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THE ROLE OF NATURAL BIOLOGICAL PROCESSES IN THE NATURAL ATTENUATION OF CONTAMINANTS IN GROUND WATER
Citation:
Wilson*, J T. THE ROLE OF NATURAL BIOLOGICAL PROCESSES IN THE NATURAL ATTENUATION OF CONTAMINANTS IN GROUND WATER. European Conf. on Natural Attenuation, Heidleberg, Germany, 10/15-17/2002.
Description:
As a practical matter, the time required for a site to reach cleanup goals is controlled by the rate of natural attenuation of the source of contamination, not the rate of natural attenuation of the contaminants once they are in the ground. As a consequence, in the USA the most common application of natural attenuation is to control the source of contamination through excavation, in-situ destruction, capping or containment, followed by monitored natural attenuation of the pre-existing contaminants in ground water. Once the source is removed or contained, the time required for natural attenuation to clean-up the ground water plume is controlled by the maximum concentrations remaining in the plume, the clean-up goal, and the rate of attenuation of contaminants in the plume. If the source is left in place, the extent of contamination (the perimeter of the plume) is controlled by the maximum concentration remaining, the clean-up goal, the rate of attenuation of contaminants in the plume, and the seepage velocity of the ground water. The relative contribution of biological processes was evaluated by calibrating the model BIOSCREEN (USEPA, 1996) to a series of hypothetical plumes, using a variety of initial concentrations of contaminant and a variety of plume seepage velocities. Natural biological degradation is the major process contributing to natural attenuation. Dilution and dispersion may meet goals within a reasonable time frame when the initial concentrations are 1,000 g/L or less, and when seepage velocities are 35 meters per year or more. When concentrations are higher, or seepage velocities are smaller, there is little chance that dilution and dispersion alone will attenuate the plumes. When the rate of natural biological degradation is 1.0 per year, all the simulations reached the goal in a reasonable time frame.