REFINING THE SPATIAL REGULATORY ZONES OF THE EDWARDS AQUIFER: CAN WE IMPROVE URBAN GROWTH PATTERNS?

The Edwards Aquifer in central Texas is comprised of three segments: The San Antonio Segment, The Barton Springs Segment, and the Northern Edwards Segment. All development projects that occur within the Edwards Aquifer Recharge Zone (EARZ) of these segments must undergo geologic assessments to identify karst features, and are reviewed by the Texas Commission for Environmental Quality (TCEQ) and other aquifer management entities where applicable. The TCEQ uses findings to determine project design considerations for potential groundwater contamination into the aquifer. The EARZ is currently only defined by the surface outcrop of the Edwards Group Limestone (Person and Kainer Formations), as no additional geologic, hydrologic, or environmental factors are considered when determining if a project area lies within the regulated zone or not. Additionally, no spatial aquifer vulnerability variation is used within the EARZ to identify zones that may be more susceptible to aquifer contamination than other areas.

Sufficient additional data exists to refine degrees of aquifer recharge vulnerability in the EARZ. These data include: 1. thousands of karst features recorded by previous geologic assessments and other surveys, 2. dye tracer studies, 3. surface hydrologic drainage patterns into losing streams, 4. land use-land cover relationships, 5. speleogenetic information, 6. geologic structural fabric, and 7. karst development variation in different geologic members of the Edwards Group limestone. By combining scaled sensitivity values for these metrics and possibly others in a GIS environment, it is possible to define zones of higher aquifer vulnerability and zones less sensitive within the EARZ as well as the adjacent contributing zone. Resulting spatial extents of this analysis could then identify zones of preferred urbanization in the rapidly growing region.