Natural remediation of marsh soil contaminated by oil-field brine containing elevated radium levels, southern Louisiana

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1 Natural remediation of marsh soil contaminated by oil-field brine containing elevated radium levels, southern Louisiana Matthew W. Totten Sr., Mark A. Hanan, and Sheri Simpson ABSTRACT The long-term behavior of radium associated with oil-field brines is not well known. A production facility located on an interdistributary delta plain in southern Louisiana discharged brine into an estuarine marsh from 1957 until early 1983, when the facility began injecting produced water into an injection well. Produced water at this facility has elevated radium concentrations. A study of the marsh soil adjacent to the facility in 1980 reported elevated radium concentrations. The 1980 sample sites were resampled for this study and analyzed for radium. Concentrations are now below natural background levels. The largest reductions were observed in samples that previously reported the highest values. The mineralogical host of the radium appears to be a solid barium sulfate (BaSO 4 ) phase, in contrast to previous reports of radium being adsorbed on clay minerals. The study area was severely impacted by Hurricane Katrina in 2005, lying directly in the path of the eye. Some of the production facilities that handle naturally occurring radioactive material (NORM) were destroyed, and spills of both oil and formation water occurred. Study results indicate that remediation of the marsh is occurring naturally in a time frame as short as two decades. The longterm effects of discharging oil-field brines with NORM in an area with active sedimentation appears to be minimal. AUTHORS Matthew W. Totten Sr. Kansas State University, Manhattan, Kansas 66506; mtotten@ksu.edu Matthew W. Totten Sr. is an associate professor of geology at Kansas State University, after serving on the faculty at the University of New Orleans from 1992 to He received his B.S. degree in geology from the University of Kansas (1977) and his M.S. degree (1979) and his Ph.D. (1992) from the University of Oklahoma. His primary research interests include the mineralogy and chemistry of finegrained sedimentary rocks. Mark A. Hanan Department of Earth and Environmental Sciences, University of New Orleans, New Orleans, Louisiana 70148; mhanan@uno.edu Mark Hanan has degrees in geology from the University of Kansas (B.S. degree, 1978) and the University of New Orleans (M.S. degree, 1981, and Ph.D., 1998). Prior to his current position as unitization geologist with the Minerals Management Service, he was a production, staff, and joint-interest geologist for Exxon. He is an adjunct professor of earth and environmental sciences at the University of New Orleans. Sheri Simpson Chevron Corporation, New Orleans, Louisiana; SheriSimpson@chevron.com Sheri Simpson has worked for Chevron since 2001 as an inorganic geochemist and primarily works as an interpreter of produced water data for enhanced recovery, scale and corrosion control, and disposal issues. She received her B.S. degree in biology from the University of New Orleans in 1998 and her M.S. degree in geology in INTRODUCTION The extraction of hydrocarbons almost always results in produced formation water as a waste byproduct. This water is commonly highly saline and toxic to the surface environment. Because of this, ACKNOWLEDGEMENTS The authors acknowledge Brent McKee at Tulane University for gamma spectrometry of the 1999 samples. Copyright #2007. The American Association of Petroleum Geologists/Division of Environmental Geosciences. All rights reserved. DOI: /eg Environmental Geosciences, v. 14, no. 3 (September 2007), pp

2 Figure 1. A 1982 photograph of production facilities immediately after filling of settling pit and conversion of producing well into an injection well to dispose of formation water with elevated radium activity. safe disposal is a long-standing issue in oil-producing areas (Baird et al., 1990). Particularly troublesome is the oil-field brine that contains elevated naturally occurring radioactive material (NORM), commonly in the form of radium. As brine is brought to the surface, changes in pressure, or other chemical conditions, initiates precipitation of scale that commonly contains radium (Canadian Association of Petroleum Producers, 2000). High radium content is present in many oil-field brines in the Gulf of Mexico oil and gas province. In a study of 32 oil-field brines produced from wells in Louisiana, 80% of these brines had 226 Ra activities that exceeded 500 dpm/l (Kraemer and Reid, 1984). Over time, they reported an apparent decrease in 226 Ra activity of the brine, which was interpreted to be the