Vertical Distribution Of Microbial Abundances And Apparent Resistivity At An Lnapl Spill Site

In an attempt to better understand the anomalously high conductivities in and below free<br>product/residual Light Non-Aqueous Phase Liquid (LNAPL) plumes, continuous soil<br>samples were obtained from four locations in the Carson City Park, which is located<br>adjacent to the former Crystal Refinery in Carson City, MI. The samples were taken<br>from borings next to monitoring wells, and Vertical Resistivity Probes (VRPs). Two of<br>the collection sites extended off the free product plume and include one site within the<br>dissolved product plume and another, considered the control, located outside of known<br>contamination. The two remaining locations occur within the LNAPL free product<br>plume. Sub-samples, used for counts of cultured bacteria, were removed from the sides<br>of the original cores at small vertical intervals. The bacterial counts were correlated with<br>the bulk apparent resistivities measured in the corresponding VRPs, and with the<br>sediment descriptions. In general, there is an orders-of magnitude increase in bacterial<br>abundance at the levels where the apparent resistivity is at a minimum. The control site<br>gave a good indication of natural vertical and lateral background variability in the<br>absence of LNAPL. The results indicate that apparent resistivity measurements can<br>provide a window into the biogeochemical processes ongoing at LNAPL-impacted sites.<br>The results continue to encourage the use of resistivity as an option to monitor the natural<br>or enhanced bioattenuation of such sites.