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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Association of Selected Metals with Colloidal and Suspended
Particulate Material in Shallow Ground Water and Surface Water at Pinal
Creek, Arizona
by
Judson W. Harvey (U.S. Geological Survey, Menlo Park, Calif.)
and Christopher C. Fuller (U.S. Geological Survey, Menlo Park, Calif.)
Abstract
Trace metals are potentially transportable as solid phases in ground
water and surface water in association with colloids or suspended particulates.
Field data that specifies the partitioning of metals between dissolved and
suspended solid phases is necessary for developing physically based models
of metal transport. The purpose of the present study was to determine colloidal
and suspended-particulate concentrations for selected metals in shallow
ground water and in streamflow of the perennial reach of Pinal Creek during
base-flow conditions. Concentrations of manganese (Mn), iron (Fe), nickel
(Ni), copper (Cu), and cobalt (Co) were measured in unfiltered water samples,
and compared with 0.45 µm (micrometer) and 0.001 m filtrates of the
same water samples. Total metal concentrations in unfiltered water were
partitioned into suspended particulate (>0.45 µm), colloidal (0.001
- 0.45 µm), and dissolved (<0.001 µm) components. Median
colloidal and suspended-particulate concentrations for Mn, Ni, Cu and Co
were several percent or less of total concentrations of those metals. In
contrast, the sum of Fe colloidal and suspended- particulate phases was
a large percentage of total Fe concentrations in some cases, which indicated
that a colloidal or particulate Fe phase was significant at Pinal Creek.
At present total Fe concentrations in suspension are low in shallow ground
water and in streamflow at Pinal Creek during base-flow conditions. Colloids
that do form do not appear to be significant sorbents of other trace metals,
compared to Mn and Fe solid phases on the streambed. Colloid- facilitated
metal transport will likely increase in importance if acidic ground water
(which has Fe greater than 50 milligrams per liter) reaches Pinal Creek.
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