Texas Groundwater Wells and Unconventional Oil and Gas Brines Pollution




Njesada, Ndolembai


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  1. Objective: A comparative study of groundwater quality in Texas was performed to assess the impact of oil drilling, unconventional shale gas horizontal drilling and hydraulic fracturing (fracking) technology on groundwater quality during years 2000-2007 and 2008-2015 given the increased number of fracking wells and production in the last eight years. This study analyzed whether anthropogenic activities from natural gas extraction has affected the salinity of groundwater using accepted brines ratio (Na+ to & Cl-) to Total Dissolved Solids (TDS) commonly used in evaluating brine impact from oil extraction.
  2. Material and Methods The data was from the United States Geological Society (USGS) Water Quality Samples for the Nations: Discrete Water Quality Samples database of historical conductivity field readings. The dataset is a comprehensive set of water constituents comprising decades of collections. Specific ratios of chemical constituents have been determined to reflect impact of energy extraction on water quality. In line with this determination, we analyzed chloride and sodium (mg/L), dissolved solids or TDS, and strontium (mg/L). The ratios of (Na+ + Cl-)/ to TDS, lithium to bromide, sodium to chloride, sodium to bromide, or bromide to chloride individually or collectively were analyzed, as they are indicators of water pollution by brines when exceeding a corresponding threshold.
  3. Results If a ratio of (Na+ + Cl-)/ TDS is greater than or equal to 0.64, it is an indicator of pollution of water by brines. A total of 11,786 wells were statistically analyzed. Chi square (X2) statistical test was used for the unadjusted data, and logistic regression was used for the adjusted variable to assess the groundwater and fracking brines’ pollution. For the unadjusted analysis, the P-value (0.005) is significant, as it shows a negative association. When controlling for wells used for public supply and irrigation use, the result is statistically significant, with a negative association (-.0014). These results suggest that groundwater wells from 2008 to 2015 have a lower level of brines despite the increase in fracked wells in Texas. The decrease in brines does not imply that the quality of groundwater has improved.
  4. Conclusion The brine ratio used to assess the impact of oil extraction on water quality indicated that the salinity of groundwater wells seems to improve as years pass. The (Na+ + Cl-) to TDS ratio may not be an appropriate predictor of the impact of natural gas extraction on water quality. The reduction of brines concentration overtime does not necessarily mean the groundwater quality has improved. Further statistical analysis will be conducted examining chemical constituents’ relationships to determine if a more predictive ratio reflective of natural gas extraction impact can be generated.