The Effects of LNAPL Biodegradation Products on Electrical Conductivity Measurements

Abstract

Field geophysical studies have identified anomalously high conductivities in and below the free product zone at many sites with aged contamination by light, non-aqueous phase liquids (LNAPL). Laboratory experiments were conducted to test the hypothesis that these anomalously high conductivities can result from products of LNAPL biodegradation. Soil from a hydrocarbon-impacted site with anomalously high conductivities was washed repeatedly to remove soluble constituents, recontaminated with diesel fuel (DF), and the pores filled with water to simulate a saturated smear zone. Nutrients were provided at levels observed at the site, which resulted in anaerobic conditions due to DF biodegradation. Within [Formula: see text], the increase in specific conductivity from microbial activity was [Formula: see text], caused by an increase in total dissolved solids (DS) of over [Formula: see text]. The increase in DS was due to mineral (mostly carbonate) dissolution and to the production of organic acids and biosurfactants. Under aerobic conditions (i.e., without added nutrients) products of DF biodegradation increased the total DS and conductivity by [Formula: see text] and [Formula: see text], respectively. The results show that products of LNAPL biodegradation can drastically increase the conductivity at impacted sites.