GENERAL31095

• Permit No: C1981013
• IBM Index Class Name: General Documents
• Doc Date: 12/30/2002
• Doc Name: 2002 Annual Report Methane Assessment
• Permit Index Doc Type: General Correspondence
• Media Type: D
• Archive: No

1.0 Previous Investigation and Si[e
1.0 PREVIOUS INVESTIGATION AND SITE HISTORY
The methane seepage problem was first reported in late 1998. Discovery of methane seepage was
via the apparent loss of vegetation on the site.
' 1.1 METHANE INVESTIGATION ACTIVITIES
This report presents the results of monitoring from 2002 and cumulative results of the 3-year
monitoring period. This report amends the previous methane surveys conducted near the former
Golden Eagle Mine located near Weston in Las Animas County, Colorado (Figure I). As part of
' previous investigations at the site, 25 monitoring points (B 1 through B25) were installed on site to
evaluate the extent and concentrations of methane in the shallow subsurface soils (Figure 2). Most
of these sites are located within the zone of impact. Several of the sites are located near two
abandoned coal bed methane wells located south of the area of visual impacts. These sites have
been monitored over time using a Landtec GA-90 methane gas detector. Concentrations have been
' measured approximately every 2 months since these points were installed in March 1999, until the
beginning of the year 2000. During the years 2000 to 2002, the monitoring frequency was adjusted
to a quarterly schedule.
' Concentrations of methane within the monitoring points have ranged from below detection limits
to 100 percent (the Landtec GA -90 methane gas detector has an accuracy of +/- 10 percent).
' 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. These data do 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.
Ten additional monitoring points were installed in June 2000 and monitored as the previous 25
points. These points were installed in and outside of areas with stressed vegetation to attempt to
monitor and delineate impacts. A surface survey was also conducted at the site during July 2001.
' The surface survey consisted of monitoring of the ground surface at the site using a flame
ionization detector (FID).
' When the gas wells at the site were plugged and abandoned, four of the methane monitoring points
that were installed as part of the investigation were destroyed. These points are B18, B19, B27,
and B28. In addition, two monitoring points (B20 and B21) appear to have been moved.
During the previous investigation, four additional monitoring points (AMl throughAM4) were
installed. These points were installed with selected intervals of the subsurface screened for the
detection of methane. These additional monitoring points were monitored in June and August
2001.
Meth{292)-I1-02.doc, 11/20/2002