CORRESPONDENCE_2014-2015 - Laserfiche WebLink

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Currently, the LFG-to-Energy (LFGTE) power plant utilizes all the LFG recovered from the landfill. The County is contractually required to provide all collected LFG to the plant and any modifications or expansion of the system must be mutually agreed upon. It should be noted that a landfill's GCCS is typically expanded in phases or stages only when needed to comply with applicable regulations (noted above) and not above the limits of the landfill to generate LFG, nor above the limits of the permitted control devices to handle the collected LFG. An important factor when modifying a GCCS is to install extraction wells in stages to avoid over applying vacuum to the refuse landfill mass thus causing the possibility of the intrusion of oxygen that could not only damage the methanogenic bacteria but also potentially cause a landfill fire by promoting aerobic decomposition versus anaerobic decomposition. To address periodic detections of volatile organic compounds in the vadose zone and to mitigate VOCs intermittently detected in groundwater at MW -3, the County proposes installing potentially up to 12 new extraction wells in Module "I" in a phased approach. Phase I LFG Extraction Well Installation In an effort to remediate the VOCs detected in groundwater and in the vadose zone, as Part of Phase 1, the County proposes to install initially four (4) new LFG extraction wells in Module "I" in 2015. These initial four (4) wells will target areas where potential LFG is trapped and potentially impacting groundwater. The four (4) wells will consist of two (2) LFG extraction wells installed near MW -3 and two (2) LFG extraction wells installed in the over -liner section between Module "I" and Area 1. The purpose of these target extraction wells will be to provide enhanced vacuum within the refuse mass in close proximity to MW -3 and below the over lying impermeable liner believed to be trapping LFG and promoting migration vertically downward toward groundwater. Four (4) wells are proposed in Phase 1. These wells are intended to: 1. Immediately focus LFG recovery on the groundwater impacts at MW -3; 2. Limit the dilution of the existing LFG stream to the LFG-to-Energy power plant in phases while additional LFG is generated in Area 1 as it is developed; and 3. Assess the actual Radius of Influence (ROI) at the site prior to designing additional extraction wells. The new wells in Phase 1 will be operated and monitored similarly to the existing program detailed below. Phase I LFG Well Radius of Influence Assessment As part of Phase 1, the ROI for the existing wells in Module "I" will be assessed via field investigation (see below). This data will be used to finalize the design locations of proposed wells in Module "I" and for future additional wells in Phase 2 discussed below. Foothill Sanitary landfill 6 Department of Public Works, Solid Waste Division Revised Engineering Feasibility Study County of San Joaquin — December 19, 2014