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United States Department of Agriculture

Agricultural Research Service

Title: Vadose Zone Clay Lens Impacts on Groundwater Loading Rates

Authors
item Bosch, David
item Truman, Clinton
item Davis, Frank

Submitted to: International Symposium on Preferential Flow
Publication Type: Proceedings
Publication Acceptance Date: December 20, 2000
Publication Date: January 3, 2001
Citation: BOSCH, D.D., TRUMAN, C.C., DAVIS, F.M. VADOSE ZONE CLAY LENS IMPACTS ON GROUNDWATER LOADING RATES. INTERNATIONAL SYMPOSIUM ON PREFERENTIAL FLOW. Pp. 69-72. 2001.

Interpretive Summary: Transport of agricultural chemicals from the upper foot of the soil into lo areas in the soil profile results in decreased effectiveness, economic loss and adverse environmental impacts. Once below the upper soil horizon, the transport of agrichemicals is dramatically effected by the properties ofthe deeper soil horizons. A detailed field and modeling study was conducted to characterize the impact of these deeper soil features on the quality of th water recharging ground water. These features were expected to increase the contaminant yields to the ground water by concentrating the water flow. However, while point observations of flows to ground water increased, the composite effect decreased overall groundwater contamination. The period over which the solutes were delivered to the water table was increased, decreasing the concentration of contaminant going into the ground water at any one time.

Technical Abstract: Pesticide leaching to ground water has been shown to be a significant environmental problem. Detailed investigations conducted on a 1 ha corn field near Plains, Georgia indicated that clay lenses 18 to 30 feet below the ground surface altered the flow of water and water soluble agrichemicals. High pesticide concentrations in this area of the soil and significant concentrations in ground water were observed. A computer simulation model (VS2DT) was used to quantify transport rates and examine the impacts of preferential flow along clay lenses. The lenses induced ponded water in the vadose zone and redirected flow. While point observations of solute concentration of flows to ground water increased in some positions under the clay lens, the composite effect decreased overall groundwater contamination. The lenses increase the period over which the solutes were delivered to the water table, decreasing the concentration i ground water at any one time.

Last Modified: 9/22/2014
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