Factors affecting public-supply well vulnerability in two karst aquifers.
Bottom Line: The geochemistry of samples from a selected PSW or wellfield in each aquifer was compared with that from nearby monitoring wells and regional PSWs.Geochemistry results were integrated with age tracers, flow modeling, and depth-dependent data to refine aquifer conceptual models and to identify factors that affect contaminant movement to PSWs.Specific consideration of water-quality protection efforts, well construction and placement, and aquifer response times to land-use changes and contaminant loading are discussed, with implications for karst groundwater management.
Affiliation: U.S. Geological Survey, Tallahassee, FL 32303.Show MeSH
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Mentions: Hydrogeologic flow models and particle-tracking were used to simulate the mixture of water of different ages produced by the selected PSWs (detailed by Crandall et al.  and Lindgren et al. ). Comparison of the resulting groundwater travel-time (age) distribution for water from the selected PSWs indicates that both are dominated by young (<10 years of age) groundwater (Figure 5). These results are consistent with measured age-tracer results and conceptual aquifer models, which are indicative of rapid flowpaths. Based on modeled age distributions, 88% of the water from the EA PSW is <5 years of age and 96% is less than 10 years of age; for the UFA PSW, 43% of the water is <5 years of age and 52% is less than 10 years of age. The UFA PSW has a larger component of slightly older water than the EA PSW, with 31% of the PSW water from 10 to 30 years in age, whereas only 4% of the EA PSW water is within this range. Young groundwater is inherently more susceptible to contamination and the dominance of young groundwater that contributes to the selected PSWs indicates that both aquifers are particularly susceptible to existing contamination sources (Figure 5). This susceptibility is confirmed based on frequent detections of nitrate and organic contaminants (Table 1; Figure 3).