MEMORANDUM

TO: Lisa Biddle, EPA

FROM: Sarah Yates, ERG

Betsy Bicknell, ERG

DATE: March 31, 2015

SUBJECT: Radioactive Materials in the Unconventional Oil and Gas (UOG) Industry

(DCN SGE00933)

Radioactive materials, such as radium, radon, and uranium, have been detected in 

wastewater generated by the UOG extraction industry (DCN SGE00241, DCN SGE00704). The 

Technical Development Document for Proposed Effluent Limitations Guidelines and Standards 

for Oil and Gas Extraction (TDD) (DCN SGE00704) presents UOG extraction wastewater 

concentrations for certain radioactive materials. To supplement the TDD, this memorandum

provides background information about radioactive materials in UOG extraction wastewater, 

including general background about radioactivity and how it is measured, issues related to the 

analysis of radioactive materials in UOG extraction wastewater, ongoing studies, and potential

concerns about radioactive materials in UOG extraction wastewater.

This memorandum will refer to the following terms used throughout the TDD and the 

supporting memoranda: 

 Unconventional oil and gas (UOG) resources

1

– crude oil and natural gas2

produced by a well drilled into a low porosity, low permeability formation 

(including, but not limited to, shale gas, shale oil, tight gas, tight oil). For the 

purpose of the proposed rule, the definition of UOG does not include CBM.

 UOG extraction wastewater – sources of wastewater pollutants associated with 

production, field exploration, drilling, well completion, or well treatment for 

unconventional oil and gas extraction (e.g., drilling muds, drill cuttings, produced 

sand, produced water)3.

 

1 UOG resource types are categorized into shale and tight formations.

2 Natural gas can include “natural gas liquids,” components that are liquid at ambient temperature and pressure.

3

Stormwater is not considered a source of UOG extraction wastewater. In general, no NPDES permit is required for 

discharges of stormwater from any field activities or operations associated with oil and gas production, except as 

specified in 40 C.F.R. 122.26(c)(1)(iii) for discharges of a reportable quantity or that contribute to a violation of a 

water quality standard. States may impose additional requirements for management of drilling site stormwater. 

Drilling wastewater (the liquid waste stream separated from recovered drilling fluid (e.g., mud) and drill cuttings) 

and produced sand are not discussed in this memorandum. Additional information about drilling wastewater can be 

found in ERG’s Unconventional Oil and Gas Drilling Wastewater memorandum (DCN SGE00740).
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 Produced water – the water (brine) brought up from the hydrocarbon-bearing 

strata during the extraction of oil and gas. This can include formation water, 

injection water, and any chemicals added downhole or during the oil/water 

separation process. Based on the stage of completion and production the well is 

in, produced water can be further broken down into the following components:

o Flowback – the produced water generated in the initial period after hydraulic 

fracturing (i.e., fracturing fluid, injection water, any chemicals added 

downhole, and varying amounts of formation water). After the hydraulic 

fracturing procedure is completed and pressure is released, the direction of 

fluid flow reverses, and the fluid flows up through the wellbore to the surface. 

The water that returns to the surface is commonly referred to as “flowback.” 

Flowback is typically reported as a percentage of fracturing fluid volume in 

literature and by industry.

o Long-term produced water (LTPW) – the produced water generated during the 

production phase of the well after the initial flowback process. Long-term 

produced water includes increasing percentages of formation water that make 

up the total volume of long-term produced water. Long-term produced water 

continues to be produced throughout the lifetime of the well and is usually 

reported in terms of flow rates in literature and by industry.

1.0 BACKGROUND: RADIOACTIVITY AND HOW IT IS MEASURED

Radioactivity and Ionizing Radiation. Radioactivity is the property of some unstable 

atoms that causes them to spontaneously decay and give off energy (radiation) as particles or 

rays. This phenomenon is known as radioactive decay. Because the radiation emitted during 

radioactive decay has enough energy to break chemical bonds, it is referred to as ionizing 

radiation. The three main kinds of ionizing radiation are (DCN SGE00936):

4

 Alpha particles, which include two protons and two neutrons (essentially a helium 

nucleus);

 Beta particles, which are essentially high-speed electrons; and

 Gamma rays and x-rays, which are pure energy (photons).

The descriptions of these types of ionizing radiation provided below are taken from 

Keenan 1971 (DCN SGE00179) and EPA’s radiation protection website (DCN SGE00936).

Alpha particles emitted from a given nuclide5have energies confined to a few discrete 

values, so that the energies of alpha particles can identify the nuclide from which they are 

emitted. Some nuclides emit alpha particles at more than one speed. For example 226Ra (radium226) emits alpha particles at either 1.517e9 or 1.488e9 centimeter/second (cm/sec). The emission 

of the slower particle is followed by the emission of a gamma ray, such that equal energy is 

emitted in each case. The loss of an alpha particle reduces the mass of the nucleus and also 

 

4 Other kinds of ionizing radiation exist but are not germane to this discussion (e.g., neutrons).

5 Nuclide is an atomic species characterized by the specific constitution of its nucleus, i.e., by its number of protons,

its number of neutrons, and its energy state. An element is a substance in which all atoms have the same number of 

protons; atoms of the same element with different numbers of neutrons have differing atomic weights and are called 

isotopes (DCN SGE00179). 226Ra and 228Ra are isotopes of radium with atomic weights of 226 and 228, 

respectively.
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changes the atom to a different element (the number of protons determines the element). For 

example, when radium-226 (

226Ra) emits an alpha particle, it loses two protons and two neutrons. 

The atomic mass is reduced from 226 to 222 and the 226Ra atom becomes an atom of 222Rn 

(radon-222), a radioactive gas.

Beta particle emission occurs when the ratio of neutrons to protons in the nucleus is too 

high. In this case, an excess neutron transforms into a proton, which stays in the nucleus, and a 

beta particle (high speed electron) is ejected energetically. Unlike alpha particles, beta particles 

are emitted at all possible speeds (term of art: beta spectrum). When the ejection of the beta 

particle does not rid the nucleus of sufficient energy, the nucleus releases the remaining excess 

energy in the form of gamma radiation. Like alpha particle emission, emission of a beta particle 

also changes the atom to a different element. For example, 228Ra (radium-228) is a beta emitter. 

