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Michael Kalish February 5, 2001 Page 2 of 6 A network of twelve perimeters LFG monitoring probes has been installed at the site. The probes are located near the property line or agency-approved compliance boundaries. Since installation of the LFG collection system, all perimeter monitoring probes have shown combustible gas concentrations below regulatory limits with the exception of GW-3. Levels of 5% to 7% by volume (v/v)have been detected in GW-3 in recent monitoring events. In addition, the flare has shut down due to low gas quality on occasion. GW-3 was installed at the landfill compliance boundary near a series of wastewater aeration ponds serving an adjacent County-sponsored migrant worker housing complex. It is our understanding that combustible gas concentrations in GW-3 had been below regulatory limits for a period of time prior to the system experiencing a series of unscheduled shut-downs. Since that time,combustible gas concentrations in GW-3 remained just above the regulatory threshold until the most recent monitoring event. During the last monitoring event,combustible gas levels detected in G -3 were again below the regulatory limit. The County has received notice from the Local Enforcement Agency (LEA)that it is to attempt to bring GW-3 into compliance with CCR Title 27 for gas migration control. The County has requested that SCS assist them in lowering the combustible gas concentrations in GW-3 to acceptable limits. SCOPE OF WORK For this project, we are proposing a staged approach. Our work will begin with an overall assessment of LFG extraction system operational data. Operational procedures will be adjusted if it appears that there is an opportunity to enhance control of LFG migration in this manner without negatively affecting flare performance or surface emission control. If it appears that further steps are necessary(e.g.,physical modifications to the existing extraction system), we will recommend improvements and prepare concept level sketches. Note that at our site meeting, we discussed whether or not detections at GW-3 may be from a source other than the landfill (e.g., adjacent sewage aeration ponds). Based on probe monitoring data we've seen to date, this appears unlikely, and would be difficult to confirm in this situation. If results of our data review show the possibility that combustible gas is migrating into the GW-3 from off-site, we will make recommendations regarding possible future confirmation testing. Task 1 Review Data and Assess Strategies for Compliance SCS will obtain and review relevant background information that will help us understand site conditions, the existing LFG collection system, and other conditions affecting LFG management, including: