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Geophysical Assessment of a Proposed Landfill Site in Fredericktown, Missouri.
Citation:
Johnson, C., K. Pappas, E. White, Dale Werkema, N. Terry, R. Ford, S. Phillips, K. Limes, AND J. Lane Jr. Geophysical Assessment of a Proposed Landfill Site in Fredericktown, Missouri. FastTIMES. Environmental and Engineering Geophysical Society, Denver, CO, 25(2):98-106, (2020).
Impact/Purpose:
This work presents field research results using non-invasive geophysical techniques and hydrogeology techniques for the geologic and hydrogeologic characterization of a proposed landfill site. This site is considered by Region 7 to serve as a lead contaminated sediment landfill for lead mine waste sediments from the City Lake in Fredricktown, MO. The investigation involved four different non-invasive geophysical methods and groundwater – surface water hydrologic assessments. The combined interpretation of these methods characterized the site as a potential landfill for the dredging of the lead impacted lake sediments, the hydraulic connectivity from the site to the City Lake, and informed Region 7 on critical geologic conditions to aid decision makers and landfill design considerations. This paper will be included in the August 2020 issue of FastTIMES published by the Environmental and Engineering Geophysical Society.
Description:
In cooperation with the U.S. Environmental Protection Agency (EPA), the U.S. Geological Survey (USGS) collected numerous types of geophysical data at a site in Fredericktown, Missouri in June 2018. Various geophysical surveys were collectively used to help evaluate the overall suitability of the site for use as a mine waste-soil and sediment repository, and to evaluate the suite of geophysical methods for rapid collection and preliminary assessment of sites with shallow sediments with a very limited budget. Land-based geophysical methods, which included frequency-domain electromagnetic induction (FDEM), electrical resistivity tomography (ERT), horizontal-to-vertical spectral ratio passive seismic (HVSR), and shear-wave refraction, were used to determine the depths to crystalline bedrock and characterize the unconsolidated sediments (or regolith) overlying it. Water-borne FDEM profiles and forward-looking infrared (FLIR) thermal image surveys were conducted along the Fredericktown City lake shoreline to identify locations of potential interactions between groundwater and surface water. Sediment temperature profilers were installed at two locations along the shoreline to further characterize and support the interpretation of the other geophysical surveys. Certain geophysical methods were used to rapidly evaluate the thickness and distribution of the overburden sediments of the site. The results of these methods were compared to reference geophysical methods with greater accuracy that are more labor intensive and time-consuming. A goal of the project was the evaluation of the validity and reliability of this suite of reconnaissance geophysical methods as a means by which very shallow sediments can be rapidly assessed. Two orthogonal ERT survey profiles, which used 28 electrodes spaced 1 m apart in dipole-dipole and combined Wenner-Schlumberger configurations, were collected to determine the subsurface resistivity. The results were inverted to produce electrical resistivity profiles that were compared to the FDEM and HVSR survey results. The FDEM data were collected along cleared paths through the proposed disposal cell locations (Fig. 1). The data were collected with a hand-held, multi-frequency instrument carried approximately 1 m above the land surface at walking speeds. The data were inverted to generate depth-dependent estimates of electrical conductivity along the transects. An analysis of the depth of investigation (DOI) indicated the FDEM imaged to depths of about 3 m below land surface. The ERT, FDEM, and HVSR indicated the depth to crystalline bedrock was approximately 1.5 m below land surface with shallower and deeper areas.
