Biological Remediation of Groundwater

Use of Dehalococcoides to Remediate Chlorinated Solvents in Groundwater

Historical operation of various industrial facilities and other land uses throughout Southern California have resulted in contamination to underlying aquifers. Such facilities have included manufacturing, metal plating, aerospace manufacturing, dry cleaning, and landfills. These aquifers have commonly been impacted by chlorinated volatile organic compounds (CVOCs), such as tetrachloroethene (PCE) and trichloroethene (TCE), which are highly soluble and difficult to clean up. ​

Several remedial technologies are available to remediate CVOCs. Recently, a growing number of sites are being remediated and closed by regulatory agencies where injection of dehalococcoides (DHC) into the aquifer has occurred. DHC is a bacteria species group known to dechlorinate stubborn PCE and TCE compounds under anaerobic conditions. The PCE and TCE compounds are degraded to daughter products cis-1,2-dichloroethene, vinyl chloride, and then to ethene which is non-toxic.

Enriched microbial consortium containing species of DHC is available on the market by several manufacturers. When combined with another carbon source and nutrients, populations of microbes responsible for reductive dechlorination will develop in-situ after a period of time. Addition of DHC results in the direct application to the subsurface (i.e. seeding) of a bacterial population capable of complete reductive dechlorination to ethene. During reductive dechlorination, anaerobic microbes substitute hydrogen (electron donor) for chlorine on the CVOC molecule, thus converting the CVOC to a degradation product with one less chlorine atom.

Application of DHC with carbon substrates to aquifers are typically conducted by injection through pre-installed wells, or by use of a direct-push drilling rig. Alta Environmental recently conducted in-situ bioremediation at a project site using DHC as a bioaugmentation step to significantly reduce TCE concentrations.

While site conditions vary, bioremediation can be 2 to 4 times less expensive than conventional methods such as pump and treat or air-sparging, and generally at least twice as fast at remediation. But some sites are very stubborn and do not clean up as quickly, and may require reinjection of the microbes.

DHC and other amendments are approved on the 2014 Los Angeles Regional Water Quality Control Board (LARWQCB), Revised General Waste Discharge Requirements (WDR) list, dated September 11, 2014. For additional information regarding use of DHC, please contact Steve Ridenour (steve.ridenour@altaenviron.com) or Mike Cassidy (mike.cassidy@altaenviron.com). We can also be reached by phone at 562-495-5777.