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Bioremediation - Case History: French Limited Superfund Site

Case History: French Limited Superfund Site

 

Background

French Limited in Crosby, Harris County, Texas (EPA Region 6) was a 25-acre sand mining site from 1950-1965. It was under permit from the Texas Water Quality Board for Petrochemical Waste Disposal as an industrial waste disposal facility until 1972. From 1966-1971, 70 million gallons of petrochemical wastes were disposed in the depressions that were created from sand extraction (an unlined 12-acre lagoon). In 1973, the permit was revoked. The primary contaminants in this waste were benzo(a)pyrene, vinyl chloride, and benzene. Benzene was at concentrations ranging from 400-500 mg/kg. Other primary contaminants in the sludge, soil, ground water, surface water, and air were volatile organic compounds (VOCs), phenols, heavy metals, and polychlorinated biphenyls (PCBs). These pose potential health risks including central nervous system disorders, liver damage, and cancer upon direct exposure.

In 1980, Superfund was enacted demanding immediate remediation of hazardous waste sites. In 1982, the EPA Superfund team, per request from the state department, constructed a large dike around the lagoon to protect from contamination spreading. This needed to be repaired later in the year. Some contaminated sludge was put back into the lagoon and some was placed in an approved landfill. In 1983, the French Limited was added to the EPA’s National Priorities List (NPL), which includes the most severe uncontrolled sites eligible for cleanup under the Superfund program.

In 1987, the EPA decided to try bioremediation, which was the first time that technology was used at a Superfund site.

Site Map


Figure 12 shows the map of the French Limited Superfund Site

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Figure 12French Limited Site Map (Environmental Protection Agency, 2013)

 

The site was extremely vulnerable because of its proximity to water sources and people. It is located within l00-year floodplain of the San Jacinto River and a shallow ground water system (20-50 feet deep) is in use by nearby residents. Figure 13 shows how flooding can spread the contaminants at the site. The nearest residence is within 300 feet of the main pit and the nearest drinking water well is within 1,500 feet of the main pit. This is a concern for the approximately 10,000 residents in Crosby and nearby communities. There are 300 residents within one mile of the site. Additionally, groundwater and surface water are used for drinking water and irrigation. 

 

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Figure 13 – Schematic of contamination at French Limited (Environmental Protection Agency, 1993)

 

Treatment

Bioremediation was chosen because it offered a less expensive option to destroy the same amount of waste as an incinerator in the same amount of time.

In-situ slurry-phase bioremediation was conducted to remedy the site. Bioremediation of the lagoon sludge and water, surface water, and ground water began in 1992 after a year of technical design and construction. To aid the treatment process, pumps were used to mix lagoon sludge with lagoon liquids. First the bottom sludge is broken up and then contaminated soil beneath the sludge is brought up and mixed with the lagoon liquids. The process utilized microorganisms that were present at the site. After all the sludge and liquids in the lagoon was treated the lagoon water was sent to the water treatment facility on site. Figure 14 shows a schematic of the treatment system. Also after treatment, the soil was mixed with clean fill and the surface later used for vegetation. The ground water treatment was governed by VOC concentration. Monitoring will continue for 30 years after initial treatment. Treatment was done in two 17 million gallon cells. A technology known as Mixflo was used for aeration. This system minimized air emissions during the bioremediation process. The treatment process took 11 months and 300,000 tons of soil and sludge were treated overall.

To compensate damage to fouled habitat from lagoon spillage of hazardous waste, the French Limited Task Group (FTLG) planted 23 acres of new wetlands near the site. 

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Figure 14 – Schematic of treatment at French Limited (Environmental Protection Agency, 1993)

 

Post-treatment 

The concentration of benzene post-treatment was in the range of 7-43 mg/kg. Overall, the total cost, including treatment, pilot studies, technology development, and backfilling, was $49 million.

After initial remediation, the French Limited site has been revisited several times to mitigate contamination from floods. These floods caused spills and dispersed hazardous wastes into nearby areas. From 1980-1983, the EPA was involved in three remediation projects. In 1989, flooding affected the drinking water source. A wall was constructed to mitigate this issue and in 1994 when another flood occurred, the wall functioned successfully. In 1993, bioremediation was performed on the main waste lagoon. In 1996, a ten-year Natural Attenuation program began. The first Five-Year review was approved in 1995 and a second Five-Year review was approved in 2002. From 2002 to 2005, in-situ bioremediation was performed. The EPA conducted analyses and wrote Ground Water Monitoring Reports in 2007, 2008, 2009, 2010, 2011, and 2012. 

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