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Environmental Health - Toxic Substances


U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings of the Technical Meeting, Colorado Springs, Colorado, September 20-24, 1993, Water-Resources Investigations Report 94-4015

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Potential Long-Term Effects of Phosphate Contamination in a Sand and Gravel Aquifer, Cape Cod, Massachusetts


Kenneth G. Stollenwerk (U.S. Geological Survey, Denver, Colo.)


Phosphate in the Ashumet Valley sewage plume, located near Falmouth, Massachusetts, could increase the rate of eutrophication in Ashumet Pond. A series of column experiments has been initiated to identify the geochemical processes affecting transport of phosphate in this aquifer. The principal focus of these experiments is to determine the amount and rate of phosphate desorption from aquifer sediment after sewage disposal is stopped. The first set of column experiments simulated the oxic zone that surrounds the core of the plume. Results indicate that the sediment has a relatively high capacity to adsorb phosphate and that adsorption is kinetically controlled. The rate of desorption is slow. Approximately 160 pore volumes were eluted before the phosphate concentration decreased to levels considered not to cause eutrophication; half the phosphate was still adsorbed on the sediment. A one-dimensional solute transport code simulated the column data reasonably well; however, a kinetic term needs to be included in the model to improve accuracy.

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