Optimizing In Situ Remediation Using Advanced Diagnostics Presented by: Matt BurnsContact Information: WSP Environment & Energy 300 Trade Center, Suite 4690 Woburn, MA, 01801 781/933-7340 firstname.lastname@example.org http://www.linkedin.com/in/mattburns wspIntroductionIn situ remediation has been widely appliedto address groundwater contamination overthe past 10 years. Unfortunately, the barrierto applying the technology is low and poorlyconceived and planned applications areaffecting the credibility of the technology. Successful selection and application of in situ technologies begins with a conceptual model that is not biased by preconceived or irrelevant factors and is tested analytically. The limitations of potential remedies should be given as much consideration as their potential benefits, keeping in mind the concepts of integrated site remediation that bundle complementary technologies for sequential application.Analytical Assessment ToolsAnalytical testing of proposed in situ remedies is complicatedby two key facts: x The mechanisms of degradation are unseen and not well understood. x The physical effects of amendment application (e.g., dilution and displacement) can affect concentration data in a manner similar to the desired reactive mechanism.
Until recently, analytical testing protocols to better understand insitu degradation processes have been limited by cost, timeliness,and data tangential what is really necessary: x Will the proposed amendment application destroy the contaminant or just push around and dilute it? x What is the mechanism of destruction and can it be monitored directly?New cost-effective analytical tools are now commercially available to answer these questions.Compound specific isotope analysis (CSIA) provides definitive information on contaminantdestruction that is not concentration related and molecular biological tools (MBTs) identifymicrobial-mediated mechanisms of destruction. Proper use of these tools during remedyselection and performance monitoring results in better application of technologies such asmonitored natural attenuation, bioremediation and in situ chemical oxidation and reduction.These tools also have applications for environmental forensics that, for example, can segregatecomingled groundwater plumes or identify vapor intrusion sources as originating from above orbelow the slab.Compound Specific Isotope AnalysisCSIA distinguishes destructive reactions from non-destructive processes by tracking the fate ofheavy stable isotopes. Stable isotopes are naturally occurring and not radioactive. Carbon forexample, has two stable isotopes 13C and 12C (note the 14C is radioactive and not stable). Thenatural abundance of these isotopes is about 99 percent and 1 percent respectively. The basisof CSIA as a degradation assessment tool is that heavier isotopes (e.g., 13C) form strongerbonds. Therefore, the degradation rate of contaminant molecules that contain heavy isotopes isslower than contaminant molecules composed solely of lighter isotopes (e.g., 12C). The slowerreactivity results in an accumulation of heavier isotopes which are measured by CSIA.Degradation rate and reaction percent completion can be calculated using CSIA data. Chocolate Fractionation used with permission from Dr. Mike Hyman, Department of Microbiology North Carolina State University
CSIA measures the ratio of heavy isotopes to light isotopes. The analytically derived ratio isnormalized to an international standard and reported in units as part per thousand (per mil or‰), expressed as the difference (del or δ) from the standard.Key concepts of CSIA datainterpretation include: x parent compound fractionation is unequivocal proof of degradation x daughter product fractionation alone does not prove daughter product degradation x the non-degrading daughter product can get no heavier than the initial signature of the parent x daughter product isotopic signature greater than the initial signature of the parent compound indicates daughter product degradationMolecular Biological ToolsMBTs quantify microbial populations and their activity by assessing unique nucleic acid basedor lipid based biomarkers. Many analytical techniques that quantify these biomarkers areavailable with quantitative polymerase chain reaction (qPCR) and phospholipid fatty acid (PLFA)being the most commonly used for environmental applications. MBTs can be used to answersite specific questions to assess naturally occurring conditions directly or experimentally bymanipulating local conditions with proposed remediation amendments before their use. MBT samples can be collected discretely from extracted and filtered groundwater or a time-integrated sample can be collected using a growth matrix such as a bio-trap® sampler (manufactured by Microseeps of Rockford, Tennessee). Both sampling methods are capable of collecting microbes for MBT evaluation of existing conditions. Bio-trap samplers have the added utility of being amendable to test proposed remedial strategies and answer site-specific questions. Electron acceptors (e.g., ORC), electron donors (e.g., HRC), microbial augments (e.g., SDC-9), contaminant analogs (e.g., trichlorofluroethene), and isotopically labeled contaminants can beincorporated within the bio-trap® matrix. Comparing amended bio-trap® data to non-amended(i.e., control) bio-trap® data provides information on the potential success of field-scaleapplication of remediation amendments.
Amending specifically manufactured contaminants that contain isotopically enriched carbon (i.e.,13 C at a very high abundance) is referred to as stable isotope probing (SIP). SIP can providethe most definitive evidence of attenuation available. The SIP technique involves tracking thefate of the carbon that comprise the contaminant into biomass and/or dissolved inorganiccarbon. SIP is only applicable where the contaminant is used as a source of cellular synthesisor for energy derivation.ConclusionsAdvanced diagnostic tools optimize in situremediation by definitively identifyingcontaminant destruction and themicrobial-mediated mechanism ofdestruction. The tools are versatile andwith proper experimental construction cananswer site questions. Overall,incorporation of advanced diagnosticswithin the remedial selection and remedyperformance process leads to betterdecisions and increased success rates ofin situ technologies.Additional Resources A Guide for Assessing Biodegradation and Source Identification of Organic Ground Water Contaminants using Compound Specific Isotope Analysis (CSIA) (December 2008). Burns, M. and Myers, C. (2010), Evolution of predictive tools for in situ bioremediation and natural attenuation evaluations. Remediation Journal, 20: 5–16. doi: 10.1002/rem.20259 at WSP we help our clients with everything from building skyscrapers to using microbes to clean up hazardous waste