established; geochemical data suggest that coal aquifers and other alluvial groundwater aquifers do not interact to any great degree in studied parts of the Powder River Basin (see discussion in e.g., Frost et al., 2010; Bartos and Ogle, 2002; see also Chapter 2). Anecdotally, CBM production has been linked to some losses of drinking water or dry wells where the water wells were close to the CBM development and/or were completed in the coals which serve as a primary aquifer.
In addition to geochemical information that can help determine the degree of connectivity between CBM coalbeds and other groundwater aquifers, groundwater monitoring networks are being used to measure the degree to which CBM production may affect water levels in shallow aquifers. The Montana Bureau of Mines and Geology (MBMG) maintains and samples a regional network of groundwater monitoring wells that includes wells installed in the late 1970s and early 1980s to monitor the effects of coal mine dewatering, a separate activity from CBM operations, and more recent wells installed specifically to monitor CBM production. The MBMG receives funding from the Bureau of Land Management (BLM) in support of this monitoring program. In Wyoming, in response to concerns about potential effects to groundwater from CBM development in the Powder River Basin, BLM established a regional groundwater monitoring program that is outlined as part of the Wyodak CBM Final Environmental Impact Statement (BLM, 1999). The program was designed to collect information regarding hydraulic connectivity between producing coals and adjacent sandstone units and to measure the extent of groundwater drawdown in the CBM-producing coal zone on federally owned lands. Results from both the Montana and Wyoming groundwater well monitoring programs are briefly summarized below.
Many of the monitoring wells are completed in the Dietz (associated with the Anderson coalbeds) and Canyon coalbeds in the Powder River Basin (Wheaton and Metesh, 2002; see also Figure 2.4b). The monitoring network has been sampled for seven consecutive years (2003–2009), in addition to sporadic monitoring for nearly three decades before CBM development was initiated in the area, and the data are available in annual reports through the 2008 sampling event.1
Data from this network indicate that static water levels in the Dietz coalbeds, from which CBM is being extracted, have been lowered by as much as 150 feet. Static water levels in the Canyon coal, also a coalbed from which CBM is being extracted, have been lowered as much as 600 feet in limited areas (Meredith et al., 2008). CBM-related drawdown of 20 feet of the static water level in the Canyon and Dietz coalbeds currently extends to