In situ biological treatment, or bioremediation, has been increasingly successful as a remedial application, especially as new products and systems are being developed to better support the biological degradation process. One such process, known as enzyme-catalyzed Dissolved Oxygen In Situ Treatment (DO-IT), is consistently proving itself extremely effective at in situ treatment of petroleum hydrocarbon contaminants, including methyl tertiary butyl ether (MTBE). This article discusses the problems associated with MTBE remediation, and summarizes the retrofit of a pump and treat (P&T) system with the revolutionary DO-IT technology. Using this supplemental remediation approach, site soil and groundwater cleanup goals for dissolved BTEX and MTBE were achieved within one year.

MTBE…Why so difficult?

As concern about MTBE contamination in groundwater continues to grow, the need for remediation technologies capable of treating this compound becomes more critical. In comparison to petroleum products, MTBE poses significant problems when it escapes into the environment through gasoline releases, typically from underground storage tank (UST) systems, aboveground storage facilities, or pipelines. MTBE is capable of traveling rapidly through soil, is much more soluble in water than most other petroleum constituents, and is considered more resistant to biodegradation. Therefore, it often travels farther than other gasoline constituents, making it a more likely threat to impact public and private drinking water wells.

Because of its solubility in water and, consequently, its tendency to form large contaminant plumes, petroleum releases with MTBE are more difficult, costly, and time-intensive to remediate than petroleum releases that do not contain MTBE. Furthermore, traditional remediation methods such as pump-and-treat, soil vapor extraction, and air sparging have had difficulty showing consistent MTBE reductions. However, the DO-IT process has successfully achieved MTBE treatment at numerous sites, including use as a retrofit of existing treatment systems that have reached their performance limits.

How the DO-IT Technology Works….

Bioremediation is the process of using bacteria and other biological enhancements under controlled conditions to convert organic compounds (in this case, petroleum hydrocarbons) to carbon dioxide, water, and energy for cell production. The enzyme-catalyzed DO-IT process promotes this process by using proprietary biological products in combination with a highly specialized in situ oxygenation equipment platform to obtain rapid reduction of petroleum contaminants. The biological enhancements includes a proprietary multi-enzyme complex solution that significantly increases the rate of contaminant degradation by catalyzing the conversion of aromatic and aliphatic hydrocarbons to fatty acid. In combination with a highly specialized TPH-specific bacterial consortium, petroleum hydrocarbons are degraded to the endproducts of carbon dioxide and water.

As with most in situ bioremediation efforts, contaminant degradation is usually limited by the amount of available oxygen (the electron acceptor in aerobic biological processes). Therefore, the DO-IT technology includes a unique equipment platform, the BioBox™, which contains a specialized pure-oxygen mixing process that generates high-dissolved oxygen water at concentrations of approximately 40 ppm. These dissolved oxygen levels are approximately 4 times what conventional systems can provide; since oxygen is usually rate limiting, the DO-IT technology can effectively quadruple the rate of contaminant degradation. The BioBox™ injects the oxygenated, biologically-amended water into the subsurface for continuous continuous support of biological degradation. For treatment of adsorbed soil contamination in the vadose zone and the hydraulic zone of fluctuation (“smear zone”), the DO-IT process includes vapor-phase air/oxygen injection capability. This feature provides unlimited flexibility for site applications.

The ideal DO-IT application is a closed-loop extraction/enhancement/re-injection scenario, which recycles the oxygenated treatment water throughout the zone of contamination. This provides biological contact and support, improving in situ treatment efficiency and decreasing overall treatment time. The following paragraphs summarize a DO-IT retrofit at a Connecticut gasoline station.

Site Treatment…A Definite Challenge

The site is an active gasoline station property located in a rural area, with a surface water stream downgradient from the contaminant plume. Previous gasoline releases occurred on the site as a result of leaky dispenser piping. Subsequent site characterization activities indicated MTBE and BTEX contaminants as well as gasoline-range petroleum constituents in the soil and groundwater. Remediation of contaminated soil and groundwater at the site was necessary to control any offsite migration and potential impact to the downgradient stream.

A P&T system was installed in the mid-1990s. After 4 years of operation, the system had achieved only marginal contaminant reductions, with no additional mass removal evident (based on site groundwater and system O&M data). The DO-IT process was retrofitted to the existing P&T system in an effort to reduce groundwater contaminant concentrations to the desired regulatory levels.

