Groundwater in Lee and Chatham counties contains miniscule amounts of methane and other impurities, based on chemical analysis conducted in advance of shale gas exploration, according to the U.S. Geological Survey.
The well water tests mark one the first such studies conducted to establish the presence of foreign substances in local water sources before fracking activities get underway. The lab testing was conducted between October 2011 and August 2012 at no charge for property owners who agreed to participate.
Disputes over water contamination in states have led to industry claims that methane had intruded into local wells long before fracking began. Because fracking remains under moratorium in North Carolina until next year, the state offers an ideal opportunity to conduct groundwater testing to establish baseline water quality.
The USGS sampled 56 wells and 1 spring in the two counties where fracking is most likely to take place, based on geological assessments of the underlying Mesozoic-era shale rock formations. All samples were analyzed for major ions and dissolved gases, and some were analyzed for other constituents.
Sign Up and Save
Get six months of free digital access to The News & Observer
Up to 9 percent of the wells contained constituents above federal and state drinking water standards, the USGS said Wednesday, but the wells contained only trace amounts of naturally occurring methane.
Methane levels are not a safety concern until they reach 10 milligrams per liter. In the lab analyses, well water in Chatham and Lee counties ranged between about 0.00007 milligrams and 0.48 milligrams per liter, the latter being about 21 times lower than unsafe concentrations.
Methane is a common marker of water contamination associated with drilling activities, typically leaking out through faulty well shafts into nearby aquifers. The colorless and odorless gas is not toxic, but is considered dangerous because it can catch fire and potentially explode at high concentrations.
In all, the USGS collected data on 305 wells in a 79-square mile areas that’s home to 14,903 people. The wells were dug between 1850 and 2012 and ranged in depth from 26 feet to 720 feet below land surface in northwestern Lee County and southeastern Chatham County. Technically the region is known as the Sanford sub-basin, within the Deep River Basin, which lies in the Triassic Basin.
North Carolina’s proposed fracking rules, currently being completed by the N.C. Mining and Energy Commission, also include requirements for baseline water testing before, during and after drilling operations.