DHC and Me: Is it time to DNA test your property?

Cheap, fast and informative DNA kits are no longer just for puppies and relatives, now they’re for your groundwater too! No, we can’t tell if your water originally came from Ireland, but we can tell you whether or not the bacteria in it are capable of bioremediating potential pollutants. For example, quantifying a healthy population of Dehalococcoides (DHC) in a site’s groundwater is a cause for celebration if you have a chlorinated solvent problem – keep them well-fed and DHC can make most of your problems go away.

Groundwater Bioremediation

Depending on how you ask the question, the concept of bioremediation has been around for a long time; that is, harnessing the action of microorganisms to do our dirty work. Septic systems are a great example of this, and have been in use since the mid to late 19^th century. Anaerobic bacteria get the process started in the oxygen-deprived tank, and aerobic bacteria take over in the relatively oxygenated drainfield. When these systems are properly designed[1] they can effectively manage the waste of a single household.

Harnessing bioremediation for commercial/industrial pollutants started gaining traction following successful application of enhanced aerobic bioremediation for oil spills in the early to mid-1970s. Treatment consisted of withdrawing groundwater, adding oxygen and nutrients, and recirculating it through the subsurface. This works because the aerobic microorganisms involved subsist on energy created by converting contaminants into carbon dioxide (produced when the contaminant is oxidized) and water (produced when O² is reduced). Recirculating oxygen and nutrients through the groundwater guarantees that the microorganisms have everything they need to thrive on a diet of your contaminant. Common applications of aerobic bioremediation include benzene, toluene, ethylbenzene and xylene (BTEX) contamination and fuel releases.

Chlorinated solvents are the typical targets for anaerobic reductive bioremediation, sometimes referred to as biodechlorination. In this process, anaerobic microorganisms subsist on energy created by replacing the chlorines on a contaminant molecule like tetrachloroethylene (PCE) with hydrogen atoms until only ethene, water, and chloride remain. Importantly, organic carbon must be present on site as it consumes oxygen as it degrades, helping to maintain anaerobic conditions and generating the hydrogen necessary for reductive dechlorination to take place through fermentation.

In the past, bioremediation confirmation was a bit more obscure; think “If you build it, they will come” – make conditions ideal for the bacteria you want to encourage, and then get confirmation that it worked once child products start showing up. Using a modern DNA Toolkit opens up the possibility to explore effectiveness of your remedy.

DNA Toolkits

So while you probably know which contaminants are causing problems at your property’s groundwater, you might be a lot less certain about which bacteria are comingling with it. Adding a DNA test to your next round of groundwater sampling can go a long way in helping create and defend a closure strategy involving bioremediation. Cost-wise, the analysis (commonly referred to as quantitative polymerase chain reaction, or qPCR) is on par with the other typical analyses run (VOCs or SVOCs, for example), so for most sites it just makes sense to eliminate the guesswork. A map of contaminant concentrations, groundwater conditions (aerobic vs anaerobic), and bacteria type/quantities allows you to decide whether or not current conditions are adequate for your closure goals. If they aren’t, your project manager can intelligently design an injection plan that addresses the three things that matter for your groundwater: the type and amount of bacteria, the amount of their non-contaminant food sources, and the amount of oxygen present.

If you’re interested in some further reading, we’d suggest looking at the USEPA’s December 2013 publication Introduction to In Situ Bioremediation, or at the various resources available from laboratories that specialize in microbiological analysis.

[1] Caviar Shortages, Sewage Overload, and Country Club Trespassers: Inside COVID-19 Winter in the Hamptons, Vanity Fair, January 29, 2021. “That’s sparked emergency calls for systems that have completely failed. And failure isn’t pretty. “It could be lawn seepage, or it could back up into the house—the basement, the tub or washer or toilet—wherever it can exit,” said Danielle Quackenbush, co-owner of the company. “If you’re doing laundry or have just taken a bath, it could be a lot. If you have a water filtration system, it could happen while you’re out.””