Res 1984-074 - Laserfiche WebLink

Home Browse Search

INTRODUCTION Growth is rapidly accelerating in and qround San Marcos. This growth, if not properly planned, could adversely affect the quality of ground water in the Edwards Aquifer thus endangering the city's water supply in the San Marcos river. Past sampling of the San Marcos spring orifices suggests that the quality of the ground water deteriorates after storm events due to local contaminated storm water runoff infiltrating and recharging the Edwards Aquifer, Also ground water tracing experiments have shown that water in Ezell's cave (near Wonder World) travels to the city's wells at the end of Spring Lake within only seven days. Therefore, improperly planned development on the recharge zone or areas draining onto the recharge zone could adversely impact our water supply. Thus, it is important for the city to know the exact location of recharge points such as caves, sinkholes, faults, and fractures. It is also important to know more about the directions and velocity of ground water movement around San Marcos as well as the depth to the water table at the various environmentally sensitive areas. Ground water can be contaminated even where there are rocks overlying the Edwards Aquifer if this cover is too thin. In San Antonio, some of the ground water has already been contaminated by a landfill and a gasoline leak where the cover over the Edwards Aquifer was too thin. This demonstrated the need for a map that shows the thickness of cover over the Edwards Aquifer around San Marcos. Another needed map is one that outlines the small, first- order basins that feed into Purgatory and Sink creeks. Although much of San Marcos has developed on hills underlain by the rock sequences overlying the Edwards, much of the run-off from these areas rapidly flows into Pyrgatory and Sink creek basins where the water quickly sinks and recharges the Aquifer. Special care should therefore be taken in many of the upland areas. Past studies performed by researchers from San Antonio and Austin have not been particularly detailed for the San Marcos area. Now that growth has the potential to affect our groundwater, the time has come to gather the geologic and hydrochemical data accumulated in the San Marcos area by the author of this proposa1, and combine this with published data, and new data collected from the proposed study pe¡'iod for the purpose of producing maps that can be used for land-use planning purposes. LOCATION OF STUDY AREA The proposed study area is shown on Figure 1.