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vol = [(K)(h/1)(A)] _ [(1E-07 cm/sec / 30.48 ft/cm) (3 ft head / 2 ft liner) (1' cm) (4 leaks per <br />acre) (60 seconds/minute)(60 minute/hour)(24 hour/day) = 0.0017 ft'/day <br />Where: <br />K = hydraulic conductivity (ft/d) <br />h/1= gradient <br />A = Area <br />Since much of the future landfill footprint has already been developed, and recognizing the <br />high moisture adsorptive capacity of refuse in existing waste disposal areas and the small <br />volumes of leachate that are calculated to potentially leak through the new liner system, <br />leachate migration from new wastes to native units is expected to be restricted to the 127 <br />acre area at the Austin Road Landfill that is currently undeveloped. Using the unit leakage <br />volume calculated above, the total leakage to native units is calculated as: <br />vol = (unit rate / acre) (acres) _ (0.0017 ft'/day) (127) = 0.22 fe/day <br />3.1.2 Volume of Potentially Impacted Groundwater <br />Aquifer pumping tests completed by Camp Dresser McKee Inc. (1999) and groundwater <br />modeling that was completed for the existing Austin Road Landfill by HA/AEE (2001) <br />indicate that the hydraulic conductivity of upper aquifer materials in the area is <br />approximately 250 ft/d. This value is consistent with values listed in the literature (Driscoll, <br />IS 1986) for medium- to coarse-grained sands and appears to closely approximate the types of <br />materials encountered within water -bearing zones in monitoring wells at the site. <br />Conservatively using half the hydraulic conductivity value selected by HA/AEE (250 ft/d / 2 <br />= 125 ft/d), an average groundwater gradient of 0.003 percent, and conservatively assuming <br />that mixing of vertically migrating leachate mixes in the upper four inches of the 5200 -foot <br />wide aquifer that flows beneath the site, the volume of potentially impacted groundwater is: <br />vol = [(K)(h/1)(A) _ [(125 ft/d) (0.003) (5200) (4/12) = 650 ft' <br />/day <br />3.1.3 Magnitude of Groundwater Impact <br />The magnitude of potential impacts to groundwater were evaluated assuming a mix of <br />leachate with impacted groundwater at the site. The mixing calculations presented <br />below address both potential organic (VOCs) and inorganic impacts to groundwater <br />quality at the site, and assume that groundwater mixing takes place within the upper 4 <br />inches of groundwater. These analyses also assume that no leachate attenuation occurs <br />within the clay liner or vadose zone, and that the volume of leachate that mixes with <br />groundwater is equal to the volume of leachate that may leak from the landfill. <br />Potential Inorganic Impacts <br />As indicated below, the average Total Dissolved Solids (TDS) concentration of Forward <br />Landfill leachate (2470 mg/L) was used together with the statistically determined <br />CA2002-002\Revised Appx A - Leakageldoc\09/19/02 <br />Geologic Associates <br />