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Draft Supplemental Environmental Impact Report Page IV.E-13 Forward Inc. Landfill 2018 Expansion Project of soot in the gas collection system. At times,underground combustion/oxidation will go undetected until a sinkhole or smoke appears. Normally flames are not visible during this type of fire unless the subsurface fire is excavated and exposed to the atmosphere. With the correct conditions present, spontaneous combustion can occur in household trash or at construction debris facilities. This type of combustion will produce excessive amounts of CO and other trace gases due to incomplete oxidation. To confirm SSO by using CO measurements, the results must be acquired through quantitative laboratory analysis. The CalRecycle staff considers levels of CO in excess of 1,000 ppm to be a positive indication of an active underground landfill SSO event. Levels of CO between 100 and 1,000 ppm are viewed as suspicious and require further air and temperature monitoring. Levels between 10 and 100 ppm may be an indication of SSO but not active combustion. The Forward Landfill has standard operating procedures in place to address landfill SSO events. If physical indications of an SSO event are noted, the environmental manager and landfill manager are immediately notified. An initial investigation is performed and a physical inspection conducted that includes visual observation, infrared thermometer surveys, and measurements at nearby landfill gas wells. The data is then analyzed and a course of action is developed. The actions include removing oxygen from the SSO area by shutting down wells that may have caused the SSO, shutting down wells in the surrounding area, capping or repairing any items that may have contributed to the oxygen intrusion, and replacing cover materials where necessary. Following the corrections and repairs, the SSO area is monitored until the indicators of SSO are no longer noted. The Forward Landfill had one SSO event in 2007 and six in 2008. The two events are described in the 2013 FEIR. In consultation with representatives of Cal Recycle and the San Joaquin County Health Department--Local Enforcement Agency,Forward Landfill made improvements to its landfill gas collection system and placed additional intermediate cover in the areas that had experienced these events. Forward Landfill has not had any SSO events since the improvements were implemented and the consent decree (2:11-cv-00590 EFB)specifying the LFG Collection System improvements has been completed and terminated. (Lewis,pers. com). The following procedures are proposed as part of the project: • Where required by State and Federal regulations,the landfill gas monitoring, gas control and collection system will be installed, extending to the new areas of the expanding landfill and operating in conformance with applicable regulations. • The existing gas extraction system, or an equivalent system, will continue to operate. • Regular gas monitoring will be conducted to prevent landfill gas accumulation in onsite buildings or beneath temporary buildings. The landfill operator will install an automatic combustible gas detection and alarm system for structures at the site. • The landfill operator will not construct or otherwise locate any structure in an area of known landfill gas build-up.