Contamination Attenuation Indices for Sandy Soils: Tools for Information Transfer

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07/01/1990 - 06/30/1991

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  • Kevin McSweeney, UW-Madison
  • Fred Madison, WGNHS

The inherent characteristics of sandy soils–rapid permeability, low organic matter and clay content, limit their ability to degrade and attenuate movement of contaminants.  In areas with shallow aquifers overlain by sandy soils, the risk of contamination is generally considered great.  Nevertheless, well monitoring data and column studies have shown differences in rates and amounts of atrazine leakage beneath seemingly similar sandy soils.  Intrinsic differences among these soils may explain the differences in transport rates.  The objective of this study was to characterize the major chemical properties of the mineral and organic components of five sandy soils (representing a broad range of the variation found in the State) and relate them to adsorption of atrazine.

The estimates of the secondary crystalline Fe-oxides and noncrystalline Fe- and Al-oxides did not significantly correlate with the adsorption coefficients (Kd) of atrazine.  No significant correlation resulted between the clay content, silt content and pH, and the Kds.  The amount of organic carbon (% OC) was the most important constituent in terms of atrazine adsorption, the correlation coefficient (r) was 0.95. When the correlation was done by horizon, r increased to 0.98 for the A horizons, and decreased to 0.85 for the B horizons.  Physical properties that affect rate and pathways of water movement differ among the soils examined.  We postulate from data obtained in this and allied studies, that sandy soils with very uniform grain size and no morphological evidence of hydrological discontinuities are associated with rapid transport of water and probably less potential for contaminant adsorption than those with more heterogeneous particle size distributions.

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