Evaluating Hypersaline Surface Water Conditions in a South Texas Production Field

A series of surface water impoundments caused by mining operations in an area of active petroleum production were determined to be characterized by hypersaline conditions.  An evaluation was conducted to characterize the source of these conditions. The evaluation included analyses of the water quality, soil salinity, historical aerial photographs, and a hydrologic budget analysis. In particular, water quality measurements indicated the pond water contains elevated concentrations of calcium, magnesium, potassium, sodium, chloride, and sulfate. The concentrations of sodium and chloride were particularly elevated averaging 18,900 mg/L and 29,650 mg/L, respectively.  By utilizing aerial photographs from 2004, 2005, 2006, 2008, and 2010, the elevations of the water in the impoundments were determined. Based on the aerial photographs the water level in the caliche pits ranged approximately 4 feet. Correlation of the water levels with precipitation indicated that the changes in water level in the caliche pits are the result of trends in rainfall – water levels are low during periods of low precipitation and rise when increases in rainfall occur. Moreover, it was determined that the concentration of sodium and chloride decreased with increasing water levels.

Results of the analyses indicated that the hypersaline conditions were derived from natural conditions. Specifically, soluble compounds are leached from the vadose zone, transported via groundwater to the pits, and collected in the pits as water loss occurs due to the high evaporation rates. This process has been ongoing over a period of at least 40 years, which has produced the elevated accumulation of chlorides in the water impoundments.