Comparison of soil-to-water suspension ratios for determining electrical conductivity of oil-production-water-contaminated soils

Abstract

Soil salinity caused by oil-production-water (brine) contamination is a major issue in regions of oil and gas development. However, rapid site assessment tools such as soil-to-water suspension electrical conductivity (EC) methods and conversion equations have not been previously calibrated and validated for brine-contaminated soils. Our objective was to compare three soil EC methods and derive conversion equations for EC values commonly observed at brine-spill sites. Brine-contaminated soils from western North Dakota were assessed for salinity. Electrical conductivity was determined using 1:1 and 1:5 soil-to-water suspensions (EC1:1, EC1:5) and saturated paste extracts (ECe). Soil EC equilibration times for soil-to-water suspensions were also assessed. Significant relationships (r2 = 0.91 to 0.97, P < 0.0001) existed among all methods for EC values ranging between 0 and 126 dS m−1. Conversion equations were developed based on these relationships and then validated with an independent data set. These new equations reduced ECe prediction errors by 2 to 4.5 times when compare with 14 predictive equations reported in the literature. The conversion equations developed here are recommended for use in remediation efforts when converting EC1:1 and EC1:5 data to ECe on brine-contaminated and noncontaminated soils where ECe is highly correlated to Na concentrations.