At this site, Chlorinated Volatile Organic Compounds (CVOCs) were detected in groundwater in bedrock supply wells. Due to naturally occurring reducing conditions, the most complex CVOCs have degraded to below action levels. However, 1,2-DCE (a very recalcitrant CVOC) continued to be detected in groundwater above its action level. To address this issue, the client retained AGES to design and implement an Enhanced Reductive Dechlorination (ERD) program.
Enhanced Reductive Dechlorination (ERD) Technology
Anaerobic (reducing) conditions in groundwater are conducive to biodegradation of CVOCs through the process of reductive dechlorination. During this process, indigenous microbes will oxidize an organic carbon source to obtain energy. The organic carbon source will serve as an electron donor, while the CVOCs and other constituents, such as nitrates, sulfates, iron and manganese act as electron acceptors and are therefore reduced and degraded.
For reductive dechlorination to occur microbes must be present and a sufficient organic carbon substrate must exist to support microbial growth. Given a carbon source and microbial population, biodegradation of more complex CVOCs such as Perchloroethene (PCE), Tricholorethene (TCE) will occur readily under moderately reducing conditions. Efficient biodegradation of more recalcitrant CVOCS such as DCE generally require more strongly reducing conditions.
ERD of recalcitrant compounds in aquifers can be accomplished through the injection of a degradable carbon source such as molasses, whey or vegetable oil. Microbial degradation of the injected carbon material will create more strongly reducing conditions. Under these conditions, even recalcitrant compounds can be effectively dechlorinated.
Impacted Bedrock Aquifer
At this site, AGES designed and implemented an ERD program based on in-situ conditions. Three (3) existing wells at the site were retrofitted to allow for a series of injections of a carbon substrate (molasses). Approximately fifty (50) gallons of molasses per well were mixed with one hundred fifty (150) gallons of groundwater to create two hundred (200) gallons of injectable substrate. Prior to injection, the aquifer was amended with nutrients to foster microbial growth and increase the effectiveness of the remedial action.
Following the injections of the molasses substrate, quarterly groundwater sampling was continued at the site. After several rounds of sampling, concentrations of 1,2 DCE have decreased to below the applicable action level. Based on these results, the facility owner will be able to eventually re-sell the property without deed restrictions, which will significantly increase the value of the property.
1.) Application of the ERD technology was effective at reducing CVOCs concentrations in a very cost-effective manner.
2.) Because all groundwater treatment is in-situ—above ground treatment of waste is eliminated. This significantly reduces remedial costs.
3.) Reduction of CVOC levels will allow the property owner to re-sell the site without deed restriction.