fractionation of radium into barium sulfate precipitates as the brine cooled. Oil-field equipment (casing, pipe, storage tanks, separators, and fittings) exposed to these brines is commonly coated with BaSO 4 scale deposits that also contain higher-than-background levels of NORM ( Wilson and Scott, 1992; White and Rood, 2001). Because of their chemical affinity, radium is concentrated in these barium-rich scales and is the likely source of the NORM. Until the late 1980s, common practice was to clean the scale from piping and other equipment by scraping and depositing the scale directly onto the ground at the facility (Scott and Hebert, 1992). Louisiana was the first state to implement guidelines for controlling and disposing NORM to protect the public health and environment in 1981 (Bohlinger, 1990). Oil and gas are separated from produced wastewater by passing the petroleum-brine mixture through a series of gravity separators. The lighter density petroleum is extracted from the top of the separator and sent to either storage tanks or a pipeline. The denser produced formation water is extracted from the bottom of the separators. In southern Louisiana, this water was released into large settling pits for further separation fromanyoilysludgenotremovedbytheseparators. Gravitational separation allowed the dense brine to settle, whereas the oily sludge remained floating in the water within the pit. Skimmers near the surface collected the floating oil, and the brine was discharged from the bottom of the pit by siphons laid over the pit levees. Until the regulatory change in 1981, produced water in southern Louisiana was intentionally discharged into a marsh environment. The purpose of this study is to investigate the effects of the regulatory change upon sites where produced water with elevated NORM was previously discharged. LOCATION OF STUDY The study area includes production facilities in the Baptiste Collette subdelta of the Mississippi River delta alongemelinepass(figure1).theproducedwaterat a production facility contains an elevated concentration of radium (i.e., NORM). Large quantities of produced water were released into the marsh from the settling pit from the start of production in 1957 until The settling pit was filled with sand in early 1983, and a formerly producing well was converted into 114 Remediation of Marsh Soil Contaminated by Oil-Field Brine with Elevated Radium

3 a saltwater disposal well. Produced water is now injected 3000 ft (914 m) below the surface, so it no longer enters the marsh. An initial investigation of radium levels was conducted at this facility in 1980 when the practice of openpit disposal was still in operation (Hanan, 1981). Radium levels in sediments near the settling pits were found to average twice the background level. Radium uptake in sediments appeared to be influenced by the location of the brine discharge. Radium concentrations were lowest in the sediment sample location nearest the brine-discharge siphon. It was concluded that the low radium at this location was caused by high salinity. High salinity levels have been reported to promote the removal of radium from sediments (Li et al., 1973) and inhibit radium adsorption in sediments (Landa and Reid, 1983). In addition, a strong correlation was found between the percentage of clay and the concentration of radium at the site. A 20-yr interval exists between the change in disposal method and the most recent sample collection at this facility. This provides a natural laboratory to address questions concerning the fate of oil-field NORM over time in a marsh environment. What is the current levelofnormatwhatoncewasasitewithdocumented elevated concentration? Where does any elevated NORM reside in this environment? Does the correlation between radium and clay percentage still exist? If radium is adsorbed on clay surfaces, has it been mobilized? Is the site currently safe or does it call for additional remediation? The results of this study are particularly relevant in post-katrina Louisiana. Many surface production facilities in the study area were destroyed as the eye wall of Katrina passed directly across these sites, commonly causing spills of both oil and formation water. The results of this study should be considered in designing remediation plans for NORM-impacted sites. (Finch, 2006). By reevaluating a particular oil-field facility that has conformed to current guidelines for NORM disposal, this question may be addressed. The objectives of this study were to (1) duplicate the sampling locations of the previous 1980 study; (2) determine the current vertical distribution of radium; (3) compare the site data; and (4) determine the fate and transport of radium in the environment over time after contaminant