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July 9,1998 0 Austin Road Landfill Landfill Gas Migration and Control Evaluation I. Introduction The purpose of this report is to brief the California Integrated Waste Management Board (Board) staff on the status of the City of Stockton's(City's) activities to bring the Austin Road Landfill(ARL) into compliance with landfill gas (LFG)control requirements. The City submitted a proposed compliance schedule to address gas migration,and other operational concerns,in correspondence dated April 23, 1998,to the Board. In a response dated May 6, 1998,the Board approved the compliance schedule and requested project status reports within ten days of each task identified on the schedule. This report presents the status of Task 2,"Determine extent of LFG migration plume and evaluate LFG control options." Detection of gas concentrations which exceeded the 5%lower explosive limit for methane at soil gas probes SGP13 and SGP14 precipitated the requirement to expand the existing landfill gas recovery system (Figure 1). Proposed LFG system modifications will be developed to address gas migration on the northeast portion of the landfill perimeter in the vicinity of these two probes. This report is organized into four sections including this introduction. The following section,Field Investigation,documents the activities performed to establish the baseline conditions of the gas extraction system and assess gas migration plume extent. Section III,LFG Control Options, presents the two gas control system alternatives considered with the report concluding with Section IV,Implementation Plan. II. Field Investigation The objective of the field investigation was to establish the current operating conditions of the existing LFG gas extraction system and to determine its influence on the perimeter gas probes on the north side of the site. A thorough understanding of the existing system is necessary to facilitate the design of a system expansion which will be effective in controlling gas migration. The current system consists of approximately 51 gas extraction wells installed through the waste fill at locations depicted on Figure 1. Extracted LFG is conveyed to an energy recovery system,located at the northwest corner of the site,where the gas is combusted in an engine and electrical power generated. All conveyance pipelines are located aboveground with condensate knockouts located at the energy recovery plant site and at the far east end of the extraction system. Due to ongoing landfill operations,portions of the gas extraction system may be temporarily taken off-line. As depicted in Figure 1, gas extraction wells extend to the midpoint of the landfill on the north side, approximately in-line with SGP10. The primary design and operational intent of the existing gas extraction system is to generate electricity. The gas rights at the ARL are owned by Ogden Power Pacific,Inc. (Ogden Power)who is responsible for the operation and maintenance of the gas recovery and electrical generation systems. CDM Camp Dresser&McKee 1 WM500/015