| Laboratory procedures were developed to evaluate change in soil hydraulic conductivity around subsurface drip emitters. A tank 110 cm in depth and 80 cm x 80 cm in cross section was constructed and packed with soil. A drip emitter was installed at the center of the tank at 0.20 m beneath the soil surface. The tank was supplied with domestic septic tank effluent. A soil moisture retention curve was determined at 10 cm x 10 cm grid points. The saturated hydraulic conductivity was determined at each grid point utilizing soil retention data.; A field study was performed in Weslaco, Texas, using an on-site wastewater treatment system receiving domestic wastewater. Triplicate soil samples were collected from the drip fields at different depths and distances from the emitter. The collected soil samples were analyzed for total nitrogen, potassium, phosphorus, sulfate, sodium, calcium, magnesium, salt content, and total organic carbon. Undisturbed soil core samples were collected from different depths and distances from the emitter. The undisturbed soil cores were utilized to determine saturated hydraulic conductivity, pore size distribution, and soil water retention.; A mathematical model was developed to simulate transient flow from a subsurface drip emitter in anisotropic and nonhomogenous variably-saturated porous media. A finite difference scheme was used to approximate the flow equation in space and time. Model results were tested utilizing experimental data and by comparing with results from available analytical solutions.; The developed laboratory procedure provides a method to evaluate changes in soil saturated hydraulic conductivity with time and distance from the emitter without destroying the soil profile. Results of the field study indicate that application of wastewater resulted in an increase in the soil water retention, a decrease in the volume of pores with large radii, and a decrease in saturated hydraulic conductivity. The most pronounced influence of applied effluent on soil hydraulic properties occurred in the area below the emitter. Comparison of model results with the analytical solution and experimental data indicated that the model precisely simulated flow from a subsurface drip emitter. |
