UNSATURATED FLOW IN A LAYERED, GLACIAL-CONTACT DELTA-DEPOSIT MEASUREDBY THE USE OF O-18, CL- AND BR- AS TRACERS

How much of a surface pollutant will reach the groundwater is strongly determined by how the flow occurs in the unsaturated zone,The aim of this study was to investigate the flow pattern through a sandy, hetero geneous glacial deposit, Soil water was extracted frequently, using su ction cups installed horizontally in a trench wall, during the 1 1/2 y ear period after solute application, Naturally infiltrating water (rai n and meltwater) was followed down to a 220-cm depth using Cl-, Br- an d O-18 as tracers, Different results were obtained according to whethe r a surface applied solute (e.g., Cl- or Br-) or a variation in O-18/O -16 in the water itself was used for flow tracing,The meltwater (O-18) was detected earlier than Cl-. Meltwater and intense rain percolated very rapidly along narrow, preferential flow paths, whereas the solute s may have been transported by a smaller amount of the infiltrating wa ter in a more matrix-dominated flow, High spatial variation in flow ve locities and solute concentrations were found, Tile results are discus sed in light of different theories of flow mechanisms, The presence of preferential flow implies that a small soil volume may rapidly conduc t a dissolved pollutant down to the groundwater.