An Investigation of Naturally Occurring Radioactive Materials in Oil and Gas Wells in New York State
This report presents the findings of the New York State Department of Environmental Conservation (NYSDEC) that New York State oil and gas production equipment and wastes are not significantly contaminated by naturally occurring radioactive materials (NORM). The concentrations of NORM found on oil and gas production equipment and wastes pose no threat to the public health and the environment. The research and analysis supporting this conclusion were performed in 1996. Direct measurements of the radioactivity at well sites were performed. Samples of scales, sludges, sediments, soils, water, rock, brines, waxes, and oils were taken and analyzed by gamma spectrometry.
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Pulled 2" pipe at a recently plugged
and abandoned oil well. This is the
type of equipment sampled for NORM
NORM can be found in many geological formations and may be brought to the surface during oil/gas drilling and abstraction. Once at the surface it may accumulate in scales and sludges on and within drilling and processing equipment. It may also accumulate in brines and sediments within holding tanks or ponds.
During the 1980's, elevated concentrations of NORM were found on oil and gas mining equipment in the North Sea and in the Southern United States (Escott, 1984). This discovery generated concern in the United States and Europe. Elevated NORM concentrations may subject oil and gas workers to unnecessary radiation exposure. Concern was also raised about public exposure to people through the recycling of radioactively contaminated equipment or from the application of radioactive brines to roads for snow and ice removal.
In 1990, the New York State Department of Environmental Conservation Region 9 office performed an initial survey to determine if elevated concentrations of NORM existed at any of 17 western New York State oil and gas wells or on the related equipment. Using Geiger-Mueller (G-M) detectors for the survey, no significant contamination (defined as more than twice background levels) was found. The State of Pennsylvania found similar results during a 1994 NORM investigation of oil and gas well waste.
Drilling at the Avoca natural gas storage project, Steuben County, August, 1996.
The derrick on the left is at the deep disposal well no. 6. The derrick on the
right is at the shallow cavern well 3-A. Naturally occurring radioactive materials
(NORM) can be a concern at oil and gas drilling locations.
However, since the 1990 New York State investigation was limited (no samples were taken and only a small number of sites (17) were visited), the former Bureau of Pesticides and Radiation (BPR) planned a more extensive survey for 1996. This survey included a wider representation of New York State gas and oil fields and took physical samples to determine the actual concentration of the radionuclides involved.
Radiological Sampling and Surveying
The investigation was performed by the BPR with the assistance of staff from the Division of Mineral Resources (DMN) and the respective NYS DEC regional offices. The BPR staff made six different field excursions, each to a different geographic location, to sample and/or take selected survey instrument readings at a total of 74 oil and gas well sites. Sampling and limited radiological surveys were performed in the following counties: Madison, Erie, Genesee, Wyoming, Cattaraugus, Livingston, Ontario, Seneca, Cayuga, Tioga and Chautauqua. A total of 101 samples were collected by field staff for analysis at the BPR gamma spectroscopy unit in Albany, New York, and/or the BPR's contract laboratory. Samples included water, brines, separator pit sediments, pipe scales, soils adjacent to oil/gas operations, and scales and sludges from tank bottoms. Eleven soil and rock samples were taken from nearby areas to establish background concentrations. Twenty-nine samples were taken to search for oil well contamination, 59 to search for gas well contamination, and two samples were taken from a mixed oil and gas area.
Survey instrument readings were taken at well heads, pipe exteriors, tank exteriors, soil beneath drains and spigots, drainage pits, and ditches. The more efficient thallium activated sodium iodide [NaI(Tl)] detectors (with a 2"x2" probe for most investigations, a 1"x 1" probe for the remainder) were used in lieu of the G-M instruments employed in the previous survey. For comparison, background readings were taken near each selected survey site.
Samples were analyzed for 10 NORM isotopes. Radium-226 (Ra-226) and radium-228 (Ra-228) were of primary concern as these isotopes, due to their relative solubility, have been shown to accumulate in oil/gas production equipment and wastes. Ninety-one percent (71 out of 80) of samples from oil/gas equipment and wastes showed radium concentrations that were within twice the background concentration of local soils and rock. Background concentrations were found to average around 5 pCi/g total radium. (Total radium is defined as the sum of the radioactivity of Ra-226 and Ra-228.) No comparative background values existed for brines, oils, and waxes. Therefore the concentrations were judged solely on their radiological effects. The nine exceptions - three at gas well sites and six at oil well sites - are discussed below.
