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Dokou, Zoi

Civil and Environmental Engineering

PhD

DNAPL (Dense Non-Aqueous Phase Liquid) contamination poses a major threat to the groundwater supply, thus, success remediation of the contaminated sites is of paramount importance. Delineating and removing the DNAPL source is an essential step that renders remediation successful and lowers the estimated remediation time and cost significantly. This work addresses the issue of identifying and delineating DNAPL at its source. The methodology employed here is based upon the rapidly evolving realization that it is unlikely to identify and adequately define the extent of a DNAPL source location using field techniques and strategies that focus exclusively on directly locating separate phase DNAPL. The goal of this work is to create an optimal search strategy in order to obtain, at least cost, information regarding a DNAPL source location. The concept is to identify, prior to a detailed site investigation, where to initially sample the subsurface to determine the DNAPL source characteristics and then to update the investigative strategy in the field as the investigation proceeds.
The search strategy includes a stochastic groundwater flow and transport model that is used to calculate the concentration random field and its associated uncertainty. The model assumes a finite number of potential source locations. Each potential source location is associated with a weight that reflects our confidence that it is the true source location. After a water quality sample is selected, an optimization algorithm is employed that finds the optimal set of magnitudes that corresponds to the set of potential source locations. The simulated concentration field is updated using the real data and the updated plume is compared to the individual plumes (that are calculated using the groundwater flow and transport simulator considering only one source at a time). The comparison provides new weights for each potential source location. These weights define how the concentration realizations calculated by the stochastic groundwater flow and transport model will be combined. The higher the weight for a specific source location, the more concentration realizations generated by this source will be included in the calculation of the mean concentration field. The steps described above are repeated until the weights stabilize and the optimal source location is determined. The algorithm has been successfully tested using various synthetic example problems. of increasing complexity. The effectiveness of the search strategy in identifying a DNAPL source at a field site by performing a 'blind test' is also demonstrated. The site chosen for the test is the Anniston Army Depot (ANAD) in Alabama. The contaminant of interest at the site is trichloroethene (TCE).