| The Paluxy aquifer in north-central Texas is a minor aquifer composed primarily of Cretaceous age clastics. The examination of water from twenty-seven wells in the study area reveals pronounced chemical evolution. Shallow, up-dip waters are dominated by Ca2+ and HCO3 -. The most likely source of these dominant cations and anions in this portion of the aquifer is from dissolution of calcite cement and reaction of dissolved CO2 with silicate minerals. Down-dip, Na+ and HCO3- dominate the water chemistry. The change in the dominant cation is a result of cation exchange with clays. In the deepest portion of the aquifer the water evolves into a Na+ and SO42- dominated water. 87Sr/86Sr and delta 34S of Paluxy water in the deepest parts of the aquifer reflect Cretaceous rock values, therefore, the groundwater chemistry in this portion of the aquifer is a result of mixing of water from the underlying Cretaceous Glen Rose Limestone with Paluxy water.; Using the GRASS 4.1 Geographic Information System combined with a modified DRASTIC approach, allows one to assess the groundwater vulnerability of the Paluxy aquifer. Using this method of investigation, the pollution potential map for the study area classifies 47% of the area as having low vulnerability, 26% as having moderate vulnerability, 22% as having high vulnerability, and 5% as having very high vulnerability to contamination. These results are based on the evaluation of variables such as depth to water, net recharge, aquifer media, soil media, topography, impact of the vadose zone and conductivity of the aquifer.; Combining the results of the vulnerability assessment with land use/land cover data allows one to evaluate the pollution susceptibility of the Paluxy aquifer. The pollution susceptibility map classifies 32% of the study area as having low pollution susceptibility, 41% as having moderate pollution susceptibility, 25% as having high pollution susceptibility, and 2% as having very high pollution susceptibility. When comparing these modeling results with water chemistry data from wells within the Paluxy aquifer, the four wells with the highest concentration of nitrate contamination are all found within regions of very high pollution potential. |
