INFLUENCE OF HYDROLOGICAL CONDITIONS ON PUMP-AND-TREAT REMEDIATION IN A TCE-CONTAMINATED SITE, WONJU, KOREA

Abstract

Chlorinated solvents including trichloroethylene (TCE), tetrachloroethene (PCE), carbon tetrachloride (CT), and chloroform (CF) are common contaminants found in the groundwater of urban and industrial areas in Korea. The chlorinated solvent TCE has various uses across many industrial fields

for example, it has been used as a degreasing solvent, a heating transfer medium, and a solvent base. Recently, TCE has been detected in groundwater and soil in both residential and industrial areas in Korea. The study area is an industrial complex located in Wonju, Republic of Korea. Groundwater in the study area has been contaminated by TCE and CT. The main source of the chlorinated solvents has been identified as the Road Administrative Office (RAO) of Gangwon Province, and additional minor sources are scattered throughout the industrial area. The chlorinated solvents were mainly used by the RAO in laboratory tests over a 16-year period from 1981 to 1997. However, there are no accurate records of the amounts used or the treatment of the waste chlorinated solvents in the main source area. Pilot tests of the pump and treat system were conducted in front of the main building of the RAO. The KDPW7 and KDPW8 wells were used as pumping wells to constrain the migration of TCE towards the downgradient area. The KDMW7, KDMW8, KDMW9, KDMW10, and SKW2 wells were used as monitoring wells to evaluate the effectiveness of the pump and treat system to constrain TCE migration. Pilot tests of the pump and treat system were performed five times over 139 days in the TCE contaminated aquifer, and both groundwater levels and TCE concentrations were measured at two pumping and five monitoring wells. Using the results of these tests, the relations between groundwater levels, TCE concentrations, and pumping rates were examined. The 1st, 2nd, and 3rd pilot tests were conducted during the wet season, while the 4th and 5th pilot tests were conducted during the dry season. During the wet season, the TCE concentrations were negatively correlated with the groundwater levels at both pumping wells and some of the monitoring wells because TCE concentrations were considerably diluted due to heavy rainfall. While at the other monitoring wells, they were positively correlated, which could be attributed to the influence of residual TCE around the wells. During the dry season, there were positive correlations at the pumping wells and most monitoring wells, which suggest that the influence of residual TCE in the dry season was greater than that in the wet season. TCE concentrations were also influenced by the pumping rates during high groundwater level periods, when residual TCE was involved. However, TCE concentrations did not show any correlation with the pumping rates in times of low groundwater levels because they were hardly influenced by residual TCE, which suggests that residual TCE is present in the high groundwater level zone. Consequently, when the pump and treat approach is applied to this contaminated aquifer, the effects of rainfall and residual TCE in the unsaturated zone should be considered.