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File: S-1008-21/12 :337 <br /> _Revised: July 8, 1986 <br /> Page 11 <br /> Methane Gas Sampling <br /> If , as proposed, the top of the wells are outfitted <br /> with a valve or stop-cock, a vacuum pump can be directly <br /> connected to the access tubing. Sampling of the gas will be <br /> accomplished by evacuating 3-5 bore volumes of air to assure <br /> the vapor being sampled is solely from the formation of <br /> interest , and then obtaining a vapor sample. A standard gas <br /> monitoring meter such as the Gastech Methane Meter, or <br /> equivalent , will be used to obtain direct measurements of <br /> methane gas levels in the field. As with the ground water <br /> samples, testing for methane should be performed on a <br /> quarterly basis. <br /> Potential for Methane Recovery <br /> The potential for methane recovery should be evaluated <br /> after the vapor monitoring wells are in place . Previous <br /> investigations at the northwest corner of the site indicate <br /> that the gas occurs in isolated pockets . However , no <br /> exploratory work has been performed within the landfill to <br /> evaluate methane gas . Recovery may be feasible if <br /> sufficient quantities of methane gas are found in the <br /> landfill . <br /> VADOSE ZONE MONITORING <br /> At this time, installation of unsaturated or vadose zone <br /> monitoring facilities is not required at the Harney Lane <br /> Landfill . Vadose zone monitoring is intended to provide early <br /> detection of leakage from waste management units. Installation <br /> of these monitoring facilities are effective and beneficial when <br /> installed during the construction of a new facility. <br /> Retrofitting the existing Harney Lane Landfill with vadose zone <br /> monitoring would be neither efficient nor cost effective for the <br /> following reasons: <br /> o Installation of vadose zone monitoring equipment in the <br /> landfill portion of the facility would require either <br /> removal or drilling through landfilled material at <br /> about a dozen or more locations. Installation costs <br /> would be in the range of $200 - $210/hour plus at least <br /> $750 per installation. Total cost estimate would be in <br /> the range of $20,000 to $30,000 . <br />