discharge has ceased. METHODS The study area was sampled in the summer of 1999, almost 20 yr after the initial study of surface sediment with elevated NORM. An attempt to sample the same sites of the earlier study was undertaken using the sample map from the 1980 study (Figure 2). The disposal well provided an accurate location from which the appropriate distance was measured to each site along a compass bearing as determined from the site location map (Hanan, 1981). Twelve cores were collected using a ball-valvecoring device. This is a hand-held device (the same apparatus used in 1980) that uses a partial vacuum to OBJECTIVES The focus of this research is to gain an understanding of the overall change in NORM concentration that has occurred over time as the process of disposal has changed. Many researchers (Landa and Reid, 1983; Baird et al., 1990; Scott and Hebert, 1992) have questioned whether elevated radium concentrations associated with petroleum facilities continue to pose a potential radiation health risk to the public. The health risk from elevated NORMcontinuestobeanissueinthecourtsystem Figure 2. Site map showing core sampling locations relative to settling pit, injection well, tank battery, square area shown in Figure 4, and line of cross section for Figure 7. Totten et al. 115

4 hold the sediment within a 3.75-cm (1.47-in.)-diameter polyvinyl chloride pipe. The depth of each core was dependent on the operator s ability to push the device from a Cajun pirot into the wetland sediment. Most cores reached slightly deeper than 20 cm (8 in.). An exception was core 5 that sampled 80 cm (31 in.). The cores were separated into 5-cm (2-in.) sections and dried in an oven at 100jC for 2 days. For each sample, an aliquot was hand crushed using a mortar and pestle, placed in an aluminum pan sealed with electrical tape, weighed, and labeled with the date and time of containment. 226 Ra and 210 Pb concentrations were determined by gamma spectrometry at the Tulane University isotope lab using a sodium iodide scintillator with a germanium gamma-ray detector. Radium concentrations of the 1980 sample set were analyzed using a radon emanation technique (Hanan, 1981). A separate aliquot of each sample of approximately 5 g was weighed, rehydrated, and disaggregated using an ultrasonic vibrator. The samples were separated by size using micromesh sieves and ultrasonic energy ( Totten and Blatt, 1993). Sieve sizes included 62.5, 30, 20, and 10 mm. Data were extrapolated to 1 mm for calculating grain-size statistical measures. Clay mineralogy was determined by x-ray diffraction methods (Drever, 1973) at the University of New Orleans. Additional analytical details are reported in Lasserre (2000). A density separation was performed on several of the samples exhibiting the highest levels of radium using lithium meta-tungstate to concentrate the mineral fraction with a density greater than 2.85 g/cm 3 (Hanan and Totten, 1996). This fraction was examined under a scanning electron microscope to determine the presence of barium sulfate that has a density of at least 4.2 g/cm 3. RESULTS The radium concentration as well as the sand and clay content for each sample are listed in Table 1. Data are presented for both the 1980 and 1999 sample sets. The 1980 radium concentrations within the upper 20 cm (8 in.) of sediment ranged from 1.65 to dpm/g (0.75 to 6.23 pci/g), and averaged 7.22 dpm/g (3.28 pci/g). The 1999 radium concentrations range from 2.07 to dpm/g (0.93 to 4.51 pci/g), and average 3.62 dpm/g (1.63 pci/g), within the upper 20 cm (8 in.) of sediment. Additional data from the deeper sampled core 5 are reported in Table 2. The general character of the soils in both sample sets is similar. Similarities include sand/clay ratio and clay mineralogy. The mineralogy of the clay fraction is a distribution of smectite, mixed-layer illite-smectite, illite, and kaolinite. The only obvious difference between the two sets is the level of NORM. The original samples were not analyzed for barium sulfate, but a white precipitate was reported during the radon emanation technique. Given the high barium concentrations reported in the produced water (Hanan, 1981; Landa and Reid, 1983), the precipitate was likely a barium sulfate scale, typically found in oil-field equipment associated with the produced water. DISCUSSION Comparison of the two data sets suggests that radium concentrations have substantially decreased during the 20 yr between sampling. The average total reduction is approximately 50% with the sites having the highest values in 1980 showing the greatest reduction. Figure 3 compares the activities of radium in disintegrations per minute between sample sets for each sample site. For the soil horizon