Chemical Mixing Company located in Cincinnati, Ohio

Site Summary:

Contamination by a wide range of volatile organic chemicals was found in soil and ground water at a former chemical mixing company. The contamination resulted from the accumulation of years of incidental spills.

After the nature and extent of contamination was determined, the property owners found that remediation options were beyond their financial means. The owners’ only option was to install a containment system to prevent further migration of contamination. A pump and treat containment system was installed at the property line to control the ground water contamination in 1993.

In 2001 the property was sold to a new owner who wanted to develop the site and was willing to remediate the source area and terminate the obligation to provide ground water containment.

Geology

The setting of the site is a complex fluvial glacial region where tills and channel deposits are often interbedded. The surface material at the site was mostly industrial fill over silty clay till. At approximately 8 feet deep perched ground water was encountered in a sandy gravel zone. Dense silty clay, which was 90 feet thick with few scattered sandy zones, was underneath the perched aquifer.

Hydrogeology

The affected aquifer was a perched sandy gravel zone approximately 4 feet thick. The perched aquifer appeared to be a small buried channel with limited horizontal extent.

Ground Water Contamination

The hydraulic conductivity of the perched aquifer zone was approximately 10^-4 cm/sec. The flow direction was controlled by the boundaries of the buried channel.

Soil Contamination

The volume of soil contamination within the source area was estimated to be 2,200 tons. The soil contaminants were mainly tetrachlororethene (PCE) and trichloroethene (TCE), and 1,1,1-trichloroethane (1,1,1-TCA). The soil concentrations were as high as 2,200 ppb.

Remediation Design

Six injection points were installed in the contaminated soil area. The injection points were installed in nests to increase the distribution through the soil profile. At each nested pair, one injection screen was set near the surface of the soil (1 to 2 feet deep), and a second screen was set in the water-bearing formation at 9 to 12 feet deep.

During each injection, 275 to 385 gallons of inoculant was injected into the subsurface. The inoculant was split among the injection points so that 40 to 55 gallons of solution was injected into each pair of injection points.

Inoculations were made on a 30-day schedule to maintain the high microbial population for six months.

Results

Tracking showed that there was immediate degradation of contamination. After the first inoculation the concentrations of TCE and PCE were reduced by more than 50%. The concentration of 1,1,1-TCA and cis-1,2-DCE were also reduced significantly. After eight months, nearly all of the target compounds were below drinking water standards. Only vinyl chloride and cis-1,2-DCE were above drinking water levels.

The last inoculation was made in November 2001. The post-closure monitoring showed that the contaminant concentrations continued to decrease through March 2002. Six months after treatment, the ground water contaminant concentrations were within drinking water standards.

Concentrations are in µg/L

The combined total cost to remediate both soil and ground water was about $80,000. This total includes the installation of injection wells, monthly application of bioremediation for eight months, and ground water monitoring during bioremediation. The unit costs based on the volumes treated are $36.00 per ton of soil or $0.76 per gallon of ground water.