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Radioactive sources are used for logging formation parameters. Radioactive tracers, along with the other substances in hydraulic-fracturing fluid, are 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.

Use of radioactive sources for logging

Sealed radioactive sources are routinely used in formation evaluation of both hydraulically fractured and non-fracked wells. The sources are lowered into the borehole as part of the well logging tools, and are removed from the borehole before any hydraulic fracturing takes place. Measurement of formation density is made using a sealed caesium-137 source. This bombards the formation with high energy gamma rays. The attenuation of these gamma rays gives an accurate measure of formation density; this has been a standard oilfield tool since 1965. Another source is americium berylium (Am-Be) neutron source used in evaluation of the porosity of the formation, and this has been used since 1950. In a drilling context, these sources are used by trained personnel, and radiation exposure of those personnel is monitored. Usage is covered by licenses from International Atomic Energy Agency (IAEA) guidelines, SU or European Union protocols, and the Environment Agency in the UK. Licenses are required for access, transport, and use of radioactive sources. These sources are very large, and the potential for their use in a 'dirty bomb' means security issues are considered as important. There is no risk to the public, or to water supplies under normal usage. They are transported to a well site in shielded containers, which means exposure to the public is very low, much lower than the background radiation dose in one day.

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.

Radiotracers and markers

The oil and gas industry in general uses unsealed radioactive solids (powder and granular forms), liquids and gases to investigate or trace the movement of materials. The most common use of these radiotracers is at the well head for the measurement of flow rate for various purposes.

Use of these 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 are to 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 are required to 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. Federal and state nuclear regulatory agencies keep records of the radionuclides used.

As of 2003 the isotopes Antimony-124, argon-41, cobalt-60, iodine-131, iridium-192, lanthanum-140, manganese-56, scandium-46, sodium-24, silver-110m, technetium-99m, and xenon-133 were most commonly used by the oil and gas industry because they are easily identified and measured. Bromine-82, Carbon-14, hydrogen-3, iodine-125 are also used.

Examples of amounts used are:

In hydraulic fracturing, plastic pellets coated with Silver-110m or sand labelled with Iridium-192with may be added to a proppant when it is required to evaluate whether a fracturing process has penetrated rocks in the pay zone.

Some radioactivity may by brought to the surface at the well head during testing to determine the injection profile and location of fractures. Typically this uses very small (50 kBq) Cobalt-60 sources and dilution factors are such that the activity concentrations will be very low in the topside plant and equipment.

Potential health impact in the US

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 NRC and approved state agencies regulate the use of injected radionuclides in hydraulic fracturing in the United States.

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.

