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San Joaquin County Environmental Checklist County must submit an annual stormwater protection report to the Central Valley Water Board. Landfill Gas. As described in Section III,Aar Quality,MSWs placed in the NCRC&SL undergo natural chemical and biological decomposition following landfilling. The byproducts of biological decomposition of organic wastes are solids,liquids,and gases. The byproducts of aerobic(presence of free oxygen) decomposition of MSWs are carbon dioxide,water,and nitrates. Typical primary byproducts of anaerobic(lack of oxygen)decomposition are methane, carbon dioxide,water, organic acids,nitrogen,ammonia,iron sulfides, manganese,and hydrogen. These byproducts are the primary factors controlling the quality and quantity of leachate and LFG produced. The percentage by volume of methane in the gas may range from 50%to 60%,and carbon dioxide may range from 30%to 50%(Boyle 1977). Methane production from MSW will continue for periods ranging from a few years to hundreds of years, depending on specific environmental parameters: refuse composition, oxygen present, moisture content,pH,alkalinity, and temperature. Subsurface migration of combustible LFG, and the safety of onsite habitable structures,is monitored in accordance with the Methane Monitoring Program and CCR Title 27, Section 20919. To monitor subsurface migration,the County has installed seven monitoring probes along the perimeter of the landfill facility. These wells are near the landfill property boundary and consist of triple- completion wells to monitor at shallow,intermediate, and deep zones. The terms VOC and ROG apply to the same compounds. In July 2002,three VOCs were confirmed at well G-4,prompting the county to install a new groundwater monitoring well,G-6,and soil gas wells SG-1 through SG-8. Monitoring at G-6 indicates no groundwater impact at that location. VOC detections are sporadic and inconsistent. VOCs were found at many of the soil gas wells;however,the presence of VOCs in the soil gas does not impair the use of the site. One soil gas well, SG-6,has shown combustible gas consistently above 20%,indicating a possible breach in the landfill liner near that well. Because of the proximity of this well to the interface between Modules 2 and 3, it was speculated that the breach was on the anchor trench berm. The County speculates that the cause of impact at groundwater well G-4 was LFG and that sporadic detections at G-4 were likely to occur unless corrective action was taken. The County will install an LFG system in 2006 to control LFG migration and alleviate possible concerns for groundwater impacts. It is anticipated that installation of the LFG collection and treatment system, in addition to the final cover that will be constructed over all fill areas once the landfill is closed, would eliminate the release of LFG. Consequently,releases of LFG are considered less than significant, and no mitigation is required. Groundwater well and soil gas well monitoring will continue following installation of the LFG collection and treatment system. It is anticipated that the soil gas collection and treatment system will be sufficient to maintain VOC concentrations within their currently permitted limits,reducing potential impacts to less-than-significant levels. No additional mitigation is required. Notice of Preparation for the June 2006 North County Recycling Center and Sanitary Landfill 2_54 Jas os307.os Permit Revision