Investigating Groundwater Flow Between Edwards and Trinity Aquifers in Central Texas

Abstract

Understanding the nature of communication between aquifers can be challenging when using traditional physical and geochemical groundwater sampling approaches. This study uses two multiport wells completed within Edwards and Trinity aquifers in central Texas to determine the degree of groundwater inter-flow between adjacent aquifers. Potentiometric surfaces, hydraulic conductivities, and groundwater major ion concentrations and Sr isotope values were measured from multiple zones within three hydrostratigraphic units (Edwards and Upper and Middle Trinity aquifers). Physical and geochemical data from the multiport wells were combined with historical measurements of groundwater levels and geochemical compositions from the region to characterize groundwater flow and identify controls on the geochemical compositions of the Edwards and Trinity aquifers. Our results suggest that vertical groundwater flow between Edwards and Middle Trinity aquifers is likely limited by low permeability, evaporite-rich units within the Upper and Middle Trinity. Potentiometric surface levels in both aquifers vary with changes in wet vs. dry conditions, indicating that recharge to both aquifers occurs through distinct recharge areas. Geochemical compositions in the Edwards, Upper, and Middle Trinity aquifers are distinct and likely reflect groundwater interaction with different lithologies (e.g., carbonates, evaporites, and siliceous sediments) as opposed to mixing of groundwater between the aquifers. These results have implications for the management of these aquifers as they indicate that, under current conditions, pumping of either aquifer will likely not induce vertical cross-formational flow between the aquifers. Inter-flow between the Trinity and the Edwards aquifers, however, should be reevaluated as pumping patterns and hydrogeologic conditions change.

Relay Ramp Structures and Their Influence on Groundwater Flow in the Edwards and Trinity Aquifers, Hays and Travis Counties, Central Texas

“…Studies have long recognized the importance of faulting for the development of the Edwards Aquifer (Hill and Vaughan, 1898;DeCook, 1963;Sharp, 1990). More recently, studies have addressed the hydrologic connection within the Edwards and Trinity Aquifers Gary et al, 2011;Wong et al, 2014;Smith et al, 2015) with some studies focusing on structure (Ferrill et al, 2008). However, the influence of faults and the related "relay ramp" structures on groundwater flow have not been fully characterized.…”

New occurrence records for Eurycea sosorum Chippindale, Price & Hillis, 1993 (Caudata, Plethodontidae) in Travis and Hays counties, Texas, USA

“…Although the Edwards and Trinity aquifers have historically been treated as distinct hydrogeologic units from scientific and management perspectives, recent work provides evidence of lateral continuity between the two aquifers, with Onion Creek specifically acting as an important hydrologic link (Wong et al 2013, Hunt et al 2015. Eurycea sosorum has not been documented from the northern portion of the contributing zone in the upper Barton Creek watershed, but this species may eventually be found there considering its occurrence in this drainage downgradient over the recharge zone.…”

Geophysical mapping of Mount Bonnell fault of Balcones fault zone and its implications on Trinity-Edwards Aquifer interconnection, central Texas, USA

“…The Upper Glen Rose member underlying the Edwards Aquifer units has historically been interpreted as a confining zone (Rose, 1972; Edwards Aquifer website: http://www.edwardsaquifer.net/geology.html). However, recent awareness of a significant connection between the Edwards and Trinity aquifers has resulted in a number of hydrogeologic investigations documenting that they actually operate as a single system in some locations and under certain circumstances (Smith and Hunt, 2010;Gary et al, 2011;Wong et al, 2014, Hunt et al, 2015. Wong et al (2014) indicates that the uppermost 150 ft (46 m) of the Upper Glen Rose is likely part of the Edwards Aquifer, while the remainder of it is an aquitard, and portions of Upper Glen Rose are karstic.…”