BUILDING COMMUNITY-BASED WATER RESOURCE SUSTAINABILITY AND RESILIENCE: A CASE STUDY OF SHALLOW GROUNDWATER AVAILABILITY AND VULNERABILITY IN SOUTH TEXAS

The South Texas Sand Sheet (STSS) covers six counties and consists predominantly of medium to fine grain eolian sand deposits and sand dunes. Estimated STSS’ thickness varies between a few centimeters to tens of meters. Groundwater contamination is of concern as groundwater resource is the main water source for agricultural activities in this area. The preliminary conceptual model implies that the STSS is a significant hydrologic component and has potential for water storage and resource management. Water (fresh/brackish) held in the STSS should be considered when managing regional water sources, e.g., groundwater recharge and storage, flood control, and discharge to coastal areas. Geospatial analysis was conducted using digital elevation model (DEM) data with GIS spatial analysis tools using preliminary drilling from field and well logs from Texas Water Development Board (TWDB) groundwater database to develop subsurface 3D model for STSS in GIS and Rockworks. A DRASTIC model developed within a GIS framework was then used to evaluate the groundwater vulnerability of the STSS. Predicted groundwater vulnerability index suggests that areas with high risk to pollution are mainly located in the eastern portions of the STSS, which are closely attributed to the hydrogeologic environments and landscape factors affecting how contaminants can move into the subsurface and shallow groundwater. Kenedy County for instance is almost entirely within the zone with high vulnerability. These results can provide a preliminary screening tool for regional water resource management, headwater protection, mitigation planning, and emergency responses in and around the STSS. Results can also be used to evaluate and build resiliency to environmental and economic impacts to the adjacent Lower Laguna Madre (LLM), which is one of the important lagoon ecosystems on the Texas coast.