Metals Manufacturing Facility located in Cincinnati, Ohio

Site Summary:

Contamination by a wide range of volatile organic compounds (VOCs) was found in ground water at a metals machining company. The contamination resulted from the accumulation of incidental spills over years of operation. The operations included the use of a wastewater underground storage tank, a drum storage area and underground press pits.

In 2001, bioremediation was used to reduce the overall contaminant load in the ground water. CL-Out microbes were injected in the source area on a monthly basis for three months.

Geology and Hydrogeology

The property geology consists of a thin layer of unconsolidated silt and clay soil overlying glacial till deposits. Near the surface (4 to 7 feet below the surface) is a fine-grained silt and clay. A wet sand seam, two feet thick, is found 7 feet below the surface. Below the sand seam there is a silt zone with a varying clay component that graded into a confining glacial till. The till is underlain by shale and interbedded limestone bedrock to an unknown depth. The property is level to gently sloping, and the elevation decreases to the southeast. The ground water yield from the wet sand seam is 0.1 to 3 gallons per minute.

Ground Water Contamination

The remediation target was the VOCs in the wet sand zone. The area of ground water contamination exceeding 1 part per million (ppm) was approximately 560,000 cubic feet. The main contaminants were trichloroethene (TCE), cis-1,2-dichloroethene (1,2-DCE), and vinyl chloride. The highest concentration of VOCs found in ground water was 1.7 ppm.

Remediation Design

The main objective of the remediation was to decrease the VOC concentrations in the ground water so that acceptable risk standards could be achieved to facilitate the property sale. CL-Out bioremediation was implemented in the ground water downgradient of the source area. The CL-Out injections were coupled with 15 minutes of air injection to increase the microbial distribution and dissolved oxygen concentrations. The property owner’s objectives required fast results that did not disrupt the property use.

CL-Out was introduced through 26 one-inch diameter injection points that were installed using a direct push sampler. The small diameter injection points were installed to cover the area of the ground water plume. The injection point screened intervals were 5 to 15 feet deep. The injection points were placed approximately 30 feet apart.

During each injection, 385 gallons of CL-Out was injected into the subsurface. The inoculant was split among the injection points so that 10 to 25 gallons of solution was injected into each injection point.

Inoculations were made every 30 days to maintain the high microbial population for three months.

Results

After three inoculations the average total VOC concentrations were reduced by 67%. The total cost to remediate the ground water was about $80,000. This total included all injection well installations, monitoring, reporting and inoculations. The unit cost based on the ground water volume was $0.063 per gallon of ground water.