measured, the reduction in radium levels at the entire site is striking, having been reduced to below background levels and well below the Louisiana Department of Environmental Quality (LDEQ) acceptable levels of 5 pci/g (11.1 dpm/g) above background. The background levels in this area are less than 3 dpm/g (1.3 pci/g) based on a control core taken in 1980 by Hanan (1981). The distribution of radium in the upper 5 cm (2 in.) across the study area for the two periods is shown in Figure 4. The study area has undergone a natural remediation after the change in disposal practice. Two possibilities exist to explain the reduction of NORM. One possibility is that the radium has desorbed from exchangeable sites on clay mineral surfaces and migrated elsewhere. The second possibility is that the soil layers with high radium values have been buried by accretion of new sediment because the site lies within the dynamic Mississippi delta. In either scenario, what mineralogical site the radium was originally held in is of interest. If simply held in exchangeable sites, the likelihood of eventual migration to the surface is still possible even if the 1980 sampled soils are buried. If held in a more stable mineral form, this is not as likely, and burial will insulate the radium from the near-surface environment indefinitely. One of the conclusions drawn from the earlier study was the location of radium as ions adsorbed at claymineral sites (Landa and Reid, 1983). This conclusion was based primarily on the excellent correlation 116 Remediation of Marsh Soil Contaminated by Oil-Field Brine with Elevated Radium

5 Table 1. Grain Size Distribution and Radium Activities of Each 5-cm Section of Sediment Cores from 1980 and Sample % Sand % Silt % Clay Ra (dpm/g) % Sand % Silt % Clay Ra (dpm/g) 1A, 0 5 cm A, 6 10 cm A, cm A, cm A, 0 5 cm A, 6 10 cm A, cm A, cm A, 0 5 cm A, 6 10 cm A, cm A, cm A, 0 5 cm A, 6 10 cm A, cm A, cm A, cm A, cm A, 0 5 cm A, 5 10 cm A, cm A, cm A, 0 5 cm A, 6 10 cm A, cm A, cm A, cm A, 0 5 cm A, 6 10 cm A, cm A, cm A, 0 5 cm A, 6 10 cm A, cm A, cm A, cm A, cm A, 0 5 cm A, 6 10 cm A, cm A, cm A, 0 5 cm A, 6 10 cm A, cm A, cm Totten et al. 117

6 Table 2. Grain Size Distribution and Radium Activities of Each 5-cm Section of Deep Sediment Core 5 from 1999 Sample Ra (dpm/g) % Sand 5A, cm A, cm A, cm A, cm A, cm A, cm (r = 0.74) between clay percentage and radium in the 1980 samples (Figure 5A). This correlation no longer exists in the more recent samples (Figure 5B). No significant difference in clay mineralogy or the amount of clay was found between the 1980 and 1999 data sets. The major minerals of the clay fraction are smectite, illite, kaolinite, and quartz in reasonably consistent proportions. Although the clay mineralogy is the same, the radium may have migrated elsewhere. An alternative interpretation of the original data is that radium was not adsorbed on clays, but occurred as a minor component as a barium sulfate scale. Because barium does not occur in quartz, both the clay percentage and the barium sulfate percentage would be reduced with increases in silt-size quartz. This would result in an apparent correlation between radium and clay, but both are actually controlled by the dilution of all components (except silica) with the addition of quartz. Although the 1980 samples were not analyzed for the presence of barium sulfate, scale has been reported as a consistent production problem in the area (Anderson, 1990; Aharon, 2003). The lack of correlation between radium and clay concentrations in the 1999 samples is generally caused by a lack of significant variation in radium because the whole site is at background concentrations. Barium sulfate background levels are consistent with the very low concentrations observed in the 1999 samples. In particular, barium sulfate was detected in the highest concentration within the heavy-mineral fraction of sample 11 (Figure 6) of the 1999 data set. The presence of barium sulfate would explain the slightly higher concentration of radium greater than background levels at this sample site. Furthermore, this location is closest to the tank battery. The barium sulfate could be scale deposited from past production practices, whereby oil-field workers scrape scale from nearby production facilities. The mineralogical site of the radium is important in assessing the potential mobility of the radioactivity. Radium contained structurally within barite is potentially more stable than radium ions adsorbed on exchangeable clay mineral surfaces. Chemical changes within pore waters as the sediment is buried could release adsorbed ions. Even without substantial chemical gradients, adsorbed ions might be expected to migrate to exchangeable sites on newly deposited clays shallower than the contaminated soils. This is not observed at this location. Figure 3. Radium activity for each sample location and depth for both data sets. All core sites except site 4 show a significant decline in radium activity. Site 4 was already at background level in Remediation of Marsh Soil Contaminated by Oil-Field Brine with Elevated Radium

