SBIR-STTR Award

Predicting the rate of soil water movement and the impact of agri-chemicals on water resources is vitally important to managing agriculture, for optimizing productivity and minimizing environmental impact. Sophisticated models for making such predictions are available, but data OD soil hydraulic properties are difficult and often expensive to obtain. In fact, at depths below the root zone there is no field method available to determine what is often the single most important soil property, unsaturated hydraulic conductivity. The proposed research is directed toward developing a practical field tool to determine unsaturated hydraulic conductivity in situ in discrete intervals over any depth. In Phase I our first task is to compile existing analytical solutions that may be relevant to developing our unsaturated soil permeameter. The second task will be to evaluate the suitability of the existing solutions using mathematical analyses, as well as numerical simulations. We will also explore the feasibility of developing new analytical and numerically-based regression solutions. The third task is to assess the feasibility of developing field equipment necessary to satisfy the boundary conditions and data requirements specified by the mathematical model. In Phase II we would propose to construct and test the field equipment, and in Phase 111 the apparatus would be commercially developed and marketed.Applications:The application of our new methodology would provide a timely response to a very significant data requirement faced not only by many soil scientists, but also geotechnical engineers and hydrologists concerned about seepage from impoundments and land fills, hazardous waste movement in soil, remedial action programs, and high level radioactive waste storage in the unsaturated zone. Modelers and regulators will have significantly greater confidence in predictions of unsaturated flow and transport if a reliable tool is used to obtain data at all depths in the field at the scale of interest.

Sophisticated models are available for predicting the rate of soil water movement and the environmental impact of chemical migration, but sufficient data on soil hydraulic properties are difficult and expensive to obtain. There are few methods available to characterize both saturated and unsaturated hydraulic conductivity in situ, and these are usually very time-consuming, especially in low-permeable soil. The proposed research is intended to develop a new rapid, field permeameter to obtain both saturated and unsaturated hydraulic conductivity in situ from a single test. In Phase I we derived an approach modified from Philip's solution for ponded infiltration, which we applied to single ring infiltrometer tests under constant head conditions. For saturated hydraulic conductivity, the important information includes infiltration rate and position of the base of saturation above the wetting front. For unsaturated hydraulic conductivity, the new solution requires characterization of the water content profile. The analysis of data is based in part on type-curves and is readily programmable. In Phase II we propose to construct and test the new permeameter in the laboratory and field. The results of the new apparatus and analysis will be compared to extensive tests by other laboratory and field permeameters.

Anticipated Results:
The application of our new methodology would provide a timely response to a very significant data requirement faced not only by many soil scientist, but also geotechnical engineers and hydrologists concerned about seepage from impoundments and landfills, hazardous waste movement in soil, remedial action programs, and high-level radioactive waste storage in the unsaturated zone. Modelers and regulators will have significantly greater confidence in predictions of unsaturated flow and transport if a reliable tool is used to obtain data at all depths in the field at the scale of interest.