POTENTIAL FOR SUBSURFACE CONTAMINANT TRANSPORT IN FLOODPLAINS ADJACENT TO MUNICIPAL LANDFILLS

River and groundwater resources adjacent to landfills have the potential to become contaminated due to the high permeability of alluvium. Consequently, development of methods for evaluating plume movement away from landfills has application for remediation and land use planning. On the basis of core and conductivity surveys, our analyses indicate that a contaminated point bar on the Canadian River adjacent to the Norman Landfill contains five zones or layers. The package of mud, sand and gravel is about 12m thick though only the upper 3m of the point bar appears to be active today. The base of the sediment package is in contact with Permian redbeds. This contact probably marks the base of an incised valley. Grain size in the amalgamated bars decreases upward at all scales from gravel at the base to very-fine sand at the surface. Permeability estimates calculated from sediment texture suggest that the basal layer has the greatest permeability. Importantly, the basal gravel is not derived from local bedrock. This suggests the main permeability pathway in the alluvium is controlled by upstream sediment provenance sometime after formation of the incised valley. Considerations for classifying floodplain contamination risk adjacent to a landfill for a given climate include: 1) river type, 2) permeability of the underlying incised-valley fill surface, 3) depth of the incised surface, 4) depth of modern channel erosion, 5) grain size of provenance, 6) rate of meander migration, 7) frequency of avulsion, and 8) orientation of bars relative to position of the landfill.