Technical Approach

Researchers will sample groundwater from pre-existing monitoring wells at sites with ongoing remediation and investigation efforts. CO₂ will be collected via two methods. A groundwater sample will be collected, preserved, and sent to a commercial laboratory for dissolved inorganic carbon (i.e., CO₂) radiocarbon analysis. Gas will be drawn from the sealed well and recirculated through a sodium hydroxide trap (to collect CO₂). CO₂ will be collected for a set period of time. A zone of influence (ZOI) model will be created based on the well and local soil characteristics. These include the well construction (casing dimensions, depth to water), temperature, atmospheric pressure, and soil permeability values. Analysis of well logs and prior well tests in the project area will be used to develop a hydrogeologic model of the site. This information will be coupled with development of a CO₂ equilibrium simulation model to create the ZOI model. Researchers will couple ¹⁴C-content measurements, a standard isotopic mixing model to determine the proportion derived from the contaminants of interest, and hydrogeologic model (ZOI) data to determine the flux of contaminants of interest through microbial cycles or abiotic oxidation processes to CO₂. Comparing in-plume measurements with reference site(s) measurements will allow source apportioning in situ microbial assemblage carbon demand and allow determining contaminant biodegradation rate (and/or abiotic degradation rate). These measurements will address all of the technology high priority needs appropriate for monitoring natural attenuation or engineered approaches.