7 Figure 4. Distribution of radium in disintegrations per minute per gram in the upper 5 cm (2 in.) of soil for 1980 (A) and 1999 (B). The only elevated sample in 1999 was collected adjacent to the tank battery. That the original highly radioactive samples were buried is strongly suggested. As seen in Figure 7, levels of radium at depths below 80 cm (31 in.) in core 5 approach levels observed at 10 cm (4 in.) in the earlier study. A similar trend in the same core is seen with sand percentage. An accretion rate of 3.6 cm/yr (1.4 in./ yr) would be required to bury the 10-cm (4-in.) samples of 1981 to the present 80 cm (31 in.) in 1999, which is within the rates observed in the area (Reed et al., 1997). We propose the following model to explain the results of the two studies. Radium began to be released to the marsh as produced water was siphoned over the leveeofthesettlingpit(figure8a).thissameprocess continued during the next yr, resulting in a significant buildup of radium (probably within barium scale) in the wetland sediments (Figure 8B). After regulations halted the practice of releasing produced water into the marsh, a producing well was converted into an injection well, and produced water was disposed of in the subsurface. The settling pit was no longer needed, so it was filled with sand (Figure 8C). Sediment accretion at normal rates buried the elevated soils to below depths that Louisiana NORM regulations consider hazardous; hence, the site has undergone a natural remediation (Figure 9). Only cores drilled deep enough to penetrate the older soils show elevated NORM. Deep Figure 5. Radium concentration in dpm/g versus percent clay for 1980 samples (A) and 1999 samples (B). The strong correlation found in the 1980 samples no longer occurs. Totten et al. 119

8 released into the marsh or aquatic environment. Natural accretion will rebury the NORM to acceptable levels within a 20-yr time frame. CONCLUSIONS The primary objective of this research was to compare data from 1980 and 1999 to determine the fate of radium after the change in disposal practice. The concentration of radium within the upper 20 cm (8 in.) has dramatically decreased from that measured 19 yr earlier. The comparison between the upper 20 cm (8 in.) of sediments between 1980 and 1999 show an average decrease of 3.6 dpm/g (1.7 pci/g) in radium concentration, which is a reduction of 50%. Sites having the highest values in 1980 show the greatest amount of reduction. The radium concentrations today are at background levels and are well below the LDEQ s acceptable levels. The local environment shows no long-term effects because of the release of radium-containing brines into the marsh. Figure 6. Scanning electron microscopy photomicrograph of heavy-mineral separate from core 11. Point 1 is a barium sulfate grain as seen in the accompanying energy-dispersive spectra from that spot. soils also tend to contain elevated barium sulfate, suggesting that the scale is the source of elevated radium activity when encountered. Regardless of the mechanism, the site no longer exceeds LDEQ regulations for NORM. The site has remediated naturally within 15 yr of the cessation of the release of formation waters with elevated radioactivity. The upper 20 cm (8 in.) of soil is now below background levels of radioactivity. The study results suggest that natural sediment accretion at Katrina-impacted sites will remediate NORM contamination because of formation water discharges in as little as 20 yr. Radium is most likely sequestered within barium sulfate, which is much less mobile than radium adsorbed on exchangeable clay mineral surfaces. Active sediment mobilization during severe storms like Katrina may redistribute the barium sulfate to shallower levels, but it seems unlikely that this radium will be Figure 7. Sand percentages and radium concentrations versus depth in core 5 for 1980 and 1999 sample sets. Dashed lines represent correlations of equivalent strata based on these data. 120 Remediation of Marsh Soil Contaminated by Oil-Field Brine with Elevated Radium

9 Figure 8. Proposed model for observed radium activities in wetland soil during the history of oil production at the studied location. Line of cross section is from Figure 2. (A) Release of radium during the initial 26 yr of production. (B) Buildup of elevated NORM during 26-yr discharge of produced water. (C) Conversion of facility to satisfy 1982 LDEQ regulations. Radium is no longer released to the wetlands. Figure 9. Burial of soil with elevated NORM by natural accretion of new sediment. Only deepest cores encounter elevated radium activity. Totten et al. 121

