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Californ° egional Water Quality C Tirol Board <br />Central Valley Region <br />Karl E. Longley, ScD, P.E., Chair <br />Linda S. Adams , , i- Arnold <br />Secreta Sacramento Office <br />rY1or Environmental 11020 Sun Center Drive 8200, Rancho Cordova, California 95670-6114 Schwarzenegger <br />Protection wt x� Phone (916) 464-3291 •FAX (916) 4644645 r Governor <br />hup:Hww.waterboards.ca.gov/centralvalley 7 <br />5 August 2008 <br />Mr. Kevin Basso, General Manager <br />Forward Inc. <br />1145 West Charger Way <br />Stockton, CA 95206 <br />ALTERNATIVE FINAL LANDFILL COVER, EQUIVALENCE TO TITLE 27 PRESCRIPTIVE <br />COVER, FORWARD LANDFILL, SAN JOAQUIN COUNTY <br />Regional Water Board staff has reviewed the "Second Year Moisture Monitoring Performance <br />Report" (Report) submitted on 21 July 2008. The Report uses temperature, precipitation, soil <br />moisture and soil suction potential data collected over two years to demonstrate -that Forward's <br />alternative ET cover performs as well as a prescriptive cover. <br />Forward constructed a minimum 4 -foot thick monolithic soil cover on the north slope of the <br />Austin Road landfill as an alternative final cover demonstration. The cover was constructed of <br />clayey silt from an onsite soil borrow area and was hydroseeded with native vegetation seed <br />mix. Two monitor stations to collect soil moisture and soil suction potential data at 12 -inch, <br />24 -inch and 36 -inch depths were installed. The monitoring stations were installed in July 2006 <br />and have collected two years of cover performance data. The only problem with the test is <br />both years had below normal rainfall. <br />Based on the cover design model, the pre -construction materials testing, the cover <br />construction testing, the cover performance data (this Report) and on other published <br />alternative cover performance results (information generated by the ACAP program) staff <br />makes the following conclusions: <br />1. The ACAP testing has demonstrated that properly designed and constructed ET <br />alternative landfill covers perform as well and may have some advantages over Title 27 <br />prescriptive covers in climates like California's Central Valley. <br />2. Design modeling indicates that a four -foot thick alternative ET cover constructed with <br />Forward's specific soils and under Forward's specific climatic conditions will outperform <br />a prescriptive cover even in high rainfall years. <br />3. The cover performance monitoring collected over a two year period demonstrates that <br />this cover performed as well as or better than a prescriptive cover. Moisture did not <br />percolate through the cover into the waste and likely dry season evapotranspiration <br />exceeded wet season percolation (net negative flux). <br />California Environmental Protection Agency <br />0 Recycled Paper <br />