IDENTIFYING SOURCES OF RAPID SALINIZATION IN A LOCAL GROUNDWATER SYSTEM USING GEOCHEMISTRY AND GEOPHYSICS: THE ROLE OF PETROLEUM PRODUCTION AND OTHER SITE-SPECIFIC SOURCE INFLUENCES

Increasing stress on water resources in Texas is bringing focus on groundwater quality and availability. This study investigates an abrupt groundwater salinization event in a localized aquifer system in North Central Texas occurring over the past three years (2010-2013). Salinization increases observed in this system are potentially related to petroleum production, agriculture and livestock activity or natural interaction with deeper groundwater. Total dissolved solids (TDS) at this site varied from 410 - 1530 ppm during the study monitoring period (2012-2013). Analysis of hydrogeochemical data revealed unusual Ca-Mg-Cl waters with little HCO₃⁻ or Na⁺ measured. Cl⁻ anion proportion correlated directly with TDS. Leaching of soil samples revealed a direct correlation between soils-derived-TDS and distance from the nearest oil producing well. Surface resistivity measurements identified a shallow high-conductivity zone extending down-gradient from the well, possibly representing a saline plume flow path. Indications of conductive material were observed in both the near surface (0-10m) in the 2D resistivity profile and at about 30m depth in the VES profile. Low NO_3⁻ levels indicated that agriculture and livestock contributions to salinization are unlikely. Minimal SO_4^2- and low Na⁺/Cl⁻ ratios suggest little contribution from evaporites. High TDS and low Na⁺/Cl⁻ ratios infer petroleum production activities as the likely contributor to groundwater quality reduction at this site. Additionally, resistivity profiling and soil sampling indicated a feasible flow path for saline fluids from the up-gradient petroleum well towards the direction of the down-gradient active groundwater well. Whether these fluids arise from the oil production interval or from intervening brackish aquifers is still unknown.