc., 2006). ' 3.0 VEGETATION CHARACTERISTICS The finished surface of the alternative final cover system was hydroseeded after completion of closure construction and some areas were re-seeded in the fall of 2007, after minor grading repairs to the final cover were completed. Hydroseeding was completed using the seed mixture stipulated in the final closure documents (BAS, 2003). At the end of the first year of monitoring, vegetation at the site was in a post-emergent stage with a vegetative cover fraction estimated to be in excess of 20-30 percent overall. It is estimated that roots, in areas with established vegetation, extend to a depth in excess of 12-18 inches. Currently, the vegetative cover fraction for the North Slope area is estimated to be 30-40 percent. Roots continue to develop and it is estimated that vegetative rooting depths still average around 12-18 inches. Some plants and vegetation are still immature and the dry conditions typical at this site have stunted the development of vegetation. As a result,the ultimate performance of the alternative cover has not yet been realized. ' Mowing of the established vegetation also stunts the development of a robust vegetative community. Though mowing is conducted to limit the potential of a fire risk, mowing of plants that are trying to evolve into a mature vegetative community limits the alternative ' (evapotranspiration) cover system from full realization of its moisture control capabilities. Appendix A includes recent pictures taken in early 2009 at each of the monitoring station locations and illustrates the limited vegetation that has been allowed to develop within each of the monitored locations. 4.0 MONITORING SYSTEM The installation of final cover monitoring instrumentation was completed on July 28, 2006 in accordance with the manufacturer's recommendations as outlined in the equipment manuals. Heat dissipation sensors (HDU 229-L) from Campbell Scientific Inc., soil moisture probes (Echo ' Sensors from Decagon Devices, Inc.), and two Gee Passive Capillary Lysimeters manufactured by Decagon Devices, Inc., were installed at each of the two monitoring locations. Figure 2 illustrates the configuration of the instruments installed at each monitoring location. As part of 3 Geologic Associates