FIELD-SCALE TRANSPORT FROM A BURIED LINE SOURCE IN VARIABLY SATURATEDSOIL

Lateral subsurface flow through the upper soil layers (stormflow zone) during storm events has been shown to be a dominant mechanism of cont aminant transport in forested watersheds. Data bases for multi-region flow and transport modeling for hydrogeologic conditions where stormfl ow predominates are lacking. Direct measurement of the tracer flux und er field-scale conditions are non-existent. The objective of this pape r was to evaluate the significance of three hydrologic pore regions to stormflow. Two tracer releases were made from a buried line source du ring storm events and the spatial and temporal variability in solute c oncentration and the tracer fluxes were measured. During one of the in jections, macropore flow was extremely rapid with solute transport to a downslope trench 65 m from the line source taking just 3.2 h. Mesopo re flow appeared to be significant for short distances in that tracer movement to solution samplers just 3 m downslope of the line source oc curred within 3 h of the release. Soil sampling 6 months after the sec ond release revealed that the tracer plume was refracted in the direct ion of the fractured bedding plane, and therefore did not coincide wit h the array of samplers for distances greater than 13 m downslope of t he source. Soil sampling data suggested that micropores served as a si nk/source for Br- with 47% of the non-reactive tracer remaining immobi lized by micropores at the termination of the study. Interaction betwe en the upper 2 m of the stormflow zone and the groundwater system was believed minimal: however, lateral flow below 2 m was concluded to be significant.