A Case History
In this project, ETTL Engineers & Consultants Inc. was authorized by Sonat Exploration Company to bioremediate petroleum-contaminated soil at a site within Tyler State Park, just north of Tyler, Texas. The site was located in close proximity to an approximately 35-acre recreational lake. Oil exploration, pumping, and gathering operations conducted at the site for years had resulted in significant petroleum hydrocarbon contamination. Crude oil storage tanks on the site had been removed before the project began, leaving, in some places, actual puddles of oil. The contaminated soil was shallow (approximately 1 to 1-1/2 feet in depth). So it was decided to remediate the soil in situ with ETTL's bioremediation process, which used indigenous microbes harvested from the site, multiplied in the laboratory, and then reintroduced into the site in a solution that also contained nutrients and biodegradable surfactants, and which was sprayed on (see the above photo). The project was closely monitored by the Texas Parks & Wildlife Department and the Texas Railroad Commission.
Initial site assessment and limited feasibility studies began in January 1994. Samples taken from the contaminated soils when initially analyzed were found to have TPH readings greater than 25,000 ppm. A target clean-up standard was established at less than 10,000 ppm, according to standards of the Texas Railroad Commission. A total of some 1250 cubic yards of soil was remediated to below target level - less than 1300 ppm - in approximately eight weeks of treatment. In some areas, readings were as low as 470 ppm. Remediation was completed, and the site leveled and seeded to restore it to its original condition in May 1944.
Following initial assessment activities, soil samples were retrieved and delivered to Dr. James Stewart of the University of Texas at Tyler (UT-Tyler), consultant to ETTL, who identified and isolated those site-specific indigenous microbes which could be used for biotreatment of the site, monitored their proliferation in the laboratory, and supplied freeze-dried microbial concentrates for the treatment phase of the project. The in situ treatment process used a modified land-farming method. The area where the biotreatment was to take place was cleared and then graded to drain at approximately 2% grade. A 2-ft high berm was constructed around the facility, and a sump area was constructed at the lower end. Soils were deep-plowed to a depth of approximately 2 ft, then thoroughly tilled for homogeneity. Once homogenized, the soils were treated with the microbial solution. Regular tilling at approximately 2-week intervals was performed to aerate soils, and additional plowing was twice performed to loosen the soil matrix. Petroleum hydrocarbon levels, microbial enumeration, pH, soil temperature, and moisture were monitored regularly to maximize effectiveness.
Run-on was limited to rainwater that fell into the immediate treatment area; and no run-off was permitted. Partially or fully remediated run-off was recycled to the treatment area to provide appropriate moisture. The run-off was inoculated with the same treatment solution. All water collected within the treatment area was consumed in the bioremediation process. Additional moisture, nutrients, pH adjusters, oxygen, microbes and surfactant were added as needed to assure continued viability of the bioremediation system. Following the initial inoculation (spraying on of the microbial solution), only one additional microbial inoculation was required. Most moisture that was applied came from rainfall.
The results exceeded the expectations and requirements of the client, providing cost savings over more typical treatment methods, as well as a cost slightly less that the original price quoted by ETTL. The client and the two state agencies involved were very pleased with the results of the project.
For more information on this project, contact
ETTL's Steve Kennedy
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