SiREM technician loading GC auto-sampler for headspace analysis of dissolved hydrocarbon gases.
SiREM offers competitively priced specialty chemical analytical services to monitor remediation processes and progress including:
- Dissolved hydrocarbon gases
- Volatile fatty acids
- Compound Specific Isotope Analysis
Dissolved Hydrocarbon Gas Analysis
SiREM’s custom gas chromatographic dissolved hydrocarbon gases (DHG) analysis is based on a modified RSK-175 method developed by the US EPA. DHG analysis is used to quantify aqueous concentrations of methane, ethene, ethane and can also quantify propene, propane and acetylene.
Use SiREM DHG Quantification to:
- Confirm complete dechlorination of chlorinated ethenes, ethanes and propanes
- Quantify methanogenesis
- Quantify gases used in cometabolic remediation
Volatile Fatty Acids Analysis
Volatile fatty acids (VFAs) quantification in groundwater is used to assess electron donor status in bioremediation systems. When commonly used electron donors, such as lactate, emulsified vegetable oils (EVO) or alcohols, are fermented, VFAs are often observed. Detection of VFAs confirms that electron donor fermentation is occurring and indirectly indicates that hydrogen generation, the ultimate electron donor used by most reductive degradation microbes, is likely occurring. Quantification of VFAs also provides additional insights into electron donor status compared to total organic carbon (TOC) analysis. SiREM uses a custom ion chromatographic method for VFA quantification of lactate, acetate, propionate, formate, butyrate and pyruvate.
Use SiREM VFA Quantification to:
Chart on left is predominantly acetate and not ideal for hydrogen generation/dechlorination. Chart on the right has acetate and other VFAs and is a more optimal electron donor
- Minimize unnecessary electron donor application leading to more effective and efficient use of electron donor and reduced costs
- Confirm the fermentation of slow release and soluble electron donors
- Determine the need for additional electron donor for complete reductive dechlorination
Anion quantification in groundwater is used to assess water quality, redox conditions, and stable tracers in remediation systems. During the onset of reducing conditions during bioremediation, common polyanionic species like nitrate and sulfate are reduced to their less oxidized states (i.e., nitrogen gas and sulfide). These changes in nitrate and sulfate concentrations are often indicators that biologically mediated changes in the redox chemistry of the aquifer are occurring. The concentrations of these analytes can also impact the dosage of electron donors, as these species can consume more electron donor than site compounds of interest. Quantification of anionic tracers, such as bromide, can also be used in determining groundwater velocities or flow paths. SiREM uses a custom ion chromatographic method for anions quantification based on US EPA Method 300 to quantify chloride, bromide, nitrite, nitrate, sulfate and phosphate.
Use SiREM Anion Quantification to:
- Assess the concentrations of redox-sensitive anionic species including nitrate and sulfate
- Confirm the onset of suitable reducing conditions required for reductive dehalogenation
- Trace the groundwater velocity and flow path using stable anionic tracers, such as chloride or bromide
Compound Specific Isotope Analysis
Compound Specific Isotope Analysis (CSIA) is a proven technology used to evaluate the extent of contaminant degradation, versus non-degradative losses (i.e. dilution, dispersion, sorption), as well as “fingerprinting” contaminants for source identification and differentiation. The addition of CSIA expands SiREM’s portfolio of advanced tools that also includes analytical testing, molecular genetic testing (Gene-Trac®), treatability studies and other analyses used to understand and optimize remediation processes.
CSIA is a powerful tool for remediation performance monitoring and contaminant source information as stable isotope ratios from chemical elements such as carbon, hydrogen, oxygen, nitrogen, chlorine, sulfur, can be traced back to specific degradation processes and/or origin. CSIA provides a quantitative approach to differentiate between biotic and abiotic degradation reaction pathways and between contaminant sources and can be applied as a line of evidence for monitored natural attenuation (MNA).
HOW IT WORKS
Stable Isotopes are “light” and “heavy” atoms of the same element
Stable isotopes are atoms of an element that contain the same number of protons but different numbers of neutrons in their nucleus. For example carbon exists in a light 12C and a heavy 13C form that has an additional neutron. In nature, stable isotopes occur in a relatively constant ratio, for example 13C is around 1% of all carbon however, various chemical, physical and biological processes can lead to a minimal (but easily measurable) shift in the ratio of heavy and light isotopes (the isotope signature) in a substance. The ratio of heavy and light isotopes (e.g. 13C/12C) is expressed as delta notation (δ13C), which refers to an international standard. Due to the preferential transformation of the lighter isotope species in (bio)chemical reactions, compounds bearing a heavy isotope, especially in the reactive position, accumulate in the residual fraction of the reactant (normal isotope effect).
Conversely, when a chemical is synthesized, the incorporation of heavy isotopes into the molecules depends on certain kinetic conditions leading to a marginal (but measurable shift) in the isotope ratios in this substance. Differences geographically or in synthetic conditions therefore produce different isotope signatures of the same substance. On this basis, CSIA allows the determination of different pollutant sources at a contaminated site.
Physical processes such as dilution, dispersion, evaporation or sorption might cause changes in the isotope ratio, however, the impact of physical processes is mostly minor or negligible compared to degradation and, thus, does not influence the assessment of pollutant degradation based on CSIA.
CSIA and Contaminant Site Characterization
Given the subtle differences in stable isotope ratios, CSIA is a powerful tool that can be used to evaluate the extent of contaminant degradation versus non-degradative losses as well as “fingerprinting” contaminants for source identification and differentiation. When combined with molecular biological tools (Gene-Trac®) and advanced analytical testing and/or incorporated into treatability studies it can substantially enhance the understanding of potential sources as well as optimization of remediation processes and progress.
Learn more in our CSIA Technology Spotlight.
CSIA Strategic Partnership
SiREM is proud to offer CSIA services though our strategic partnership with Isodetect GmbH of Leipzig, Germany. Isodetect offers isotope analytical services and scientific expertise to stakeholders in groundwater remediation, the oil and gas industry as well as environmental monitoring worldwide. Isodetect holds key knowledge and intellectual property for natural attenuation monitoring, source identification and in situ remediation at contaminated sites (e.g., BTEX, chlorinated ethenes, HCHs, MTBE, PAH, TPH, micropollutants, pesticides, explosives). Isodetect’s services include CSIA, Stable Isotope Probing (SIP), in situ microcosms (BACTRAPs®), laboratory microcosm studies, metabolite analysis, molecular genetic techniques (qPCR) and GC-MS screening.