Flowback verses first-flush: new information on the geochemistry of produced water from mandatory reporting

River water influenced by shale gas wastewater discharge for paddy irrigation has limited effects on soil properties and microbial communities

The processes of hydraulic fracturing to extract shale gas generate a large amount of wastewater, and the potential impacts of wastewater discharge after treatment are concerning. In this field study, we investigated the effects of the irrigation of paddy fields for 2 consecutive years by river water that has been influenced by shale gas wastewater discharge on soil physicochemical properties, microbial community structure and function, and rice grain quality. The results showed that conductivity, chloride and sulfate ions in paddy soils downstream of the outfall showed an accumulative trend after two years of irrigation, but these changes occurred on a small scale (<500 m). Two-year irrigation did not cause the accumulation of trace metals (barium, cadmium, chromium, copper, lead, strontium, zinc, nickel, and uranium) in soil and rice grains. Among all soil parameters, the accumulation of chloride ions was the most pronounced, with concentrations in the paddy soil at the discharge site 13.3 times higher than at the upstream control site. The use of influenced river water for paddy irrigation positively increased the soil microbial diversity, but these changes occurred after two years of irrigation and did not occur after one year of irrigation. Overall, the use of river water affected by shale gas wastewater discharge for agricultural irrigation has limited effects on agroecosystems over a short period. Nevertheless, the possible negative effects of contaminant accumulation in soil and rice caused by longer-term irrigation should be seriously considered.

Recovery of Critical Metals from Aqueous Sources

Critical metals, identified from supply, demand, imports, and market factors, include rare earth elements (REE), platinum group metals, precious metals, and other valuable metals such as lithium, cobalt, nickel, and uranium. Extraction of metals from U.S. saline aqueous, emphasizing saline, sources is explored as an alternative to hardrock ore mining. Potential aqueous sources include seawater, desalination brines, oil-and-gas produced waters, geothermal aquifers, and acid mine drainage, among others. A feasibility assessment reveals opportunities for recovery of lithium, strontium, magnesium, and several REE from select sources, in quantities significant for U.S. manufacturing and for reduction of U.S. reliance on international supply chains. This is a conservative assessment given that water quality data are lacking for a significant number of critical metals in certain sources. The technology landscape for extraction and recovery of critical metals from aqueous sources is explored, identifying relevant processes along with knowledge gaps. Our analysis indicates that aqueous mining would result in much lower environmental impacts on water, air, and land than ore mining. Preliminary assessments of the economics and energy consumption of recovery show potential for recovery of critical metals.

Is Food Irrigated with Oilfield-Produced Water in the California Central Valley Safe to Eat? A Probabilistic Human Health Risk Assessment Evaluating Trace Metals Exposure

Reuse of oilfield-produced water (OPW) for crop irrigation has the potential to make a critical difference in the water budgets of highly productive but drought-stressed agricultural watersheds. This is the first peer-reviewed study to evaluate how trace metals in OPW used to irrigate California crops may affect human health. We modeled and quantified risks associated with consuming foods irrigated with OPW using available concentration data. The probabilistic risk assessment simulated OPW metal concentrations, crop uptake, human exposures, and potential noncancer and carcinogenic health effects. Overall, our findings indicate that there is a low risk of ingesting toxic amounts of metals from the consumption of tree nuts, citrus, grapes, and root vegetables irrigated with low-saline OPW. Results show increased arsenic cancer risk (at 10^-6 ) for adult vegetarians, assuming higher consumption of multiple foods irrigated with OPW that contain high arsenic concentrations. All other cancer risks are below levels of concern and all noncancer hazards are far below levels of concern. Arsenic risk concerns could be mitigated by practices such as blending high-arsenic OPW. Future risk assessment research should model the risks of organic compounds in OPW, as our study focused on inorganic compounds. Nevertheless, our findings indicate that low-saline OPW may provide a safe and sustainable alternative irrigation water source if water quality is adequately monitored and blended as needed prior to irrigation.

The impact of using low-saline oilfield produced water for irrigation on water and soil quality in California

The consecutive occurrence of drought and reduction in natural water availability over the past several decades requires searching for alternative water sources for the agriculture sector in California. One alternative source to supplement natural waters is oilfield produced water (OPW) generated from oilfields adjacent to agricultural areas. For over 25 years, OPW has been blended with surface water and used for irrigation in the Cawelo Water District of Kern County, as permitted by California Water Board policy. This study aims to evaluate the potential environmental impact, soil quality, and crop health risks of this policy. We examined a large spectrum of salts, metals, radionuclides (²²⁶Ra and ²²⁸Ra), and dissolved organic carbon (DOC) in OPW, blended OPW used for irrigation, groundwater, and soils irrigated by the three different water sources. We found that all studied water quality parameters in the blended OPW were below current California irrigation quality guidelines. Yet, soils irrigated by blended OPW showed higher salts and boron relative to soils irrigated by groundwater, implying long-term salts and boron accumulation. We did not, however, find systematic differences in ²²⁶Ra and ²²⁸Ra activities and DOC in soils irrigated by blended or unblended OPW relative to groundwater-irrigated soils. Based on a comparison of measured parameters, we conclude that the blended low-saline OPW used in the Cawelo Water District of California is of comparable quality to the local groundwater in the region. Nonetheless, the salt and boron soil accumulation can pose long-term risks to soil sodification, groundwater salinization, and plant health; as such, the use of low-saline OPW for irrigation use in California will require continual blending with fresh water and planting of boron-tolerant crops to avoid boron toxicity.

An integrative method for identification and prioritization of constituents of concern in produced water from onshore oil and gas extraction

In the United States, onshore oil and gas extraction operations generate an estimated 900 billion gallons of produced water annually, making it the largest waste stream associated with upstream development of petroleum hydrocarbons. Management and disposal practices of produced water vary from deep well injection to reuse of produced water in agricultural settings. However, there is relatively little information with regard to the chemical or toxicological characteristics of produced water. A comprehensive literature review was performed, screening nearly 16,000 published articles, and identifying 129 papers that included data on chemicals detected in produced water. Searches for information on the potential ecotoxicological or mammalian toxicity of these chemicals revealed that the majority (56%) of these compounds have not been a subject of safety evaluation or mechanistic toxicology studies and 86% lack data to be used to complete a risk assessment, which underscores the lack of toxicological information for the majority of chemical constituents in produced water. The objective of this study was to develop a framework to identify potential constituents of concern in produced water, based on available and predicted toxicological hazard data, to prioritize these chemicals for monitoring, treatment, and research. In order to integrate available evidence to address gaps in toxicological hazard on the chemicals in produced water, we have catalogued available information from ecological toxicity studies, toxicity screening databases, and predicted toxicity values. A Toxicological Priority Index (ToxPi) approach was applied to integrate these various data sources. This research will inform stakeholders and decision-makers on the potential hazards in produced water. In addition, this work presents a method to prioritize compounds that, based on hazard and potential exposure, may be considered during various produced water reuse strategies to reduce possible human health risks and environmental impacts.