BLM- Further Environmental Monitoring and Baseline Database

Due to BLM concern for potential environmental impact from gas production in the northern San Juan Basin of Colorado, the concept of establishing a groundwater quality baseline was expanded from the HD EIS periphery to water wells adjacent to other BLM jurisdictional lands. The initial reconnaissance ascertaining groundwater quality implemented by the BLM-SJRA in 1993 was limited to approximately 200 sites, including the HD EIS periphery water wells, within a presumed radius of influence extending one-half mile beyond jurisdictional lands. Seventy-five percent of the wells tested showed measurable methane; twenty-five percent showed significant concentrations. The threshold of immediate concern was established at 1.0 milligram of methane per liter of water. This was in response to the laboratory finding that a 1.0-milligram per liter concentration of water-entrained methane was shown to have the ability under controlled conditions in a confined environment to exsolve sufficient methane to create an explosive atmosphere (Harder and others, 1965). Critical areas were defined by including a buffer zone extending up to one mile from any domestic water well(s) with entrained concentration(s) of 1.0 milligram (or greater) methane per liter of water.

The checkerboard of split-estate land surface and mineral lease ownership in southwestern Colorado dictated the importance of Federal, state and tribal agencies and private landowners collaborating in an effort to gather and analyze comprehensive data countywide. In a combined effort by the BLM-SJRA, the COGCC, and local landowners, a comprehensive infill-testing program to augment 1993 test data was implemented in 1994 to characterize water quality throughout the San Juan Basin of Colorado within La Plata County. On the basis of that study, 17 areas of elevated entrained methane in groundwater were defined including buffer zones as before. The identified areas with greater than 1.0-ppm entrained-methane in groundwater are outlined and shaded in the accompanying map (Appendix B: Maps and Cross-Sections 8.)