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Draft Environmental Impact Report Page IV.F-19 Forward Inc. Landfill Expansion 2008 monitoring data. This significant reduction is likely a result of dilution from infiltrating clean recharge water into the infiltration basins because the previous modeling studies (EDM, 2001) showed well MW-11 lies outside of the capture zone of the extraction swells EW-1 and EW-2. The apparent improvement of the groundwater may be also be the result of a combination of natural attenuation and plume migration and dispersion. Indicators of the natural breakdown(dechlorination)of the PCE and TCE to the daughter products DCE and VC are not apparent in the data. On the other hand concentrations at the wells AMW-13 and AMW14 further downgradient showed 25 ug/L and 18 gg/L PCE, respectively. Leachate Generation, Treatment, and Monitoring Leachate monitoring is a requirement of the landfill operation as described in the Project description in this report. Initially the landfill attempted to dispose the leachate to the City of Stockton wastewater treatment plant, but the toxicity of the leachate was prohibitive. The responsibility for the appropriate storage and treatment of any generated leachate was transferred to Forward Landfill now implements pumping all leachate generated to leachate evaporation ponds along with excess drainage not used in landfilling operation). The leachate impoundment was sized based on actual leachate generation records from 1991 to 1997 and has a design capacity of approximately 3.5 million gallons, a significantly greater capacity than the EPA HELP model predictions (JTD,2007 update). The leachate collection and removal system (LCRS)is summarized in the Project Description. This LCRS will be utilized in the new proposed landfill expansion phases. The LCRS is the first line of defense for the protection of groundwater from any leachate generated from the landfill. The system uses two configurations for the two types of liner gradients to be constructed for the base and the slopes of the landfill. Three leachate evaporation ponds are planned for the site. These are designed to be sufficient for the maximum projected leachate generation. An existing evaporation pond built in 1999, WMU-F North, currently provides containment for leachate from the active portions of the existing Forward Landfill. A second impoundment, WMU-F South, is proposed as part of the project to service the southwest region of Forward Landfill through Phase 10 of the project. Construction of the third evaporation pond along the southwest border of the existing Austin Road Landfill is proposed to service later buildout phases. The leachate liner and collection system are sized to meet the potential leachate generation predicted by the EPA Hydrologic Evaluation of Landfill Performance (HELP) model. The HELP model predicted the most significant peak of lubricate generation in the new expansion areas to be in the fifth year when total annual leachate generation would reach 223,000 gallons with a daily peak at 2,150 gallons. However, the HELP model results contrast significantly with the much larger leachate volume projection that are base don the historical leachate production records form the exiting landfill operations from Y1998 when high rainfall(25 inches) occurred. In that year 6,210, 350 gallons of annual leachate—or 31, 052 gallons per day, were generated. Thus the HEMP model may under-predict the leachate generation. The Austin Road Landfill unit has a leachate collection system built above the unlined Class III landfill (that had no leachate collection system) as part of its expansion into a Class II facility. Required leachate monitoring consists of daily inspections of the system and sumps for the presence of leachate. If leachate is present, the sumps are pumped and the leachate is disposed. Leachate detected in a previously dry sump is sampled and that sump will be added to the semi-annual sampling program. The leachate samples are analyzed for the constituents and parameters listed in the site's WDRs, and include the field parameters discussed in the surface