EVALUATION OF NEAR-SURFACE GEOPHYSICAL METHODS TO MAP HISTORIC SITES IN THE SOUTHEASTERN UNITED STATES

Context for late 18^th and early 19^th century buildings listed on the National Register of Historic Places is often incomplete because of the destruction and removal of supporting structures. Mapping the layout of these sites including outbuildings, privies, garden paths and roadways provides a complete picture of site history. Near-surface geophysical methods including Ground Penetrating Radar (GPR), gradiometer, and Electrical Resistivity Tomography (ERT) can be used to image subsurface structural components of cultural features. In our experience, landscaped upland sites are ideal for geophysical surveys.

Cultural components identified with shallow geophysics include cellars, kitchens, smoke houses, wash houses, privies, roads, and paths. GPR surveys provide a rapid method for screening relatively large areas for potential anomalies. However, GPR images reflection patterns from different depths in the subsurface and cannot identify the material composition. Gradiometer surveys can observe magnetic anomalies related to past use of the site, including the contrast in magnetic properties between cultural features and surrounding soil such as ferrous debris or in situ burning. ERT surveys, although time consuming, detect structural remnants of anomalous materials (rock, brick, and rubble fill) and can accurately measure the depth to buried surfaces. After processing and interpreting GPR slices (which can be done in the field), gradiometer grids and ERT transects can be run at focused targets depending on the anomalies detected.

At Ingleside Plantation (Lincoln County, NC) a previously unknown 5 x 5 m stone-lined cellar, likely filled with chimney rocks and metal objects was imaged with both GPR and ERT surveys. Archival research indicates that a cabin with a Revolutionary War History sat above the cellar. Privies were detected by reflection free anomalies produced by homogenous backfill in contrast to reflective soil horizons. At the Benjamin Hubbard House (Wilkes County, NC) imaged features include a gravel pad for the wash house and a runoff trough, a magnetic anomaly for the ash hopper, and a work area inside a fenced front yard. Features imaged at Hopewell Plantation (Pickens County, SC) include a smokehouse floor, kitchen, privy, and driveway. A cistern was imaged at Elkwood Plantation, Woodford, KY.