Over the past few months there has been a growing focus on the use of hydraulic fracturing for gas extraction, including an Oscar nomination for the controversial documentary Gasland and even a CSI episode on contaminated groundwater. Although hydraulic fracturing has been around for decades, EPA is poised to begin a study on the potential adverse impact the process may have on drinking water.
Last fall EPA conducted a series of stakeholder meetings in key regions affected by hydraulic fracturing. Based on that input, EPA developed a draft study plan that is currently in the hands of its Science Advisory Board in the Environmental Engineering Committee.
EPA expects to initiate the study this year and have initial study results available by late 2012.
In most cases hydraulic fracturing is used in geologic formations far below the water table. Well casings are designed to insure that fracture fluids, produced brine water and natural gas are isolated and the freshwater bearing zones are protected. However, casing failures can lead to groundwater contamination.
Fifty thousand to 350,000 gallons of water may be required to fracture one well in a coalbed formation while two to five million gallons of water may be needed to fracture one horizontal well in a shale formation.
For all the water that goes into a well, a significant percentage comes back out in the form of flowback or produced water. Estimates of the fluids recovered range from 15-80% of the volume injected depending on the site. Wastewater from the hydraulic fracturing process may be disposed in several ways. For example, it may be returned underground using a permitted underground injection well, reused for additional fracturing operations, or discharged to surface waters after treatment.
Surface water discharges of flowback and produced water are regulated by the National Pollutant Discharge Elimination System (NPDES) program. Treatment is typically performed by wastewater treatment facilities, either at the well-head or at nearby industrial or municipal facilities.
Contaminants of concern to drinking water include fracturing fluid chemicals and degradation products and naturally occurring materials in the geologic formation (e.g. natural gas, salts, metals, radionuclides) that are mobilized and brought to the surface during the hydraulic fracturing process.
EPA studied hydraulic fracturing used in coalbed methane reservoirs in 1999 to evaluate the potential risks to drinking water supplies. Coalbed methane reservoirs are typically closer to the surface and groundwater sources compared to conventional gas reservoirs. In a report issued in 2004, EPA concluded that there was little to no risk of fracturing fluid contaminating underground sources of drinking water during hydraulic fracturing of coalbed methane production wells.
Given the US demand for natural gas, it's clear the use of hydraulic fracturing will only grow over the next few years. The main issues I see are insuring proper well construction to prevent groundwater contamination and developing and using water treatment systems that economically remove the pollutants of concern to protect surface waters. Growth in water reuse systems will help reduce the high demand for water the process requires.
While the threat to public water systems should be minimal, the push for the development of gas fields in densely populated regions of the country will remain a concern for the next several years. Technology and regulation must keep pace to protect the environment and water resources.
James Laughlin, Editor
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