Activated carbon (AC) particulates are a class of materials that treat a variety of hazardous chemicals, such as chlorinated solvents, petroleum hydrocarbons, and per- and polyfluoroalkyl substances (PFAS) by adsorption and/or degradation. The success of in situ treatment, especially with AC particulates, depends on delivering the particles effectively in the subsurface with direct contact of the particulates and the chemical of concern. Several injection approaches for these particulates are available, but well-controlled field data for injection techniques and monitoring methods to verify distribution are lacking. Particulate distribution is difficult to determine by standard well sampling, but electrical resistivity tomography (ERT) offers a means to track injection of particles in 3-D or in 2-D cross-sections and has been successfully applied for tracking injection of other amendments. 

The overarching objective of this work is to improve the technical understanding of how AC particulates can be distributed in the subsurface to a treatment zone. Specific objectives are to provide field data for (1) injection of particulates by direct injection, direct injection with shear-thinning polymers, and hydraulic fracturing; and (2) use of ERT for tracking particulate injection in 3-D and in selected 2-D cross-sections. In addition, the products of the effort will provide guidance for Department of Defense (DoD) installations, including performance, cost, and monitoring information to enable appropriate evaluation of AC particulates as a potential treatment approach.

With ERT, data for particulate distribution can be quantified for (1) use in a treatment implementation and (2) quantitative evaluation of different injection methods (as will be applied in this project work). ERT is a geophysical technique whereby voltage is applied in a specific pattern with an array of either surface electrodes, down-hole electrodes, or both. The electrical response indicates the bulk conductivity distribution in the subsurface that is related to subsurface properties and the properties of injected materials. Applying ERT with temporal surveys enables imaging amendment injection as it is occurring. The recently released E4D code facilitates near real-time interpretation and reporting of temporal ERT data and will be used on this project to track particulate injection. E4D will also be applied upfront to design the ERT system for each injection process as an integrated way to incorporate ERT monitoring with injection design and design of complementary sampling. This integrated design will be used to conduct a field demonstration for three primary particulate injection methods so that useful field-scale data are collected for subsequent use by installations considering treatment with AC particulates.

Installations will benefit from having a rigorous set of data for AC particulate injection to use in evaluating potential treatment applications. In addition, the project work will demonstrate ERT as a monitoring technique for in situ injection, including guidance for how the E4D code can be applied as an upfront design tool to integrate injection design, ERT monitoring, and other sampling-based monitoring approaches. AC particulates have promise as a remediation technique; this project will provide DoD installations and the remediation community with a technical basis for evaluating this potential, effectively including AC particulates in feasibility studies, and designing appropriate injection and monitoring approaches. (Anticipated Project Completion - 2024)