The original contaminant plume exhibited a flowpath along the natural south-southeast groundwater gradient, and covered approximately approximately 8,000 square feet. The hydraulic zone of fluctuation, or “smear zone”, was approximately 3-4 feet annually. The groundwater lies within a silty sand matrix at approximately 6-8 feet bgs. Four main groundwater monitoring wells, MW-3, MW-5, MW-8, and SP-1 exhibited BTEX and MTBE contamination.

Treatment Goals

The Connecticut Department of Environmental Protection (CTDEP) rates the groundwater aquifer as GA (denotes a potable potential-use aquifer), which requires cleanup to GA Groundwater Protection Criteria (GA GPC). Soil contamination is regulated by the GA Pollutant Mobility Criteria (GA PMC) limits. The following table summarizes these regulatory limits.

Groundwater (and soil) monitoring was the independent responsibility of the environmental consultant on the project. This monitoring was performed quarterly for most monitoring points. All laboratory results were independently analyzed by an accredited, licensed laboratory.

DO-IT…The Ideal Supplement

The critical application component for any in situ bioremediation project is adequate contact of the biological enhancements with the contaminants in the soil and/or groundwater. As discussed above, the DO-IT process uses a liquid extraction/enhancement/re-injection scenario to accomplish this contact. For this site, the DO-IT process was installed as a retro-fit of the existing P&T system. The site consultant utilized as much of the existing infrastructure as possible, including extraction wells and pumps. Vertical injection points were installed throughout the plume and the capture zone of the extraction wells. This DO-IT system also included an integrated bioreactor component for groundwater treatment prior to re-injection.

This layout allowed for both hydraulic control of the dissolved-phase contaminants and continuous movement of the treated groundwater (with dissolved oxygen, bacteria, and nutrient amendments) throughout the site. Monitoring wells within the contaminated plume were used to measure remedial progress. No injection into the monitoring/sampling points was performed, so that representative data points could be maintained throughout treatment.

DO-IT System Operation

An initial inoculation with the enzyme complexes and the specialized TPH-degrading bacterial consortium was performed in mid-1999. Since that time, the DO-IT system has performed automatic oxygenated water injection into the vertical injection points on a near-continual basis. Additionally, enzymes and the TPH-degrading bacterial culture are continuously metered into the oxygenated water to maintain a healthy degrading biological population. Water samples are collected monthly and/or quarterly to monitor both the nutrient concentrations and the bacterial plate count population within the aquifer. When water samples indicate deficient nutrient levels, a specialized nutrient blend is added to the injection water and applied to the subsurface.

Treatment Results…An Unqualified Success!

Significant degradation of the benzene, MTBE and TPH compounds was reported after the first 90 days of treatment. Contaminant degradation continued throughout 1999 and early 2000. Currently, benzene and MTBE levels in all wells are below the GA GPC limits for groundwater. Furthermore, recent soil sampling results also indicate degradation of all BTEX, MTBE, and TPH constituents below the GA PMC soil limits. DO-IT system operation is ongoing, with anticipated shutdown within 2-3 months.

With the DO-IT system, MTBE is being successfully degraded. The groundwater sampling results from this site show rapid and complete degradation of dissolved-phase MTBE. This capability by the DO-IT process has been verified under laboratory studies, and is being successfully utilized at other sites. Initial results at these sites further exhibit the effectiveness of the DO-IT technology for MTBE treatment as well as TPH cleanup.

Conclusions

In situ bioremediation, through the use of the DO-IT system, has achieved remarkable treatment of dissolved-phase benzene and MTBE compounds as well as adsorbed-phase BTEX and TPH contaminants. The success of this in situ bioremediation project can be attributed to a number of factors, including 1) consistent addition of highly active bacterial and enzyme enhancements, 2) process support from the automated DO-IT platform (for continuous site-wide oxygenation and process control), and 3) a well-designed injection/extraction system by the site consultant.

The integrated application of the DO-IT technology has resulted in rapid and effective groundwater cleanup of the MTBE, BTEX, and petroleum contaminants. The DO-IT process is a proven treatment system that should be considered when analyzing remedial alternatives for any petroleum-contaminated site. As this discussion illustrated, the DO-IT technology can be an extremely effective supplemental treatment component to any existing remediation system, and may be the answer to achieving your site cleanup goals.

For more information regarding the in situ technology presented in this article, please contact:

Mr. David Laughlin
Enzyme Technologies, Inc.
David@enzymetech.com
(503) 254-4331
www.enzymetech.com

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