Hydraulic fracturing is the propagation of fractures in a rock layer by pressurized fluid. Induced hydraulic fracturing or hydrofracking, commonly known as fracking, is a technique used to release petroleum, natural gas (including shale gas, tight gas and coal seam gas), or other substances for extraction, particularly from unconventional reservoirs. [1] Radionuclides are associated with fracking in two main ways. 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 fracking. [2] In addition, fracking releases naturally occurring heavy metals and radioactive materials from shale deposits, and these substances return to the surface with flowback, also referred to as wastewater. [3]
There are naturally occurring radioactive material (e.g., radium and radon) in shale deposits. [4] Hydraulic fracturing can dislodge naturally occurring heavy metals and radioactive materials from shale deposits, and these substances return to the surface with flowback, also referred to as wastewater or brine. [4] [5] [6] [7] These naturally occurring radionuclides are of more concern than some man-made radionuclides used in fracture monitoring because of their long half lives. Radium-226 is a product of Uranium-238 decay, and is the longest-lived isotope of radium with a half-life of 1601 years; next longest is Radium-228, a product of Thorium-232 breakdown, with a half-life of 5.75 years. [8] Radon (Rn) is a naturally occurring product of the decay of uranium or thorium. Its most stable isotope, Radon-222, has a half-life of 3.8 days. Strontium is also naturally occurring and may be dislodged by the process. [5] Higher levels of Lead-210, the decay product of Radon-222, have been found on the airborne particulate matters that are collected downwind of wells completed with hydraulic fracturing. [9]
Injection of 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. [2] Patents describe in detail how several tracers are typically used in the same well. Wells are hydraulically fractured in different stages. [10] Tracers with different half-lives are used for each stage. [10] [11] Their half-lives range from 40.2 hours ( Lanthanum-140) to 28.90 years ( Strontium-90). [12] Amounts per injection of radionuclide are listed in the US Nuclear Regulatory Commission (NRC) guidelines. [13] The NRC guidelines also list a wide range or radioactive materials in solid, liquid and gaseous forms that are used as field flood or enhanced oil and gas recovery study applications tracers used in single and multiple wells. [13] According to the NRC, some of the most commonly used include Antimony-124, Bromine-82, Iodine-125, Iodine-131, Iridium-192, and Scandium-46. [13] A 2003 publication by the International Atomic Energy Agency (IAEA) provides a detailed description of tracer use, confirms the frequent use of most of the tracers above, and says that Manganese-56, Sodium-24, Technetium-m, Silver-m, Argon-41, and Xenon-133 are also used extensively because they are easily identified and measured. [14] Other potentially suitable tracers are named in various patents. [10] [11] [15] In terms of quantities used, the NRC gives the following examples: Iodine-131, gas form, 100 millicuries total, not to exceed 20 millicuries per injection; Iodine-131, liquid form, 50 millicuries total, not to exceed 10 millicuries per injection; Iridium-192, "Labeled" frac sand, 200 millicuries total, not to exceed 15 millicuries per injection; Silver-110m, liquid form, 200 millicuries total, not to exceed 20 millicuries per injection. [16]
Other gamma-emitting tracer isotopes used are Antimony-121, Antimony-122, Antimony-123, Antimony-125, Antimony-126, Antimony-127, Carbon-14, Chromium-51, Cobalt-57, Cobalt-58, Cobalt-60, Gold-198, Iodine-127, Iodine-128, Iodine-129, Iodine-130, Iron-59, Krypton-85, Lanthanum-140, Potassium-39 (activated to Potassium-40), Potassium-41 (activated to Potassium-42), Potassium-43, Rubidium-86, Scandium-45, Scandium-47, Scandium-48, Silver-110, Sodium-22, Strontium-85, Strontium-90, Tritium, Zinc-65, and Zirconium-95. [10] [11] [12] [13] [15]
Concerns have been expressed that both naturally occurring radionuclides and radioactive tracers may return to the surface with flowback and during blow outs. [17] [18] Wastewater from the wells is released into rivers, injected into wells, and evaporated from ponds. [4] The 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. [19] Recycling the wastewater has been proposed as a solution but has its limitations. [20] The New York Times has reported on radium and gross alpha radiation levels in wastewater (also called flowback) from natural gas wells. It collected data from more than 200 natural gas wells in Pennsylvania. The New York Times has compiled a map of these wells and their wastewater contamination levels. [4] [6] [21]
