2006-11-16_GENERAL DOCUMENTS - C1981044

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1.0 PREVIOUS INVESTIGATION AND SITE HISTORY The methane seepage problem was first reported in late 1998. Methane seepage was discovered via the apparent loss of vegetation on the site. 1.1 METHANE INVESTIGATION ACTIVITIES This report presents the results of the monitoring activities from 2006 and cumulative results of the 7-year monitoring period. This report amends the previous methane surveys conducted near the former Golden Eagle Mine, located near Weston, Las Animas County, Colorado (Figure 1). As part of previous investigations at the site, 28 monitor points (B 1 through B28) were installed onsite to determine extent and concentrations of methane in the shallow subsurface soils (Figure 2). Most of these points are located within the zone of impact. Several of the points are located near two abandoned coal bed methane wells south of the area of visual impacts. These points have been monitored over time using a Landtec GA-90 methane gas detector. Concentrations were measured approximately every 2 months since the installation of these points in March 1999 through the beginning of the year 2000. In addition to these 28 points, the interior of the mine's fan house was monitored for methane concentrations through May 1999. The monitoring frequency for the 28 monitoring points was adjusted to a quarterly schedule in the year 2000. This changed to a semi-annual schedule in 2001 and returned to a quarterly schedule in 2002. Monitoring occurred annually in 2003, 2004, 2005 and 2006. t Methane concentrations within the monitoring points have historically ranged from below detection limits to 100 percent (the Landtec GA -90 methane gas detector has an accuracy of +/-10%). Table 1 summarizes the measurements from all investigations. Examination of the data in Table 1 indicates that concentrations of ' methane in the monitoring points exhibit a decreasing trend over time. This data does not account for changes in weather conditions that may influence the liberation of methane. Higher atmospheric pressure may result in lower methane liberation and vice-versa. Seven additional monitoring points were installed in June 2000 (1329 through B35) and monitored, as were the previous 28 points. These points were installed within and outside of areas with stressed vegetation to ' attempt to monitor and delineate impacts. A surface survey was also conducted at the site in July 2001. The surface survey consisted of monitoring the ground surface at the site utilizing a flame-ionization detector (FID). ' During the plugging and abandonment of the gas wells at the site in late 2000, four of the methane monitoring points installed as part of the investigation (1318, B19, B27, and B28) were destroyed. In addition, two monitoring points (B20, B21) appear to have been moved. In June 2001, four additional monitoring points (AM1 through AM4) were installed. These points were installed within selected intervals of the subsurface and screened for the detection of methane. These additional points were monitored in June and August 2001. AM1, AM2, and AM3 appear to have been destroyed since the 2004 monitoring event. ' In August 2001, four additional monitoring points were installed in areas where methane had been consistently elevated, next to a former coal bed methane (CBM) well, and outside of a residence at the site (Deep Set Next to B24, Deep Set Next to B33, Deep Set at CBM Well, and Deep Set West of House). These ' points were installed within selected intervals of the subsurface and screened for the detection of methane. Additionally, monitoring began at the north and south air shafts for the former mine workings. Monitoring occurred at these locations from August 2001 to June 2004. During the site investigation in November 2005, only the Deep Set Next to B33 was found to be in-tact. All others had been destroyed. 1 _ 2006 Methane Monitoring Report (11.02.06).doc 1-1 I