119 Recent Investigations of the Hydrogeology Edwards (Balcones Fault Zone) Aquifer, the Trinity (Hill Country) Aquifer, and Their Interactions, South-Central Texas

Recent research into the hydrogeological characteristics of the Edwards (Balcones Fault Zone) and/or Trinity (Hill Country) aquifers, south-central Texas, including their inter-aquifer connections, vulnerability, and prospects for long-term sustainability given changes in population, land use, and climate of the region.

Monday, 20 October 2025
1:30 PM - 5:30 PM
HBGCC, 209

PFAS and Water Quality Indicators of Aquifer Vulnerability in the Edwards–Trinity System

Paper number: 119-12
Program: Technical Sessions
Time: 4:30 PM – 4:45 PM

Authors

Abstract

The Edwards and Trinity aquifers in South-Central Texas are increasingly vulnerable to contamination due to expanding urbanization, wastewater discharge, and atmospheric deposition. This study combines PFAS analysis with conventional water quality monitoring to assess surface and subsurface contamination in the Cibolo Creek watershed and nearby recharge zones between February 2021 and January 2023.

 

PFAS compounds were detected across spring and stream samples using EPA Method 533 and LC-MS/MS. A total of 73 surface water and groundwater samples were collected over a two-year period, with 20 PFAS compounds analyzed quantitatively—including 9 perfluorocarboxylic acids (PFCAs), 4 perfluorosulfonic acids (PFSAs), 3 fluorotelomer sulfonates (FTSAs), 2 perfluoroether carboxylic acids (PFECAs), and 2 perfluoroether sulfonic acids (PFESAs).

 

Total PFAS concentrations ranged from 4.58 ng/L to 77.51 ng/L, with a mean of 22.55 ng/L. The most abundant compounds were PFOS (3.99 ng/L), PFPeA (2.13 ng/L), PFBA (1.88 ng/L), and 8:2 FTS (1.78 ng/L). Positive correlations were observed between PFHxA and PFHpA, 8:2 FTS and PFDA, and PFBS and PFHxA, suggesting potential inputs from aqueous film-forming foams (AFFF). No spatial trends were evident for FTSA, PFECA, or PFESA.

 

In the Cibolo Creek watershed, PFCA and overall short-chain PFAS concentrations declined downstream in rural sites but increased in urban zones. Short-chain PFAS were lowest in summer months and increased nearly two-fold during winter and spring. Although no consistent patterns emerged for individual compounds, total PFAS concentrations increased up to 2.6 times after heavy rainfall events compared to dry or steady-rain periods.

 

Water chemistry data from the same sites reveal elevated sodium, chloride, and nitrate levels, further underscoring anthropogenic impacts. These trends correspond spatially with PFAS concentrations and indicate contributions from both point and non-point sources.

 

The integration of PFAS concentration mapping, ion chemistry, and hydrogeologic context provides a comprehensive assessment of contaminant risk in this vulnerable karst setting. Findings underscore the need for enhanced monitoring in recharge areas and proactive land-use planning to protect water quality in one of Texas’s most productive aquifer systems.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-413674

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