A study of 100 private water wells in and near the Barnett Shale deposit in North Texas has revealed elevated levels of potential contaminants such as arsenic and selenium closest to natural gas extraction sites.
“This study alone can’t conclusively identify the exact causes of elevated levels of contaminants in areas near natural gas drilling, but it does provide a powerful argument for continued research,” said Brian Fontenot, a University of Texas at Arlington PhD in quantitative biology and lead author of a new paper on the study.
“We expect this to be the first of multiple projects that will ultimately help the scientific community, the natural gas industry, and most importantly, the public, understand the effects of natural gas drilling on water quality,” he added.
The research team, led by UT Arlington associate professor of chemistry and biochemistry Kevin Schug, believes the increased presence of metals could be attributed to a variety of factors, including industrial accidents such as faulty gas well casings, mechanical vibrations from natural gas drilling activity disturbing particles in neglected water well equipment, or the lowering of water tables through drought or the removal of water used for the hydraulic fracturing process. Any of these scenarios could release dangerous compounds into shallow groundwater.
On average, researchers detected the highest levels of contaminants within three kilometers of natural gas wells, including several samples that had arsenic and selenium above levels considered safe by the Environmental Protection Agency (EPA). For example, 29 wells that were within the study’s active natural gas drilling area exceeded the EPA’s maximum contaminant limit of 10 micrograms per liter for arsenic, a potentially dangerous situation. The maximum concentration from an extraction area sample was 161 micrograms per liter, or 16 times the EPA safety standard set for drinking water. The EPA warns that people who drink water containing arsenic in excess of the safety standard for many years “could experience skin damage or problems with their circulatory system, and may have an increased risk of getting cancer.”
Selenium was also found in 10 samples near extraction sites, and all of those samples showed levels higher than the historical average. Two samples exceeded the standard for selenium set by the EPA. Circulation problems as well as hair or fingernail loss are some possible consequences of long-term exposure to high levels of selenium, according to the EPA.
Strontium was found in almost all the samples, with concentrations significantly higher than historical levels in the areas of active gas extraction. A toxicological profile by the federal government’s Agency for Toxic Substances and Disease Registry recommends no more than 4,000 micrograms of strontium per liter in drinking water. Seventeen samples from the active extraction area and one from the non-active areas exceeded that recommended limit. Exposure to high levels of stable strontium can result in impaired bone growth in children, according to the agency.
The researchers recommend further examination of levels of methanol and ethanol in water wells. Twenty-nine private water wells in the study contained methanol, with the highest concentrations in the active extraction areas. Twelve samples, four of which were from the non-active extraction sites, contained measurable ethanol. Both ethanol and methanol can occur naturally or as a result of industrial contamination.
The results of the North Texas well study have been published online by the journal Environmental Science & Technology. The peer-reviewed paper focuses on the presence of metals such as arsenic, barium, selenium and strontium in water samples. Many of these heavy metals occur naturally at low levels in groundwater, but disturbances from natural gas extraction activities could cause them to occur at elevated levels.