Characterization and bioremediation viability of polycyclic aromatic hydrocarbon contamination in the banks of the Mahoning River

Abstract

Discharge of wastes into the lower Mahoning River in Northeastern Ohio since the 19th century has resulted in the accumulation of toxic hydrocarbons, including PAHs, in the river channel and river bank sediments. This study characterizes the polluted bank sediments and evaluates the feasibility of cleanup using in situ bioremediation. Characterization was undertaken in order to study the feasibility of in situ bioremediation. This was accomplished through the collection of 208 samples from 37 soil borings from both banks at five locations along the river. Samples were then analyzed by grain-size analysis and hydraulic conductivities were estimated using the Hazen method. Soil borings also revealed the following: depth to groundwater, depth to bedrock, the upper and lower limits of hydrocarbon contamination, and the thickness of the hydrocarbon contamination in the river banks. Slug tests were performed at four locations to evaluate hydraulic conductivity in very fine-grained sediments, which could not properly be evaluated by the Hazen method. Flow between the groundwater in the bank and the river channel was monitored at four locations for a period of up to one year. Monitoring confirmed the active exchange of flow between the river channel and the banks. This exchange is capable of recontaminating the river's channel by transporting the dissolved contaminants from the bank, via groundwater if the banks are not remediated. PAHs were analyzed in soil samples taken from five locations which verified PAH impact at all four locations. Based on groundwater flow directions, sediment makeup, hydraulic conductivity distribution, thickness of contamination, and PAH availability, this study suggests first, the probability of leaching from impacted bank sediment to groundwater and second, based on the values of hydraulic conductivity that in situ bioremediation is feasible.