See also

• List of additives for hydraulic fracturing
• Hydraulic fracturing proppants

References

1. Reis, John C. (1976). Environmental Control in Petroleum Engineering. Gulf Professional Publishers.
2. "Iodine 131 Found in Philadelphia's Drinking Water" (Press release). Bucks County Water & Sewer Authority. 12 April 2011. Retrieved 11 May 2012. In response to these results, PWD is working with the EPA and DEP and taking the following actions: Developing a Joint PADEP, EPA, PWD Action Plan for all Radionuclides; Initiating a focused sampling program for Iodine; Developing an aggressive track down program with EPA and DEP to identify the potential sources of Iodine 131 in our source waters.
3. Staff. "Radon in Drinking Water: Questions and Answers" (PDF). US Environmental Protection Agency. Retrieved 7 August 2012.
4. "Public Health Fact Sheet on Radon - Health and Human Services". Mass.Gov. Retrieved 2011-12-04.
5. Weinhold, Bob (19 September 2012). "Unknown Quantity: Regulating Radionuclides in Tap Water". Environmental Health Perspectives. NIEHS, NIH. Retrieved 11 February 2012. Examples of human activities that may lead to radionuclide exposure include mining, milling, and processing of radio­active substances; wastewater releases from the hydraulic fracturing of oil and natural gas wells... Mining and hydraulic fracturing, or "fracking", can concentrate levels of uranium (as well as radium, radon, and thorium) in wastewater... {{cite web}}: soft hyphen character in |quote= at position 117 (help)
6. Heather Smith (7 March 2013). "County's potential for fracking is undetermined". Environment / Pollution. Discover Magazine. Retrieved 11 August 2013.
7. Helman, Christopher (23 January 2013). "Energy's Latest Battleground: Fracking For Uranium". Forbes. Retrieved 11 August 2013. Fracking for uranium isn't vastly different from fracking for natural gas. UEC bores under ranchland into layers of highly porous rock that not only contain uranium ore but also hold precious groundwater. Then it injects oxygenated water down into the sand to dissolve out the uranium. The resulting solution is slurped out with pumps, then processed and dried at the company's Hobson plant.
8. ^ Urbina, Ian (26 February 2011). "Regulation Lax as Gas Wells' Tainted Water Hits Rivers". The New York Times. Retrieved 22 February 2012. The level of radioactivity in the wastewater has sometimes been hundreds or even thousands of times the maximum allowed by the federal standard for drinking water. Cite error: The named reference "Urbina 26Feb2011" was defined multiple times with different content (see the help page).
9. Linda Marsa (1 August 2011). "Fracking Nation. Environmental concerns over a controversial mining method could put America's largest reservoirs of clean-burning natural gas beyond reach. Is there a better way to drill?". Environment / Pollution. Discover Magazine. Retrieved 5 August 2011.
10. White, Jeremy; Park, Haeyoun; Urbina, Ian; Palmer, Griff (26 February 2011). "Toxic Contamination From Natural Gas Wells". The New York Times.
11. "TENORM Sources". United States Environmental Protection Agency. Retrieved 2012-09-12.
12. "Oil and Gas Production Wastes". United States Environmental Protection Agency. Retrieved 2012-09-12.
13. ^ Radiation Protection and the Management of Radioactive Waste in the Oil and Gas Industry (PDF) (Report). International Atomic Energy Agency. 2003. pp. 38–40. Retrieved 20 May 2012. Beta emitters, including H and C, may be used when it is feasible to use sampling techniques to detect the presence of the radiotracer, or when changes in activity concentration can be used as indicators of the properties of interest in the system. Gamma emitters, such as Sc, La, Mn, Na, Sb, Ir, Tc, I, Ag, Ar and Xe are used extensively because of the ease with which they can be identified and measured. ... In order to aid the detection of any spillage of solutions of the 'soft' beta emitters, they are sometimes spiked with a short half-life gamma emitter such as Br...
14. ^ Jack E. Whitten, Steven R. Courtemanche, Andrea R. Jones, Richard E. Penrod, and David B. Fogl (Division of Industrial and Medical Nuclear Safety, Office of Nuclear Material Safety and Safeguards) (June 2000). "Consolidated Guidance About Materials Licenses: Program-Specific Guidance About Well Logging, Tracer, and Field Flood Study Licenses (NUREG-1556, Volume 14)". US Nuclear Regulatory Commission. Retrieved 19 April 2012. labeled Frac Sand...Sc-46, Br-82, Ag-110m, Sb-124, Ir-192{{cite web}}: CS1 maint: multiple names: authors list (link)
15. Dina Murphy and Larry Huskins (8 Sep 2006). "letter filed with Department of Environment, New Brunswick, CA" (PDF). Penobsquis, CA government: 3. Retrieved 29 July 2012. engineer who works with this radioactive material for a living is exposed to less radiation than an individual who smokes 1.5 packs of cigarettes a day." {{cite journal}}: Cite journal requires |journal= (help)
16. ^ "Radioactive Waste from Oil and Gas Drilling" (PDF). United States Environmental Protection Agency. April 2006. Retrieved 2013-08-11.
17. ^ 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.
18. US EPA, are EPA’s drinking water regulations for radionuclides? What are EPA's drinking water regulations for radionuclides?, accessed 15 Sept. 2013.
19. "Regulation Lax as Gas Wells' Tainted Water Hits Rivers". New York Times. February 26, 2011. {{cite journal}}: Cite journal requires |journal= (help)
20. "Letter to PADEP re:Marcellus Shale 030711" (PDF). EPA. 7 March 2011. Retrieved 11 May 2012. ...several sources of data, including reports required by PADEP, indicate that the wastewater resulting from gas drilling operations (including flowback from hydraulic fracturing and other fluids produced from gas production wells) contains variable and sometimes high concentrations of materials that may present a threat to human health and aquatic environment, including radionuclides....Many of these substances are not completely removed by wastewater treatment facilities, and their discharge may cause or contribute to impaired drinking water quality for downstream users, or harm aquatic life...At the same time, it is equally critical to examine the persistence of these substances, including radionuclides, in wastewater effluents and their potential presence in receiving waters. {{cite journal}}: Cite journal requires |journal= (help); Unknown parameter |authors= ignored (help)
21. Ian Urbina (7 March 2011). "E.P.A. Steps Up Scrutiny of Pollution in Pennsylvania Rivers". The New York Times. Retrieved 23 February 2012.

• Hydraulic fracturing
• Radioactivity