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Geography, Geology and the Environment


Eric Peterson

Mentor Department

Geography, Geology and the Environment


Increase in chloride (Cl-) concentration in surface water and groundwater from anthropogenic sources including deicing salts, agriculture, septic effluents, and wastewater treatment plants is a growing cause for concern all over the world. In non-urban areas where there is less impervious surface cover, agriculture could account for a larger percentage of Cl-source in water systems. One of the major sources of Cl-in non-urban areas is potash (KCl), an agricultural fertilizer used annually to grow soybean and corn throughout the Midwest especially in Illinois. This study is being conducted in a saturated buffer zone (SBZ) adjacent to an agricultural field in McLean County with wells installed to monitor water chemistry. Samples collected from 34 locations on the site over a six-year period will be analyzed (for major ion concentration), with subgroups compared based upon location and time. Subgroups will be delineated based on location into: deep groundwater (DW), downgradient shallow groundwater (DGSW), upgradient shallow groundwater (UGSW), diversion box (DB), and stream (ST). While the seasons will be divided according to equinoxes and solstices, corresponding with agricultural practices: spring/planting (April - June), summer/growing (July - September), fall/harvesting (October - December), and winter/fallow (January - March). Anion and cation concentrations will be measured using both the Ion Chromatograph (IC) and Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES) respectively. Results from these analyses will be used to (1) identify the number(s) of contributory population of Cl- using cumulative probability plots calculated with Cl-and K+values and (2) assess seasonal variations in Clconcentration among the different subgroups using a two-way ANOVA test. Background concentration for Cl-will be established using cumulative percent probability from the analyzed samples. Inflection points representing “thresholds” of background concentration and other contributing population(s) will be determined using the cumulative probability plots of Cl-and K+ in the area. Two-way ANOVAs will be used to test Cl-and K+concentration against time (seasons) as well as location (subgroups). It is expected that there will be at least one or more contributing sources of Cl-and K+in the study area and that Cl-and K+concentration would be higher in the DGSW subgroup during the spring (planting) season and highest in the ST subgroup in the winter (fallow) season.

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