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PURPOSE The purpose of this Plan is to establish the procedures by which control of off-site subsurface migration of combustible gas from the Harney Lane Landfill will be re-established. BACKGROUND The Harney Lane Landfill is provided with 12 perimeter landfill gas migration monitoring wells (Figure 1), each of which is a"nested" set of three probes, installed at varying depths within the well. These wells are monitored quarterly at a minimum in accordance with the applicable sections of Title 27. Adjacent to the landfill is the Migrant Labor Housing. The structures of this facility are provided with foundation vent pipes that allow venting of any gasses that might accumulate beneath the foundation, and the measurement of combustible gas concentration of any vented gas. Normal monitoring includes quarterly monitoring the migration monitoring wells and the foundation vents of the structures immediately adjacent to the landfill. To date, combustible gas has not been detected in any foundation vent. The landfill is provided with a landfill gas (LFG) collection system installed to prevent off-site migration of LFG and to mitigate groundwater impact by LFG. Control subsurface LFG migration is accomplished by maximizing LFG collection at each well while avoiding excessive overdraw of the refuse. Excessive overdraw may cause a subsurface refuse fire. LFG is collected from 80 LFG wells, each of which is provided with sampling ports and a valve to measure the quality of LFG collected and to adjust the flow rate. Collected LFG is carried in pipes installed beneath the landfill surface to the LFG flare station, where the LFG is combusted. The vacuum to collect the LFG is provided by a blower, also located in the flare station. A significant aspect of LFG system operation is that landfill gas condensate (primarily water with trace LFG contaminants) forms daily within the collection pipes. Unless removed from the system, this condensate will block the LFG piping and prevent the collection of LFG. To avoid this blockage, the LFG system is designed with sloping pipes, allowing the condensate to drain to pre-selected low spots. A sump and pump is located at each low spot. The condensate is pumped from the sumps to the LFG flare station, where it is injected into the flare for destruction. Proper functioning of a LFG system depends, among other things, on the proper slope of the LFG pipes to drain condensate to the sumps. Another significant aspect is the continual settlement of the landfill surface in which the LFG piping is installed due to continuing decomposition of the refuse beneath. Because the refuse does not decompose at the same rate in all locations, some areas will settle faster than others. As the Remediation Plan for LFG Migration San Joaquin County Public Works/Solid Waste Harney Lane Sanitary Landfill May 23,2007