Occurrence and sources of radium in groundwater associated with oil fields in the southern San Joaquin Valley, California

Environmental Science & Technology
By: , and 

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Abstract

Geochemical data from 40 water wells were used to examine the occurrence and sources of radium (Ra) in groundwater associated with three oil fields in California (Fruitvale, Lost Hills, South Belridge). 226Ra+228Ra activities (range=0.010-0.51 Bq/L) exceeded the 0.185 Bq/L drinking-water standard in 18% of the wells (not drinking-water wells). Radium activities were correlated with TDS concentrations (p<0.001, ρ=0.90, range=145-15,900 mg/L), Mn+Fe concentrations (p<0.001, ρ=0.82, range=<0.005-18.5 mg/L), and pH (p<0.001, ρ=-0.67, range=6.2-9.2), indicating Ra in groundwater was influenced by salinity, redox, and pH. Ra-rich groundwater was mixed with up to 45% oil-field water at some locations, primarily infiltrating through unlined disposal ponds, based on Cl, Li, noble-gas, and other data. Yet 228Ra/226Ra ratios in pond-impacted groundwater (median=3.1) differed from those in oil-field water (median=0.51). PHREEQC mixing calculations and spatial geochemical variations suggest the Ra in oil-field water was removed by co-precipitation with secondary barite and adsorption on Mn-Fe precipitates in the near-pond environment. The saline, organic-rich oil-field water subsequently mobilized Ra from downgradient aquifer sediments via Ra-desorption and Mn/Fe-reduction processes. This study demonstrates that infiltration of oil-field water may leach Ra into groundwater by changing salinity and redox conditions in the subsurface rather than by mixing with a high-Ra source.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Occurrence and sources of radium in groundwater associated with oil fields in the southern San Joaquin Valley, California
Series title Environmental Science & Technology
DOI 10.1021/acs.est.9b02395
Volume 53
Issue 16
Year Published 2019
Language English
Publisher American Chemical Society
Contributing office(s) California Water Science Center, Colorado Water Science Center, Crustal Geophysics and Geochemistry Science Center
Description 9 p.
First page 9398
Last page 9406
Country United States
State California
Other Geospatial San Joaquin Valley