Spatial analysis and simulation of selected hydrogeologic and groundwater quality parameters in a glacial till aquitard

Assessment of the variability of groundwater quality or nutrient loss in a glacial till aquitard necessitates spatial analysis and simulation of hydrogeologic properties and groundwater quality parameters. Geostatistical analysis was performed to characterize the spatial behavior of hydraulic conductivity obtained from slug tests and NO3-N groundwater concentration observed in spatially scattered shallow and deep wells. Ordinary kriging was employed to determine values of these parameters at unsampled locations. Numerical simulation of groundwater recharge was consequently performed using a three-dimensional transient inverse groundwater modeling approach. Nitrate-Nitrogen loading rates were similarly estimated. A comprehensive evaluation of the groundwater quality at two selected glacial till sites in terms of NO3-N and herbicide occurrence and distribution during the most recent years was also carried out;Results of this research indicate that the hydraulic conductivity of the glacial till aquitard averaged 1.9 x 10-6 m/s and 9.6 x 10-8 m/s for the oxidized and unoxidized till layers, respectively, and exhibited a highly erratic spatial behavior. Groundwater NO3-N concentrations similarly exhibited a poor spatial structure. Groundwater recharge ranged from 18.7 mm/yr to 33.2 mm/yr, corresponding to 2.3% to 4.3% of the annual precipitation in the area. On the other hand, NO3-N loading rates ranged from 0.53 kg/ha to 0.75 kg/ha over the last five years. Groundwater NO3-N concentrations at the selected glacial till sites indicated field average values lower than the EPA\u27s drinking water standard of 10.0 mg/L, although a number of individual shallow wells exhibited concentrations exceeding this level. Herbicide concentrations observed at both sites were all below the established drinking water standard