Isotopic and element ratios fingerprint salinization impact from beneficial use of oil and gas produced water in the Western U.S

Bonnie McDevitt; Molly C McLaughlin; David S Vinson; Thomas J Geeza; Jens Blotevogel; Thomas Borch; Nathaniel R Warner

doi:10.1016/j.scitotenv.2020.137006

Isotopic and element ratios fingerprint salinization impact from beneficial use of oil and gas produced water in the Western U.S

Sci Total Environ. 2020 May 10:716:137006. doi: 10.1016/j.scitotenv.2020.137006. Epub 2020 Jan 31.

Authors

Bonnie McDevitt¹, Molly C McLaughlin², David S Vinson³, Thomas J Geeza⁴, Jens Blotevogel², Thomas Borch⁵, Nathaniel R Warner⁶

Affiliations

¹ Department of Civil and Environmental Engineering, The Pennsylvania State University, United States of America.
² Department of Civil and Environmental Engineering, Colorado State University, United States of America.
³ Department of Geography and Earth Sciences, University of North Carolina at Charlotte, United States of America.
⁴ Department of Civil and Environmental Engineering, The Pennsylvania State University, United States of America; EES-14, Los Alamos National Laboratory, Los Alamos, NM 87544, United States of America.
⁵ Department of Civil and Environmental Engineering, Colorado State University, United States of America; Department of Chemistry, Colorado State University, United States of America; Department of Soil and Crop Sciences, Colorado State University, United States of America.
⁶ Department of Civil and Environmental Engineering, The Pennsylvania State University, United States of America. Electronic address: nrw6@psu.edu.

PMID: 32069772
DOI: 10.1016/j.scitotenv.2020.137006

Abstract

Salinization of global freshwater resources is a concerning health and economic issue of the 21st century and requires serious management and study to understand how, and by what mechanism, Total Dissolved Solids (TDS) is changing in major watersheds. Oil and gas (O&G) produced water is a complex and saline (10-300 g/L TDS) wastewater often disposed to surface waters post-treatment. However, in western U.S. states, beneficial use of minimally treated O&G produced water discharged to ephemeral streams is permitted through the USEPA National Pollutant Discharge Elimination System (NPDES) for agriculture and wildlife propagation. In a remote Wyoming study region, beneficial use of O&G NPDES effluents annually contributes 13 billion L of water to surface water resources. The primary O&G TDS constituents are sulfate and sodium followed by chloride and calcium. Significant TDS increases from 2013 to 2016 in a large perennial river (River C) impacted by O&G effluent disposal, slight TDS increases in a perennial river (River B) and chronically elevated TDS (upwards of 2500 mg/L) in a smaller tributary (Tributary A) comprised mainly of O&G effluents led to an investigation of O&G impacts to surface waters in the region. Chloride-normalized metal ratios such as Br/Cl and δ²H and δ¹⁸O distinguished evaporation as the mechanism for increasing TDS derived from O&G on Tributary A, which is causing O&G effluents that meet NPDES regulations to not only exceed outfall regulations downstream where it is beneficially used for irrigation and drinking water but also exceed aquatic life and livestock recommended limits. ⁸⁷Sr/⁸⁶Sr and δ³⁴S_SO4 suggested minor impacts from O&G TDS loading on River C but also support an additional salinity source, such as streambed geological controls, the cause of significantly increasing TDS. While lithium isotopes provided insight into the O&G effluent origin (δ⁷Li ranged 9-10‰) and water-sediment interactions along O&G effluent streams, they did not function as distinct salinity tracers in the larger downstream rivers. This study suggests a multi-isotope (⁸⁷Sr/⁸⁶Sr and δ³⁴S_SO4) approach is often necessary for fingerprinting salinization sources and determining best management practices because multiple salinity sources and environmental mechanisms may need to be identified to protect water quality.

Keywords: Agriculture; Evaporation; Lithium; Strontium; Sulfate; TDS.