Groundwater is an important source of freshwater supply in Thailand, particularly in dry season for non-irrigated area. Unfortunately, our groundwater supply has generally not been adequately protected from natural and anthropogenic contaminants. At least 2 subsurface contaminated sites in Thailand have been identified with extent of groundwater plume migration. Monitoring wells are drilled and numbers of groundwater samples are collected as typical steps in normal practice to delineate the contaminant plume. To accurately capture the extent of the plume, a large number of sampling wells are generally required. In most contaminated groundwater aquifer site characterization and/or remediation efforts, however, it is not economically feasible or operationally practical to fully characterize the full extent of contamination distribution with certainty, even in the most homogeneous aquifers. This paper aims to develop an inverse solution to estimate the amount of pollution, its source location, time origin, and other important hydraulic parameters based on input spatial concentration distribution from real observations which are typically limited. The developed inverse model is being tested within desirable confidence levels using the original contaminant profiles from 2 contaminant sites in Thailand. Compare to the traditional technique of random groundwater sampling technique, the sampling protocol developed from inverse probabilistic model can help delineate the plume more cost-effectively, and allow tracking backwards in time and space to identify pollutant origin. Further practice to predict future contaminant plume evolution may also be made possible.
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