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Non-Water Release Corrective Action Plan Corral Hollow Sanitary Landfill • anticipated that moderate gully erosion along the bench surface and adjacent channel areas would occur due to the channel overtopping. Therefore, erosion impacts to the channels are reasonable foreseeable. The western stormwater retention pond has capacity (3,600,000 cubic feet) to retain the volume of run-off from 1,000-year, 24-hour storm event even if the pond is approximately 95% full. The eastern stormwater retention pond has capacity (369,690 cubic feet) to retain the volume of run-off from the 1,000-year, 24-hour storm event even if the basin contains stormwater at a depth of approximately 7 feet. However, additional volume can be discharge to the Corral Hollow Creek to the south. Therefore, no impacts to the stormwater retention basins reasonably foreseeable. 4.3 FIRE IMPACTS Fires at landfills are either subsurface fires or surface fires (wildfires). The potential for these fires to occur are dependent on the location of the landfill relative to wildfires, management of waste that is still smoldering, accidents or arson and availability of vegetation for fuel for a fire. • 4.3.1 Subsurface Fires Subsurface landfill fires are most commonly caused by the intrusion of oxygen into the refuse prism from overdrawing of the gas collection system, which increases aerobic decomposition, resulting in the generation of methane and increased temperatures. This can cause ignition of the landfill-generated methane gas resulting in a fire. This underground combustion/oxide can cause damage to the landfill gas collection systems and potentially the intermediate and final cover. As described in the October 26, 2012 amendment to the Final Closure Plan (FCP) prepared by the County, a system of 44 vertical landfill gas extraction wells have been installed since 2011 with an additional 7 landfill gas extraction wells being installed during the closure cap extension project. The landfill gas extraction system has been completely installed and is operational. To determine if a subsurface fire exists, one must have visual confirmation or other conditions present. Generally a subsurface fire can be confirmed by: Substantial settlement over a short period of time; Smoke or smoldering odor emanating from the gas extraction system or landfill; • 0 Levels of carbon monoxide (CO) that exceed 1,000 parts per million (ppm); 13 Geo—Logic ASSOCIATES