USING GEOSTATISTICAL MODELING TO DETERMINE THE BEST REMEDIATION PLAN FOR AN ABANDONED FEEDLOT

Elevated nitrate-N concentrations have been identified in a domestic well in Henderson County, Kentucky. The source of the elevated nitrate-N is believed to be an abandoned dairy feedlot. Eight monitoring wells have been installed at the abandoned feedlot to better identify the source of nitrate-N, the extent of contamination, and the ground-water flow direction.

Two sets of soil cores were collected in and around the abandoned feedlot in order to locate areas of large quantities of manure organic matter, as well as large quantities of resulting nitrate-N, and to improve our understanding of the influence of fragipans and paleosols on the movement and fate of nitrate-N in the vadose zone above this hydrologic setting (deep loess over sandstone). Data indicate that organic matter levels decrease with depth, whereas nitrate-N concentration increases with depth, and that surficial organic matter positively correlates with deeper nitrate in a part of the farmstead.

One of the most important environmental factors affecting the balance between nitrate-N oxidation and reduction is soil moisture. Soil moisture depends on climate, soil properties, and landscape topography. Geostatistics were used to spatially characterize organic matter and the resulting nitrate-N, and non-parametric geostatistics (NPG) were used to relate the probability of specific soil conditions to the distribution of nitrate-N concentrations in deeper soil layers. Soil properties were considered to be spatially continuous, and soil moisture to be generally related to landscape position. NPG successfully described the spatially probabilistic distribution of water-saturated soil layers in the landscape. The analysis helped explain the areas with high surficial organic matter that were underlain by deeper soil low in nitrate-N. In these areas, the perched water was inducing denitrification. Existing soil maps showed an excellent relationship between the Loring soil and a high probability of water-saturated subsoil. Apparently, although surficial organic matter generated the nitrate-N found at the deeper depths, in some areas the nitrate-N was attenuated by landscape-induced denitrification.