Sources and Occurrence Rate of Groundwater Methane

Microbially-generated methane, rather than high-volume hydraulic fracturing, is the primary source of dissolved methane present in the area’s groundwater

The rate of groundwater contamination due to natural gas leakage from oil and gas wells has remained largely unchanged in northeastern Colorado’s Denver-Julesburg Basin since 2001.

Old and faulty oil and gas wells contribute a smaller percentage than microbially-generated methane, with the risk of groundwater contamination due to a leak estimated to be between 0.12 percent of all the water wells in the region to 4.5 percent of the water wells that were tested.

Oil and gas development — particularly the introduction of horizontal drilling and high-volume hydraulic fracking — has generated public concern in Colorado over potential groundwater contamination due to the possibility of leakage from oil and gas wells. When present, natural gas can turn drinking water flammable, a safety hazard observed in numerous historical cases.

In data dating back as far as 1988, dissolved methane was discovered in 523 of the 924 water wells sampled, a rate of about 64 percent. However, based on a geochemical analysis, the researchers determined that 95.5 percent of that methane was generated by naturally-occurring microbial processes, a result of proximity to shallow coal seams criss-crossing northeastern Colorado.

Aside from the microbial methane, oil and gas wells have been found to leak methane and other natural gases such as propane and butane due to faulty or unsuitably shallow surface casings.  Older gas wells built as far back as the 1970s were typically cased to a depth of approximately 300 feet, leaving the state’s deepest water aquifers unprotected from potential gas leaks. Updated regulatory standards have since required that new wells be cased far deeper and a number of older wells are currently being repaired. 

Between 2001 and 2014 (the last year of complete data), dissolved gas that could be directly linked to deep oil- and gas-bearing formations affected 42 water wells in 32 separate incident cases, a rate of about two cases per year. That rate did not change after the introduction of horizontal drilling and high-volume hydraulic fracturing in the state in 2010. Eleven of those cases could be linked to older, vertical wells drilled before 1993. The remaining 21 cases were either settled privately with the landowner, or remain unresolved due to lack of data.

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Taxonomy

• Groundwater
• Groundwater Modeling
• Groundwater Pollution
• Groundwater Mapping