Rock and soil contain natural radioactivity, which can dissolve into the groundwater. This is known as Naturally Occurring Radioactive Materials, or NORM. Commonly found NORM includes uranium, thorium, and potassium-40 and their decay chain products, including radium and radon. When oil and gas (O&G) are extracted from the earth, NORM may also be co-extracted depending upon the formation geochemistry and operating conditions. This extracted NORM is a byproduct that must be disposed of and is classified as Technologically Enhanced Naturally Occurring Radioactive Material, or TENORM, because it has been concentrated or exposed to the environment.
The Pennsylvania Department of Environmental Protection (PA DEP) noticed an increase in waste generated by O&G production that contained TENORM being disposed of in Commonwealth landfills. This increased activity and regulatory concern over the potential impacts of TENORM, if not properly handled, led to the PA DEP initiating a study to determine the potential impact of TENORM disposal on workers and the public. The study report, released in January 2015, included the results of the radiological surveys that specifically examine the many pathways that could lead to worker and public radiation exposure, and several observations and recommendations.
The PA DEP study included testing solid, liquid, gas, and filter sample matrices associated with wastes generated from O&G exploration and production. Solid waste matrices included surface soil, drill cuttings, proppant sand, filter cakes, drilling socks, soils, and sludge. Liquid waste matrices included wastewater treatment plant (WWTP) influent and effluent liquids, landfill leachates, and well site-related liquids (i.e., hydraulic fracturing fluid, flowback fluid, and produced water).
The liquid and solid waste matrices were tested for uranium, thorium, and potassium-40, along with several decay products including radium-226 and radium-228, by gamma spectroscopy using direct or inferred energy lines. A total of 11 radionuclides were included in the survey. The liquid waste matrices were also analyzed for gross alpha and gross beta using US EPA Method 900.0, a gas proportional counter (GPC) method, and a subset of the soil samples was analyzed for uranium and thorium radionuclides using alpha spectroscopy. X-Ray Fluorescence (XRF) was also used to measure non-radiological uranium and thorium. The uranium and thorium XRF measured values were then converted to uranium and thorium isotope radiological concentrations using common conversion factors to infer secular equilibrium. The natural gas samples were collected using scintillation cells with photomultiplier tubes and analyzed for radon. The filter waste samples were analyzed for gross alpha and gross beta using a scintillation detector. The PA DEP study report noted fundamental issues and assumptions with several of the methods used. Environmental Standards’ chemistry team reviewed different radiological methods, including those used in this study, and noted QA/QC quality indicators as part of a properly executed sampling and analytical study. Environmental Standards’ findings will be presented in a separate blog post.
The PA DEP study concluded that there was little or limited potential for radiation exposure to workers or the public due to normal processes. In the event of a fluid or filter cake spill/release, there is potential for radiological environmental impacts; therefore, it was recommended that the associated disposal protocols be reviewed further. Further studies were recommended for facilities that treat O&G waste and for companies using O&G brine for dust suppression and/or road stabilization.
One aspect of O&G exploration activities that is of particular concern is the collection and disposal of produced water and flowback fluid. These aqueous-based fluids are integral parts of the shale fracturing process. Upon testing, the PA DEP found that the produced water and flowback fluid contain levels of radium-226 and radium-228, well above the US EPA maximum contaminant level (MCL) for drinking water. On a worst case scenario, the levels of radium-226 and radium-228 might be of concern for any produced water or flowback fluid that was inadvertently released into the local groundwater. Many public drinking water systems within Pennsylvania obtain their source water from local groundwater (i.e., rivers, streams, and lakes). Inadvertent release of produced water or flowback fluid into the local drinking water source could potentially lead to US EPA MCL exceedances. Radiological testing of produced water and flowback fluid appears prudent under these worst-case release scenarios.
An important consideration when performing radiological testing is the usability and defensibility of the data. Unfortunately, current radiological testing methods are open to broad interpretation by commercial laboratory personnel. The methods are essentially written as guidelines, and during the significant number of commercial laboratory audits performed nationwide, our team has observed significant variations between the laboratory procedures. It is clear that the radiological analysis methods were developed for less complicated matrices than those associated with the O&G waste samples. The high total solids content in flowback fluids and produced water are known to confound the accurate measurement of gross alpha, gross beta, radium-226, and radium-228. In addition, gamma spectroscopy does not allow for direct analysis of several radiological analytes and can suffer from interferences and different interpretation. Laboratory personnel can adopt or revise the methods as they see fit as long as they pass performance evaluation samples and internal quality control guidelines. Clearly, this freedom to alter methods can affect data comparability between laboratories.
My colleagues at Environmental Standards have extensive experience with radiological methods of analysis. This expertise can be used to evaluate laboratory preparation and analytical methods in detail as companies develop analytical programs. Once radiological data are obtained, it is important to subject these data to independent third-party data validation, which provides a second approach in assessing data quality and is one way to ensure that the radiological data received are consistent and of proper quality for defensible sample disposal.