Radionuclides associated with hydraulic fracturing
Radionuclides associated with hydraulic fracturing are man-made radionuclides which are used in the hydraulic fracturing process as radioactive tracers or naturally occurring radionuclides released by this process. Injection of man-made radioactive tracers, along with the other substances in hydraulic-fracturing fluid, is often used to determine the injection profile and location of fractures created by hydraulic fracturing. In addition, hydraulic fracturing releases naturally occurring radioactive materials (NORM) from shale deposits, and these substances return to the surface with wastewater. Concerns have been expressed over the potential health and environmental impact of these materials.
Naturally occurring radionuclides
There are naturally occurring radioactive materials (NORM), for example radium, radon, uranium, and thorium, in shale deposits. Brine co-produced and brought to the surface along with the oil and gas sometimes contains naturally occurring radioactive materials; brine from many shale gas wells, contains these radioactive materials. When NORM is concentrated or exposed by human activities, such as hydraulic fracturing, it is classified as TENORM (technologically enhanced naturally occurring radioactive material). Naturally occurring radionuclides are of more concern than man-made radionuclides used in fracture monitoring because the former have longer half lives and so remain in the environment longer.
Injection of a wide range of radioactive tracers in solid, liquid or gaseous forms, is often used to determine the injection profile and location of fractures created by hydraulic fracturing. Use of radioactive tracers is strictly controlled. It is recommended that the radiotracer is chosen to have readily detectable radiation, appropriate chemical properties, and a half life and toxicity level that will minimize initial and residual contamination. Operators must ensure that licensed material will be used, transported, stored, and disposed of in such a way that members of the public will not receive more than 1 mSv (100 mrem) in one year, and the dose in any unrestricted area will not exceed 0.02 mSv (2 mrem) in any one hour. They must also secure stored licensed material from access, removal, or use by unauthorized personnel and control and maintain constant surveillance of licensed material when in use and not in storage.
As of 2003 the isotopes manganese-56, sodium-24, technetium-99m, silver-110m, argon-41, and xenon-133 were used extensively in the oil industry because they are easily identified and measured. Antimony-124, bromine-82, iodine-125, iodine-131, iridium-192, and scandium-46, are also used.
Examples of amounts used are:
|Iodine-131||Gas||100 millicuries (3.7 GBq) total, not to exceed 20 mCi (0.74 GBq) per injection|
|Iodine-131||Liquid||50 millicuries (1.9 GBq) total, not to exceed 10 mCi (0.37 GBq) per injection|
|Iridium-192||"Labeled" frac sand||200 millicuries (7.4 GBq) total, not to exceed 15 mCi (0.56 GBq) per injection|
|Silver-110m||Liquid||200 millicuries (7.4 GBq) total, not to exceed 10 mCi (0.37 GBq) per injection|
Concerns about environmental impact
||The examples and perspective in this section deal primarily with the United States and do not represent a worldwide view of the subject. (March 2014)|
Wastewater from the wells is released into rivers, injected into wells, and evaporated from ponds. An estimated 90 percent of frac flowback and oil and gas produced water in the United States is disposed of into deep EPA-licensed Class II disposal wells, with the remaining less than 10 percent reused, evaporated, used for irrigation, or discharged to surface streams. In the United States, according to the US EPA, discharges to surface waters must be made under National Pollutant Discharge Elimination System (NPDES) permits. Discharging oil and gas produced water to surface streams without an NPDES permit is a federal crime.
However, others point out exclusions and exemptions for hydraulic fracturing under United States federal law. Exemptions were made in the Clean Water Act, as part of the Energy Policy Act of 2005, also known as the "Halliburton Loophole." These exemptions included stormwater runoff from gas and oil construction activities which includes "oil and gas exploration, production, process, or treatment operations and transmission facilities" as part of the definition of construction activities. Amendments to the Safe Drinking Water Act involved the definition of underground injection. Underground injection related to hydraulic fracturing was exempted from the Clean Water Act, except if it uses diesel fuel. An exemption was also made to Toxics Release Inventory Reporting (Section 313). The oil and gas industry gets an exemption under the EPCRA, which usually requires the EPA and States to collect data on releases and transfers of listed toxic chemicals. Facilities are required to report at the discretion of the Administrator of the EPA by adding or deleting them from the Standard Industrial Classification list. Oil and gas facilities have not been added to this list and are therefore exempt from the EPCRA Finally, under the under Section 9601(14) of the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), commonly known as Superfund, hazardous waste definitions congruent with RCRA and SWDA exclude petroleum, including crude oil, natural gas liquids, and any mixture containing natural gas. If spills that would be otherwise classified under the Superfund contain any gas mixture, they are exempt from the remedies associated with this federal statute unless certain conditions are met. These limits to EPA's ability to hold a polluting industry liable for cleanup efforts continue to be tested in the courts.