During its radioactive decay, a neutron in the nucleus converts to a proton and the nucleus emits 

a beta particle. The number of protons increases from 88 to 89, changing the atom from radium 

to actinium (DCN SGE00936). Even though the atom is a different element, because neutrons 

and protons have the same mass, the atom retains the same atomic mass number: beta decay 

converts 228Ra to 228Ac (actinium-228).

Gamma radiation emission occurs when the nucleus of a radioactive atom has too much 

energy. It often follows the emission of a beta particle and can also follow the emission of an 

alpha particle (there are no pure gamma emitters). In either case, the energies of the gamma 

radiation from a given nuclide are limited to a few discrete values, that is, discrete wavelengths, 

and can be used to identify the nuclide. 

Measuring Radioactivity. Radioactivity is measured using electronic detectors coupled 

to instrumentation used to count the number of atomic disintegrations per unit of time. Whether a 

radioactive material emits alpha particles, beta particles, or gamma rays, the quantity of 

radioactive material is expressed in terms of its radioactivity (or simply its activity), in units of 

measure of the curie (Ci) or becquerel (Bq) (DCN SGE00977).

A curie (Ci) is a non-SI unit for radioactivity, defined as 37 billion disintegrations per 

second6. Thus, a radioactive sample that has an activity of 74 billion disintegrations per second 

has an activity of 2 curies. The curie is a very large unit for quantities found in the environment. 

Scientists use the following fractions of a curie as well:

 Picocuries (pCi) are 1 trillionth of a curie (1 x 10-12 Ci). Picocuries are used in 

measuring the typically small amount of radioactivity in air and water.

 Other fractions such as millicuries (mCi), or 1/1000 Ci and nanocuries (nCi), or 1 

billionth of a curie, are used as needed (DCN SGE00936). 

A Becquerel (Bq) is the SI unit for radioactivity and is defined as the activity of a 

quantity of radioactive material in which one nucleus decays per second. Therefore, the 

 

6 The curie was originally a comparison of the activity of a sample of radioactive material to the activity of one gram 

of radium, which at the time was measured as 37 billion disintegrations per second. When more accurate techniques 

measured a slightly different activity for radium, the reference to radium was dropped (DCN SGE00936).
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Becquerel is the same as an inverse second (s-1). The conversion between Becquerel and curie is 

1 Ci = 3.7 × 1010 Bq.

Measuring Radiation. The units for exposure in air are the roentgen (R) and 

coulomb/kilogram (C/kg). There are also similar units for measuring absorbed dose in tissue (rad 

and Gray) and dose equivalent for the absorbed dose and biological effects (rem and Sievert).

Instrumentation for Detecting Radioactivity. The energy of radioactive decay can be 

detected by a variety of instruments that quantify the amount of radioactivity present in a sample 

(the disintegrations per second). Some techniques can also measure the detected energy and 

identify the radioactive isotope that is emitting the radiation. The following descriptions of 

common radioactivity measurement techniques are taken from U.S. EPA, 2011 (DCN 

SGE00937).

Liquid Scintillation Counting – a radioactive sample is mixed with solvent and chemicals 

that emit light pulses when they are excited by radiation. This technique is typically used to 

measure the radioactivity of beta emitting radionuclides, such as 3H (tritium). With analysis of

the energy of the emitted radiation and the duration of pulses, liquid scintillation counters can 

identify the alpha and beta emitting isotopes present in a sample.

Gas Flow Proportional Counting – a radioactive sample causes a gas inside a detector 

tube to ionize and release electrons. The released electrons move to the anode and the signal is 

recorded. Gas proportional counters are sensitive detectors for alpha and beta particle emissions

and are used for EPA Method 900.0 (gross alpha and gross beta radioactivity screening).

Alpha Spectrometry – alpha particles emitted from a radioactive sample collide with 

atoms in a germanium or silicon crystal detector, releasing electrons that are amplified and 

detected as an electric pulse. Because nuclides emit alpha particles at discrete energies, alpha 

spectrometry can sometimes identify the radionuclide in a purified sample, in addition to 

counting its activity.

Gamma Spectrometry – crystal detectors interact with gamma rays from a radioactive 

sample by absorbing energy and re-emitting it as light. Crystals used for gamma ray detectors 

include thallium-doped sodium iodide and high-purity germanium (HPGe). HPGe crystals must 

be cooled to liquid nitrogen temperature7for use in gamma spectrometry. HPGe detectors can 

distinguish energy of gamma ray sources and identify the radionuclides in a sample. Activity of 

radionuclides that emit only alpha particles and beta particles with no accompanying gamma 

radiation will not be detected by gamma spectrometry.

Naturally Occurring Radioactive Materials. Certain radionuclides occur naturally in 

minerals and rocks in the earth’s crust. As radioactive elements decay, the parent elements form 

new elements (progeny or daughter products). If the progeny are also radioactive, they will 

continue to decay in a chain that continues until a stable (non-radioactive) end product is 

reached. Uranium and thorium are naturally occurring radioactive elements found in trace 

amounts in most rocks and soils (DCN SGE00782, DCN SGE00783), including formations from 

which UOG are extracted. Uranium and thorium decay chains include radium, radon, and other 

 

7 Liquid nitrogen held at atmospheric pressure maintains a temperature of −321o F/ −196 o C, its boiling point.
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radionuclides, and ultimately reach a stable non-radioactive lead isotope that does not decay 

further (DCN SGE00795). Uranium and thorium decay chains are depicted in Figure 1-1. Other 

naturally-occurring elements that are non-series radionuclides include 40K (potassium-40) and 

87Ru (rubidium-87). 40K is often present in mineral samples. Rubidium is also ubiquitous and 

used in dating mineral samples.
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Figure 1-1. Decay Chains for (A.)

238U and (B.)232Th

U-238

4.5 x 109y

U-234

2.5 x 105y

P a-234

6.7 h

Th-234

24. 1 d

Th-230

7.5 x 104y

Ra-226

1600 y

Rn-222

3.8 d

P o-218

3.1 m

P b-214

26.8 m

Bi-214

19.9 m

P o-214

1.6 x 10-4 s

Bi-210

5.0 d

P o-210

138.4 d

P b-210

22.2 y

P b-206

(stable)

Uranium

Protactinium

Radium

Radon

Polonium

Bismuth

Lead

Thorium

A. Uranium-238

EXPLANATION

Alpha Decay

Beta Decay

Th-232

1.4 x 1010y

Th-228

1.9 y

Ac-228

6.15 h

Ra-228

5.75 y

Ra-224

3.6 d

Rn-220

55.6 s

P o-216

0.145 s

TI-208

3.05 m

P b-212

10.6 h

Bi-212

60.6 m

P o-212

3.0 x 10-7 s

P b-208

(stable)

Uranium

Actinium

Radon

Polonium

Bismuth

Lead

Thallium

Radium

B. Thorium-232

EXPLANATION

Alpha Decay

Beta Decay

Decay Chains for A. Uranium-238 and B. Thorium-232

Source: DCN SGE00241.
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Naturally occurring radioactive material (NORM) is a term often used to refer 

collectively to material that contains radionuclides at concentrations found in nature. 

