Case Study of In-Situ Bioremediation of Recalcitrant Organics

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.

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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

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.


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.


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


Houston, Texas Dry Cleaner Site Remediation in Less than 6 Months


Dry cleaning solvents were found in the ground water adjacent to a dry cleaning facility located in a commercial shopping center in Houston, Texas. InControl Technologies, Inc. of Houston, Texas was the environmental consulting firm that completed the site investigation and remediation.

CL-Out® bioremediation was implemented to reduce the mass of contamination in the source area. CL-Out® is a consortium of Pseudomonas sp. that produces constitutive enzymes to cometabolize PCE and other halogenated aromatic compounds.  Dextrose is added with CL-Out® to provide a substrate for microbial growth.  Application of CL-Out® bioremediation at this site achieved the cleanup goals in less than 6 months.  The cleanup goals were maintained for more than one year to achieve project closure.

Geology and Hydrogeology

The site is located on a coastal plain where the geology is characteristically interbedded silt and sand deposits overlying a thick cohesive clay formation.  The affected aquifer was a silty sand zone approximately 40 to 55 feet below grade.  The aquifer ground water yield was low and the ground water was classified as Class 3 ground water.

The ground water aquifer was naturally aerobic.  Dissolved oxygen measurements taken from monitoring wells in the source area ranged from 2.6 to 5.4 mg/L.  The oxidation-reduction potential (ORP) measured in the same wells ranged from 89 to 303 mveq.  The aerobic conditions of the aquifer favored aerobic CL-Out® cometabolism.


Monitoring wells were installed on all sides of the dry cleaners, but access restrictions prevented the installation of monitoring wells inside the building.  The site layout including sampling and treatment locations are shown on the attached figure.  PCE and concentrations of daughter products, including TCE and cis-1,2 DCE were found in ground water adjacent to the dry cleaners and down gradient businesses.  PCE concentrations in the source area ranged from 0.260 mg/L to 0.860 mg/L prior to remediation.  The TCE concentrations ranged from 0.031 mg/L to 0.085 mg/L. The cis-1,2 DCE concentrations ranged from 0.096 mg/L to 0.67 mg/L.  Vinyl chloride was not detected prior to remediation.  The sampling results are summarized in the attached table.  The contamination plume was estimated to be 7,500 square feet.

While the presence of breakdown products suggested natural attenuation by biological destruction was occurring, bioaugmentation was implemented to accelerate the site remediation.

Remediation Design

CL-Out bioremediation was implemented in the ground water in the source area and accessible down gradient locations.  Most of the down gradient plume, however, was inaccessible for direct treatment.  Due to limited access, the down gradient areas were treated by attenuation as the source mass was destroyed up gradient.  Eight temporary injection wells were installed around the dry cleaner building and source area.  The injection points were set with 10-foot-long screened intervals from 40 to 55 feet deep.  The temporary injection wells allowed for repeat inoculations without additional drilling costs.

CL-Out® organisms were injected into the affected aquifer in two events.  On April 15 and June 30, 2005, 50 gallons of hydrated CL-Out® were injected into the temporary injection wells.   Approximately 10 gallons of CL-Out® solution was gravity fed into each injection well without additional pressure.

Monitoring Results

Ground water samples were taken from the monitoring wells for laboratory analysis for the contaminants and field measurements of dissolved oxygen and ORP.  The field parameters show that after application of CL-Out® bioaugmentation the dissolved oxygen levels and ORP decreased.  This decrease confirms aerobic metabolism was taking place.  The PCE and TCE concentrations also decreased immediately following the injections.  However, there was also an increase in the cis-1,2 DCE concentrations following the bioaugmentation.  The cis-1,2 DCE concentrations decreased to the pretreatment levels in each of the source area wells except MW-4 during the post treatment monitoring.  Vinyl chloride was detected in MW-1 and occasionally in MW-8 and MW-11 after bioaugmentation, but persisted in only MW-1.  Maintaining aerobic conditions would have reduced or prevented the accumulation of the daughter products. Nevertheless, the daughter product concentrations did not exceed the Class 3 Standards applicable to the site.

The following tables show the PCE concentration trends during remediation.  MW-2, shows the concentration of PCE in a well outside of the treatment area remained relatively constant during the same time.


