SMITH, LINDA V., Texokan Exploration Services, Santa Monica, CA, RICHARD C. SLADE, Richard C. Slade & Associates, North Hollywood, CA, and ANNE S. CHILDRESS, SCS Engineers, Long Beach, CA

ABSTRACT: Paleochannel Features and their Possible Influence on Contaminant Migration in Ground Water

The presence of paleochannel features in the subsurface environment may play a significant role in the flow of groundwater and the movement of contaminants. These paleochannel features, due to their greater hydraulic conductivities, may provide preferential migration pathways for contaminant transport. Contour maps of contaminant concentrations prepared for sites with subsurface paleochannels indicate the influence of these features on plume geometry. At some sites, contaminant plumes are localized by a paleochannel to the extent that the preferential direction of contaminant migration appears to be along the paleochannel rather than directly downgradient as would normally be expected.

A case history is provided for a confidential site in California in which preferred flow paths are interpreted to be influencing contaminant migration. Paleochannel features at this site consist of coarser grained deposits (medium to coarse-grained sands) within a finer grained matrix (fine-grained sand and silt). Geologic boring logs, cross sections, and fence diagrams prepared for this site all indicate the presence of these features. Contaminant contour maps also indicate the influence of these features on migration of dissolved chemical species.

AAPG Search and Discovery Article #90992©1993 AAPG Pacific Section Meeting, Long Beach, California, May 5-7, 1993.