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In Situ Chemical Oxidation for Groundwater Remediation - Technology Practices Manual
Dr. Robert Siegrist | Colorado School of Mines
In situ chemical oxidation (ISCO) involves the subsurface delivery of chemical oxidants to destroy organic chemicals (e.g., chlorinated organic solvents, fuels) and to remediate a site to a risk-based cleanup goal. ISCO can be implemented alone to treat a contaminant source zone or an associated groundwater plume, or used in combination with other remedial technologies. Several ISCO oxidants are available (e.g., catalyzed hydrogen peroxide, potassium permanganate, sodium persulfate, and ozone) in concert with various subsurface delivery options (e.g., direct push probes, injection wells, soil fracturing, and soil mixing). Effective site-specific ISCO engineering requires a knowledge base and tools to resolve key issues such as amenability of target contaminants to oxidative degradation; ISCO effectiveness in destroying nonaqueous phase liquids (NAPL); optimal oxidant loading (dose concentration and delivery) for a particular subsurface setting; managing unproductive oxidant depletion; mitigation of potential adverse effects (e.g., mobilizing metals, forming toxic byproducts, reducing formation permeability, and generating off-gases and heat); coupling of ISCO with other remediation technologies (e.g., pre-ISCO surfactant flushing or post-ISCO bioattenuation); length of operation to achieve cleanup goals; and methods for process monitoring and performance assurance. This project builds on research conducted under SERDP project ER-1290 and captures valuable information from other research efforts and field experiences at Department of Defense (DoD) and other sites.
Objectives of the Demonstration
The overall goal of this project was to advance the standard of practice for ISCO by integrating the state of knowledge into the remediation process and practices typically employed at DoD sites. To this end, specific objectives included development of a design protocol for ISCO built on the state of knowledge and know-how for determining ISCO viability and best practices for site-specific conditions. This entailed evaluation of ISCO application case studies and comparison of design protocol-generated best practices against case study results to determine performance prediction ability. Subsequently, the ISCO design protocol was refined as appropriate (including the decision support tools and models), based on field study results and technical peer review. The culmination of these efforts was the production of a comprehensive Technology Practices Manual (TPM) that provides knowledge- and experience-based information along with the decision support tools and design models, as well as a Frequently Asked Questions guide for DoD site managers.
The ISCO TPM is composed of several documents:
- E-Protocol for Site-Specific Engineering and Application – Included is a text guide to facilitate the ISCO decision-making process. The protocol is deployed through a series of processes where information is gathered or analyzed and decision points where a course of action is decided. Flow diagrams illustrating typical procedures are provided and range from screening to conceptual design to detailed design to implementation. Tools for key processes and decision points include lookup tables, spreadsheet calculators, and modeling tools.
- Case History and Analysis Data Base – The interactive DISCO tool provides case study details from field-scale ISCO projects. The tool enables queries from selection of subsets of data within DISCO and provides results as narrative discussions and summary tables and graphs.
- Supplemental Information and Tools – Included are a literature review used to develop the E-Protocol, a summary of the current ISCO scientific knowledge, and summary information of each study site, as well as a Technology Practices Workshop Report with ISCO user community insights and perspectives, discussion of inherent ISCO limitations, and insight into ISCO best practices. Finally, included is CORT3D, a 3-D, permanganate-ISCO, reactive transport simulation model offering visualization and optimization of various oxidant delivery options.
- Frequently Asked Questions Guide – This guide contains 25 commonly asked questions by the ISCO user community and offers a concise overview of ISCO applicability, design, implementation, and performance for groundwater remediation.
Fundamentally, ISCO success depends on having enough of the correct oxidant in contact with the contaminant(s) over sufficient time. Enough oxidant must include enough to degrade the contaminant(s) and account for natural oxidant demand, reduced metals, and oxidant decomposition. Distribution occurs at the DNAPL scale, the lithological scale, the plume scale, and the site scale. All of these must be addressed in ISCO design.
The TPM offers a suggested data checklist as a basis for ISCO screening and design. It is acknowledged that not all sites will initially have this extensive of a dataset, and such data may need to be collected in later phases. The degrees of parameter refinement will vary depending on the stage of the project. To delineate the extent of contamination, monitoring wells spaced every 300 ft may be adequate for very large sites, but this spacing may not be adequate where the radius of influence of an injection well may only be 25 ft. A conceptual site model should be developed and can be prepared in various ways ranging from purely graphical to text supplemented with key graphics (e.g., contaminant mapping, hydrogeological cross sections). Projects lacking datasets can proceed with the TPM’s e-protocol; however, data gaps will likely introduce design uncertainty.