Ground Water Sampling Results Summary Table

Monitoring Date PCE TCE cis-1,2 DCE VC D.O. ORP
Well   (mg/L) (mg/L) (mg/L) (mg/L) (mg/L) (mveq)
GW Class 3 PCL 0.5 0.5 7 0.2    











3/24/04 0.800 0.090 0.500 <0.001 5.8 131.7
8/13/04 0.700 0.100 0.510 <0.001 5.8 134.3
11/23/04 0.660 0.045 0.550 <0.005 5.4 154.6
3/30/05 0.750 0.067 0.550 <0.001 5.0 303.5
First CL-Out Inoculation
6/2/05 0.230 0.045 1.100 <0.001 0.9 -131.1
 Second CL-Out Inoculation
9/19/05 0.065 0.044 0.900 0.0032 3.0 -105.4
12/29/05 0.016 0.0084 0.650 0.021 3.0 -30.8
3/17/06 0.0054 0.0021 J 0.600 0.030 0.9 -104.7
6/8/06 0.018 0.018 0.120 0.039 1.2 -107.7











3/23/04 0.540 0.036 0.110 <0.001 4.9 128.1
8/13/04 0.760 0.039 0.140 <0.001 5.0 128.0
11/23/04 0.530 0.026 0.130 <0.005 5.2 141.2
3/30/05 0.410 0.019 0.096 <0.001 5.1 220.3
 First CL-Out Inoculation
6/2/05 0.330 0.019 0.120 <0.001 4.2 -79.3
Second CL-Out Inoculation
9/19/05 0.390 0.028 0.140 <0.0003 3.4 -81.8
12/29/05 0.410 0.031 0.200 <0.001 2.8 -20.8
3/17/06 0.089 0.021 0.410 <0.0003 0.6 -102.6
6/8/06 0.250 0.032 0.300 <0.00017 1.1 -103.2










8/23/04 0.580 0.046 0.220 <0.001 3.1 88.7
11/23/04 0.260 0.028 0.280 <0.001 4.7 157.8
3/30/05 0.700 0.039 0.330 <0.001 3.7 287.0
 First CL-Out Inoculation
6/2/05 0.150 0.031 0.250 <0.001 3.0 95.9
Second CL-Out Inoculation
9/19/05 0.045 0.0095 0.920 0.00051 J 4.2 24.1
12/29/05 0.011 0.0013 0.420 0.0027 3.3 33.6
3/17/06 0.0045 J <0.0023 <0.0029 <0.003 1.1 34.4
6/8/06 0.0024 J <0.00025 0.300 0.0024 J 1.0 -106.3










8/13/04 0.580 0.085 0.420 <0.001 2.8 129.1
11/23/04 0.580 <0.2 0.480 <0.2 3.3 150.5
3/30/05 0.860 0.074 0.670 <0.001 2.6 278.3
First CL-Out Inoculation
6/2/05 0.270 0.031 0.490 <0.001 2.8 161.3
 Second CL-Out Inoculation
9/19/05 0.180 0.023 0.720 0.00081 J 3.5 77.9
12/29/05 0.096 0.0083 0.120 0.0017 2.9 61.9
3/17/06 0.046 0.0062 J 0.057 <0.003 1.5 108.2
6/8/06 0.056 0.007 0.470 0.0039 J 0.9 62.2

After one year, the contaminant concentrations continued to meet the cleanup goals in the source area and a Certificate of Completion was recommended for the project.  The total CL-Out® remediation cost was less than $10,000.  More information can be obtained by contacting CL Solutions at 513-284-5940 or

Using Cl-Out to Finish Remediation Following Chemical Oxidation

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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Cometabolism of 1,1,1-TCA in a Mixed Solvent Plume

One of the benefits of CL-Out cometabolism is that the enzymes produced by the Pseudomonas sp. organisms convert a wide range of organic chemicals into organic acids that can be metabolized.  The aggressive application of CL-Out organisms to soil and ground water at a chemical mixing company removed the source of ground water contamination by chloroethanes and chloroethenes,  including PCE and 1,1,1-TCA.  The aerobic cometabolism of these compounds achieved MCLs in less than 6 months.  Click here to view the case study Mixed Solvent Plume Cometabolism by CL-Out