NEW INSIGHTS ON THE KARSTIC BARTON SPRINGS COMPLEX FROM MULTIPORT WELL DATA, AUSTIN, TEXAS.

Barton Springs (BS) is a karst spring complex located in Austin, Texas and fed by the BS Segment of the Edwards Aquifer. While the spring system has been studied extensively at the spring outlet locations, little monitoring well data exists in the vicinity of the spring complex, and thus little is understood about the hydraulics and water quality of the Edwards Aquifer and underlying Trinity Aquifer nearby to the BS outflow locations.

In 2024 a multiport monitoring well was installed south of Barton Springs Pool approximately 500 feet from the Main BS outflow. The multiport well is 560 feet deep and penetrates the entire thickness of the Edwards Formation and approximately 200 feet into the top of the Upper Glen Rose Formation (UGR) and has 15 monitoring zones hydraulically separated from one-another with inflatable packers within the borehole. Six hydraulic head profiles were collected from the multiport well between May and December 2024. Water quality samples were collected from 14 multiport zones and analyzed for pH, specific conductance (SC), temperature, and oxidation reduction potential (ORP).

Multiport head data showed similar head elevations across the Edwards Formation (zones 7-13), with 0.79-1.55 feet of difference across zones. Head elevation dropped significantly (31.6-48.2 feet) between the Edwards and Walnut Formation (zone 6) suggesting a hydraulic separation between the Edwards and underlying UGR in the vicinity of the BS complex. This contrasts with multiport data in the southern, upgradient portion of the BS segment of the aquifer, which showed hydraulic connectivity between the Edwards Formation and UGR. Heads in the UGR zones declined over the period of measurement, while Edwards zone heads showed short-term responses to rainfall events, suggesting that the Edwards zones are more closely linked to surface hydrology.

Water quality data varied between Edwards zones, with SC between 601.38-1510.3 uS/cm. Zone 7 had the lowest SC (601.81 uS/cm) and highest pH (7.88) indicating the large voids intersecting this zone may represent a karst conduit system which transmits younger meteoric water through the aquifer. UGR zones had significantly higher SC (1965.9-4587.1 uS/cm) which may indicate evaporite mineral dissolution and/or mixing with the saline Edwards Aquifer to the east.