Radionuclides found in NORM associated with UOG extraction include uranium, thorium, and 

their respective decay products (DCN SGE00795). The term technologically enhanced naturally 

occurring radioactive materials (TENORM) is now used to distinguish clearly between 

radionuclides as they occur naturally (NORM) and NORM radionuclides that human activity has 

concentrated or exposed to the environment (TENORM) (DCN SGE00973). Examples of human 

activity that exposes and/or concentrates NORM are oil and gas extraction, mining, and water 

and wastewater processing.

The radioactive elements uranium and thorium commonly occur in the same sedimentary 

sandstones and shale formations as UOG (DCN SGE00241). For example, Rowan et al., 2011 

(DCN SGE00241) studied radium content in a UOG formation (the Marcellus Shale, an 

organically-rich black shale). They explain that organic carbon, the source of oil and gas, is 

known to play a role in concentrating uranium. As shown in the decay chains depicted in Figure 

1-1, 238U (uranium-238) decays to 226Ra, while 232Th decays to 228Ra. Water found in the pores of 

UOG formation rocks (i.e., formation water) is typically highly saline and found in oxygen-poor, 

reducing environments. Uranium and thorium are poorly soluble under these conditions, but 

radium solubility is enhanced (DCN SGE00241). For this reason, formation water is relatively 

enriched in radium isotopes compared to their parent nuclides, 238U and 232Th (DCN SGE00975).

2.0 MEASUREMENT OF RADIOACTIVITY IN UOG EXTRACTION INDUSTRY WASTEWATER

Chapter C.3 of the TDD (DCN SGE00704) presents UOG wastewater concentrations of 

226Ra, 228Ra, and the parameters gross alpha and gross beta. This section discusses the methods 

used for measuring radioactivity in UOG extraction wastewater reported in the TDD.

2.1 EPA Approved Test Procedures for Radioactive Materials in Wastewater

EPA identifies approved test procedures (methods) for the analysis of pollutants in 

wastewater in 40 CFR Part 136. EPA requires the use of these test procedures whenever the 

waste constituent is required to be measured for NPDES permit applications and NPDES permit 

compliance reports. As shown in Table 2-1, for radioactive materials, 40 CFR Part 136 includes 

test procedures for:

 Gross alpha and gross beta radioactivity (Method 900.0);

 Alpha emitting radioisotopes of 223Ra, 

224Ra and 226Ra(Method 903.0); and



226Ra, radon emanation technique (Method 903.1).
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Table 2-1. List of Approved Radiologic Test Procedures

Parameter and Units Method EPA Reference1

Alpha-Total, pCi per liter Proportional or Scintillation Counter 900.0

Beta-Total, pCi per liter Proportional Counter 900.0

Radium Total, alpha emitting 

isotopes, pCi per liter

Proportional Counter 903.0

226Ra, pCi per liter Scintillation Counter 903.1

Source: 40 CFR Part 136. Table IE.

1

Prescribed Procedures for Measurement of Radioactivity in Drinking Water, EPA-600/4-80-032 (1980), U.S. 

Environmental Protection Agency, August 1980. Appendix B provides method for measuring alpha and beta 

counting error.

EPA does not have an approved method for measuring uranium and thorium in 

wastewater. EPA approved methods are described in this section.

900.0 Gross Alpha and Gross Beta Radioactivity Summary: This method covers the 

measurement of gross alpha and gross beta particle activities. The method is a screening 

technique for alpha and beta particle activities. An aliquot of a preserved sample is evaporated to 

a small volume and transferred quantitatively to a tared 2-inch stainless steel counting planchet. 

The sample residue is dried to constant weight, reweighed to determine dry residue weight, and 

then counted for alpha and/or beta radioactivity using a gas-flow proportional counting system or 

scintillation detector system. Counting efficiencies for both alpha and beta particle activities are 

selected according to the amount of sample solids from counting efficiency vs. sample solids 

standard curves.

Interference Issues: Alpha and beta particles have lower energy than gamma radiation 

with limited ability to pass through solids. Because Method 900.0 requires drying a standard 

volume water sample, a sample with high salt concentration typical of some UOG wastewater

will produce a thick solids residue. To ensure the alpha and beta particles in the sample can be 

counted, the solids thickness must be limited by reducing the sample volume. This reduces the 

method sensitivity, making it difficult to measure low levels of radioactivity in a sample of 

highly saline UOG wastewater. 

As further explained in DCN SGE00974: “The amount of [suspended and dissolved] 

solids in a sample limits the size of sample that can be processed and thereby the sensitivity of 

the measurement. Method 900.0 restricts residue thickness for gross alpha measurements to a 

maximum of 5 mg/cm2. In a 50-mm diameter stainless-steel planchet, this is equivalent to 100 

milligrams of solid residue. While this method is applicable to samples which generally have 

solids content under 500 mg/L ... [UOG wastewater] samples may have solids content in the 

hundreds of thousands of mg/L and sample sizes would be restricted to a small fraction of a 

milliliter in order not to exceed the maximum residue thickness. For this reason, the capability of 

the method to detect activity could be decreased by a factor of one-thousand and the ability of 

the evaporation approach to detect radioactivity in ... [UOG wastewater] becomes questionable 

at best.”

903.0 Alpha-Emitting Radium Isotopes Summary: This method covers alpha emitting 

radioisotopes of radium:

223Ra, 224Ra, and 226Ra. Radium in a water sample is collected by co-
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precipitation with barium and lead sulfate, and purified by re-precipitation from 

ethylenediaminetetracetic acid (EDTA) solution. Citric acid is added to the sample to assure that 

complete interchange occurs before the first precipitation step. The final barium sulfate (BaSO4)

precipitate, which includes 226Ra, 

224Ra, and 223Ra is alpha counted to determine the total 

disintegration rate of the radium isotopes.