Political, governmental, and industry pressures have prevented the United States Environmental Protection Agency (EPA) from studying risks associated with radionuclides [22] or other chemicals in hydraulic fracturing fluids in wastewater, [23] source water, and drinking water. [22] [24] [25] [26] [27] The scope of the EPA Hydraulic Fracturing Draft Study Plan was narrowed to exclude them. [22] [26] [28]
As radon decays, it produces radioactive decay products. If the contaminated dust of these "radon daughters" are inhaled, they can lodge in the lungs and increase the risk of developing lung cancer. [29] Iodine in food is absorbed by the body and preferentially concentrated in the thyroid where it is needed for the functioning of that gland. When Iodine-131 is present in high levels in the environment from hydraulic fracturing flowback and blowouts, it can be absorbed through contaminated food and water, and will also accumulate in the thyroid. As it decays, it may cause damage to the thyroid. The primary risk from exposure to high levels of iodine-131 is the chance occurrence of radiogenic thyroid cancer in later life. Other risks include the possibility of non-cancerous growths and thyroiditis. [30] [31] The level of radiation in hydraulic fracturing wastewater has been measured to be as high as 18,035 pCi/L, [6] thousands of times the maximum allowed by the federal standard for drinking water, [4] [6] and there are concerns about radiation exposure during spills and blowouts. [17] [18] Long term exposure to low level radiation is associated with stochastic [32] health effects; the greater the exposure, the more likely the health effects are to occur. [32] A group of doctors from the United States have called for a moratorium on hydraulic fracturing until health effects are more thoroughly studied. [33] [34]
The US Nuclear Regulatory Commission (NRC) and approved state agencies regulate the use of injected radionuclides in hydraulic fracturing in the United States. [13] Federal and state regulators do not require sewage treatment plants that accept drilling waste 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. [35] 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. [36] [37] Safe drinking water standards have not yet been established to account for radioactivity levels of hydraulic fracturing waste water, [4] and although water suppliers are required to inform citizens of radon and other radionuclides levels in their water, this doesn't always happen. [38] Radioactive tracers are not yet listed on FracFocus, [39] a website indicating chemical composition of fracking fluid of individual wells, but federal and state nuclear regulatory agencies keep records of their use. [13]
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.
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.
labeled Frac Sand ... Sc-46, Br-82, Ag-110m, Sb-124, Ir-192
Beta emitters including H-3 and C-14 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-46, La-140, Mn-56, Na-24, Sb-124, Ir-192, Tc-m, I-131, Ag-m, Ar-41, and Xe-133 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-82...
Radioactive tracers can be detected with wireline gamma-logging equipment in the wellbore, but their use poses additional environmental and safety concerns.[ dead link]
But some members of the chartered SAB are suggesting that the fracking panel revise its recommendation that the agency scale back its planned toxicity testing of chemicals used in the hydraulic fracturing, or fracking, process, because of the limited resources and time frame ... Chesapeake Energy supported the draft recommendation, saying that "an in-depth study of toxicity, the development of new analytical methods and tracers are not practical given the budget and schedule limitation of the study."
Flowback and Produced water ... Chesapeake agrees that an indepth study of toxicity, the development of new analytic methods and tracers are not practical given the budget and schedule limitations of the study ... Wastewater Treatment and Waste Disposal ... Chesapeake believes there was unjustified emphasis on the surface disposal of produced water to treatment plants in the SAB's Review ... Chesapeake disagrees with the inclusion of water distribution network corrosion and burden of analyzing for contaminants by POTW's into the study.
While environmentalists have aggressively lobbied the agency to broaden the scope of the study, industry has lobbied the agency to narrow this focus
More than a quarter-century of efforts by some lawmakers and regulators to force the federal government to police the industry better have been thwarted, as E.P.A. studies have been repeatedly narrowed in scope and important findings have been removed
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