Development and Field Evaluation of an Aquifer Stratification Testing System

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2006

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An aquifer stratification testing system was designed, constructed, and tested. The system was designed to characterize vertical profiles of both quantity and quality of water produced from actively pumping groundwater wells. During testing, all systems functioned properly and either met or exceeded anticipated performance requirements. The system was first tested in an irrigation well completed in the Edwards aquifer and owned by the Onion Creek Club located in Manchaca, Texas, just south of Austin. The purpose of the exercise was to assess test systems performance and to develop and refine testing procedures. Dye-tracer injection tests were performed at five depths from 325 to 405 ft, and a velocity/discharge profile was generated for that interval. The profile was consistent with the karst nature of the Edwards aquifer. Water sampling procedures were tested and evaluated, but no samples were analyzed.

Further testing was performed in two public water supply wells completed in the Ogallala Formation of the High Plains aquifer and belonging to the City of Wolfforth, Texas, to investigate arsenic and fluoride concentration distributions, which both exceed maximum contaminant level (MCL) standards for arsenic (10 μg/L) and fluoride (4 mg/L) in produced water. The results indicated vertical trends in both arsenic and fluoride aquifer concentration profiles, although concentrations at all depths exceeded MCL standards for both arsenic and fluoride. Despite distinctly different water discharge profiles between wells, a consistent inverse depth relationship between arsenic and fluoride concentrations was identified in both wells. Aquifer arsenic concentrations generally decreased, and aquifer fluoride concentrations generally increased with increasing depth. Aquifer arsenic concentrations ranged from 11.4 to 14.1 μg/L in Well 8 and from 16.0 to 22.2 μg/L in Well 5. Aquifer fluoride concentrations ranged from 5.53 to 7.98 mg/L in Well 8 and from 4.28 to 5.87 mg/L in Well 5.

Future system and procedural modifications should focus on improving and enhancing the flexibility and data acquisition capabilities of the system. Future field testing programs should be performed to develop a water quality stratification database to enhance general understanding of groundwater quality and flow processes and provide insight on potential contamination sources.

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