Interference Issues: Because Method 903.0 requires a co-precipitation of radium with 

barium sulfate, high test sample concentrations of Group II elements (magnesium, calcium, 

strontium, barium) will interfere with the radium recovery and result in inaccurate 

measurements. As shown in TDD Table C-16, UOG wastewater Group II element concentrations 

can reach tens of thousands of mg/L, so that the accuracy of Method 903.0 for UOG wastewater 

may be reduced. 

903.1 226Ra, Radon Emanation Technique. Summary: This method is specific for 226Ra, 

and is based on the emanation and scintillation counting of 222Rn, a daughter product of 226Ra.

226Ra in the water sample is concentrated and separated by coprecipitation on barium sulfate. The 

precipitate is dissolved in EDTA reagent, placed in a sealed bubbler and stored for ingrowth of 

222Rn. After ingrowth, the gas is purged into a scintillation cell. When the short-lived 222Rn

daughters are in equilibrium with the parent (after about four hours), the scintillation cell is 

counted for alpha activity.

All of the alpha-emitting radium isotopes 226Ra, 

224Ra, and 223Ra undergo decay to radon 

isotopes. However, only the progeny of 226Ra, 

222Rn, has a half-life long enough to be useful for

analytical measurements. The other radon isotopes have half-lives of less than one minute. Thus 

when the 222Rn is separated from all the other radium isotopes, the other radon progeny decay 

quickly enough so that they do not interfere with the measurement of 222Rn and its progeny.

Interference Issues: The method reports that there are no radioactive interferences in this 

method. Because the method requires a co-precipitation of radium with barium sulfate, high test 

sample concentrations of Group II elements (magnesium, calcium, strontium, barium) may

interfere with the radium recovery and result in inaccurate measurements. As shown in TDD 

Table C-16, UOG wastewater Group II element concentrations can reach tens of thousands of 

mg/L, so that the accuracy of Method 903.1 for UOG wastewater may be reduced.

2.2 EPA Approved Test Procedures for Radioactive Materials in Drinking Water

Only the methods listed in Table 2-1 are approved for use in the NPDES permit program. 

EPA has additional approved test procedures for radiological parameters in drinking water that 

researchers have applied to UOG wastewater. These methods include test procedures for:



228Ra in Drinking Water (method 904.0);

 Gamma emitting radionuclides in drinking water (method 901.1).

904.0 228Ra Summary: This method covers the measurement of 228Ra in drinking water. 

Although it is not approved for use in the NPDES program, researchers have used it to measure 

228Ra in UOG wastewater. Radium in the water sample is collected by co-precipitation with 

barium and lead sulfate and purified by re-precipitation from EDTA solution. Both 226Ra and 

228Ra are collected in this manner. After a 36 hour ingrowth of 228Ac from 228Ra, the 228Ac is 
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carried on yttrium oxalate, purified, and beta counted. If 226Ra is also desired, the activity in the 

supernatant can be reserved for co-precipitation on barium sulfate, dissolved in EDTA and stored

for ingrowth in a sealed radon bubbler (see Method 903.1).

Interference Issues: Because the Method 904.0 requires a co-precipitation of radium with 

barium sulfate, high test sample concentrations of Group II elements (magnesium, calcium, 

strontium, barium) will interfere with the radium recovery and result in inaccurate 

measurements. As shown in TDD Table C-16, UOG wastewater Group II element concentrations 

can reach tens of thousands of mg/L, so that the accuracy of Method 904.0 for UOG wastewater 

may be reduced.

901.1 Gamma Emitting Radionuclides in Drinking Water Summary: This method 

covers the use of gamma spectroscopy for the measurement of gamma photons emitted from 

radionuclides without separating them from the sample matrix. This technique is used to measure 

concentrations of specific gamma emitters in a drinking water sample. Although it is not 

approved for use in the NPDES program, researchers have used it with modern gamma 

spectrometers to measure 226Ra and 228Ra in UOG wastewater. The method requires:

 The container configuration for the standards and the samples to be identical (i.e., 

geometry of the sample with respect to the detector), and

 The sample to be properly acidified and not contain any sediment.

Interference Issues: Interferences result from the presence of more than one gamma 

emitting radionuclide in the sample. Resolution of modern (HPGe) detectors is very good; 

however, they cannot resolve gamma-ray energies that are within ~ 0.5 kiloelectron volt (keV) of 

each other. Evaluation of the spectra by a trained spectroscopist is necessary to ensure proper 

reporting.

2.3 Development of Methods for Determination of Gross Alpha and Gross Beta and 

Radium Levels Specific to UOG Extraction Wastewater

Because of the generally high ionic strength (i.e., salt concentration) of UOG extraction 

wastewater, the accuracy of methods such as EPA Methods 900.0, 903.0, and 904.0 is 

questionable for analysis of UOG extraction wastewater. Because of these difficulties, EPA and 

other researchers are developing methods tailored to UOG extraction wastewater. This section 

summarizes published results of the development of two methods specific to UOG extraction 

wastewater. 

Gross Alpha and Gross Beta Activity. In response to the difficulty of applying 

approved methods to UOG extraction wastewater samples, EPA’s National Analytical Radiation 

Environmental Laboratory and National Exposure Research Center cooperated in the 

development of the Rapid Radiochemical Method for Gross Alpha and Gross Beta Activity in 

Flowback and Produced Water from Hydraulic Fracturing Operations (FPWHFO)( DCN 

SGE00974). As reported in this document, the optimized method consists of measuring activity 

of alpha emitters by two methods (liquid scintillation counting and gamma spectrometry). The 

results of these measurement methods, described further below, may be summed to represent 
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total gross alpha. Beta emission activity of 228Ra is measured separately by gamma spectrometry, 

as described below (DCN SGE00974).

Thorium (Th), uranium (U), and polonium (Po) Gross Alpha by Liquid Scintillation 

Counting. A 300 mL sample is treated with permanganate in ammoniacal solution to 

coprecipitate all radionuclides in the naturally occurring series. The mixture is settled and the 

supernatant solution discarded. The residue is dissolved in hydrochloric acid and passed through 

a TRU ResinTM column (Eichrom Technologies, LLC, Lisle, IL).Thorium, uranium, and 

polonium are eluted from the resins using ammonium oxalate. The eluent is transferred to a 

liquid scintillation vial as the final sample test source and counted in the alpha emission region of 

the liquid scintillation spectrum. The final sample test source is counted for 30 minutes.

