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LFG Collection System The LFG Collection System was designed to prevent LFG migration from the refuse into the vadose zone, thus preventing both LFG migration beyond the perimeter and groundwater contamination. The system began operating in October 1996. tThe LFG system consists of 80 vertical wells installed in refuse, connecting piping, and a flare station containing flare,blowers, and controls. Each well is provided with a control valve to adjust the rate of collection from the well, and sampling ports to measure the quality of LFG collected. A vacuum is induced in the piping at the flare station, allowing LFG to be withdrawn from each well. Collected LFG is burned in a flare to remove VOCs in accordance with the Permit to Operate issued by the San Joaquin Valley Air Pollution Control District. The system is operated to maximize collection of LFG from the landfill by inducing a negative pressure in the refuse. If the refuse is under negative pressure, then LFG will not move from the refuse towards groundwater. The LFG wells are adjusted according to measurements taken at both the perimeter migration monitoring wells and the LFG collection wells. Vacuum at the LFG collection wells is increased until the concentration at the perimeter(soil gas)wells falls below the regulatory limit of 5 percent (to zero if possible). However, excess withdrawal, as indicated by the reduction of methane content in an individual LFG well to below 35 percent, indicates the potential for a subsurface landfill fare. Note that LFG is approximately 55 percent methane at the point of production within the landfill. Methane content below this value indicates dilution by air drawn through the soil into the refuse caused by the negative pressure at the well. Maximizing LFG collection while minimizing air intrusion is the"balancing act"when operating a LFG migration control system. After repairs and adjustments to the LFG header on the west side of the primary site combustible gas concentrations were below 5 percent at all but one probe(GW-3D). A new dual extraction well was completed in March 2005 and connected to the LFG collection system and has reduced the concentrations at all the perimeter wells to less than 5%methane. Harney Lane Sanitary Landfill 1-3 Department of Public Works/Solid Waste 1s'Quarter 2007 Groundwater Monitoring Report County of San Joaquin—April 15,2007