Contaminant Flux Reduction Barriers for Managing Difficult-to-Treat Source Zones in Unconsolidated Media
ER-201328
Objective
The overall objective of this project is to demonstrate how to use inexpensive flow reduction agents to manage difficult-to-treat chlorinated solvent source zones. This approach will reduce the mass flux of contaminants leaving the source zone so monitored natural attenuation (MNA) can be used as a closure technology and increase the natural rate of biodegradation within the source by diverting competing electron acceptors (dissolved oxygen, nitrate, and sulfate) from the treatment zone. Specific objectives for the demonstration project are to: (1) evaluate two different flow-reduction materials, recalcitrant edible oils and silica gels, in terms of cost, ease of installation, and effectiveness; (2) determine cost factors of this technology relative to conventional remediation strategies for chlorinated solvents in terms of key unit costs ($ cubic yard and $ per acre); (3) determine if a 1 order of magnitude or greater reduction in mass discharge from actual treatment zones is achievable using this flux reduction technology; and (4) demonstrate benefits from electron acceptor diversion around chlorinated solvent treatment zones.
Technology Description
The technology to be demonstrated combines the concepts of source zone attenuation, high-resolution mass flux, and improving the efficiency of biodegradation reactors. It aims to reduce groundwater flow through the “mobile porosity” of a subsurface, which is estimated to be 0.02 to 0.10. By creating a barrier around a treatment zone, groundwater flow carrying competing electron acceptors will be diverted, resulting in an engineered reaction zone similar to the Enhanced Reductive Dechlorination Zone (ERDZ) concept previously developed, which is part of the Biobalance Toolkit. The reduction in competing electron acceptors in the treatment zone enables the appropriate geochemical environment for an enhanced reductive dechlorination zone.
The technology demonstration involves the testing of two flux reduction materials: silica gel (sodium silicate or colloidal silica) and a vegetable-oil formulation. Several vegetable oil-formulations will be created and tested in laboratory-scale batch and column studies to determine the most effective formulation for creating barriers. Additionally, the extensive scientific literature regarding properties and field injection protocols of silica gel will be used to select the most cost-effective silica gel material (either sodium silicate or colloidal silica) and the specific silica gel electrolyte/reagent necessary for subsurface gelling. The results of this evaluation will be used to select one type of silica gel and one type of vegetable-oil formulation for the small-scale field demonstration. In this field demonstration, two treatment cells will be established, testing the two different flux reduction materials in a clean zone. Pumping tests will be conducted at each cell to determine the reduction in transmissivity due to barrier installation. Based on the results of this small-scale demonstration, the best-performing flux reduction material will be chosen for the large-scale demonstration. In this field demonstration, detailed hydrogeological data will be obtained using cone penetrometer technology at several locations, while passive flux meters will be used to determine the reduction of mass flux after barrier installation. Also, geochemical parameters will be analyzed to calculate the reduction in competing electron acceptors. Performance objectives include: (1) reduction in groundwater flow of at least 1 order of magnitude (OoM), (2) life-cycle cost for flux clog application less than50% of current in situ treatment technologies, and (3) mass flux reduction of at least 1 order of magnitude.
Benefits
The technology, if successful, has the potential to be an important remediation alternative for hard-to-treat chlorinated source zones, particularly ones with large, persistent matrix diffusion sources over large areas. Costing models show that it has the potential to be significantly cheaper (less than $15 per cubic yard for large sites), provide better performance, and be more predictable and reliable than existing technologies. Additionally, little to no maintenance and operating costs are involved, making this a cost-effective technology over the long term.
Unlike most remediation systems in which costs are directly proportional to the size of treatment areas, this technology has decreasing costs per source zone area. If proven to be feasible, the methods are also easy to implement and scale up, making them attractive options for closing large sites. (Anticipated Project Completion - 2015)
Points of Contact
Principal Investigator
Dr. Charles Newell
GSI Environmental Inc.
Phone: 713-522-6300
Fax: 713-522-8010
Document Types
- Fact Sheet - Brief project summary with links to related documents and points of contact.
- Final Report - Comprehensive report for every completed SERDP and ESTCP project that contains all technical results.
- Cost & Performance Report - Overview of ESTCP demonstration activities, results, and conclusions, standardized to facilitate implementation decisions.
- Technical Report - Additional interim reports, laboratory reports, demonstration reports, and technology survey reports.
- Guidance - Instructional information on technical topics such as protocols and user’s guides.
- Workshop Report - Summary of workshop discussion and findings.
- Multimedia - On demand videos, animations, and webcasts highlighting featured initiatives or technologies.
- Model/Software - Computer programs and applications available for download.
- Database - Digitally organized collection of data available to search and access.