226Ra Alpha by Gamma Spectrometry. A sample test source of 3 L is counted directly by 

gamma ray spectrometry. The activity concentration of 226Ra is determined by gamma ray 

analysis using a specified energy gamma ray region (the 186 keV photopeak) and assumes no 

significant amount of 235U (uranium-235) compared to the amount of 226Ra in the sample8. The 

sample is counted for 12 hours or long enough to achieve the required method uncertainty.

228Ra Beta by Gamma Spectrometry. The sample test source of 3 L is counted directly by 

gamma ray spectrometry. In addition to 228Ra being determined indirectly by analysis of its first 

progeny,

228Ac, several other radionuclides are determined directly by their gamma ray emission 

and others may be determined indirectly through analysis of a parent or progeny radionuclide 

that is a gamma ray emitter. The sample is counted for 12 hours or long enough to achieve the 

required method uncertainty.

The method developers noted that additional work was needed to optimize and validate 

portions of the method. Also, because the activity of samples containing natural decay chain 

activity, especially 226Ra and 224Ra, changes over time due to radioactive ingrowth and decay

processes, questions about timing of wastewater generation, sample collection, preparation and 

counting must be addressed (DCN SGE00974).

226Ra and 228Ra. Researchers from the University of Iowa examined alternative methods 

for determining radium levels in UOG extraction wastewater. Working with a sample of 

Marcellus shale wastewater from northeastern Pennsylvania, Nelson et al., 2014 (DCN 

SGE00975), found that barium sulfate coprecipitation, the basis for EPA method 903.0, resulted 

in very poor recovery of radium (<1% of spiked activity of 226Ra). The researchers explored four 

alternative methods and determined that HPGe gamma spectroscopy was the most promising 

method for determining levels of 226Ra in UOG extraction wastewater, using a 3 L sample 

(stabilized with agar) counted for 17 hours. Researchers are continuing to evaluate the use of an 

electronic radon detector (Durridge RAD7) to quantify radium by measuring radon decay 

products. Although counting times with the radon detector method are shorter than HPGe gamma 

spectroscopy, sufficient hold time for radon ingrowth, 4 to 30 days, is required. Researchers are 

continuing development of this method.

 

8 Gamma-ray spectrometry may also be used to determine the activity of the 226Ra beta-gamma emitting progeny, 

214Pb (lead-214) and 214Bi (bismuth-214); however, these emissions are not included in the quantitation of 226Ra by 

the method described in DCN SGE00974.
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3.0 STUDIES OF RADIOACTIVE MATERIAL IN UOG EXTRACTION WASTEWATER

The following subsections describe studies related to radioactivity in the UOG industry. 

This is not a comprehensive review but includes studies that EPA identified during the 

development of the proposed pretreatment standards for UOG extraction wastewaters.

3.1 Pennsylvania Department of Environmental Protection (PA DEP) TENORM Study

(DCN SGE01028)

In January 2015, PA DEP announced the results of a study of radioactive elements in 

UOG extraction wastewater, sludge, and drill cuttings. Liquid and solid samples were analyzed

for alpha, beta, and gamma radiation and gas samples were analyzed for radon using the 

following methods (DCN SGE01028):

 EPA Method 901.1: Gamma spectroscopy to identify TENORM radionuclides;

 DOE Health and Safety Laboratory (HASL) 300: Alpha spectroscopy to identify 

isotopic uranium and isotopic thorium; and

 EPA Method 900.0: Gross alpha and gross beta.

In samples of flowback fluid and produced water, 226Ra concentrations were elevated, 

ranging up to 26,600 pCi/L. 228Ra was also detected in these samples, at up to 1,900 pCi/L. 

Although PA DEP concluded, “...[t]here is little potential for radiological exposure to workers 

and members of the public from handling and temporary storage of [flowback fluid and] 

produced water on natural gas well sites,” they did conclude “...[t]here is a potential for 

radiological environmental impacts from spills of produced water [and flowback fluid] on natural 

gas well sites and from spills that could occur from the transportation and delivery of ...[these] 

fluid[s].”

At ten POTWs, PADEP sampled treated and untreated wastewater and wastewater 

treatment sludge (filter cake). Six of the 10 POTWs are considered influenced (POTW-I) by 

having received wastewater from the oil and gas (O&G) industry, mainly the effluent of CWTs. 

Four of the sampled POTWs never received wastewater from the O&G industry. Because the 

measured concentrations shown in Table 3-1 are higher than concentrations found in surface 

water (see TDD Table C-20) and soil (DCN SGE01028 Table 2-2), there may be some potential 

for radiological contamination by discharges from POTWs treating UOG extraction wastewater.

Table 3-1. Radium Concentrations, Influent vs. Effluent for Six POTWs receiving Oil and 

Gas Wastewater

Sample Description 226Ra (pCi/L) 228Ra (pCi/L)

Influent, Unfiltered (Average) 190 28.1 

Effluent, Unfiltered (Average) 103 10.4

Source: DCN SGE01028 Table 4-18

Samples of filter cake from the six POTWs receiving O&G wastewater showed “Ra-226 

and Ra-228 present above typical background concentrations in soil. The average Ra-226 result 

was 20.1 pCi/g with a large variance in the distribution, and the maximum result was 55.6 pCi/g. 
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The average Ra-228 result was 8.32 pCi/g, and the maximum result was 32.0 pCi/g Ra-228.” 

(DCN SGE01028)

PADEP concluded, “...[t]here is little potential for radiological exposure to workers and 

members of the public from handling and temporary storage of filter cake at POTW-I’s. 

However, there is a potential for radiological environmental impacts from spills and the longterm disposal of POTW-I filter cake”. (DCN SGE01028)

3.2 Argonne National Laboratories (ANL) Bakken NORM Study

The North Dakota Department of Health contracted Argonne National Laboratories to 

conduct a risk assessment of radioactive waste generated from UOG drilling in North Dakota’s 

Bakken formation. North Dakota does not allow disposal, within the state, of radioactive waste 

containing greater than or equal to 5 pCi/L. However, North Dakota has experienced problems 

with trucking companies illegally dumping radioactive waste, including waste generated from 

the management of UOG extraction wastewater (DCN SGE00968, DCN SGE00970).

