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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.

 

In Situ CL-Out Bioremediation of Industrial Solvents

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Case Study :

Industrial Manufacturing Site, Illinois

Remediation Summary

Leaks from an aboveground solvent tank impacted soil and ground water quality at a manufacturing site in Illinois.  The impact was found under the adjoining building as well as the area near the tank.  The soil and ground water were treated in situ with CL-Out® bioremediation microbes.  Through cometabolism CL-Out® microbes reduced the contaminant concentrations to acceptable levels in less than one year.

Contaminants Soil Results (mg/Kg) Ground Water Results (mg/L)
Pre-Treatment Post- Treatment Pre-Treatment Post- Treatment
PCE 41.8 1.69 5.59 0.006
TCE 4,670 632 15.6 0.026
Cis 1,2-DCE 171 56.6 7.43 0.029
Vinyl Chloride BDL BDL 0.095 0.013

Implementation and Results

Soil Type:  Silty clay till

Treatment Area:  15,000 sq. ft.

Unsaturated soil thickness:  16 ft.

Saturated aquifer thickness:  5 ft.

Treatment: Two applications, initial treatment with 13 units of CL-Out® and follow up treatment with 5 units.

Product Cost: $30,000

Conclusions

CL-Out® bioremediation quickly and cost-effectively reduced the contaminant concentrations to acceptable levels.  Through cometabolism the parent and daughter products were removed simultaneously.  CL-Out® bioaugmentation accelerated the site remediation and reduced uncertainty by applying the right microbes where they were needed.

Aerobic Cometabolism of PCE at an Industrial Site in Tampa, Florida

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Project Summary

Degreasing solvents were found in the ground water at an industrial manufacturing facility in Tampa, Florida.  The solvents include PCE and its associated breakdown products. The source of the ground water contaminants was found to be a former water treatment system drain field.  CL-Out® bioremediation was implemented to reduce the volume of contamination in the source area and down gradient. CL-Out® is a consortium of Pseudomonas sp. that produces constitutive enzymes to cometabolize PCE and other halogenated solvents.  Dextrose is added with CL-Out® to provide a substrate for microbial growth.  Application of CL-Out® bioremediation at this site reduced the total chlorinated solvent concentrations as much as 99% in less than 6 months.

Geology and Hydrogeology

The site is located in Tampa, Florida where the geology is characteristically interbedded silt and sand.  The background ground water redox conditions of the aquifer are not known.

Contamination

The PCE and elevated concentrations of daughter products were found in ground water down gradient of the former drain field.  The PCE concentrations were as high as 280 µg/L and DCE concentrations were as high as 4,400 µg/L, which indicates that there was significant contaminant degradation occurring, but the natural degradation stalled at DCE.   Petroleum hydrocarbons were also present in the ground water and may have served as an oxygen sink during the degradation of the petroleum products.

Remediation Design

CL-Out bioremediation was implemented in the ground water to accelerate the remediation of the source area.  A 55-gallon slurry of  CL-Out was injected on February 11, 2003.

Monitoring wells in the source area and surrounding area were sampled to assess the progress of the remediation.   The following table shows the pre-treatment and post-treatment CVOC concentrations in a source area monitoring well (MW-1) near the application of CL-Out.

 Source Area (MW-1)

Sampling Date CVOC Concentrations (µg/L)
  PCE TCE DCE VC
3/28/02 280 750 4,400 BDL
12/19/02 86 120 1,100 BDL
2/11/03 CL-Out Injection
2/24/03 350 280 1,600 BDL
7/7/03 4.6 6.0 63 BDL

RESULTS

After application CL-Out bioaugmentation the chlorinated solvent concentrations in MW-1 decreased by as much as 99%.  Overall the total mass of contamination was significantly diminished by the bioaugmentation in a short period of time to accelerate the natural degradation.

Using Cl-Out to Finish Remediation Following Chemical Oxidation

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CL-Out was used to complete the remediation of ground water contaminated by chlorinated solvents from a former dry cleaning site in Rockville, Maryland.  The ground water contamination had migrated from leaking sewer lines to underlying bedrock fractures.  Fenton’s Reagent was first applied to the site, but the PCE concentrations increased due to desorption.  Subsequently, sodium permanganate was applied to the site.  After the application of 5,000 kilograms of sodium permanganate in 50 locations, the PCE concentrations decreased from the post-Fenton’s Reagent high, but was still three times higher than the original concentrations.

The conditions of the aquifer shifted to more aerobic after the chemical oxidation.  CL-Out aerobic cometabolism was applied to remove the residual contamination and accelerate natural attenuation.  CL-Out was applied in one 165-gallon injection followed by the addition of dextrose as a cometabolic substrate. The natural recharge of oxygen and residual iron, sulfate and manganese are believed to be the electron acceptors for the cometabolism.

According to the reporting author, ” bioremediation is very effective at treating chlorinated solvent contamination at the site.”

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