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CAMP DRESSER & McKEE D~, William F; Pilkington July 2'7, 1990 page 2 Passive gas vents - One option involves installing a passive gas collection system. Holes are bored into ~he completed landfill and perforated riser pipes are installed as passive vents. Methane gas moves to the riser pipes which vent the gases into -the atmosphere. In some cases, these risers are equipped with a flare that is ignited to bum off the methane gas. Active gas removal system - active gas removal systems use blowers to withdraw the gas fi.om the landfill or the stmounding formations. Collection wells are drilled into the a~feeled area and the gases are collected and either vented to the atmosphere or burned off with a flare. An adaptation of the active system is lo pump air into the ground to block the further movement of methane gas. Active gas removal system with energy recoverv - the active gas removal system described above can be ~uipped with a turbine or gas burner Io recover energy from the methane gas collected by generating steam or elect'icily. Methane gas cut-off vent U'ench - venting trenches can be dug between the COmpleted/active lancffill areas and the adjoining properties being affected. The trench is cons~'ucted down to the groundwater table to insure that all migrating gas is capful. Perforated Pvc pipe is laid in the trench to collect gases (see attached Exhibit A). Collected gases are vented to the atmosphere through PVC standpipes at 150 to 175 feet spacings along the ~'ench. Recommendation Passive gas vents are suitable means of methane migration conb"ol where the escape of gas in the su.~ounding formations does not present a high degree of hazard. They rely upon changes in barometric pressure and the physical processes of diffusion and pressure gradients to remove the gas from the landfill. Should the vent become blocked by moisture or frost conditions, the gas will seek other routes including movement into surrounding formations. Active gas collection systems are generally more r~liable and are usually installed when: a higher degTee of reliability is needed than can be accomplished with a passive collection syslem, ltowever, both active gas collection systems with or without energy recovery are much more capital intensive and involve higher operating costs. Given the age and size of the landfill, and the depth of the garbage, which affect the economic feasibility of the energy recovery option, and the capital and op,'rating costs involved, we do not feel the active system allematives ~e appropriate at this dine. This may change, however, if the recommended option does not mitigate the pmbh:m,