The study focused on the concentrations of radioactive elements in UOG industry solid 

waste generated during the management of UOG wastewater (e.g., scale, sludge, filter cakes, 

filter socks) and provided background information on TENORM waste streams. It also evaluated 

the radiological doses associated with a number of scenarios associated with oil and gas well site 

operations, improperly managed wastes, transportation of TENORM, and disposal of TENORM in 

Industrial Waste and Special Waste Landfills. Study results were released November 2014 (DCN 

SGE01018). The study supported revisions to North Dakota’s rules for radioactive waste 

disposal, which were proposed December 2014 (DCN SGE01019). 

4.0 RADIOACTIVE MATERIALS IN UOG EXTRACTION WASTEWATER AND ASSOCIATED 

CONCERNS

Oil and gas formations contain varying levels of NORM resulting from uranium decay, 

which may be transferred to UOG extraction wastewater. This section presents the 

concentrations of radioactive constituents compiled for the TDD, discusses, in general terms, the 

harm caused by ionizing radiation (whether from UOG extraction wastewater or other sources), 

and discusses the particular concerns associated with TENORM in UOG extraction wastewater.

4.1 Radioactive Materials Measured in UOG Extraction Wastewater

The EPA identified only limited radioactive constituent concentration data for UOG 

extraction wastewater. As presented in Table 4-1

9

, most available data characterize produced 

water from the Marcellus formation; limited data were available from the Niobrara formation. 

226Ra and 228Ra are both found in UOG produced water in both of these UOG formations, with 

226Ra concentrations generally two to five times greater than 228Ra concentrations. The EPA also 

identified limited data about radioactivity in drilling wastewater10; Table C-18 in the TDD (DCN 

 

9 The generation of the data in Table 4-1 is explained in the Unconventional Oil and Gas (UOG) Produced Water 

Volumes and Characterization Data Compilation memorandum (DCN SGE00724). This memorandum includes a 

description of the underlying data sources, data analysis, and QC procedures.

10 Information about radioactive constituent concentrations in UOG drilling wastewater can be found in the 

Unconventional Oil and Gas (UOG) Drilling Wastewater memorandum (DCN SGE00740).
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SGE00704) presents a summary of 5 data points for gross alpha and gross beta concentrations in 

UOG drilling wastewater from the Marcellus shale formation.

Table 4-1. Concentrations of Radioactive Constituents in UOG Produced Water

Parameter Formation Method(s)

Range

(pCi/L)

Median

(pCi/L)

Number 

of Data 

Points

Number 

of 

Detects

Gross alpha Marcellus 900.0 8.7 - 120,000 8,700 74 74

Gross alpha Niobrara 900.0 620 - 4,000 1,800 3 3

Gross beta Marcellus 900.0 6.8 - 21,000 1,600 73 72

Gross beta Niobrara 900.0 250 - 1,200 760 3 3

226Ra Marcellus

901.1 Mod., 903.0, 

903.1, γspectrometry 0.16 - 27,000 1,700 103 101

226Ra Niobrara 901.1 Mod. 170 - 900 620 3 3

228Ra Marcellus

901.1. 903.0, 

904.0, γspectrometry 0 - 1,900 470 94 92

228Ra Niobrara 901.1 Mod. 100 - 460 330 3 3

Source: DCN SGE00724

4.2 General Information about Harm Caused by Ionizing Radiation

Ionizing radiation is known to harm living tissue in humans and other organisms. The 

extent of harm depends on routes and duration of exposure and the energy and types of ionizing 

radiation (alpha and beta particles and gamma rays). Radiation exposure can occur externally, 

when the radiation source is outside of the organism. External exposure is of particular concern 

for radionuclides that emit gamma rays which have sufficient energy to penetrate containers, 

clothing, and skin. Internal exposure is a greater concern for radionuclides (such as radium) that 

emit alpha and beta particles. Although alpha and beta particles do not penetrate far into tissue, 

inside the body they will deposit their energy in a small volume of tissue, causing greater 

damage (DCN SGE01020). Internal exposure results mainly from ingestion (e.g., drinking water, 

food) and inhalation (e.g., inhaling a radioactive gas such as radon or contaminated dust). 

All of the radionuclides present in UOG wastewater generate ionizing radiation that is 

potentially harmful to human health and the environment; however, as discussed previously, 

because of their greater solubility in UOG formation water 11, radium isotopes (particularly 226Ra

and 228Ra) are present in UOG wastewater at higher concentrations than other radionuclides

(DCN SGE00975). Further, radium is of particular concern because its chemical behavior is

similar to calcium, magnesium and other Group II elements. Whereas external radiation is 

instantaneous (i.e., does not remain in the body after the exposure), internal deposition of 

radionuclides can present a hazard for long periods of time after the initial exposure. Because it 

behaves similarly to calcium, ingested radium may be stored in the body and can replace calcium 

in tissues, particularly bone. Long-term internal exposure to radium increases the risk of 

developing bone and other cancers. Because radium readily accumulates in the body, it is 

 

11 Formation water is water that occurs naturally within the pores of rock.
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considered to pose a greater cancer risk than most other radioactive elements (DCN SGE00980). 

Additionally, near-surface radium deposits may be a source of indoor radon in the future if 

homes are built over radium-contaminated soils.

In addition to potential harm to human health, radium that accumulates in river and 

stream sediments could harm benthic organisms. Warner, et al write, “Bioaccumulation of 

radium is known to occur in freshwater fish [and] invertebrates...Radium also accumulates in 

freshwater plants...” (DCN SGE00629). 

4.3 Potential Concerns Associated with TENORM in UOG Extraction Wastewater

Transfer of TENORM to the environment may result from management of UOG 

extraction wastewater. UOG operators use three primary practices to manage UOG extraction 

wastewater (DCN SGE00704):

 Dispose of wastewater via underground injection for disposal wells (“disposal 

wells”);

 Reuse/recycle wastewater in subsequent fracturing jobs; and

 Transfer wastewater to a centralized waste treatment (CWT) facility.

While implementing these practices, radioactive materials may be removed from the 

wastewater stream in sludges that accumulate in tanks and equipment, during filtration of 

suspended solids from wastewater, or by chemically changing radium from a soluble to insoluble 

form during wastewater treatment. The following bullets summarize the potential concerns 

identified in the literature associated with TENORM during the management UOG extraction 

wastewater.

