EVALUATION OF BIOREMEDIATION APPLICABILITY TO CONTAMINATED SITES WITH LOW HYDRAULIC CONDUCTIVITY: A CASE STUDY OF THE CONTAMINATED BANKS OF THE MAHONING RIVER, NORTHEASTERN OHIO

The Mahoning River is one of the five most contaminated rivers in the U.S.A. It is contaminated mainly by PAHs, PCBs, and heavy metals. This study investigates the most contaminated section of the river, which is 31 miles long and extends from Leavittsburg to Lowellville in northeastern Ohio.

Bioremediation is currently considered, among other options, to remediate the contaminated banks of the Mahoning River. The banks consist of heterogeneous sediments made of fine-grained sand, silty and clayey sand, silt and clay. Obviously, the low hydraulic conductivity of the sediments will limit the application of bioremediation, which is only applicable if the hydraulic conductivity of the contaminated medium is greater than 10^-4 cm/sec. The objective of this study, therefore, is to characterize the hydraulic conductivity of the banks to determine the technical feasibility of bioremediation. The use of bioremediation will result in significant cost savings compared to the other remedial options currently considered.

The hydraulic conductivity of the contaminated banks was characterized vertically and horizontally using a quick and inexpensive approach based on sediment-size analysis. Over 80 samples were analyzed for hydraulic conductivity by the Hazen formula. The samples were obtained from 19 boreholes drilled by a hand-auger in both banks of the Mahoning River. The boreholes were drilled at three sites: Lowellville (10 boreholes), Girard (4) and Warren (5). The number of samples collected from each site was 40, 20, and 22, respectively. Half of the boreholes were drilled at Lowellville because it is the most contaminated site. Depending on the banks thickness, 3 to 7 samples were collected vertically, at 1-foot intervals, from each borehole. Hydraulic conductivity values ranged from 6.25x10^-4 to 1.00x10^-2 at Lowellville, 2.25x10^-4 to 1.23x10^-3 at Girard, and 2.25x10^-4 to 2.03x10^-3 cm/sec at Warren. At the three sites, geometric mean values were 1.62x10^-3, 5.23x10^-4, and 1.00x10^-3 cm/sec, respectively. These values, which are reflective of a lithology dominated by silty/clayey sand and clean fine-grained sand, clearly show that bioremediation is technically applicable to the three sites based on hydraulic conductivity values.