A gasoline release from a fuel dispensing island on an active truckstop site impacted shallow groundwater at approximately 6-8 feet bgs. At the site, silt overburden is underlain by shallow fractured limestone bedrock, and due to a sloping bedrock horizon, groundwater intersects both the overburden soils and the fractured zone.
Targeted Environmental Media:
 Fractured Bedrock
The contaminant plume covered approximately 16,000 square feet, with seven main groundwater monitoring wells (MW-1, -2, -3, -4, -5, -6, and -7) exhibiting benzene and MTBE contamination. The hydraulic zone of fluctuation, or smear zone, was approximately 2-3 feet annually.
Major Contaminants and Maximum Concentrations:
- Benzene (13,000 µg/L)
- Methyl tert butyl ether (1,000 µg/L)
No technologies selected.
- Bioremediation (In Situ)
Comments:
Extracted groundwater from a series of extraction wells was used to supply water for the closed-loop recycle system, and existing air sparge wells, as well as several shallow injection laterals, were used for water injection. The Super-Ox™ oxygenation equipment was housed in a heated, weatherproof equipment shed located adjacent to the piping infrastructure. The extraction wells fed groundwater into the Super-Ox™ system, which treated, oxygenated, biologically-enhanced, and re-injected this water into the subsurface via the injection array.
This layout allowed for both hydraulic control of the dissolved-phase contaminant plume and continuous recycling of oxygenated treatment water throughout the site. Monitoring wells installed within the fractured bedrock zone were used to measure remedial progress. No injection into any monitoring wells was performed, ensuring that representative groundwater data could be collected throughout treatment.
5 ppb benzene and 20 ppb MTBE for the offsite plume
Significant degradation of the benzene and MTBE has been achieved within the first 5 months of system operation. Currently, the DO-IT technology has resulted in average benzene and MTBE reductions of 90% and 95%, respectively (see associated graphs). As of now, benzene and MTBE levels in all wells except MW-2 are below the Statewide Health Standards for groundwater. Site completion is anticipated by mid-2003 (a total treatment time of approximately 12 months).
With the DO-IT system, MTBE is being rapidly and successfully degraded. The groundwater sampling results from this site show ongoing, complete degradation of dissolved-phase MTBE. This MTBE degradation with the DO-IT process has been verified in both laboratory and field studies, and is being successfully utilized on numerous in situ projects.
In situ bioremediation using the DO-IT process can be a successful remediation technology for groundwater treatment in fractured bedrock formations. Successful DO-IT applications consistently achieve fast, complete treatment of dissolved-phase benzene and MTBE compounds. Requirements for effective application of the DO-IT process at fractured bedrock sites include:
1. A reasonable understanding of site geology and hydrology. In addition to plume characterization, information regarding groundwater flow patterns, flowrates, and localized hydraulic conductivites allow for successful design and implementation of a remedial strategy.
2. A powerful, complete bioremediation platform that can provide high levels of dissolved oxygen for continuous support of subsurface microbial kinetics. Automated process support from the turnkey Super-Ox™ equipment is ideal for supplying ongoing site-wide groundwater oxygenation and contact.
3. A well-conceived monitoring plan to provide ongoing data that can be used to make appropriate system adjustments throughout treatment.
The integrated application of the DO-IT technology has resulted in rapid and effective MTBE and BTEX cleanup within a fractured bedrock groundwater zone. The DO-IT process is a proven bioremediation system that can be used as a primary remediation component, or in conjunction with other technologies to cost-effectively reach regulatory treatment goals.
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