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Case Study of In-Situ Bioremediation of Recalcitrant Organics

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A history of spills and/or releases at two adjacent dry cleaning facilities near Houston, TX, resulted in significant soil and shallow groundwater contamination with PCE and daughter products. Soil was relatively permeable, with rapid groundwater flow beneath the site. A long, narrow, off-site plume extended beneath a residential neighborhood. Chemical oxidation was employed initially with only limited success in the areas of highest contamination. To take advantage of the soil permeability and other site conditions, the response action was amended to include enhanced aerobic bioremediation by cometabolism. Specialty microbes were introduced into the plume in several injections over a 15-month period. This approach achieved total contaminant level reductions in the source area from 1,600 to less than 40 µg/L, and at the front edge of the plume, levels decreased from 500 to 5 µg/L.

For the full case study click here:

Brusenhan, J.D., M.F. Marcon, and M.T. Saul, CL-Solutions, LLC. A&WMA’s 98th Annual Conference and Exhibition, 21-24 June 2005, Minneapolis, Minnesota, Paper 1069, 10 pp, 2005

Dry Cleaner Bioremediation and Brownfield Redevelopment

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Site Description

Dry cleaning solvent spills in a storage area lead to the contamination of soil and ground water on the property of a 50-year-old dry cleaners in the middle of a hot brownfield redevelopment.   After the contaminated soil was excavated for off site disposal to the most practical extent, residual perched ground water contamination impacted the redevelopment of the property.

The soil excavation was used as an infiltration gallery as part of a recirculating ground water recovery and treatment system.  The flushing reduced contaminant concentrations, but the levels were still far above the levels required to achieve no further action status.  CL-Out was added to the recirculating ground water and the cleanup goals were achieved in less than two years and were maintained through two years of  post treatment monitoring.

Site Characteristics

Geology and Hydrogeology

The site is on a fluvial terrace adjacent to the Ohio River.  The shallow soils are clayey silts to sit to eight feet deep.  An interbedded sandy zone that formed the first water-bearing zone was encountered from 8 to 12 feet deep.  Perched ground water occurred in the sandy zone at 12 feet below grade.

Ground Water Contamination

 The size of ground water plume that resulted from the spills was estimated to be 3,500 square feet.    The ground water contamination was mainly PCE with a maximum concentration of 11,000 ug/l prior to soil removal or ground water treatment.  The daughter compounds TCE and DCE were detected up to 17 and 12 ug/l respectively.  After three years of recirculation and flushing, the maximum PCE concentration was reduced to 2.3 ug/l and the daughter compounds were below detection limits.

Results

CL-Out bioaugmentation was implemented to supplement the flushing system.  By adding CL-Out on two occasions over two years, the contaminant concentrations were reduced to below drinking water standards.  During two years of post treatment monitoring the DCE concentrations rebounded to above the MCLs.  CL-Out bioaugmentation was implemented again and within three months the contaminant levels were below drinking water standards and remained below drinking water standards for nine months.  After post closure monitoring verified the cleanup goals would be maintained, the KDEP issued a “No Further Action” letter for the site.

The following chart shows the PCE contaminant trend in one of the key monitoring wells during the remediation and post closure monitoring.

Cost

The CL-Out cost during this remediation project was less than $10,000.

 

Soil Bioremediation at Dry Cleaners

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Permanently remove vapor intrusion risk

Soil bioremediation is a more effective strategy for managing the vapor intrusion risk at dry cleaners where solvents have contaminated soil or shallow ground water.  Soil bioremediation quickly eliminates the problem, while long-term vapor mitigation ties up resources in on-going operation, maintenance and monitoring costs.  Soil bioremediation eliminates the source of  vapors entering the cleaners and adjoining properties.  The source removal restores the full property value without disrupting operations.

CL-Out microbes have been used at many sites in the US and Canada to remove PCE contamination from soil at dry cleaners and other industries where solvents are used. CL-Out is a consortium of microbes selected for their ability to cometabolize chlorinated solvents under aerobic conditions.  The microbes are pumped into the soil through small boreholes in the building or surrounding area.  Once in the soil, the microbes produce metabolic enzymes that convert the PCE into carbon dioxide and water without generating harmful by products.

The following case studies are examples of how quickly and cost effectively CL-Out bioremediation removes the soil contamination:

Chicago, Illinois

CL-Out bioremediation reduced concentrations of dry cleaning solvents in soil to allow for the redevelopment of a property into luxury condos.  After the old building was removed, the contractor mixed CL-Out microbes into the PCE-contaminated soil.  After 90 days the soil was tested to verify success.

The 90-day sampling showed that the remediation met the site cleanup standards.  PCE was reduced by more than 95% from a maximum of 3,100 mg/kg to less than 120 mg/kg.  A “No Further Action” letter was submitted to IEPA.  The CL-Out cost for the project was $13,000.

Orange County, California

At a site in southern California, the soil and ground water contamination was removed at at operating dry cleaners without interrupting the business operations.  CL-Out microbes were injected into the soil and ground water through small-diameter borings.  Inside the building, hand-dug borings less than 3-inches in diameter were used for the treat the soil. Two drums of CL-Out microbial solution were injected into 80 cubic yards of contaminated soil.

After 30 days soil sampling showed the PCE concentration was reduced by 85% from 775 ug/Kg to 115 ug/Kg.  No daughter product were generated during the bioremediation.

The ground water was treated simultaneously and the contaminant concentrations were reduced by more than 90%.

The cost for CL-Out to treat both soil and ground water was $9,500.

Click here to view the full case study.

Call CL Solutions to discuss removing the vapor intrusion risk at your property.