Laserfiche WebLink
1.0 PREVIOUS INVESTIGATION AND SITE HISTORY <br />The methane seepage problem was first reported in late 1998. Methane seepage was discovered via the <br />apparent loss of vegetation on the site. <br />1.1 METHANE INVESTIGATION ACTIVITIES <br />This report presents the results of the monitoring activities from 2004 and cumulative results of the 5-year <br />monitoring period. This report amends the previous methane surveys conducted near the former Golden <br />Eagle Mine, located near Weston, Las Animas County, Colorado (Figure 1). As part of previous <br />investigations at the site, 28 monitor points (B1 through B28) were installed onsite to determine extent and <br />concentrations of methane in the shallow subsurface soils (Figure 2). Most of these points are located <br />within the zone of impact. Several of the points are located near two abandoned coal bed methane wells <br />south of the area of visual impacts. These points have been monitored over time using a Landtec GA-90 <br />methane gas detector. Concentrations were measured approximately every 2 months since the installation <br />of these points in March 1999 through the beginning of the year 2000. In addition to these 28 points, the <br />interior of the mine's fan house was monitored for methane concentrations through May 1999. The <br />monitoring Frequency for the 28 monitoring points was adjusted to a quarterly schedule in the year 2000. <br />This changed to asemi-annual schedule in 2001 and returned to a quarterly schedule in 2002. Monitoring <br />occurred annually in 2003 and 2004. <br />Methane concentrations within the monitoring points have ranged from below detection limits to 100 <br />percent (the Landtec GA - 90 methane gas detector has an accuracy of +/- 10%). Table 1 summarizes the <br />measurements from all investigations. Examination of the data in Table 1 indicates that concentrations of <br />methane in the monitoring points exhibit a decreasing trend over time. This data does not account for <br />changes in weather conditions that may influence the liberation of methane. Higher atmospheric pressure <br />may result in lower methane liberation and vice-versa. <br />Seven additional monitoring points were installed in June 2000 (B29 through B35) and monitored, as were <br />the previous 28 points. These points were installed within and outside of areas with stressed vegetation to <br />attempt to monitor and delineate impacts. A surface survey was also conducted at the site in July 2001. <br />The surface survey consisted of monitoring the ground surface at the site utilizing aflame-ionization <br />detector (FID). <br />During the plugging and abandonment of the gas wells at the site in late 2000, four of the methane <br />' monitoring points installed as part of the investigation (B18, B19, B27, and B28) were destroyed. In <br />addition, two monitoring points (B20, B21) appear to have been moved. <br />Itt June 2001, four additional monitoring points (AM1 through AM4) were installed. These points were <br />installed within selected intervals of the subsurface and screened for the detection of methane. These <br />additional points were monitored in June and August 2001. <br />Itt August 2001, four additional monitoring points were installed in areas where methane had been <br />consistently elevated, next to a former coal bed methane (CBM) well, and outside of a residence at the site <br />(lleep Set Next to B24, Deep Set Next to B33, Deep Set at CBM Well, and Deep Set West of House). <br />These points were installed within selected intervals of the subsurface and screened for the detection of <br />methane. Additionally, monitoring began at [he north and south air shafts for the former mine workings. <br />N[onitoring has occurred at these locations since August 2001. <br />292-M eth_(7.14.04).doc 1-1 <br />