Digital simulation of chloride contamination of groundwater at Shadow Lawn subdivision, Stark County, Ohio

Abstract

Digital modeling technique of solute transport in groundwater was applied to a problem of chloride contamination of groundwater at Shadow Lawn Subdivision, Bethelem Township, Stark County, Ohio. A finite-difference solute transport model, known as USGS-MOCADI, and a finite-element solute transport model, known as SUTRA, were used to simulate the chloride contamination in the groundwater. Groundwater in the study area was contaminated by surface runoff with high chloride concentration from the County's salt storage facility. Some of the wells in the study area showed chloride concentration as high as 2820 mg/l during 1986. Chloride concentration was found to be high only in those wells with casing length set at 40 to 70 ft depth. The storage facility was abandoned in March, 1987 but chloride concentration is still high in the groundwater. As the source of contamination has been removed, chloride concentration will decrease naturally in the future. Historic data on piezometric head in wells was not available, hence the models were calibrated for chloride concentrations only. The time when the chloride contamination first reached the groundwater is not known. The USGS-MOCADI model was calibrated and verified using the split data technique. The data used were recorded during 1986 to 1988. The calibrated model was then used to predict chloride concentrations in the future. SUTRA model was also used to predict chloride concentrations in the future. The SUTRA model was not calibrated independently. Instead, the calibrated and verified parameters for the USGS-MOCADI model were used int he SUTRA model. The predicted chloride concentrations by the two models were found to be identical. The models predicted that chloride concentrations will decrease to less than 250 mg/l by the year 2006. The calibrated models can be used in the future for various aquifer management programs in the study area especially for groundwater contamination protection programs.