The overall objective of this project is to provide a more comprehensive evaluation of abiotic processes as part of a monitored natural attenuation (MNA) remediation strategy. This will be accomplished by using data from a series of targeted laboratory and field analyses to develop parameters that will be used to update BioPIC, a decision support tool previously developed by ESTCP under project ER-201129. The specific objectives include:

• Evaluate the potential for abiotic degradation of chlorinated ethenes at three Department of Defense sites using a ¹⁴C-assay to measure rate constants
• Evaluate additional parameters for inclusion in the decision tool, including mineral specific rate constants, the reductive capacity of specific minerals, and microbial analysis for acetylene degraders
• Update the BioPIC tool such that environmental managers can input geochemical, mineralogical, and microbial data and receive estimates of abiotic degradation rates and time to reduce chlorinated solvent concentrations to remedial goals

Abiotic processes refer to pathways by which a chemical undergoes degradation without the direct involvement of living organisms. Abiotic processes can contribute to in situ degradation of a wide assortment of groundwater chemicals, including chlorinated ethenes. Extensive research has shown that abiotic degradation processes may play a significant role in MNA at chlorinated solvent sites, but there is little guidance on how sites can be evaluated for these abiotic reactions and tools to evaluate MNA do not include abiotic processes. BioPIC is an existing decision support software that has a particular focus on establishing quantitative lines of evidence for MNA evaluations. BioPIC will be modified to include additional input parameters such as microbial counts of acetylenoptrophs and include output parameters like rate of abiotic degradation of chemicals, assimilative capacity of the aquifer minerals, and time to reach maximum contaminant levels (MCLs). The rate values database will be obtained by ¹⁴C assays using different aquifer minerals as well as literature rate values.

This project will provide a tool for remedial project managers to use to estimate the contribution of both abiotic and biological degradation processes to MNA at chlorinated solvents sites. SERDP project ER-2622 has shown that ignoring the contribution of abiotic processes during MNA greatly underestimates the rate of degradation and provides a much longer time to reach MCLs. Knowing the true rate of MNA by both abiotic and biological degradation allows remedial project managers to provide a more realistic time to site closure as well as cost estimates to closure and has the potential to save significant amounts of money in monitoring. (Anticipated Project Completion - 2027)