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
Spatial Variability of Metal-Ion Adsorption and Hydraulic Conductivity
in a Sand and Gravel Aquifer, Cape Cod, Massachusetts
Kathryn M. Hess (U.S. Geological Survey, Marlborough, Mass.),
James A. Davis (U.S. Geological Survey, Menlo Park, Calif.), Christopher
C. Fuller (U.S. Geological Survey, Menlo Park, Calif.), and Jennifer A.
Coston (U.S. Geological Survey, Menlo Park, Calif.)
The spatial variability of metal-ion adsorption and hydraulic conductivity
was assessed from the results of laboratory experiments on 375 sediment
samples collected from 14 boreholes in a glacial outwash, sand and gravel
aquifer on Cape Cod, Massachusetts. Zinc and lead adsorption were measured
in batch experiments. Hydraulic conductivity was estimated on the basis
of grain-size distributions. Mean lead adsorption is greater than mean zinc
adsorption; mean hydraulic conductivity is similar to that measured previously
in this aquifer. All three properties vary significantly within the aquifer;
variability in zinc adsorption is greater than variability in lead adsorption.
A strong positive correlation is observed between the two metal-ion adsorptions.
There is a statistically significant, but small, negative correlation between
lead adsorption and hydraulic conductivity and a statistically insignificant
negative correlation between zinc adsorption and hydraulic conductivity.
Vertical correlation scales obtained by fitting an exponential model to
experimental semivariograms equaled 0.10-0.26 meters for the hydraulic-conductivity
and adsorption data sets. Similar vertical correlation scales were determined
in an earlier study of the variability of hydraulic conductivity measured
by use of permeameter and flowmeter tests. A horizontal correlation scale
could not be identified in this study, possibly because the horizontal spacing
between boreholes was large relative to the correlation scale, and the number
of samples was small.