In Pennsylvania the volume of oil and gas produced water treated by POTWs expanded greatly with the proliferation of Marcellus Shale wells after 2000. The EPA noted that most water treatment works are not set up to treat unconventional gas and oilfield wastes. In 2010 the Pennsylvania Department of Environmental Protection (DEP) limited surface water discharges from new treatment plants to 250 mg/l chloride; the chloride limitation was designed to also limit other contaminants such as radium. Existing water treatment plants were "grandfathered," and still allow higher discharge concentrations. In 2011, the PADEP gave unconventional oil and gas operators a 30-day deadline to voluntarily stop sending wastewater to the grandfathered treatment plants, and reported that all operators complied.
A 2012 report by the General Accounting Office found that of nine oil and gas-producing states studied, underground injection disposal was the most common method of disposal in all but Pennsylvania where there were only six active waste disposal wells. A 2012 report by the US National Renewable Energy Laboratory reported that according to government estimates, there were significant reductions in Pennsylvania's gas well wastewater was discharged through treatment plants to surface streams from 2008-2011. According the Pennsylvania Department of Environmental Protection (PA DEP), by 2011, wastewater treated at CWTs (Centralized Water Treatment centers) (about 50%), recycled in hydraulic fracturing (33.3%), disposed of in disposal wells (<10%), treated at grandfathered CWTs (not subject to updated treatment standards) (10%), treated at POTWs (<10%), or in storage (,1%). From the beginning to the end of 2011, wastewater volumes sent to “exempt” CWTs decreased by 98 percent, but the total amount of reported wastewater more than doubled. The volume of water treated at CWTs nearly quadrupled, deep-well injection more than tripled, and recycling in hydraulic fracturing operations increased by about 10%. The US National Renewable Energy Laboratory noted that there is a lack of reliable, publicly available water usage and management data, including data regarding total water withdrawals, total gas wells drilled, flowback volume per well, water recycling techniques, wastewater management, and other management practices for many regions.
In 2011, the level of dissolved radium in hydraulic fracturing wastewater released upstream from drinking water intakes had been measured to be up to 18,035 pCi/L (667.3 Bq/l), and the gross alpha level measured to be up to 40,880 pCi/L (1,513 Bq/l). The New York Times reported that studies by the United States Environmental Protection Agency and a confidential study by the drilling industry concluded that radioactivity in drilling waste cannot be fully diluted in rivers and other waterways. Recycling the wastewater has been proposed as a solution but has its limitations. A recent Duke University study sampled water downstream from a Pennsylvania wastewater treatment facility from 2010 through Fall 2012 and found the creek sediment contained levels of radium 200 times background levels. The surface water had the same chemical signature as rocks in the Marcellus Shale formation. The facility denied processing Marcellus waste since 2011. In May 2013 the facility signed another agreement to not accept or discharge wastewater Marcellus Shale formations until it has installed technology to remove the radiation compounds, metals and salts. According to the Duke researches the ‘waste treatment solids/sludge’ have exceeded U.S. regulations for radium disposal to soil. The study by Duke University also found that radium has been ‘absorbed and accumulated on the sediments locally at the discharge’.
Potential health impact
The U.S. Environmental Protection Agency and regulators in North Dakota considers radioactive material in flowback a potential hazard to workers at hydraulic fracturing drilling and waste disposal sites and those living or working nearby if the correct procedures are not followed.
Regulation in the US
The US EPA sets radioactivity standards for drinking water. Federal and state regulators do not require sewage treatment plants that accept gas well wastewater to test for radioactivity. In Pennsylvania, where the hydraulic fracturing drilling boom began in 2008, most drinking-water intake plants downstream from those sewage treatment plants have not tested for radioactivity since before 2006. The EPA has asked the Pennsylvania Department of Environmental Protection to require community water systems in certain locations, and centralized wastewater treatment facilities to conduct testing for radionuclides. and although water suppliers are required to inform citizens of radon and other radionuclides levels in their water, this doesn't always happen. Federal and state nuclear regulatory agencies keep records of the radionuclides used.
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- McMahon, Jeff (24 July 2013). "Strange Byproduct Of Fracking Boom: Radioactive Socks". Forbes. Retrieved 28 July 2013. "The U.S. Environmental Protection Agency considers NORM a hazard mostly to workers at the site: “They may inhale radon gas which is released during drilling and produced by the decay of radium, raising their risk of lung cancer. In addition, they are exposed to alpha and gamma radiation released during the decay of radium-226 and the low-energy gamma radiation and beta particles released by the decay of radium-228, according to EPA. “Gamma radiation can also penetrate the skin and raise the risk of cancer.” But North Dakota considers NORM a hazard to the public as well. The state distributes a flyer to oilfield waste haulers that recommends appropriate locations for the disposal of oilfield wastes. The only ones listed that accept radioactive waste are in Colorado, Texas, and South Dakota."
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