AAPG Southwest Section

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Soil Chemistry Analysis of Brine contaminated soils in West Texas, USA

Abstract

The focus of this project is to develop a basis for future remediation by investigating the changes in soil chemistry, mineralogy, and structure due to brine contamination at a historic site. The study area is a 14-acre brine contaminated kill zone, located about 14 miles south of San Angelo, Texas. The site is characterized by a lack of vegetation, salt crust, highly compacted soils, and low infiltration rates. Composite soil samples were collected from each section, as well as one from both upgradient and downgradient of the kill zone. Macro and micro nutrient analysis (i.e. total alkalinity, extractable calcium, chloride, total copper, extractable potassium, extractable magnesium, extractable sodium, nitrate, total phosphorous, pH, SAR, sulfate, and total kjeldahl nitrogen), Scanning Electron Microscopy (SEM), and X-Ray Diffraction (XRD) were used to characterize the soils. In the contaminated soils, concentrations of extractable sodium and chloride averaged 2,904 mg/kg and 6,086 mg/kg respectively, while the SAR averaged 25.89. XRD revealed that the dominant clay minerals in the background sample were kaolinite and halloysite. Kaolinite and halloysite were also the dominant clay minerals found in the brine contaminated soils. SEM images of the contaminated samples showed a drastic alteration in soil structure. The change in structure was caused by the excess sodium ions in the brine, which replaced the calcium and magnesium ions in the clays. The larger sodium ions increased the distance between clay particles, creating a repulsive force which pushed the clay particles apart, causing dispersion. Dispersion, in turn caused the plugging of the clay soils, which resulted in decreased infiltration rates and compaction. Overall, the clay mineralogy remained relatively constant after brine contamination, but the soil chemistry and structure were drastically altered.