Finally, A Simple Way to Measure TCE Aerobic Degradation Rates in Groundwater (and you may already have the data).
By: Will Harms, Senior Bioremediation Engineer
Commonly used as an industrial solvent, trichloroethene (also known as trichloroethylene or TCE) has been shown to break down rapidly in air and surface water but much more slowly in soil and groundwater. Cometabolism has been widely accepted as an effective approach for the biological degradation of this hazardous solvent. When it comes to documenting natural attenuation of TCE in groundwater, however, the problem is estimating just how much aerobic biological cometabolism of TCE is occurring at a site.
That is, until now. According to a recent study (Wilson et al. 2019), simple, readily available tests for bacteria DNA in groundwater can effectively predict rates of cometabolism of TCE in aerobic groundwater. This is particularly good news for aerobic TCE sites that would be candidates for a monitored natural attenuation (MNA) remedy.
The key is the correlation between the rate of aerobic TCE cometabolism and the abundance of planktonic bacteria DNA that code for five fundamental biogenic enzymes: SMMO, RDEG, RMO, TOD, and PHE. By implementing the microbial test method known as QuantArray-Chlor (or even QuantArray-Petro). Many TCE sites have already tested for an abundance of planktonic bacteria DNA expressions for these specific enzymes and, therefore, already have the data needed to estimate rates of TCE degradation by aerobic cometabolosm. The test doesn’t work for sessile bacteria, however, like those harvested from aquifer sediments or from downhole Bio-Trap passive samplers.
The costs are nominal. DNA tests for these five enzymes in groundwater samples cost about $575 per sample by a la carte qPCR method and $750 per sample for a QuantArray-Chlor test. The QuantArray-Chlor test includes these five enzyme DNA targets plus a bundle of about 20 other aerobic and anaerobic DNA targets that are known to be involved in chlorinated solvent degradation.
Through the method described in the cited report, EHS Support was able to construct a simple spreadsheet-based calculator for quantifying aerobic TCE cometabolic degradation-rate constants. Screening three sites that already have planktonic microbial assays for biogenic enzymes SMMO, RDEG, RMO,TOD, and PHE, we found remediation-relevant TCE aerobic cometabolic degradation-rate constants between 0.1 per year and 0.3 per year. (The EPA recognizes that TCE degradation-rate constants greater than 0.1 year-1 are generally useful for MNA, based on a presumptive 30-year restoration timeframe).
Simply put, EHS Support can readily screen your site for its TCE aerobic cometabolic degradation rate constant given only the results of DNA test results in your groundwater.
If you’re interested in learning more, please contact one of EHS Support’s Subject Matter Experts: