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Draft Supplemental Environmental Impact Report Page IV.E-12 Forward Inc. Landfill 2014 Expansion Project along the well casings, which penetrate the surface of the landfill), abandonment (and replacement if warranted) of non-productive wells that were drawing in excess air, and increased efforts on wellfield operations to proactively identify and resolve potential subsurface oxidation events before they happen. Since that time, Forward has been successful in resolving the subsurface oxidation problem,but continued vigilance is necessary to avoid reoccurrence, which goes for every landfill with a landfill gas collection system. In summary, the subsurface oxidation events (SSOs) were isolated, were extinguished as soon as possible, and basically they all occurred within a fairly short period of time. SSOs are fairly common at landfills, and can occur due to changes in barometric pressure, cracks in the cover material if that material has a higher percentage of clay, etc. SSOs are not necessarily caused by the well system. 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. • All site personnel who work in permanent structures will be trained to use and respond to the landfill gas monitoring and alarm system. This impact is still considered potentially significant;therefore the following additional mitigation measure is identified: — Mitigation Measure E.4: (Same as the 2013 EIR Mitigation Measure E.4.) Landfill gas monitoring shall include the volatile organic compounds in order to determine the amount of contaminant recovery, and control potential exposure to onsite personnel. Implementation of the proposed procedures and this mitigation measure would reduce the impact to a less-than-significant level because it allows the County and applicant to control potential exposure of personnel to hazardous gases. Impact E.5: Solid waste pathogens could be spread by vectors. (Same as 2013 EIR Impact E.S.) Refuse in landfills attracts vectors such as rats, moles, gulls, etc. that can carry infectious pathogens, disease and parasites. More vectors over time would likely be attracted to the landfill due to its expansion over time. This could increase the likelihood of human exposure to the pathogens carried by the vectors. The potential public health and nuisance problem from vectors is a potentially significant impact. The following procedures are proposed as part of the project: