Printed on recycled paper U.S. Department of the Interior

U.S. Geological Survey

USGS Fact Sheet FS–142–99

September 1999

Naturally Occurring Radioactive Materials (NORM)

in Produced Water and Oil-Field Equipment—

An Issue for the Energy Industry 

A

Introduction

 Naturally occurring radioactive elements such as uranium, 

radium, and radon are dissolved in very low concentrations during 

normal reactions between water and rock or soil. Ground water that 

coexists with deposits of oil can have unusually high concentrations 

of dissolved constituents that build up during prolonged periods of 

water/rock contact. Many oil-field waters are particularly rich in 

chloride, and this enhances the solubility of other elements 

including the radioactive element radium. Some of this saline, 

radium-bearing water is unavoidably brought to the Earth’s surface 

with the oil and must be separated and then disposed, usually by 

return to depth in an injection well. At some oil-field sites the pipes 

and tanks that handle large volumes of this "produced water" can 

become coated with scale deposits that contain radium. Radiumbearing scale is the type of "diffuse NORM waste" that occurs in 

the oil industry. Radium accumulation in oil-field equipment in the 

United States first became apparent in the 1980’s when scrap metal 

dealers began to routinely detect unacceptable levels of 

radioactivity in shipments of oil-field pipe. Since that time the oil 

and gas industry has sought to better define the extent of the oilfield NORM problem, and to develop techniques for the prediction, 

prevention, remediation, and disposal of oil-field NORM. In 

parallel efforts, State and Federal regulatory agencies have worked 

to develop guidelines for the control of NORM that will adequately 

protect public health and the environment. This report summarizes 

current understanding of the composition and mode of occurrence 

of oil-field NORM in the United States, briefly reviews the status 

of NORM regulations, and identifies some health and environmental issues associated with oil-field NORM. 

Location of Oil-Field NORM in the United States

 Deposits of oil are found in 30 States, but the vast majority (86 

percent) of onshore oil production is concentrated in Texas, 

Oklahoma, Louisiana, Wyoming, California, Kansas, and New 

Mexico (fig. 1A). In 1989 the American Petroleum Institute 

sponsored a preliminary nationwide reconnaissance of measurable 

radioactivity at the exterior surfaces of oil-field equipment (Otto, 

1989). The results of this nonstatistical sampling indicated that 

gamma-ray radiation levels exceeded natural background radiation 

levels at 42 percent of the sites. Radiation levels greater than five 

times the median background of all sites were found at 

approximately 10 percent of the sites. Most of the sites with 

markedly higher radioactivity were concentrated in specific 

geographical areas, such as the Gulf Coast, northeast Texas, 

southeast Illinois, and south-central Kansas (fig. 1B). Additional 

surveys by some State agencies identified radioactive oil-field 

equipment in northern Michigan and eastern Kentucky. Pipe, 

casing, fittings, and tanks that have an extended history of contact 

with produced water are more likely to contain radioactive deposits 

than other parts of the plumbing system at oil-field production 

Figure 1 (left and next page). 

Areal distribution in 

conterminous United States of 

A, producing oil and gas wells 

through 1994, and B, radioactive 

oil-field equipment (next page). 

A, from Mast and others, 1998. 

B, modified from Otto, 1989. 

Reprinted courtesy of the 

American Petroleum 

Institute—based on original API 

figure, modified by U.S. 

Geological Survey.

’’

’’

’’

’’

EXPLANATION

Oil production

Gas production

Mixed production

A
B

sites. Soil in the immediate vicinity of production sites may be 

unusually radioactive if affected by spills or leakage of 

produced water, or if contaminated by scale removed during 

pipe or tank cleaning operations. Handling of used pipe at 

pipe storage yards may also contaminate soil with radioactive 

scale. Although not discussed herein, some equipment used 

to process and transport natural gas may contain small amounts 

of radioactive decay products of radon gas. 

Form of Oil-Field NORM

 Oil-field equipment can contain radioactive scale and 

scale-bearing sludge, both of which form as coatings or 

sediments. The scale precipitates from produced water in 

response to changes in temperature, pressure, and salinity as 

the water is brought to the surface and is processed to 

separate coexisting crude oil. The scale is typically a mixture 

of carbonate and sulfate minerals. One of these sulfate 

minerals is barite (barium sulfate), which is known to readily 

incorporate radium (Ra) in its structure. Many studies of 

radioactive scale from oil-field equipment have documented 

that barite is the primary host of oil-field NORM and that the 

radioactivity is from isotopes of radium and their decay 

products. The two radium isotopes present in produced water 

and barite scale are 226Ra (half-life =1,600 years) and 228Ra 

(half-life =5.8 years). These two isotopes are produced by 

radioactive decay of uranium and thorium present in rocks of 

the oil-producing formations. The concentration of dissolved 

radium is therefore influenced by the abundance of uranium 

and thorium in reservoir rock and by the accessibility of 

water to the sites containing uranium and thorium. When 

radium is brought to the surface in produced water, the 

concentration of radium that is incorporated in barite scale is 

largely a function of (1) the concentration of dissolved 

radium and (2) the amount of produced water that moves past 

the site of barite precipitation. 

 Ongoing studies by USGS scientists are documenting 

variations in the mineralogy, chemistry, and radium 

concentration of in-place scale deposits. Better understanding of 

the specific location and texture of the most radioactive barite scale 

should contribute to more cost-effective strategies for its removal. 

Figure 2A illustrates some of the textural and mineralogical 

variability in a sample of scale from an old section of aboveground oil-field pipe. Lighter colored barite is present along with 

variable amounts of darker iron oxides. Barite occurs as intact 

layers as well as fragments of former layers that were transported 

and recemented with iron oxides. A corresponding image of 

radioactivity in this sample (fig. 2B) is recorded on a special film 

and illustrates the variable concentration of radium and its 

radioactive decay products in these layers. 

Abundance of Radium in Oil-Field NORM

 Measurement of total radioactivity with a hand-held radiation 

detection instrument permits rapid assessment of a site for NORM 

contamination, but site cleanup criteria and waste disposal options 

are based on actual concentrations of radium isotopes. Some 

specialized field instruments permit rapid estimates of the 

concentration of radium isotopes, but such estimates require 

confirmation by careful laboratory analysis of selected subsets of 

samples. Radium concentrations are generally reported as 

picocuries/gram (pCi/g) of solid material or picocuries/liter (pCi/L) 

of water or air. A picocurie equals 2.22 disintegrations-per-minute 

(dpm). Figure 3A illustrates the distribution of total radium 

concentration (226Ra and 228Ra) in barrels of oil-field NORM 

waste stored in Louisiana in 1992 (Wascom, 1994). The maximum 

radium concentration in this waste and in most reported oil-field 

scale from the U.S. is several thousand pCi/g, although very small 

quantities of scale have been reported with as much as 400,000 

pCi/g of radium. For comparison, most natural soils and rocks 

contain approximately 0.5–5 pCi/g of total radium. A uranium ore 

sample containing 1 weight percent uranium has approximately 

3,300 pCi/g of 226Ra. Most of the radium in older oil-field scale is 

226Ra, because the shorter lived 228Ra decays with a half-life of 

5.8 years. 

 Figure 3B illustrates the distribution of dissolved 226Ra 

concentration in 215 samples of produced water from seven major 

oil-producing areas (Fisher, 1998). Radium tends to be more 

EXPLANATION

No data

At background or marginally

 detectable

<5x the median background

 for all sites

>5x the median background

 for all sites

Typical readings
Figure 2. Radioactive scale deposits inside oil-field pipe (A) and the distribution of alpha-particleemitting radium and radium decay products in the same sample (B). Brighter regions on the alpha 

emission image indicate areas of scale with higher concentrations of radioactive elements. 

A

B

abundant in the more saline and chloride-rich varieties of these produced waters. 

