Traditional data collection methodologies like groundwater sampling and sparse soil sampling can be useful for site delineation and long-term monitoring; however, sometimes the resulting data can lead to the misinterpretation of remedy effectiveness or the under-utilization of natural processes. In turn, this can mean the unnecessary application of expensive long-term remedies.
Cryogenic core collection (C3), an emerging site characterization tool, overcomes many of the limitations of traditional coring techniques. C3 can also improve on direct-push technologies (e.g., membrane interface probe, or MIP) and improves preservation of biological and abiotic parameters and provides high-resolution data, which facilitates remediation managers’ ability to assess and optimize remediation performance. The data set can ultimately support understanding of ongoing processes (e.g., biodegradation), as well as contaminant distribution.
The C3 Process
The C3 technique is an innovative solution that involves freezing soil cores. The C3 technique is an innovative solution that involves freezing soil cores in situ, using liquid nitrogen, and then transporting the frozen cores to a laboratory for analysis.
C3 uses a hollow-stem auger rig with a modified core-barrel sampler. The modified core barrel allows for circulation of liquid nitrogen through a closed cell that surrounds the soil core, freezing the soil before removal from the subsurface.
Freezing the sample in situ provides several advantages over traditional soil coring:
- Recovery is improved, often near complete
- Pore fluids are locked in place, frozen water preserves distribution of non-frozen fluids, including non-aqueous phase liquid (NAPL) and soil gas
- Volatile organic compounds (VOCs) and gaseous products, including methane, ethene, and acetylene, are preserved (methane is an important redox indicator and degradation product of many organic compounds; ethene and acetylene are key indicators for in situ degradation of common chlorinated solvents)
- Microbiological properties are preserved, including DNA and possible RNA
Why Use C3?
C3 generates high-resolution, multi-parameter data that represent subsurface conditions more accurately than either traditional soil coring or groundwater sampling. It also provides quantitative data that can improve on MIP, and related direct-push technologies. These improved data can be used to assess spatial distribution of parent compounds and degradation products, natural abiotic and biological degradation potential, microbial community, mineralogy, geochemical parameters, physical properties, and other data.
Other advantages of C3 include preservation of VOCs and low-molecular weight products (e.g., ethene and acetylene), redox sensitive parameters, and microbial properties. Ultimately, up-front characterization via C3 offers the potential for substantial long-term cost savings via implementation of targeted remediation, enhanced use of natural processes, and reduction in long-term active remedies.
