Bioremediation Following Dual Phase Extraction Saves Hundreds of Thousands of Dollars

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Courtesy of CL Solutions, LLC

CL-Out® bioremediation was implemented at a dry cleaners site in Houston, Texas to reduce concentrations of residual PCE and other chlorinated solvents in groundwater following dual phase vacuum extraction.  After application of CL-Out® bioremediation the chlorinated solvent concentrations were reduced by 98% to 99% in less than 90 days.  The switch saved their client hundreds of thousands of dollars, according to In Control Technologies, of Houston, Texas, who was the project consulting and engineering firm for the investigation and remediation of the site.

Project Design and Implementation

Subsequent to the discovery of soil and ground water contamination by PCE and associated daughter products, a dual phase extraction system was implemented for 9 years.    While the dual phase extraction system had removed 1.2 million gallons of water and reduced the total CVOCs from 115,000 µg/L to 36,000 µg/L, the removal rate had reached an asymptote with PCE concentrations higher than 4,000 µg/L.  CL-Out® bioaugmentation was selected to treat the residual contamination. 

The soil and sediments beneath the site are part of the Chicot aquifer, which consists of discontinuous layers of sand and clay.  The aquifer has a relatively moderate hydraulic conductivity estimated at 10-4 cm/sec.  The area of residual ground water impact and bioremediation treatment was approximately 20,000 square feet.

CL-Out® microbes were injected into the ground water on three occasions between July 2005 and February 2006.  Based on the volumes of impacted ground water, three drums of hydrated CL-Out® were injected into the ground water on each occasion.  The total injection volume was less than .1% of the pore volume of the treated aquifer.

Results

CL-Out bioremediation reduced the contaminant concentrations by more than 98% in less than 90 days. 

The following table summarizes the results of application of bioremediation. 

Contaminant

Source Area (µg/L)

Down Gradient Results (µg/L)

Before

After

Before

After

PCE

4,100

1.9

430

<5

TCE

2,500

1.5

360

<5

Cis 1,2-DCE

34,000

65

590

8.9

Vinyl Chloride

<50

47

6.6

<5

The treatment cost for three round of bioaugmentation, including drilling and field services was less than $20,000.  For comparison, the annual cost for operation and maintenance of the dual phase extraction system was $75,000 per year.  Bioaugmentation reduced the overall project cost by eliminating years of on-going costs, saving possibly hundreds of thousands of dollars.

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