The maximum concentration of dissolved 226Ra in this limited data set is several 

thousand pCi/L, but concentrations above 10,000 pCi/L have been reported in the 

U.S. Produced water also contains dissolved 228Ra, which is typically one-half to 

twice the concentration of 226Ra. For comparison, the U.S. EPA maximum 

contaminant level for drinking water is 5 pCi/L for total dissolved radium.

Regulations for the Control of Oil-Field NORM

 There currently exist no Federal regulations that specifically address the 

handling and disposal of oil-field NORM wastes. States that have enacted 

specific NORM regulations include some important oil producers such as Texas, 

Louisiana, New Mexico, and Mississippi. New NORM regulations or 

modifications to general radiation protection statutes are under consideration in 

other major oil-producing States such as California, 

Kansas, and Oklahoma. Standards for cleanup of 

radium-contaminated soils that typically appear in 

enacted or proposed NORM regulations call for an 

average concentration of less than 5 pCi/g in the 

upper 15 cm (centimeters) of soil and an average of 

less than 15 pCi/g in deeper increments of 15 cm. 

Some States allow an average of as much as 30 

pCi/g of radium in the upper 15 cm of soil. For oilfield equipment, typical standards for release for 

other uses or for recycling require that radioactivity 

at the surface should not exceed some low multiple 

of natural background radioactivity. 

Health and Environmental Issues of 

Oil-Field NORM

 Once formed, barite is a very insoluble mineral. 

One liter of water at the Earth’s surface dissolves 

only 0.0025 grams of barite. Efficient removal of 

barite deposits from oil-field equipment requires 

special chemicals or vigorous mechanical methods. 

The process of barite removal and disposal is 

complicated by the need to minimize radiation dose 

to workers and the general public. Radiation 

exposure pathways include external gamma 

radiation (major), ingestion (minor), and inhalation 

of particulates and radon gas (major). 

 Figure 4 illustrates the relative isolation of 

NORM waste from the general public for a variety 

of possible disposal options. As degree of isolation 

increases so does the capability for disposing of 

higher radium concentrations. Currently most oilfield NORM waste is stored at production sites 

awaiting disposal in specially designated and 

permitted landfills, disposal wells, or injection wells 

(fig. 4). Surface spreading and dilution of low-level 

NORM waste (fig. 4) is a past practice that is now 

disallowed by most States with NORM regulations. 

A preliminary radiological dose assessment was 

reported for a scenario in which individuals live on 

a NORM-amended soil and consume local water, 

livestock, and food crops (Smith and others, 1996). 

For soils amended with radium to the highest 

concentration under regulatory consideration (30 

pCi/g) the additional annual radiation dose by all 

pathways was equivalent to the average annual 

background dose to the U.S. population. Current 

limits set by the Nuclear Regulatory Commission 

require that the total of such additional doses to the 

general public be limited to about 30 percent of the 

average annual background dose. 

 Prior to 1970 the regulations governing 

disposal of produced water and scale were less 

restrictive, and thus older oil-field production 

sites are more likely to have above-background 

concentrations of NORM in nearby soils and 

stream sediments. Several studies, including 

some by USGS researchers, have documented the 

presence of barite in soils contaminated with oilfield NORM. 

0.5 centimeter
Figure 4. Disposal alternatives for NORM 

wastes. Disposal of more concentrated 

wastes requires greater isolation of waste 

from the general public. Modified from 

American Petroleum Institute (1992). 

Reprinted courtesy of the American 

Petroleum Institute—based on original 

API figure, modified by U.S. Geological 

Survey.

Dr. Robert A. Zielinski

U.S. Geological Survey

Denver Federal Center, Mail Stop 973

Denver, CO 80225

(303) 236-4719

e-mail: rzielinski@usgs.gov

Dr. James K. Otton

U.S. Geological Survey

Denver Federal Center, Mail Stop 939

Denver, CO 80225

(303) 236-8020

e-mail: jkotton@usgs.gov

Figure 3. Estimated distribution of radium concentration in A, solid oil-field waste and B, produced water.