 Build-up of Radioactive Elements in Scale – During transport of UOG extraction 

wastewater, radium may precipitate with other scale-contributing constituents 

(e.g., calcium, strontium) resulting in a TENORM-containing scale in pipes and 

valves (DCN SGE00622). Conventional oil and gas (COG) wastewaters, which 

have constituents similar to UOG wastewater, have been documented to generate 

radioactive scale. As discussed in DCN SGE00136, in studies of the COG 

industry, the American Petroleum Institute found the highest concentrations of 

radioactivity in wellhead piping scale. Radium concentrations measured in the 

scale on pipes and valves used to manage COG extraction wastewater averaged 

480 pCi/g, ranging up to 400,000 pCi/g, depending on regional geology (DCN 

SGE00136). 226Ra and 224Ra, contained in the scale, decay into radon gas and 

present an inhalation hazard when workers contact the scale. Buildup of 210Pb

(lead-210) and 210Po (polonium-210) in thin films and scales on the interior of 

equipment on natural gas wells and equipment are also a concern. People working 

with scale-encrusted equipment, pipes, and valves may be exposed to radiation, 

either externally or internally via inhalation or ingestion of radioactive materials.

 Sludge and Filter Residues – As reported in DCN SGE01018, “TENORMcontaminated sludges can accumulate in the bottom of vessels that are used to 
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store or otherwise manage... [UOG extraction wastewater], including water 

storage tanks, oil/water separators, and heater treaters. Sludges typically are 

composed of solid debris, such as sand, scale, or rust particles, that settle out of 

the production stream. The primary... [radionuclides of concern] in sludges in the 

United States are 226Ra, 

228Ra, and their decay products... Typically, the radium 

takes the form of a co-precipitate with sulfate or carbonate deposits. In addition, 

filters that are used to separate particulates from produced water generate a solid 

waste referred to as filter cake. This material is likely to have a similar 

composition to the sludge that is removed from produced water storage and 

handling equipment.... Disposable filter socks are used to filter particulates out of 

produced water prior to transport and disposal. These filters accumulate sludges 

and scales over time and must be changed and disposed of on a regular basis. In 

the past year, the improper disposal of these filter socks has been a problem in the 

State of North Dakota”. (DCN SGE00970)

 Radioactivity in Discharges of UOG Extraction Wastewater from Treatment 

Plants – The treatment technologies used by wastewater treatment plants may not 

remove all of the pollutants contributing to radioactivity. As a result, these

pollutants will be discharged to surface waters. Researchers measured sediment 

concentrations at the point of discharge from a brine treatment facility that 

accepted UOG extraction wastewater. They found 226Ra at 8,732 Bq/kg (236 

pCi/g) and 228Ra at 2,072 Bq/kg, (56 pCi/g) about 200 times greater than upstream 

and background sediment concentrations. The researchers speculated that the 

contaminated sediments could pose ecological risks, particularly to benthic 

organisms (DCN SGE00629).

 Site Contamination Potential – Solid wastes generated during management of 

UOG wastewater (e.g., drilling wastewater filter residues, scale, sludge, treatment 

residuals) may contain TENORM. These wastes are often disposed of at the 

drilling site or in landfills. Improper disposal may lead to soil and/or groundwater 

contamination and/or airborne releases of radon gas (DCN SGE00622).

5.0 QUALITY CONTROL PROCEDURES

All of the analyses presented adhered to the Environmental Engineering Support for 

Clean Water Regulations Programmatic Quality Assurance Project Plan (PQAPP) (DCN 

SGE00957) and the Unconventional Oil and Gas (UOG) Supplemental Quality Assurance 

Project Plan (SQAPP) (DCN SGE00958), including collecting, evaluating, and analyzing 

existing data and information about radioactive materials in the UOG industry.

Specifically, ERG used the procedures described in Section 4 of the PQAPP to gather and 

manage existing data in support of the proposed rulemaking. ERG staff entered reference 

information for relevant sources into the UOG Literature Review database. The ERG index 

keeper reviewed all reference information, assigned each reference a Document Control Number 

(DCN), imported the reference information into the UOG Project File Index database, and saved 

referenced files in the Electronic Project File folder.
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ERG also used the procedures described in Section 3 of the SQAPP when collecting 

existing data for use in the UOG proposed rulemaking. ERG used a combination of sources, 

including reports, papers, and online databases from state regulatory agencies such as 

departments of environmental protection and oil and gas commissions. As shown in Table 6-1, 

ERG assigned a source flag (A, B, C or D) to all references used in these analyses.

ERG defines each source flag as follows: 

 Source Flag A - Journal articles and documents prepared by or for a government agency 

(e.g., site visit reports, industry meeting notes); 

 Source Flag B - Documents prepared by a verified12 source that include citation 

information (e.g., operator reports, vendor documents, university publications); 

 Source Flag C - Documents prepared by a verified source that do not include citation 

information (e.g., operator reports, vendor documents, conference presentations); and

 Source Flag D - Documents prepared by a source that could not be verified and that do 

not include citation information.

ERG followed the procedures described in the PQAPP to generate, evaluate, and analyze 

data using spreadsheets (Section 7.0) and databases (Section 8.0). ERG conducted the following 

QA checks during the analyses:

 ERG performed a 20 percent check of all data entry.

 ERG performed a 100 percent check of all analyses and calculations, and 

documented these checks in internal versions of the spreadsheets and databases.

 For all analyses performed in state specific Access databases, one team member 

created queries and another team member reviewed the design and logic of the 

queries. ERG documented these checks in the internal versions of spreadsheets 

and databases.

 ERG had a senior staff member familiar with ELGs and the UOG proposed 

rulemaking review the results from each analysis.

6.0 REFERENCES

Table 6-1 lists the sources ERG used along with their DCN and source flag. 

Table 6-1. Data Sources Containing Information on Radioactive Materials in the UOG 

Industry

DCN Source Citation

Source 

Flaga

 

12 ERG considered sources as “verified” if we were able to find information about the author outside of the reference 

document. ERG primarily verified information by looking for company/organization websites that confirmed the 

author’s affiliation with the UOG industry
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DCN Source Citation

Source 

Flaga

SGE00136 U.S. Environmental Protection Agency (U.S. EPA). 2012. Oil and Gas Production 

Wastes. Available online at http://www.epa.gov/radiation/tenorm/oilandgas.html#scale.

A

SGE00179 Keenan, Charles W. and Jesse H. Wood. General College Chemistry. Chapter 14 Nuclear 

Changes. Harper & Row Publishers, Inc., New York. 1971. A

SGE00241

Rowan, E.L., et al. Radium content of oil- and gas-field produced waters in the northern 

Appalachian Basin (USA)—Summary and discussion of data. U.S. Geological Survey 

Scientific Investigations Report 2011–5135, pg 31.

