Abstract

Upper Colorado River (West Texas) and Petronila Creek (Texas Coastal Plain) salinities exceed state regulatory standards. For a recent study, airborne conductivity surveys located points of saline influx. Hydrochemical analyses defined salinity trends and potential sources. Both streams comprise Na-Cl hydrochemical facies and are near hydrocarbon production operations.

Upper Colorado River salinity decreases downstream overall (8,430-1,540 mg/L total dissolved solids [TDS], during this study) with local trend reversals. Stream-proximal shallow Permian groundwaters are sulfate enriched from evaporite dissolution. Stream-water chloride predominance is mitigated downstream by sulfate-enriched base flow. Anomalous chloride increases along the stream path correlate with proximity to anomalously saline water wells and oil fields. Conservative (Br/Cl) mixing models suggest hydraulic connection between saline wells, deep-basin brines, and saline streams.

Petronila Creek salinity increases downstream (233-15,180 mg/L TDS). The highest salinity (28,100 mg/L) in the study area is observed in a tributary ditch that previously was used for oil-field brine discharge. Conservative mixing models suggest that either Tertiary-age oil-field brine or seawater might constitute the source of salinity. However, boron and chloride data suggest that oil-field brine is probably the source. Sulfate (relative to chloride) is more concentrated in surface water than is expected from evaporation of oil-field brine or seawater and probably reflects soil-gypsum dissolution.