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 www.cl-solutions.com.

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.”

Click here to view the USEPA Technology Innovation Report.

CL-Out Completes Remediation After Stalled Natural Attenuation

Investigation of an industrial dry cleaners near Philadelphia, Pennsylvania found concentrations of breakdown products of  PCE in the soil and ground water.  The parent PCE presumably was reductively dechlorinated to TCE, DCE and vinyl chloride.  However, since the daughter products DCE and vinyl chloride are more readily degraded under aerobic conditions, the breakdown was incomplete and natural attenuation stalled.  CL-Out was applied with an oxygen supplement to complete the remediation under aerobic conditions favorable for DCE and vinyl chloride bioremediation.


The geology of the property is interbedded sandy silt, silt and clay layers.  The contamination was found in a shallow silty sand formation that is underlain by a dense clay layer.  A sand layer directly beneath the clay layer was unaffected by the contamination in the upper sand.


The perched ground water was within a fill layer, so the hydraulic conductivity was expected to be variable.  Slug testing results showed the hydraulic conductivity in the upper sand ranged from 1.1 to 3.9 ft/day.  The ground water flow direction was consistently toward a local surface stream.  The extent of the contamination plume was approximately 10,000 square feet.

Ground Water Contamination

The contaminants found at the site were mainly TCE and DCE with trace levels of vinyl chloride.  This suite of contaminants indicated that there was natural degradation of the PCE to lesser halogenated compounds.  The maximum concentrations prior to bioaugmentation were 220 ug/L of DCE, 9.2 ug/L of TCE and 31 ug/L of vinyl chloride.


CL-Out was introduced into the ground water through one-inch diameter tubing installed using a direct push sampler.  The use of small diameter injection points made the remediation possible without disruption the dry cleaner operations.  Three injection points were installed in the high concentration area.  Additional injection was made in places where shallow soil had been excavated.

The CL-Out injection was a dosing of four drums in December 2005.


Three months after the injection of CL-Out, the DCE concentration dropped from 200 to 54 ug/L.  The vinyl chloride concentration decreased from 31 to 11 ug/L.  After seven months the TCE and vinyl chloride concentrations were below detection limits and the DCE concentration decreased to 2.9 ug/L.

Due to the relatively anoxic conditions, an oxygen supplement was added to support the aerobic cometabolism.  During the active treatment the dissolved oxygen levels increased from 1.9 to 8.5 mg/L.  The CL-Out microbial population was maintained at 200,000 cells per milliliter.

The monitoring results suggest that by supplementing the dissolved oxygen levels, the CL-Out population was maintained for an extended period.  The extended peak of CL-Out population made possible a greater level of contaminant removal.

Clu-In Reports on Aerobic Cometabolism

The US EPA Technology and Field Services Division produced a report on aerobic cometabolism of chlorinated solvents under their Contaminated Sites Clean-Up Information program on February 7, 2019.  This report includes an overview of aerobic cometabolism and guidance on application and monitoring.  Click here to link to the report.

While the report cites the research of Thomas Wood, et. al., it does not include the research demonstrating aerobic cometabolism of PCE.  The following links go to the research on aerobic cometabolism of PCE.



One of the benefits of aerobic cometabolism is the applicability of bioremediation to shallow soil and ground water that may cause vapor intrusion risk at dry cleaners.  Removing the source of the vapors under natural conditions,without business interruption, is the most economical and sustainable solution.

CL Solutions’ CL-Out consortium has been used for bioremediation of PCE and other chlorinated solvents at dry cleaners and industrial sites since 1999.  Contact CL Solutions for information and a site evaluation.

Soil Bioremediation at Dry Cleaners

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.