A

SGE00544

Marcellus Shale Coalition (MSC) and PA Independent Oil and Gas Association (PIOGA). 

2013. Field Sampling Plan: Characterization of Naturally Occurring Radioactive Materials 

in the Oil and Gas Field. (November 4)

B

SGE00622

U.S. Geological Survey (USGS). 2013. Water Resources and Shale Gas/Oil Production in 

the Appalachian Basin - Critical Issues and Evolving Developments. (August). Available 

online: http://pubs.usgs.gov/of/2013/1137/pdf/ofr2013-1137.pdf.

A

SGE00629

Warner, Nathaniel R, et al. Impacts of Shale Gas Wastewater Disposal on Water Quality 

in Western Pennsylvania. Environmental Science & Technology. (September 2013) A

SGE00704 U.S. Environmental Protection Agency (U.S. EPA). 2015. Unconventional Oil and Gas 

Technical Development Document. Office of Water Engineering and Analysis Division. A

SGE00782 U.S. Environmental Protection Agency (U.S. EPA). 2012. Uranium. (October 1). 

Available online at: http://www.epa.gov/radiation/radionuclides/uranium.html. A

SGE00783 U.S. Environmental Protection Agency (U.S. EPA). 2014. Thorium. (February 28). 

Available online at: http://www.epa.gov/radiation/radionuclides/thorium.html.

A

SGE00793 ERG. 2014. Unconventional Drilling/Hydraulic Fracturing and Natural Radioactivity 

Webinar Notes. (July 3) C

SGE00795 U.S. Environmental Protection Agency (U.S. EPA). 2012. About TENORM. (August 30). 

Available online at: http://www.epa.gov/rpdweb00/tenorm/about.html.

A

SGE00936 Understanding Radiation. Available online at: 

http://www.epa.gov/radiation/understanding-radiation-overview.html.

A

SGE00937 U.S. Environmental Protection Agency (U.S. EPA). 2011. Enhancing Radiological 

Laboratory Testing for Radionuclides in Drinking Water Training.

A

SGE00968

North Dakota Department of Health. 2014. Contractor Selected for Cleanup of Filter 

Socks in Noonan. News Release, April 8, 2014. Available online at 

http://www.ndhan.gov/media/news/view.asp?ID=1064.

A

SGE00970

Donovan, Lauren. Second Dump Site Reported in Divide County. Bismarck Tribune, 

April 24, 2014. Available online at http://bismarcktribune.com/bakken/second-dump-sitereported-in-divide-county/article_cd466f2e-cbca-11e3-885b-0019bb2963f4.html.D

SGE00973 U.S. Environmental Protection Agency (U.S. EPA). 2013. Radiation Glossary. Available 

online at http://www.epa.gov/radiation/reference-information-overview.html.

A

SGE00974

U.S. Environmental Protection Agency (U.S. EPA). 2014. Validation of Rapid 

Radiochemical Method for Gross Alpha and Gross Beta Activity Concentration in 

Flowback and Produced Waters from Hydraulic Fracturing Operations. 

EPA/600/R-14/107, July 2014.

A

SGE00975

Nelson, Andrew W. Dustin May, Andrew W. Knight, Eric S. Eitrheim, Marinea 

Mehrhoff, Robert Shannon, Robert Litman, and Michael K. Schultz. 2014. Matrix 

Complications in the Determination of Radium Levels in Hydraulic Fracturing Flowback 

Water from Marcellus Shale. Environmental Science & Technology. (February 2014)

A

SGE00977

U.S. Nuclear Regulatory Commission (U.S. NRC). 2013. Measuring Radiation. (June 

2013) Available online at: http://www.nrc.gov/about-nrc/radiation/healtheffects/measuring-radiation.html.A
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DCN Source Citation

Source 

Flaga

SGE00978

Pennsylvania Department of Environmental Protection (PADEP). 2014. PA DEP 

TENORM Study - Update: 2nd Quarter 2014 Update, July 2014. Available online at 

http://files.dep.state.pa.us/OilGas/BOGM/BOGMPortalFiles/RadiationProtection/TENOR

M-Study-Update_generic-mtg_cut-down_rv_2July2014%20(3).pdf.

A

SGE00979

Pennsylvania Department of Environmental Protection (PADEP). 2013. Sampling and 

Analysis Plan. Part II – Quality Assurance Project Plan. Prepared by Perma-Fix 

Environmental Services, Inc. Beaver, PA. April 2, 2013. Available online at 

http://files.dep.state.pa.us/OilGas/BOGM/BOGMPortalFiles/RadiationProtection/Samplin

g_and_Analysis_Plan-Part-II-Quality_Assurance_Project_Plan.pdf].

A

SGE00980

U.S. Geological Survey (USGS). 2014. Trace Elements National Synthesis Project: 

Radium Frequently Asked Questions. 2014. Available online at 

http://water.usgs.gov/nawqa/trace/radium/Ra_FAQ.html.

A

SGE01018

Argonne National Laboratory, Environmental Science Division, Radiological Dose And 

Risk Assessment of Landfill Disposal of Technologically Enhanced Naturally Occurring 

Radioactive Materials (TENORM) in North Dakota. ANL/EVS-14/13. (November 2014)

A

SGE01019 North Dakota. NDAC 33-20 and NDAC 33-10-23 (draft revised). Available online at 

https://www.ndhealth.gov/EHS/Tenorm/.

A

SGE01020

U.S. Environmental Protection Agency (U.S. EPA).Ionizing & Non-Ionizing Radiation: 

Health Effects (August 2012) Available online at 

http://www.epa.gov/radiation/understand/health_effects.html.

A

SGE01028 Pennsylvania Department of Environmental Protection. 2015. Technologically Enhanced 

Naturally Occurring Radioactive Materials (TENORM) Study Report. A

a— Source Flag A - Journal articles and documents prepared by or for a government agency (e.g., site visit reports, 

industry meeting notes).

Source Flag B - Documents prepared by a verified source that include citation information (e.g., operator 

reports, vendor documents, university publications); 

Source Flag C - Documents prepared by a verified source that do not include citation information (e.g., operator 

reports, vendor documents, conference presentations); and 

Source Flag D - Documents prepared by a source that could not be verified and that do not include citation 

information.