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62-701.500(9) LANDFILL GAS MONITORING Gas monitoring and control systems shall be designed to prevent explosions and fires, minimize offsite odors, and damage to vegetation. The explosive range of methane is 5 percent to 15 percent by volume. The lower explosive limit is generally accepted to be 5 percent. Chapter 17-701 regulations state that the concentration of methane and other gases shall not exceed the LEL at the property boundary or exceed 25 percent of the LEL (1.25 percent by volume) in onsite and offsite structures, excluding gas control or gas recovery components. Currently, gas management consists of 12 passive vents installed on the closed Segment 1 landfill and monthly gas monitoring at six locations on the north, west, and south edges of Segment 1. The location of existing gas monitoring wells is shown on Figure 3- 4 of the infill segment permit application. Four wells located at 90 -foot elevations on the east slope of Segment 1 will be modified and extended to the top surface of Segment 1. Gas under the infill sideslope liner is not expected to be a problem as the Segment 1 landfill is cleared with a clay cap which will be left intact under the sideslope liner. As additional solid waste disposal areas are developed to the east of Segment 1, the existing gas monitoring well system will be expanded. There is minimal potential for gas migration since the landfill liners are installed at grade, and the Class I disposal area is surrounded by ditches which intercept the groundwater table. The only way the gas could migrate into surrounding soils is through a damaged liner or the leachate collection system. Although the potential for landfill gas migration is limited, state and federal regulations require landfill gas monitoring at the landfill boundary. Ten gas monitoring wells are currently installed. Four additional gas monitoring wells have been constructed, one F-23 ;VA,