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
  
Potential Long-Term Effects of Phosphate Contamination in a
Sand and Gravel Aquifer, Cape Cod, Massachusetts
by
Kenneth G. Stollenwerk (U.S. Geological Survey, Denver, Colo.)
Abstract
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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