Diagnostics Can Speed Up Site Closure
When used by knowledgeable environmental professionals, advanced diagnostics provide definitive and actionable data that can expedite contaminated site closure. These diagnostics can accurately predict the effectiveness and measure the performance of in situ remedies, resulting in improved outcomes and lower costs.
To better illustrate this statement, I have included three examples:
- Microbial nucleic acid-based testing (quantitative polymerase chain reaction or qPCR) identified the mechanism responsible for the stability of a mixed chemical groundwater plume at a Georgia manufacturing site. The data were critical in persuading state regulators to approve monitored natural attenuation (MNA), which saved the responsible party more than $700,000 in lieu of a more active remedy.
- An in situ microcosm study proved the effectiveness of an in situ bio-barrier before it was installed. Now, trichloroethene-affected groundwater at a California manufacturing site is treated before migrating, passively mitigating the company's offsite liability.
- Monitoring isotopic shifts in the composition of residual contaminant using compound-specific isotope analysis (CSIA) during an in situ chemical oxidation application identified delivery limitations that were quickly corrected which, in turn, increased treatment efficiency at a solvent release site in New Jersey.
For bioremediation applications, completing in situ microcosm studies before implementing field-scale activities help refine amendment formulations and predict full-scale performance. A novel sample collection device called a Bio-Trap (Microbial Insights, Rockford, Tenn) [I have no financial interest with this company or product] can be used as a matrix for microcosm testing. The samplers are amendable with biostimulants, microbial cultures, contaminant analogs, and many other materials.
When a sampler is deployed in a monitoring well, the beads passively adsorb contaminants and provide a large surface area for biofilm growth, similar to the sediment particles comprising aquifer materials. After incubation, the samplers and any other passive samplers deployed concurrently (e.g., grab and passive diffusion samplers) are subjected to any number of conventional or advanced diagnostics. Typical advanced diagnostic analytical suites include CSIA to assess isotopic shifts/degradation of contaminants sorbed to the beads and molecular biological tools to characterize the mechanism of contaminant destruction, the colonizing microbial population. These data, when assessed comparatively against a control, provide insight into how to manipulate site conditions to quickly achieve cleanup goals.
Stable isotope probing is a particularly powerful application of advanced diagnostics. It involves amending the microcosm with a heavy isotope enriched version of the subject contaminant and tracking its fate. Detection of the heavy isotope in biodegradation end products such as microbial biomass and inorganic carbon is definitive proof of contaminant degradation. The identities of the attenuating microbes are readily determined by examining biomarkers (e.g., membrane biochemistry and nucleotides) for the presence of the heavy isotope.
In situ remediation is not applicable at all sites but, where it is, the information obtained by advanced diagnostics helps deliver the full potential of in situ remediation (e.g., green remediation, quicker remedial timeframes, and lower costs).
Posted by Matthew Burns on Feb 07, 2011