Sources of Radium Accumulation in Stream Sediments near Disposal Sites in Pennsylvania: Implications for Disposal of Conventional Oil and Gas Wastewater.

In Pennsylvania, Appalachian oil and gas wastewaters (OGW) are permitted for release to surface waters after some treatment by centralized waste treatment (CWT) facilities. While this practice was largely discontinued in 2011 for unconventional Marcellus OGW at facilities permitted to release high salinity effluents, it continues for conventional OGW. This study aimed to evaluate the environmental implications of the policy allowing the disposal of conventional OGW. We collected stream sediments from three disposal sites receiving treated OGW between 2014 and 2017 and measured 228Ra, 226Ra, and their decay products, 228Th and 210Pb, respectively. We consistently found elevated activities of 228Ra and 226Ra in stream sediments in the vicinity of the outfall (total Ra = 90-25,000 Bq/kg) compared to upstream sediments (20-80 Bq/kg). In 2015 and 2017, 228Th/228Ra activity ratios in sediments from two disposal sites were relatively low (0.2-0.7), indicating that a portion of the Ra has accumulated in the sediments in recent (<3) years, when no unconventional Marcellus OGW was reportedly discharged. 228Ra/226Ra activity ratios were also higher than what would be expected solely from disposal of low 228Ra/226Ra Marcellus OGW. Based on these variations, we concluded that recent disposal of treated conventional OGW is the source of high Ra in stream sediments at CWT facility disposal sites. Consequently, policies pertaining to the disposal of only unconventional fluids are not adequate in preventing radioactive contamination in sediments at disposal sites, and the permission to release treated Ra-rich conventional OGW through CWT facilities should be reconsidered.

Origin of Flowback and Produced Waters from Sichuan Basin, China.

Shale gas extraction through hydraulic fracturing and horizontal drilling is increasing in China, particularly in Sichuan Basin. Production of unconventional shale gas with minimal environmental effects requires adequate management of wastewater from flowback and produced water (FP water) that is coextracted with natural gas. Here we present, for the first time, inorganic chemistry and multiple isotope (oxygen, hydrogen, boron, strontium, radium) data for FP water from 13 shale gas wells from the Lower Silurian Longmaxi Formation in the Weiyuan gas field, as well as produced waters from 35 conventional gas wells from underlying (Sinian, Cambrian) and overlying (Permian, Triassic) formations in Sichuan Basin. The chemical and isotope data indicate that the formation waters in Sichuan Basin originated from relics of different stages of evaporated seawater modified by water-rock interactions. The FP water from shale gas wells derives from blending of injected hydraulic fracturing water and entrapped saline (Cl ∼ 50,000 mg/L) formation water. Variations in the chemistry, δ18O, δ11B, and 87Sr/86Sr of FP water over time indicate that the mixing between the two sources varies with time, with a contribution of 75% (first 6 months) to 20% (>year) of the injected hydraulic fracturing water in the blend that compose the FP water. Mass-balance calculation suggests that the returned hydraulic fracturing water consisted of 28-49% of the volume of the injected hydraulic fracturing water, about a year after the initial hydraulic fracturing. We show differential mobilization of Na, B, Sr, and Li from the shale rocks during early stages of operation, which resulted in higher Na/Cl, B/Cl, Li/Cl, and 87Sr/86Sr and lower δ11B of the FP water during early stages of FP water formation relative to the original saline formation water recorded in late stages FP water. This study provides a geochemical framework for characterization of formation waters from different geological strata, and thus the ability to distinguish between different sources of oil and gas wastewater in Sichuan Basin.

Brine Spills Associated with Unconventional Oil Development in North Dakota.

The rapid rise of unconventional oil production during the past decade in the Bakken region of North Dakota raises concerns related to water contamination associated with the accidental release of oil and gas wastewater to the environment. Here, we characterize the major and trace element chemistry and isotopic ratios ((87)Sr/(86)Sr, δ(18)O, δ(2)H) of surface waters (n = 29) in areas impacted by oil and gas wastewater spills in the Bakken region of North Dakota. We establish geochemical and isotopic tracers that can identify Bakken brine spills in the environment. In addition to elevated concentrations of dissolved salts (Na, Cl, Br), spill waters also consisted of elevated concentrations of other contaminants (Se, V, Pb, NH4) compared to background waters, and soil and sediment in spill sites had elevated total radium activities ((228)Ra + (226)Ra) relative to background, indicating accumulation of Ra in impacted soil and sediment. We observed that inorganic contamination associated with brine spills in North Dakota is remarkably persistent, with elevated levels of contaminants observed in spills sites up to 4 years following the spill events.

Naturally Occurring Radioactive Materials in Coals and Coal Combustion Residuals in the United States.

The distribution and enrichment of naturally occurring radioactive materials (NORM) in coal combustion residuals (CCRs) from different coal source basins have not been fully characterized in the United States. Here we provide a systematic analysis of the occurrence of NORM ((232)Th, (228)Ra, (238)U, (226)Ra, and (210)Pb) in coals and associated CCRs from the Illinois, Appalachian, and Powder River Basins. Illinois CCRs had the highest total Ra ((228)Ra + (226)Ra = 297 ± 46 Bq/kg) and the lowest (228)Ra/(226)Ra activity ratio (0.31 ± 0.09), followed by Appalachian CCRs (283 ± 34 Bq/kg; 0.67 ± 0.09), and Powder River CCRs (213 ± 21 Bq/kg; 0.79 ± 0.10). Total Ra and (228)Ra/(226)Ra variations in CCRs correspond to the U and Th concentrations and ash contents of their feed coals, and we show that these relationships can be used to predict total NORM concentrations in CCRs. We observed differential NORM volatility during combustion that results in (210)Pb enrichment and (210)Pb/(226)Ra ratios greater than 1 in most fly-ash samples. Overall, total NORM activities in CCRs are 7-10- and 3-5-fold higher than NORM activities in parent coals and average U.S. soil, respectively. This study lays the groundwork for future research related to the environmental and human health implications of CCR disposal and accidental release to the environment in the context of this elevated radioactivity.

The intensification of the water footprint of hydraulic fracturing.

Unconventional oil and gas exploration in the United States has experienced a period of rapid growth, followed by several years of limited production due to falling and low natural gas and oil prices. Throughout this transition, the water use for hydraulic fracturing and wastewater production in major shale gas and oil production regions has increased; from 2011 to 2016, the water use per well increased up to 770%, while flowback and produced water volumes generated within the first year of production increased up to 1440%. The water-use intensity (that is, normalized to the energy production) increased ubiquitously in all U.S. shale basins during this transition period. The steady increase of the water footprint of hydraulic fracturing with time implies that future unconventional oil and gas operations will require larger volumes of water for hydraulic fracturing, which will result in larger produced oil and gas wastewater volumes.