Defective wells, not hydraulic fracturing, is the primary cause of water contamination from shale gas extraction in parts of Pennsylvania and Texas, according to a study by Duke University.
Using noble gas and hydrocarbon tracers, researchers analyzed the gas content of more than 130 drinking water wells in the two states and found eight clusters of wells – seven in Pennsylvania and one in Texas – with contamination, including increased levels of natural gas from the Marcellus shale in Pennsylvania and from shallower, intermediate layers in both states.
Data showed that the contamination stemmed from well-integrity problems such as poor casing and cementing, which rules out the possibility that methane migrated up into drinking water aquifers because of horizontal drilling or fracking.
In four of the clusters, analysis showed that methane from drill sites escaped into drinking water wells from shallower depths through faulty or insufficient rings of cement surrounding a gas well’s shaft. In three clusters, the tests suggested the methane leaked through faulty well casings. In one cluster, it was linked to an underground well failure.
Gas content in 113 drinking-water wells and one natural methane seep overlying the Marcellus shale in Pennsylvania was analyzed, as well as 20 wells overlying the Barnett shale in Texas. Sampling took place in 2012 and 2013, and included wells where contamination had been debated previously, wells known to have naturally high level of methane and salts, and wells located both within and beyond a one-kilometer distance from drill sites.
Last year, two studies – one conducted in Arkansas by Duke University and one conducted in Pennsylvania by the National Energy Technology Laboratory in Pittsburgh – found that fracking was not causing local water contamination.