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0 0 TECHNICAL MEMORANDUM Evaluation of Bed Ash Disposal Forward Landfill San Joaquin, California November 1, 2016 Page 7 per unit area was calculated using the Giroud (1997) equation summarized in Table 3.4 Principal assumptions incorporated into these calculations included: • A constant leachate head of 1 foot (the maximum allowable head for Subtitle D liner systems) is always present on the liner; • Two circular 0.35-cm diameter defects are present in each unit area; • Continuous contact between the geomembrane and clay was assumed; and • The CCL is 2-feet-thick and has a saturated hydraulic conductivity of 1E-'cm/sec. As indicated in Table 3,the unit 1-acre leakage rate calculated by this procedure (QAi in Table 3) was 3.17E-6 meters per year (m/yr). For the case of bed ash disposal at Forward Landfill, and other factors being equal, the leakage rate and the time required to deplete the soluble copper in the bed ash will depend on the location and thickness of the ash within each of the areas shown in Figure 1. Because the actual disposal locations and ash thicknesses within each area are not known, two alternative disposal scenarios were considered to reasonably represent bed ash leaching potential and rates of leakage: • Disposal Alternative 1 assumed the bed ash was placed in a continuous uniform layer across the entire disposal area (Table 4A); and • Disposal Alternative 2 assumed the bed ash was sequestered in each disposal area in an approximately 2-foot-thick lift (Table 4B). The time required to deplete the source was approximated based on the median total copper concentrations,estimated leaching factors,and median STLC copper concentrations summarized in Table 2 and the annual average precipitation for the site area. As summarized below, the results of these analyses indicate a significant higher leakage rate is associated with Alternative 1. However,the time required to deplete the available copper from the bed ash is much shorter than the time required to deplete the relatively thicker source associated with Alternative 2: 4 The assumption of circular defects is not particularly important;similar results are obtained if rectangular or square defects are assumed.