Spati Al Analysis of No3 N Concentration in Glacial Till

Analysis of the spatial variability of groundwater NO3 N concentration is a logical step for a meaningfulgroundwater quality assessment, for mapping out areas of environmental concern, and for developing appropriatemanagement schemes in a glacial till aquitard. This study was conducted to characterize the spatial variability of NO3 Nconcentration in shallow (<6.0 m) and deep (>6.0 m) groundwater in a 12ha. glacial till aquitard and to estimate NO3 Nconcentration in unsampled locations. Omnidirectional and directional semivariogram analysis, statistical anisotropyanalysis, and model fitting were performed for average and extreme monthly groundwater NO3 N data. Results indicated aweak spatial structure of NO3 N concentration for both shallow and deep well data. However, the bestfitted variogrammodels generally performed satisfactorily during cross validation, yielding a mean reduced error of 0.01 to 0.074 andreduced variance of 0.6 to 2.18. Untransformed shallowwell NO3 N exhibited a lower range of correlation than deepwelldata. Statistical anisotropy was found to coincide with the general groundwater flow directions for the average and maximumobserved NO3 N concentrations in shallow wells. Geostatistical estimation using ordinary kriging indicated relatively higherNO3 N concentrations at the downgradient areas for shallow wells and at regions close to nitrogen fertilizer applicationsites for the deep wells. With satisfactory crossvalidation performance of the variogram models, the geostatistical resultsof this study may be used as basis for estimating spatially variable NO3 N loading rates in the glacial till aquitard.