A four-layer model for interpreting electrical conductivity measurements of clay soils near agricultural lagoons

Abstract

Three models were evaluated to determine their ability to predict pore water quality in the subsurface. The models interpret measurements of soil electrical conductivity taken with an electromagnetic meter. Three sites with complex clay soil profiles were chosen for evaluation. Data from the three sites were initially interpreted using a two-layer model. The results were inconclusive. The data were then interpreted using a four-layer model which provided results worse than the two-layer model. The four-layer model was reapplied using better inputs. Results were obtained which were better than the first two models. The improvement in results was caused by using borehole soil cores to estimate subsurface soil properties. The primary difficulty in applying the models was the estimation of soil parameters in the subsurface. With the complex soil profile of the three test sites, any advantage gained from using a more complex model was apparently lost to the increased number of soil parameters required. Although the models were unable to make precise predictions of electrical conductivity and anion concentration, all three were able to give good general estimates of pore water quality. These estimates of pore water quality can aid in the placement of observation wells.