Inverse Application of Age-Distribution Modeling Using Environmental Tracers super(3)H/ super(3)He

As issues of source water protection of drinking water supplies have come to the forefront, the methodology to effectively manage semiconfined aquifers is still unclear. Commonly, the area around the wellhead is considered the most risk sensitive area, but in semiconfined settings the most sensitive areas may be located some distance away from the wellhead. This research employed the use of age-distribution modeling in concert with environmental tracers (tritium/helium-3), geochemical, and other hydrogeologic data. A synthetic test case was developed to determine the suitability of the technique for identifying localized areas of recharge to a wellhead in aquifers where evidence of modern water infiltration exists. Results of the model runs based on the synthetic test case indicate that the technique presented herein is capable of identifying localized areas of recharge contributing to a wellhead, in a semiconfined aquifer setting, with only a limited amount of required data. These results and the relative ease of application make this technique a valuable tool for obtaining a greater understanding of the flow regime at a wellhead, which in turn provides more information for risk assessment of public water supplies.