OXYGEN SPARGING FOR BIOREMEDIATION OF PAHs FROM A FORMER MANUFACTURED GAS PLANT SITE
David Falatko, P.E. (d.falatko@iesionline.com) (Innovative Engineering Solutions, Inc.- Portland, Maine)
Joe Higgins, P.E., L.S.P.,
Sami A. Fam, Ph.D., P.E. L.S.P. (Innovative Engineering Solutions, Inc. - Walpole, Massachusetts)
George Pon, Ph.D. (Bioremediation & Treatability Center-
Walpole, Massachusetts)
Elizabeth Greene (National Grid - Westborough, Massachusetts)
Abstract
A former manufactured gas plant (MGP) site released coal tar from past processes which contaminated groundwater with polycyclic aromatic hydrocarbons (PAH) as well as benzene, toluene, ethylbenzene and xylene (BTEX) compounds. The PAH and BTEX compounds in groundwater migrated from the former MGP area to a downgradient sand and gravel aquifer and as a result, impacted groundwater quality. The impacted aquifer is approximately 100-feet thick with a 90-foot saturated thickness; the highest contaminant levels are present in the deepest portions of the aquifer. Site data indicated that biological degradation of the contaminants was occurring naturally but was limited by the lack of oxygen in the aquifer. Delivering oxygen to the deepest impacted zones with a typical air sparging system was not considered practical as vapors generated from the sparged air could not be efficiently recovered with a vapor extraction system. Residual dissolved oxygen levels from sparging would also be inadequate. An oxygen sparging system was selected for higher oxygen transfer efficiency relative to air sparging and will provide higher residual levels of dissolved oxygen in order to increase the biodegradation rate. The preliminary results show decreased contaminant concentrations around and downgradient of the sparge wells. Dissolved oxygen concentrations have increased significantly with levels as high as 52 milligrams per liter (mg/L) observed. Contaminant levels have decreased significantly, 75-100% downgradient of the sparge system, and continue to decrease with time as elevated oxygen levels are maintained.
