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GeoSyntec Consultants The vegetative layer will be constructed with on-site silty and clayey sands (SM) or (SC). The soils shall be placed at a minimum relative compaction of 85% (ASTM D1557). A minimum 2 -inch thick organic layer of shredded green waste or straw/hay will be placed over the vegetative layer after placing the grass seed mix. This organic layer will help retain moisture for seed germination as well as minimize raindrop impact and associated erosion. Forward has successfully used the following seed mix, from JDM Landscaping in Lodi, California, for erosion control at the site: • 50% Annual Ryegrass 15% Gosse Subterranean Clover, Pel-Koted 10% Hykon Rose Clover, Pel-oted 10% Crimson Clover, Pel-Koted 6% California Poppy 5% Bachelor Buttons 0 0 2% Garden Favorites Wildflower Mixture 2% Lupine -Blue An alternative, monolithic final cover may be pursued by Forward for the WMU B closure in lieu of the prescriptive cover. Per §21090, the RWQCB can allow any alternative final cover design that it finds will continue to isolate the waste in the Unit from precipitation and irrigation waters at least as well as would a final cover built in accordance with applicable prescriptive standards. Large-scale field demonstrations at Sandia National Laboratories have demonstrated that thick, monolithic or evapotranspiration covers can achieve lower infiltration rates than prescriptive clay covers in and climates [Dwyer, 19981. Infiltration control in a monolithic cover system relies on the storage of moisture within the cover soil during the rainy season, and on the subsequent release by evapotranspiration of the stored moisture during the dry season [Zornberg and Caldwell, 1998]. An alternative, monolithic cover is currently being installed over the OR hazardous waste landfill in Southern California [Somasundaram, et al., 19991. J.\ALLIED\FORWARD\CLOSUREPLAN\REPORT 3-8 99.11.30