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May 2020 Bulletin

Integration Of Turbidity Plume Event And Geophysical Studies To Characterize Karstic Groundwater Flow At Barton Springs, Austin, Texas
By Mustafa Saribudak
Environmental Geophysics Associates (EGA), Austin, TX
During December 18-20, 2019, Main Barton Spring in Austin started discharging plumes of turbidity flows into the Barton Springs swimming pool (BSSP). Within a couple of days, the source was found to be a geothermal drilling site at a residential neighborhood, which is located about 4,000 ft to the southwest of the pool. During the drilling operation ten closed-loop geothermal wells were drilled into the karstic Edwards Aquifer. A draft summary report concluded that a void was encountered at a depth of 240 ft (73 m), and was likely connected to a karst conduit flowing to the BSSP (BSEACD, 2019). The report projected the approximate groundwater flow direction and pathway from the drilling site into the BSSP. The estimated pathway corresponds to a trough in the potentiometric surface (BSEACD, 2019) and previously published geophysical anomalies (self potential and resistivity imaging) to the south of the BSSP (Saribudak, et al., 2013; Saribudak and Hauwert, 2017). Geophysical anomalies indicate conduit and fault-like features in the study area, which strongly suggest that the groundwater flow from the drilling site follows the conduit anomalies further to the east; then flow bends to the north due to a potential fault, where the south gate (south Zilker Park) of the swimming pool is located.
Barton Springs is a major discharge site for the Barton Springs Segment of the Edwards Aquifer and is located in Zilker Park in Austin, Texas. Barton Springs is a perennial karst spring complex that has an average flow of about 60 ft3/s (1.73 m3/s) and sustains recreational (Barton Springs swimming pool, BSSP) and environmental flows (Hunt et al., 2019). The Main Barton Spring discharges into the Barton Springs pool from the Barton Springs fault and from a cave or conduit. Additional springs in the pool issue from fissures and gravel-filled solution cavities on the floor of the pool west of the fault. The Barton Springs Fault trends to the northeast and down-to-the-southeast motion of about 100 ft (30m). The thin-bedded limestone unit on the northwest side of the fault is the regional dense member (Person Formation) of the Edwards Group, and limestone unit on the southeast side (downthrown) is the Georgetown Formation (Figure 1). Northeast of the Main Spring and along the Barton Springs Fault is Eliza Spring, which is outside of the BSSP but is the largest habitat for the endangered Salamander species. Dye tracing has established a hydrologic connection between the Main Spring and Eliza Spring. Other springs in the complex are related but have different source areas (Hunt et al., 2019).
The purpose of this paper is to integrate the previous geophysical work with the new information from the sediment plume release to better characterize groundwater flow in the vicinity of the Barton Springs complex.
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