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2.0 FIELD INVESTIGATION In early May, 2005, GeoLogic Associates, Inc. (GLA) conducted a field investigation of the on-site borrow source and existing interim cover over the proposed closure footprint of the North and Northwest slopes of the FSL(Figure 1). During these investigations, the thickness of existing interim cover was measured and representative soil samples were collected from each of the areas. The soil samples collected were tested to identify the input parameters necessary for modeling the infiltration performance of these soils when used in final cover construction at the site. 3.0 LABORATORY TESTING In accordance with ASTM and other acceptable standards, the proposed on-site borrow soils and the existing cover soils were tested for classification(ASTM D-2487),moisture content(ASTM D-2216), gradation analysis(ASTM D-422),maximum relative density and optimum moisture content(ASTM D-1557),permeability testing(ASTM D 5084) and soil matric potential (ASTM D-6836). The results of the laboratory testing conducted on the selected samples are summarized in Table 1, and complete test results are included in Appendix A. With regard to permeability, it should be noted that the bulk of the available borrow soils are expected to yield a remolded saturated hydraulic conductivity of less than 1x10-6 cm/s (the prescriptive standard for an unlined cell). As indicated by the testing of relatively undisturbed samples of the interim cover however, it is likely that these soils will weather over time to yield a long-term in-situ conductivity of greater than 1x10-6 4.0 COVER MODELING 4.1 GENERAL The infiltration modeling program LEACHM (Leaching Estimation and Chemistry Model) was selected for the alternative final cover analyses summarized herein. LEACHM is a one-dimensional finite difference computer model developed at Cornell University. The model simulates water and solute transport in unsaturated or partially saturated soils to a depth of about two meters. Estimates of plant growth and absorption of water by plant roots are included in the model as are climatic factors such as precipitation and evaporation. LEACHM is able to predict net flux through a final cover soil configuration by allowing the user to stipulate laboratory determined matric potential/soil moisture content relationships, bulk density/porosity relationships, and saturated hydraulic conductivity values. These values are transformed in a curve fitting routine to produce the air entry value and exponent ("a" and"b" coefficients)used in Campbell's retentivity equation. Unsaturated hydraulic conductivity is then estimated for a given soil moisture content using Campbell's conductivity -3- C:\2003-033\EDOM HILL ALTERNATIVE COVER.DOC\6/16/200$ GeoLogic Associates