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The waters edge: Hydrochemical interactions between the Platte River and the Lincoln Municipal Well Field, Ashland, Nebraska
Abstract
Lincoln's Municipal well field consists of 44 wells developed in an alluvial aquifer adjacent to the Platte River near Ashland, Nebraska. Induced recharge from the river is an important source of water for the well field. Water samples were collected on a periodic basis from the river and two transects of monitoring wells. The samples were analyzed for atrazine, major inorganic ions, and trace elements. Atrazine concentrations in the river and aquifer were much less than 1.0 ppb during late fall and winter, but increased to as high as 18.9 ppb during spring and summer. High levels were associated with runoff from upgradient agricultural lands (Snow and Spalding, 1988). There was approximately a 21 day lag time from the first detection of increasing atrazine concentration in the river to the first detection in monitoring wells immediately adjacent to the river. Velocities of atrazine movement ranged from 21 to 30 ft/day on one transect to 12 ft/day on another. Aquifer dispersivity had a linear increase with increasing distance and time. This linear increase made it possible to estimate contaminant concentrations in the well field. The concentration of inorganic ions was dominated by an evaporative-crystallization process followed by partial or complete resolution with rising river stage and ground water levels. Trace element concentrations were elevated in the near river zone. This was probably related to seasonal variations in river load and biological processes which resulted in changes in redox potential and precipitation/dissolution reactions. Barium and Sr were greater in concentration with depth. Other trace elements were more variable in concentration with depth. These variations indicated that Ba and Sr were derived mainly from limestone and shale bedrock units. Other trace elements were derived mainly from surface pollution. Contaminant transport modeling of a conservative tracer showed that 95% of all water produced by the well field was derived from induced recharge. This will be beneficial for well field planning and management.
Subject Area
Geology|Hydrology|Geochemistry|Environmental science
Recommended Citation
Davis, Ralph Kenneth, "The waters edge: Hydrochemical interactions between the Platte River and the Lincoln Municipal Well Field, Ashland, Nebraska" (1992). ETD collection for University of Nebraska-Lincoln. AAI9225469.
https://digitalcommons.unl.edu/dissertations/AAI9225469