10 The mineralogical site of the elevated radium in the 1980 samples was probably within barium sulfate scale formed when produced water was mixed with natural marsh water. This dense barium sulfate scale was buried by subsequent accretion. After injection of produced water commenced, no additional scale or elevated radium was released into the area, except perhaps during cleaning of production equipment near the tank battery. Natural remediation by sediment accretion is effective at the study site and is much less disruptive to the area than a more active form of remediation. Removal of the NORM-containing soil and transport to a remote disposal site would be much more costly and probably less effective than allowing the area to remediate by natural accretion of new soil. These results are particularly relevant because the study area was severely impacted by Hurricane Katrina. Multiple spills of oil and produced water occurred as surface production facilities were subjected to a significant storm surge. With respect to NORM, these spills will also be remediated naturally with continued accretion of sediment. REFERENCES CITED Aharon, P., 2003, Is drilling in deepwater Gulf of Mexico uncorking bad genes?: Gulf Coast Association of Geological Societies Transactions, v. 53, p Anderson, B., 1990, Dealing with radioactive scale in offshore production: Ocean Industry, v. 25, p Baird,R.D.,G.B.Merrell,R.B.Klein,V.C.Rogers,andK.K.Nielson, 1990, Management and disposal alternatives for NORM wastes in oil production and gas plant equipment, RAE-8837/2-1: Dallas, Texas, American Petroleum Institute, 75 p. Bohlinger, L. H., 1990, Regulation of naturally occurring radioactive material in Louisiana: Proceedings of the First International Symposium on Oil and Gas Exploration and Production Waste Management Practices, sponsored by the U.S. Environmental Protection Agency, New Orleans, Louisiana, September 10 13, p Canadian Association of Petroleum Producers, 2000, CAPP guide, naturally occurring radioactive material (NORM), Calgary, Alberta, Canada, Canadian Association of Petroleum Producers, 11 p. Drever, J. L., 1973, The preparation of oriented clay mineral specimens for x-ray diffraction analysis by a filter membrane peel technique: American Mineralogist, v. 58, p Finch, S., 2006, Louisiana Court denies Exxon bid: Times-Picayune, April 2 ed., p. 1. Hanan, M. A., 1981, Geochemistry and mobility in sediments of radium from oil-field brines: Grand Bay, Plaquemines Parish, Louisiana: Master s thesis, University of New Orleans, New Orleans, Louisiana, 88 p. Hanan, M. A., and M. W. Totten, 1996, Analytical techniques for the separation and SEM identification of accessory phases in sedimentary rocks: Journal of Sedimentary Research, v. 66, p Kraemer, T. F., and D. F. Reid, 1984, The occurrence and behavior of radium in saline formation water of the U.S. Gulf Coast region: Isotope Geosciences, v. 2, p Landa, E. R., and D. F. Reid, 1983, Sorption of radium-226 from oil-production brine by sediments and soils: Environmental Geology, v. 5, p Lasserre, S. L., 2000, Natural remediation of disposed oil-field brines with elevated radium concentrations: Master s thesis, University of New Orleans, New Orleans, Louisiana, 162 p. Li, Y. H., T. L. Ku, G. C. Mathieu, and K. Wolgemuth, 1973, Barium in the Antarctic Ocean and implications regarding the marine geochemistry of Ba and Ra-226: Earth and Planetary Science Letters, v. 19, p Reed, D. J., N. De Luca, and A. L. Foote, 1997, Effect of hydrologic management on marsh sediment deposition in coastal Louisiana: Estuaries, v. 20, p Scott, L. M., and M. B. Hebert, 1992, An estimate of the risk from naturally occurring radioactive material associated with the production of petroleum: Spectrum 92 Nuclear and Hazardous Waste Management International Topical Meeting, Idaho, August Totten, M. W., and H. Blatt, 1993, Alterations in the non-clay mineral fraction of pelitic rocks across the diagenetic to low grade metamorphic transition, Ouachita Mountains, Oklahoma and Arkansas: Journal of Sedimentary Petrology, v. 63, p White, G. J., and A. S. Rood, 2001, Radon emanation from NORMcontaminated pipe scale and soil at petroleum industry sites: Journal of Environmental Radioactivity, v. 54, p Wilson, A. J., and L. M. Scott, 1992, Characterization on radioactive petroleum piping scale with an evaluation of subsequent land contamination: Health Physics, v. 63, p Remediation of Marsh Soil Contaminated by Oil-Field Brine with Elevated Radium