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Solute-travel time estimates for tile-drained fields. III. Removal of a geothermal brine spill from soil by leaching
The time required to leach a slug of saline, sodic geothermal brine from the point of injection to the tile outlet of an artificially drained field is calculated. Sprinkler, complete, and partial ponding leaching methods are compared as a function of drain spacing and initial location of the spill, with ponding requiring more water but less time to leach brine out of the system for all situations except where the brine spill occurs near the midpoint between tile lines. Calculation results are presented in dimensionless parameters which scale the drainage system dimensions and the soil water transport properties. A simple calculation is proposed to estimate the volume of leaching fluid required to remove excess Na/sup +/ from the exchange complex, and was found to be in good agreement with the results of laboratory soil column experiments. For fine-textured soils in the Imperial Valley of California it may require up to 30 pore volumes of leaching fluid to lower Na/sup +/ concentrations if saturated gypsum solution is used in reclamation. The results of these calculations suggest that reclamation of fine textured soils could require a prohibitive amount of time unless the brine spill is localized around a drain
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