PRELIMINARY RESULTS OF AN ER/IP SURVEY IN AN URBAN BUILT ENVIRONMENT USING COMBINED DOWNHOLE AND SURFACE ARRAYS AT AN OHIO VALLEY SITE

A Service Station in Covington, KY (Cincinnati metro) presents an underground storage tank (UST) site positioned in a relatively complicated built urban environment in northern Kentucky most proximal to the Licking River, a tributary of the Ohio. A number of individual consultants have worked nearly two decades attempting to best characterize the site with various tools. In the last couple of years, geophysical techniques have just begun to be employed at the site with a ground penetrating radar (GPR) survey being conducted to discern utilities and infrastructure along with any near surface geological peculiarities. The infrastructure features appear to be in the vadose zone and are believed to minimally contribute to the distribution of Light Nonaqueous Phase Liquids (LNAPLs). In April 2018, a three-dimensional electrical resistivity (ER) and induced potential (IP) survey was conducted, using surface electrodes and a series of four electrodes placed down each of several monitoring wells. This was an effort to characterize the LNAPL plume and hydrostratigraphy via a 3-D view. We present the preliminary results of this survey in the context of significant previous work already conducted at the site. The site contains Wisconsinan outwash of primarily silt, clay and minor sand, as well as loess-derived deposits. Overall, there is a paucity of significant sand, according to boring logs, yet there appears to be a preferred fate and transport direction for the LNAPL. This plume is oriented roughly subparallel to the topographic high on the site which is reflected in ER-IP visualizations. The ER-IP method reveals a plume configuration apparently restricted by relatively more clay-rich strata and this conclusion is consistent with an aquifer pumping test conducted at the site. Preliminary results suggest that urban challenges can be met with a multi-faceted approach with respect to chosen geophysical methods and array choice.