| Summary: | Contamination events at Oak Creek, which runs through Oregon State University
Research lands, prompted investigations into alternate transport mechanisms
for moving liquid effluent from OSU Diary lands to Oak Creek. Magnetometer
surveys conducted at the Diary identified magnetic signatures spatially
associated with sub-surface locations of drain tiles, a 12-inch pipe, and other
features. These pipes may provide alternate methods of transporting effluent
to Oak Creek. Magnetometer surveys in support of the contamination study
identified an interesting variability in the Earth's local magnetic field. Magnetic
signatures spatially associated with drain tiles appear strong in the western portion
of the site, but fade out in the eastern part of the site. The cause of this
variability was investigated by examining soil iron distributions.
The Field-scale soil iron distribution was determined using a colorimetric analysis
of extractions obtained from soil core samples. This study shows larger
concentrations of iron in the western portion of the site where the magnetic
signal is strong and lower concentrations of iron where the magnetic signal is
lower. Tile-scale iron distribution over the drain tiles and in control units were
analyzed using the same colorimetric technique. This study identified a disturbance
to the natural iron distribution over the tile in the western part of the
site due to soil mixing in the back-filled tile trench resulting in a contrast in
the magnetic data. In the eastern part of the site, where there is no magnetic
signature associated with the tile, the iron distribution over the tile looks similar
to the control unit results. Analysis of the soils determined that excavating
during tile installation disturbed soil horizons, but the iron has redistributed
itself to the pre-tile configuration effectively erasing the magnetic contrast that
existed shortly after tile installation.
This project has shown that iron redistribution can adversely affect the ability
of magnetometer surveys to identify drain tiles. This project also demonstrates
that soils must be looked at as dynamic systems rather than the more common
static system approach when evaluating the success of magnetometer surveys.
Applying a dynamic view of soils can help ground-based remote sensing surveyors
avoid costly, unproductive surveys. === Graduation date: 2003
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