A New Method for Identification of Preferential Flow Paths at Sites of Groundwater Contamination

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9903103ButlerThe spatial distribution of hydraulic conductivity is a significant control on the movement of contaminants in the subsurface. A number of theories have been developed to quantify the influence of spatial variations of hydraulic conductivity on contaminant transport by using stochastic processes or fractal representations to model the conductivity variations. It is becoming increasingly apparent; however, that the modeling of the conductivity variations at a site be inadequate may have significant limitations in units composed of a complex mixture of lithologies. Clearly site-specific hydraulic conductivity distribution at a larger scale need to be quantified to reliably predicts contaminant movement in such systems. In particular, knowledge on laterally contiguous zones of high hydraulic conductivity, which serve as preferential flow paths, is often critical. The field identification of such zones, however, has proven difficult. Conventional field techniques provide information of a highly averaged nature or restricted to the vicinity of the test well. This research would develop a new field method for the estimation of spatial in hydraulic conductivity between wells. Although developed for the general task of estimation of hydraulic conductivity variations in saturated formations and this effective for the identify of preferential flow paths. This methodology involves three primary elements: 1) a recently proposed method for hydraulic tomography, 2) low-cost pressure sensors for drawdown measurements in the tubing used in multilevel sampling wells, and 3) geophysical survey data for stratigraphic control. Hydraulic tomography has the potential to produce images of the hydraulic conductivity distribution between wells at most detail than previously possible. Detailed information about vertical variations in pumping-induced head changes would be at obtained from the low-cost pressure sensors. Nonuniqueness would be addressed by using cross-hole ground-penetrating radar surveys to constrain the inversion process. The primary purpose of the research is a thorough theoretical and field assessment of this promising new methodology. The incorporation of such features into a site model should dramatically improve the quality of model predictions, thus leading to more reliable risk assessments and a more efficient allocation of resources for site characterization and remediation activities. The descriptions of hydraulic conductivity variations in the subsurface would have a level of detail that has not previously been possible. In addition, the information should help better relate hydraulic conductivity variations to their geologic origins and thus facilitate incorporation of geologic information into hydrogeologic investigations.9903103ButlerThe spatial distribution of hydraulic conductivity is a significant control on the movement of contaminants in the subsurface. A number of theories have been developed to quantify the influence of spatial variations of hydraulic conductivity on contaminant transport by using stochastic processes or fractal representations to model the conductivity variations. It is becoming increasingly apparent; however, that the modeling of the conductivity variations at a site be inadequate may have significant limitations in units composed of a complex mixture of lithologies. Clearly site-specific hydraulic conductivity distribution at a larger scale need to be quantified to reliably predicts contaminant movement in such systems. In particular, knowledge on laterally contiguous zones of high hydraulic conductivity, which serve as preferential flow paths, is often critical. The field identification of such zones, however, has proven difficult. Conventional field techniques provide information of a highly averaged nature or restricted to the vicinity of the test well. This research would develop a new field method for the estimation of spatial in hydraulic conductivity between wells. Although developed for the general task of estimation of hydraulic conductivity variations in saturated formations and this effective for the identify of preferential flow paths. This methodology involves three primary elements: 1) a recently proposed method for hydraulic tomography, 2) low-cost pressure sensors for drawdown measurements in the tubing used in multilevel sampling wells, and 3) geophysical survey data for stratigraphic control. Hydraulic tomography has the potential to produce images of the hydraulic conductivity distribution between wells at most detail than previously possible. Detailed information about vertical variations in pumping-induced head changes would be at obtained from the low-cost pressure sensors. Nonuniqueness would be addressed by using cross-hole ground-penetrating radar surveys to constrain the inversion process. The primary purpose of the research is a thorough theoretical and field assessment of this promising new methodology. The incorporation of such features into a site model should dramatically improve the quality of model predictions, thus leading to more reliable risk assessments and a more efficient allocation of resources for site characterization and remediation activities. The descriptions of hydraulic conductivity variations in the subsurface would have a level of detail that has not previously been possible. In addition, the information should help better relate hydraulic conductivity variations to their geologic origins and thus facilitate incorporation of geologic information into hydrogeologic investigations.