GEOLOGIC MAPPING OF NEAR-SURFACE SEDIMENTS IN THE NORTHERN MISSISSIPPI EMBAYMENT, MCCRACKEN COUNTY, KENTUCKY

The Jackson Purchase region of western Kentucky consists of Coastal Plain sediments near the northern margin of the Mississippi Embayment. Within this region is the Paducah Gaseous Diffusion Plant (PGDP), a uranium enrichment facility operated by the US Department of Energy. At PGDP, a Superfund site, soil and groundwater studies have provided subsurface lithologic data from hundreds of monitoring wells and borings. Despite preliminary efforts by various contractors, these data have not been utilized to develop detailed stratigraphic correlations of sedimentary units across the study area. In addition, sedimentary exposures along streams in the vicinity of PGDP have not been systematically described beyond the relatively simple geologic quadrangle maps published by the US Geological Survey in 1966–67. Our study integrates lithologic logs, other previous site-investigation data, and outcrop mapping to provide a near-surface stratigraphic framework model of the PGDP area. Preliminary findings suggest that previous ideas about gross heterogeneity of the Holocene and Pleistocene sediments composing the Regional Gravel Aquifer of the area may not be correct. Moreover, the lateral continuity of the Mounds Gravels and the Metropolis Formation may be greater than previously described. These findings may result in a more realistic model of groundwater flow beneath the site. In addition, the findings may be useful for assessing local amplification of earthquake ground motion in near-surface sediments.