I am not aware of credible evidence of pollution of groundwater by hydraulic fracking in South Texas. The images I see of people lighting the methane flowing with water from the faucet, while amusing, are not a new phenomenon. In fact it was these sorts of observations, surface oil seeps and methane in water wells that were early forms of oil exploration in many parts of the country.
I remember stories of this sort from my childhood when I would listen to my father, grandfather and uncles discuss their work in the oil fields. In fact, Upton Sinclair's 1927 novel Oil! includes a scene in which it is oil seeps that tip off the oil baron about the presence of a reservoir under land where he is hunting with his son in Chapter 4.
Oil and gas producing formations being explored in Texas today normally lie several thousand feet below water bearing formations. These formations were not producible until the advent of fracking. The reasons these formations were not producible were largely because they were deep (8k to 15k feet), "tight" non-porous formations through which fluids could not migrate and which would self seal if an attempt was made to extract gas or oil. This lack of porosity and inability for fluids to migrate within the formations (for example the Eagle Ford in South Texas) caused these formations to be excluded and considered enconomically non-productive. That is, until the maturation of hydraulic fracturing to artificially create flow channels between the rock and a drilled channel. Adventurous companies recently tested the new methods in previously excluded formations such as the Bakken and Eagle Ford shale formations and created a new domestic oil boom in various deep shale formations across the country.
The very characteristics of the geological formations that inspired the development of hydraulic fracking techniques act to protect groundwater sources. Extreme depth, high pressures and very low porosity mean that the flow channels created by fracking will remain local to the drilled channel they are designed to fill. In fact, because of the self sealing tendencies of these formations there is an entire sub-industry whose work is designed to simply keep these wells flowing by constantly cleaning and reworking the producing wells.
Drilling permits issued by the Texas Railroad Commission for horizontal drilling in the Eagle Ford (pronounced “igglferd” if you want to sound like you are an insider) reveal that the estimated depths of these wells is from 6000' to 17,000' depending upon the location. Geologic formations in South Texas tend to dip downward to the coast (get deeper). The further inland the shallower the well, both water bearing and oil and gas bearing formations show this pattern.
The mean depth for Wilcox-Carrizo fresh water wells is 398' and the range is from 250' to approximately 1050'. Mildly saline water is available to approximately 3500'.1
The differential in depth of between the Carrizo-Wilcox potable water bearing formations and the Eagle Ford oil and gas bearing formation varies from about 4000' to 10,000' in South Texas. The risk of contamination of water sources does not appear to be a realistic fear at least in South Texas.
1 Draft Technical Report; Transmissivity, Hydraulic Conductivity, and Storativity of the Carrizo-Wilcox Aquifer in Texas; Robert E. Mace, Rebecca C. Smyth, Liying Xu, Jinhuo Liang; Robert E. Mace, Principal Investigator; prepared for the Texas Water Development Board under TWDB Contract No. 99-483-279, Part 1, Bureau of Economic Geology, W. L. Fisher, Director ad interim, The University of Texas at Austin, Austin, Texas 78713-8924, January 1999