Gas well samples included 43 brine (salty waters brought to the surface as a by-product of gas production), 10 scale, two sludge, two water and one soil sample. Only two brine and one scale sample indicated radium isotope concentrations that were greater than 5.0 picocuries per gram (pCi/g) total radium (pCi/ml for liquid samples such as brines). The brine radium results, 0.95 and 24 picocuries per milliliter (pCi/ml) for one sample, and 3.8 and 7.7 pCi/ml for the other (Ra-226 and Ra-228 respectively), pose no threat to public health or the environment. This conclusion is supported by an analysis of road disposal of the brine with the U.S. Department of Energy's (USDOE) Residual Radioactive Material Guideline computer model (RESRAD). The scale result, 11 pCi/g for Ra-226 and 3.8 pCi/g for Ra-228, also poses no threat to public health or the environment due to the low amount of scale deposited in gas plant piping.
at a brine pool.
The 29 oil well samples were of more diversified origin, including four brine, one scale, six sludge, eight sediment, one water, two oil, and six wax samples. (Wax, or paraffin, may coat the interior of some pipes as a consequence of oil abstraction.) No brine, scale, wax, or oil samples appeared elevated. No radium could be detected in the one water sample collected. However, three sediment samples and three sludge samples exceeded the twice background range for local soils (up to a factor of four greater). Such concentrations should not pose a public health threat or an environmental risk given their isolated locations and low quantities. Again the USDOE's RESRAD system was used to evaluate abandoned brine pits to confirm the negligible risk posed by the sediment and sludge radioactivity concentrations.
The survey instrument readings taken at well heads, pipe exteriors, tank exteriors, soil beneath drains and spigots, drainage pits, and ditches revealed no radioactivity more than twice background.
Comparison With Other Investigations
The concentrations of NORM generated by New York State gas/oil production were slightly greater than those found in a 1994 Pennsylvania study of sediments in brine holding ponds. The analytical results from the Pennsylvania oil field wastes showed uranium and thorium chain isotopes to be present at concentrations no greater than 5 pCi/g. The amount of thorium found in this investigation was in approximate agreement with that of the Pennsylvania investigation. The amounts of radium isotopes were somewhat higher but, as stated above, neither in a location or in a sufficient quantity to pose a hazard.
The New York State NORM concentrations were significantly lower than the North Sea samples, which generated some concern (Smith, 1987; Waldram, 1988). Scale samples from the North Sea oil fields contained Ra-226 at concentrations between 2,000 and 30,000 pCi/g (New York State samples ranged from none detected to 11 pCi/g). Sludge samples contained Ra-226 from 100 to 1,300 pCi/g (from 0.2 to 7.4 pCi/g in New York State). Hence, the North Sea scale samples were more than two orders of magnitude greater, and the sludge samples more than one order of magnitude greater, than those found in New York State.
Discussion of Results
NYSDECs Cleanup Guideline for Soils Contaminated with Radiation Materials DHSM-05-01 recommends a maximum dose limit to the general public of 10 millirem per year (mrem/yr) above background for free release of a site following the cleanup of radioactively contaminated materials. Given the NORM concentrations identified in this report, there are no plausible exposure scenarios that will yield 10 mrem/yr dose rates at New York State oil and gas wells (see following section). In fact, 91 percent of sample concentrations did not appear elevated above and/or were indistinguishable from background. The low survey instrument readings (within twice background) are consistent with the sample concentrations taken from the sites. Hence, NORM contamination at oil and gas mining sites poses no threat to the public or the environment.
Disposal of Oil and Gas Well Wastes Containing NORM
The wastes from oil and gas drilling operations may contain low concentrations of elevated NORM. Of these wastes, the highest concentrations of radium were found in brines. To determine if disposal methods of these wastes may be of concern to the general public, the BPR used USDOE's RESRAD modeling program. The modeling showed that the most common method of brine disposal in New York State, spreading it on the roads to control ice and snow, does not present significant doses to the public. This is true even if it is assumed that all brines contain the highest concentration of radioactivity detected. The resulting dose from this worst-case scenario was estimated at slightly less than 3 mR/year - well below the 10 mR/year standard presented in DSHM-RAD-05-01. RESRAD modeling also showed that abandoned sludge and sediment pits (an unauthorized practice that nevertheless occurs) do not pose any significant dose to the public.
While NORM-contaminated equipment has been a concern in North Sea oil well drilling, the results of this investigation show that NORM contamination of New York State equipment is insignificant. New York State well drilling equipment and wastes do not constitute a health risk for the State's residents nor present a potential degradation of the State's environment.