Improving Pump and Treat Results
Manufacturing Site in Cincinnati, Ohio

Site Summary:

Chlorinated solvents were discovered in soil and ground water beneath a drum storage area at a manufacturing facility in Cincinnati, Ohio. The drum storage area was removed, and contaminated soil was excavated to the water table for off-site disposal. The excavation was backfilled with granular fill and used as part of a ground water recirculation system to contain and treat the residual contaminated ground water.

Gradient control and plume migration were achieved using down gradient extraction wells. Contaminants were removed from the extracted ground water by activated carbon filtration. The clean ground water was returned to the excavation to facilitate contaminant flushing. After one year of extraction and treatment, the total volatile organic compound (VOC) concentrations decreased from 6.0 milligrams per liter (mg/L) to 1.9 mg/L. CL-Out bioremediation was implemented to expedite the remediation. The VOC concentrations decreased to 0.27 mg/L after one year of bioremediation. Site closure was achieved after further periodic treatments and seasonal monitoring.

Geology

The geology of the site was typical glacial ground moraine setting with predominantly silty clay with intratill fluvial silty sand deposits. The silty clay deposits had very low hydraulic conductivity, but the silty sand deposits provided a preferred flow path and conduit for ground water and contaminant migration. At this site, the silt sand deposit was approximately 4 feet thick, but was laterally discontinuous.

Hydrogeology

The affected ground water was contained within the discontinuous fluvial silty sand. The hydraulic yield from the extraction well was less than 2 gallons per minute (gpm). The depth of the affected ground water was approximately 9 to 13 feet below the ground surface.

Soil and Ground Water Contamination

The excavation of contaminated soil removed all accessible soils in the lateral direction from the drum storage pad. Due to excavation limits, the residual soil in the floor of the excavation contained low levels of contamination. The objective of the recirculation of the clean ground water was to flush the residual contamination out of the soils and capture it in the extracted ground water.

Prior to the any treatment at the site, Tetrachloroethylene (PCE) was detected in a down gradient monitoring well of the excavation area. The maximum concentration of PCE was 6.8 mg/L.

Remediation Design

The ground water extraction started in December of 1997. CL-Out Bioaugmentation began in May 1998. The bioaugmentation consisted of adding 15 to 55 gallons of CL-Out slurry to the excavation/infiltration gallery. Within one month, the total VOC concentrations in down gradient ground water decreased by more than 50%.

The bioremediation treatment continued by adding CL-Out on a quarterly basis as the pump and treat system continued to operate. During the combined bioremediation and soil flushing, the contaminant concentrations in the ground water continued to decrease, but there was a variability that suggested that significant levels of contamination remained in the source soils.

Results

After three years of combined recirculation and treatment the contaminant concentrations were reduced to acceptable levels. Post-closure monitoring showed that the cleanup goals were maintained three years after the last treatment.

The cost for CL-Out used in this project was less than $20,000.