- Program Areas
- Installation Energy and Water
- Environmental Restoration
- Munitions Response
- Resource Conservation and Resiliency
- Weapons Systems and Platforms
New Application of Pre-Fabricated Vertical Drains to Remediate Low-Permeability Contaminated Media
Dr. Stephen Richardson | GSI Environmental, Inc.
Difficult-to-treat sites are increasing as a percentage of total Department of Defense (DoD) chlorinated solvent sites. This is due to the fact that untreated sites continue to age and transform from middle stage sites (sites where dense nonaqueous phase liquid [DNAPL] sources are active) to late stage sites (sites where matrix diffusion sources dominate), while treated sites contain low-permeability (K) source zones that are too strong to close out the site or rely on monitored natural attenuation. An inexpensive technology that reliably addresses mass flux limitations of contaminants leaving low-K source zones and enhances natural attenuation processes is needed.
The overarching objective of this demonstration is to reduce delivery problems associated with conventional injection-based remediation approaches. Specific technical objectives include demonstrating that:
- Conventional geotechnical soil consolidation/dewatering technology comprised of specially designed vehicles that can install 100 or more wick drains per day at costs of <$1 per vertical foot can be repurposed to remediate contaminated sites.
- A biodegradation agent (neat vegetable oil) can be injected into the wick drain so that oil travels vertically downward to the bottom of the drain.
- The oil will slowly release soluble electron donor into the groundwater directly outside the semi-permeable wick drain cover, creating a reaction zone in the few inches around the wick drain.
- By having closely spaced (every 2 to 3 feet) vertical reaction zones, the back diffusion rate of chlorinated solvents in low-K zones can be greatly increased, thereby significantly shortening the “long tail” that is often associated with current in situ and pump and treat (P&T) remediation projects.
This novel method for remediating contaminated sites leverages existing, pre-fabricated vertical drain technology, not to drain the soil (as in typical geotechnical applications) but to deliver amendments to the treatment zone. A production-line approach is used. Soil improvement contractors have developed specialized equipment to take large 1,000-foot rolls of the wick drains and “stitch” them into closely spaced drainage systems in soils with typical spacing on the order of 2 to 3 feet, down to a depth of 80 feet. Wick drains are used to deliver oil to the contaminated zone. Simulations and models will be used to demonstrate that, while reducing concentrations below maximum contaminant levels (MCLs) in a hypothetical well above heavily contaminated clay required more than 500 years for the base case, it only requires 12 years for an intensive wick drain treatment.
The repurposed wick drains address hard-to-treat chlorinated solvent source zones with strong matrix diffusion sources over large areas. These drains provide a method to circumvent the delivery problems associated with conventional injection-based remediation approaches and may be used in place of conventional injections. Wick drains also have the potential to reduce the longevity of long-running P&T systems by reducing the back diffusion time for contaminants that are slowly being released from clays and silts. (Anticipated Project Completion - 2019)