More Info...

Publication

CHEMICAL OXIDATION OR ENHANCED ANAEROBIC DECHLORINATION -
A SCIENCE BASED DECISION
Sami A. Fam, Ph.D., P.E. L.S.P., Donald F. Kidd, P.E., Innovative Engineering Solutions, Inc.

From a business perspective, the environmental remediation industry has matured and grown significantly over the past twenty-five years. Interestingly however, the consulting industry has not progressed as significantly in making science the basis for site remedy selection. Contaminants desorb slowly from aquifer solids and this desorption rate, along with contact with the cleansing carrier/additive, dictates the overall efficiency and progress of the remediation program. Dense non-aqueous phase liquid (DNAPL) pools, in themselves, cannot support biodegradation and cannot be oxidized by chemical oxidants. Both biodegradation and chemical oxidation must occur in the aqueous phase with both processes working solely on the halo of dissolved constituents surrounding the residual and free-phase contaminants. Electron donors and bioaugmentation cultures (if required) must be delivered to the area that requires enhancement and the "enhanced" subsurface conditions must be maintained for a period of time so as to degrade the soluble fraction, in addition to the contaminant fraction that will desorb from the soil over time (desorption from soil is enhanced by bioremediation). The idea that electron donors used in anaerobic dechlorination can diffuse to a distal location when these compounds have short half-lives is questionable as is the idea of solving contamination problems by feeding a site two or three times. It is often necessary to induce/recirculate groundwater to distribute the additives.

Enhanced anaerobic dechlorination may have electron acceptor (the targeted VOC) low concentration limitations, rendering MCL endpoints unachievable. Chemical oxidants must contact the contaminants in the dissolved phase if they are to destroy them, which begs the question of how chemical oxidation can possibly oxidize relatively insoluble tars and oils as is purported. Permangenate based oxidation systems can encrust and entomb contaminants, slowing down the rate of soil desorption and prolonging site clean-up. Many practitioners try to inject the additives by fracturing or other pressure injection methods that lead to short circuiting towards existing monitoring wells, which act as pressure relief points. This method of distribution leads to biased data in the same manner as air sparging into low permeability formations. Some practitioners believe that bioremediation is slow and propose expediting the process by first oxidizing the source area then polishing the residuals with bioremediation- why would one do this if anaerobic dechlorination can be enhanced within months, is effective at near saturation concentrations, and does not work well at low VOC concentrations? There are many fundamental questions typically remaining unanswered and a lot of misconceptions within the field. The goal of this paper is to provide some answers through our experience and over 50 project case histories.

The full version of this publication is available upon request, subject to IESI usage guidelines. 
Send requests to publications@iesionline.com.