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1.2 REGULATORY SETTING State and Federal regulations (Title 27 CCR, Section 21090 and Title 40 CFR, Subpart F, Section 258.60) require that closed landfills construct a prescriptive final cover system. In California, that prescriptive final cover system includes, at a minimum, a two foot thick foundation layer, a one foot thick low-hydraulic conductivity layer, and a one foot thick erosion resistant layer. As part of the prescriptive final cover system, the low-hydraulic conductivity layer must exhibit a saturated hydraulic conductivity of less than 1 x 10"6 cm/sec, or equal to the hydraulic conductivity of the bottom liner system or underlying natural geologic materials. 1 Alternative final cover systems are allowed if their performance is equivalent or superior to the ' prescriptive cover design. Alternative final cover systems that minimize infiltration by maximizing evapotranspiration(ET or water balance covers) are becoming a commonly accepted design for final closure of municipal solid waste facilities in California. These cover systems combine the moisture retention characteristics of moderate hydraulic conductivity soils with the evapotranspiration characteristics of an established plant community to provide infiltration control. The alternative final cover system at the FSL was constructed using 4-feet of select on-site borrow soils as described in the "Construction Quality Assurance (CQA)Report: Stage lA Partial Final Closure at the Forward Landfill" (Vector Engineering, Inc., 2006). While the initial performance of these soils satisfied the minimum performance criteria for a prescriptive final cover constructed over an unlined waste footprint, FSL elected to monitor the performance of this as-built prescriptive system for two reasons. First, it is understood that the performance characteristics of a prescriptive final cover over an unlined footprint are likely to degrade over time. As a result, it is anticipated that within relatively few years the initial prescriptive performance will degrade. As a result,while FSL considered it practical to install the final cover as a prescriptive system the intention is to maintain it as an alternative. This allows for the establishment of more robust and deeper rooting plant communities that will be more effective at controlling infiltration over the long term. Secondly, the purpose of monitoring was to establish a performance history that would allow FSL to seek regulatory approval of this final cover section as an alternative to the prescriptive final cover over lined portions of the site. ' Subsequent to final cover construction, GLA installed moisture monitoring probes and lysimeters at the site (Figures 1 and 2) and began monitoring the final cover on July 28, 2006. In August 2008, Forward Inc. received a letter from the RWQCB which stated"that the alternative cover complies with Title 27 requirements." Although the RWQCB mentions that "the only problem with the test is both [previous] years had below normal rainfall." In response to the low rainfall years Forward Landfill, Inc. has continued to operate and monitor the system for a third year. It should be mentioned in the last year, no moisture percolated through the cover ' into the waste (as measured by the lysimeters), though again, the site received below normal rainfall. I 2 Geologic Associates