A geomorphological strategy for conducting environmental impact assessments in karst areas, 1999, Veni G. ,

In their efforts to protect regional groundwater supplies, governmental agencies are increasingly requiring studies of karst areas and their features. In areas where tracer tests or geophysics are not required, funded, or otherwise feasible, geomorphological methods remain as the primary tool for assessing karst. This study proposes a geomorphologically-based environmental impact assessment strategy for karst areas. While it is supported with results from a study of the karstic Edwards Aquifer recharge zone on the Camp Bullis Military Training Installation, TX, USA, it is based on the study of several karst areas and is generalized to accommodate and be fine-tuned for regional variations. Biological and other resource issues can also be assessed with this strategy. The assessment identifies environmentally sensitive features and areas, as is often required to meet regulatory directives. In karst areas with relatively small features, excavation is a key tool for accurate assessment. Although the results of this study will help to better manage karst areas, proper management must be done on a regional scale. The highly permeable nature of karst precludes adequate management solely on a feature-by-feature basis. Studies on the relationship of water quality to impervious cover show adverse environmental impacts significantly increase when impervious cover exceeds 15% of a surface watershed. The Camp Bullis study finds similar impacts in its groundwater drainage basin, supporting the argument of 15% impervious cover as a regionally effective means of also protecting karst aquifers when coupled with protection of critical areas identified by field surveys.

Spatial and Temporal Recharge Variability Related to Groundwater Interconnection of the Edwards and Trinity Aquifers, Camp Bullis, Bexar and Comal Counties, Texas, 2011, Gary Marcus, Veni George, Shade Beverly, Gary Robin

Interconnection of the Trinity (Glen Rose) and Edwards Aquifers along the Balcones Fault Zone and Related Topics, 2011,

The proceedings volume contains nine contributions presented during the Karst Conservation Initiative Meeting held in February 17, 2011 at The University of Texas at Austin.

The Edwards and Trinity Aquifers are critical water resources, supplying high-quality potable water to over two million people in the greater Austin-San Antonio region of central Texas, USA. These Cretaceous carbonate aquifers are hydrogeologically juxtaposed by extensive Miocene tectonic deformation associated with the Balcones Fault Zone, where the younger Edwards Group limestone has been downthrown relative to the older Trinity Group. The karstic aquifers are managed separately by regional water regulatory entities, and they have been historically treated as independent systems, both scientifically and from a water policy standpoint. Recent awareness of a significant interconnection between the Edwards and Trinity Aquifers has resulted in a number of hydrogeologic investigations documenting how they may actually operate as a single system. Studies related to upland recharge variability (spatial and temporal), stream loss, phreatic dye tracing, multi-port well monitoring, geochemistry, biologic habitat analysis, geophysics, and groundwater modeling indicate that the two are much less separated than previously observed. Summaries of these investigations conclude that changes in management strategies may be required to properly protect the quantity and quality of water in the Edwards and Trinity Aquifers.

Contents (click to open individual articles)

Introduction and Acknowledgements 

I nterconnection of the Edwards and Trinity Aquifers, Central Texas, U.S.A. 
Marcus O. Gary 

Spatial and Temporal Recharge Variability Related to Groundwater Interconnection of the Edwards and Trinity Aquifers, Camp Bullis, Bexar and Comal Counties, Texas 
Marcus O.Gary, George Veni, Beverly Shade, and Robin Gary

Potential for Vertical Flow Between the Edwards and Trinity Aquifer, Barton Springs Segment of the Edwards Aquifer 
Brian A. Smith and Brian B. Hunt

Could Much of Edwards Aquifer “Matrix Storage” Actually be Trinity Aquifer Contributions from the Blanco River? 
Nico M. Hauwert

Geophysical Correlation of Haby Crossing Fault (Medina County) and Mt. Bonnell Fault (Travis County) and Their Implications on T-E Interconnection 
Mustafa Saribudak

Edwards Aquifer – Upper Glen Rose Aquifer Hydraulic Interaction 
R.T. Green, F.P. Bertetti, and M.O. Candelario

Interaction Between the Hill Country Portion of the Trinity and Edwards Aquifers: Model Results 
Ian C. Jones

Using Tracer Testing Data for Resource Management Planning 
Geary Schindel and Steve Johnson

Demonstrating Interconnection Between a Wastewater Application Facility and a First Magnitude Spring in a Karstic Watershed: Tracer Study of the Tallahassee, Florida Treated Effluent Spray Field 2006-2007  
Todd R. Kincaid, Gareth J. Davies, Christopher L. Werner, and Rodney S. DeHan

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GEOPHYSICAL INVESTIGATIONS OF THE EDWARDS-TRINITY AQUIFER SYSTEM AT MULTIPLE SCALES: INTERPRETING AIRBORNE AND DIRECT-CURRENT RESISTIVITY IN KARST, 2013, Gary M. O. , Rucker D. F. , Smith B. D. , Smith D. V. , Befus K.

Electrical and electromagnetic geophysical characterization is a proven tool for delineating obscured subterranean karstic features, such as caves, sinkholes, and solution enlarged fissures. Geophysical characterizations allow a wide range of deployment scales; airborne methods can accommodate a regional view on the order of kilometers, and ground-based methods can follow up with focused data on the order of meters. A helicopter frequency domain electro-magnetic (HFDEM) survey and ground-based direct-current electrical resistivity imaging (DC-ERI) geophysical studies at the Camp Bullis Military Training Site (Camp Bullis) in central Texas have been used to characterize permeability properties of the Edwards and Trinity Aquifers in the area. Results of three separate investigations identified zones of high density karst features and characterized specific karstic voids, including caves. In 2003, the USGS completed an HFDEM survey of Camp Bullis and nearby areas to map and image subsurface features related to the groundwater resources. The survey refined locations of mapped and previously unmapped faults and characterized the heterogeneity of the subsurface electrical signature. Karst mapping at Camp Bullis identified over 1500 features, and high density zones of features correspond with areas of high resistivity from the HEM data. DC-ERI surveys at several locations were used to infer and characterize known and hypothesized karst features. Site 8 suggests an inferred fault and 195dissolution feature. Two other sites were surveyed near major caves that directly recharge the Trinity Aquifer (indirectly to Edwards Aquifer) along Cibolo Creek. Integration of multi-scale geophysical datasets could be used to augment aquifer-wide recharge characterization and quantification.