IDENTIFYING SHALLOW BEDROCK ON THE ONONDAGA FM USING GROUND PENETRATING RADAR

Thinly-soiled karst features are a challenge for farming because of the risk of groundwater contamination due to contaminants related to liquid manure application. In New York State, five soil types may soon be off limits for farming because they occur in limestone areas with thicknesses of less than 40 inches. These thicknesses are based on soil horizon information from the generalized soil profile obtained from the county soil surveys (SSURGO). This could potentially restrict large areas of the Onondaga Fm from farming. In this study we use geological context and ground penetrating radar to assess the overburden thickness in these areas and determine if these techniques could better identify sites of concern. Results from two different sites show semi parallel features interpreted to be bedrock sloping upward in the vicinity of the “shallow soil”. The density of non-glacial erratic rock fragments, comprised of subangular chert and limestone clasts, also increases 18 fold at the surface. Precise depth measurements proved to be difficult because of the sensitivity of ground penetrating radar to dielectric-constant changes caused by shifting moisture conditions. Work will continue to catalog the GPR response characteristics of soils in known karst features in order to improve identification of high risk areas.