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J. H. KLEINFELDER & ASSOCIA-fES File: 5-1008-21/12 : 337 Revised: July 8 , 1986 Page 10 In Borings 1 , 4 , and 5 , no methane gas was detected. However, in Borings 2 and 3 methane gas was detected at. over 100 percent explosivity. The encroachment of methane gas onto the site appears limited since no gas was detected in Borings 4 and- 5 drilled west of Borings 2 and 3 . Boring 11 , drilled south of the site near the ponds, was also tested and methane gas was detected at 40 percent explosivity (Kleinfelder , September 1984) . To our knowledge this is the only portion of the site where the presence of methane gas has been verified. Proposed Monitoring Program Location of Monitoring Facilities The proposed locations for vapor monitoring wells are shown on Plate A. Methane diffuses along paths of least resistance. It will travel laterally in any direction where there is no impermeable barrier (Everett , 1985) . Therefore, the proposed monitoring points are chosen so that there are at least two monitoring points along each of the property boundaries. Methane gas production requires an anaerobic environment; therefore, newer sites will not generate methane gas until an anaerobic environment is established. In older areas of the landfill, however, it may be advisable to install additional monitoring stations if initial wells indicate the presence of methane . Well Installation and Construction The vapor monitoring wells will be installed using hollow stem augers. A generalized vapor monitoring well installation is shown on Plate E. The materials proposed for construction of the vapor monitoring wells are: a. Well Casings and Screens. 1 . Approximately 15 - 20 feet of . 2-inch diameter Schedule 40 PVC, threaded, with 0-rings to provide air tight seal . 2 . 5 - 10 feet of 2" diameter Schedule 40 PVC slotted screen, threaded (with 0-rings) , 0.020-inch machine slotted. 3 . The 2-inch PVC top cap shall be fitted with a . Tygon or Teflon access tube with a valve or stop- cock that can be directly connected to a vacuum pump or sampler.