For More Information Contact

 Barite scale is the most likely host of elevated radium in 

these soils. The extreme insolubility of barite under natural 

conditions limits the rate of release of radium to water and 

suggests that dispersal of radium will be dominated by 

physical transport of barite particles. Barite solubility is 

lowest in oxidized soils that are rich in sources of soluble 

sulfate such as gypsum. In organic-rich soils barite solubility 

is increased by the action of sulfate-consuming bacteria. The 

average age of formation of barite scale can be estimated 

based on the different rates of decay of 226Ra and 228Ra, or 

based on the buildup of radioactive decay products of these 

radium isotopes. Such information is useful for determining 

the sources and history of contamination at a site and for 

assigning possible liability. 

Current Status and Future Direction of the 

Oil-Field NORM Issue 

 The magnitude of the oil-field NORM problem in the U.S. 

has been estimated, but it remains to be completely assessed. 

Increased industry awareness and understanding of the 

problem coupled with government regulatory efforts have 

provided much better control of oil-field NORM wastes and 

have reduced the radiation exposure to workers and the public. 

Management of the present inventory of stored oil-field 

NORM waste and options for its disposal are designed to 

reduce radiation hazard to the general public. The challenge 

to the oil and gas industry will be to develop safer and more 

cost-effective methods to minimize, process, and dispose of 

future oil-field NORM. An additional challenge to industry 

and government is to identify, remediate, and if necessary, 

remove NORM contamination that remains at old or 

abandoned petroleum production sites. 

American Petroleum Institute, 1992, Bulletin on management of naturally 

occurring radioactive materials (NORM) in oil & gas production: American 

Petroleum Institute, Washington, D.C., API Bulletin E2, 45 p.

Fisher, R.S., 1998, Geologic and geochemical controls on naturally occurring 

radioactive materials (NORM) in produced water from oil, gas, and geothermal 

operations: Environmental Geosciences, v. 5, no. 3, p. 139–150.

Mast, R.F., Root, D.H., Williams, L.P., Beeman, W.R., and Barnett, D.L., 1998, 

Areas of historical oil and gas exploration and production in the conterminous 

United States: U.S. Geological Survey Geologic Investigations Series I-2582. 

Scale 1: 3,750,000.

Otto, G.H., 1989, A national survey of naturally occurring radioactive materials 

(NORM) in petroleum producing and gas processing facilities: American 

Petroleum Institute, Dallas, Texas, 265 p.

Raloff, Janet, 1991, NORM—The new hot wastes: Science News, v. 140,

 p. 264–267.

Smith, K.P., Blunt, D.L., Williams, G.P., and Tebes, C.L., 1996, Radiological dose 

assessment related to management of naturally occurring radioactive materials 

generated by the petroleum industry: Argonne, Ill., Argonne National 

Laboratory, Publication ANL/EAD-2, 65 p.

Wascom, C.D., 1994, NORM disposal options in the State of Louisiana: 

Proceedings of the 1994 Rocky Mountain Symposium on Environmental Issues 

in Oil and Gas Operations, Colorado School of Mines, Golden, Colo., 10 p.

References Cited and Suggested Reading

A B

LOW

NORM CONCENTRATION LIMIT

HIGH

DEGREE

OF ISOLATION

FROM PUBLIC

LOW

HIGH

Surface

spreading

Surface

spreading

with

dilution Burial

Oil

industry

landfill

Licensed

NORM

disposal

facility

Lowlevel

waste

facility

Surface

mine

Injection

well

Plugged

and

abandoned

wells

Hydraulic

fracture

Salt

dome

0

10

20

30

40

50

60

5-30 30-100 100-500 500-1000 >1000

PERCENTAGE OF TOTAL 

RADIUM CONCENTRATION IN NORM-CONTAMINATED

OIL-FIELD WASTE, IN PICOCURIES/GRAM 

<1-100 100-300 300-1000 1000-3000 >3000

226Ra CONCENTRATION IN PRODUCED WATER,

IN PICOCURIES/LITER 

0

10

20

30

40

50

60

PERCENTAGE OF TOTAL