Groundwater Withdrawals Associated with Oil and Gas Production from Water Supply Aquifers in Texas: Implications for Water Management Practices

Abstract

The demand for water is continuing to increase as population and industry grow. The Natural Resources Defense Council indicated that Texas is at “extreme risk” for implementation of sustainable water management practices especially since groundwater is the supplier of much of the state’s freshwater. This study is designed to assess groundwater conservation practices in association with oil and gas production from the surrounding areas of the Carrizo-Wilcox formation in Texas. The results of this study reveal that the Railroad Commission of Texas (RRC), the governing agency for Texas oil and gas development, permits produced water to be discharged into surface waters if the discharged water quality meets Texas Surface Water Quality Standards (TSWQS) set by the Texas Commission on Environmental Quality (TCEQ) for the specific receiving water body.  After careful evaluation of data provided by the Railroad Commission of Texas, it is believed that nearly 5,331,975 m³ (4,321 ac⋅ft) of produced water per year, with an average TDS of 960 mg L^-1, is being removed from the Carrizo-Wilcox aquifer through discharge permits designated as “agricultural”. The RRC is not legally required to share the discharge information with local Groundwater Conservation Districts. Based on an evaluation of the reported Whole Effluent Toxicity (WET) test data, 69 discharges amount to total suspended solid (TDS) levels of less than 1,000 mg L^-1, 35 are between 1,000-1,500 mg L^-1, and 20 between 1,500 - 4,000 mg L^-1.  Although 69% of discharges exceed the secondary drinking water standard for TDS (500 mg L^-1), the average of all discharges, 960 mg L^-1, is in line with the arbitrary upper limit for freshwater based on the suitability for human consumption. In addition, the water quality of surface discharges complies with requirements for several water reuses associated with agricultural and industrial practices. The lack of communication between groundwater users leads to conflicting groundwater practices that have negative impacts such as contribution to aquifer over-exploitation and alteration of hydraulic gradients, in turn negatively impacting existing groundwater conservation efforts.