PREFERENTIAL FLOW AND TRANSPORT OF NITRATE BENEATH FIELDS IRRIGATED WITH TREATED WASTEWATER IN FORD COUNTY, KANSAS

With increasingly limited groundwater resources, reuse of treated wastewater provides an alternative source of water for irrigation of crops and landscaping. A long-term irrigation project with treated wastewater south of Dodge City in Ford County, Kansas, is the focus of this study. The use of treated wastewater in that area, which consists of Harney and Ulysses silty clay loam soils, has resulted in high nitrate-nitrogen concentrations (10 – 50 mg/kg) throughout the upper 50-ft profile but at varying concentrations, suggesting that preferential flow processes have occurred at the proposed study area. Evaluation of the environmental impact of such land-use strategies needs to be made in order to determine if and when this process may impact usable groundwater at depth. The goal of this project is to estimate the leaching rates and time of arrival of N- (and Cl-) contaminants using preferential flow and N-cycling numerical modeling in combination with field and laboratory measurements at the study sites. This approach also aims in identifying key parameters and processes that influence N losses in agricultural soils and in facilitating evaluation of the environmental impact of different land use practices. To achieve these objectives we collected deep cores for physical, chemical, and isotopic properties characterization; installed neutron moisture probe access tubes and suction lysimeters for periodic measurements; sampled area monitoring, irrigation, and domestic wells; performed dye tracer experiments; and obtained climatic data, and crop and irrigation application rate data, and other additional information from an ongoing study in the area, which is managed by the Servi-Tech Agri/Environmental Consulting. All these data are now being used in the comprehensive N-cycling model RZWQM (which also accounts for preferential flow and transport) to identify key parameters and processes that influence N losses in the study area. This presentation details the initial data collection and analysis during the 1st year of this project and outlines the ongoing modeling and other analysis steps.