Chemical Mixing Facility located in Toronto, Canada

Site Summary:

The development of a shopping center was potentially halted after the discovery of soil and ground water contamination by chlorinated solvents from the former industrial chemical mixing facility operations. The contamination had leached from the soil underlying a drum storage area into the ground water and spread across the property. While the contamination was approximately 5,000 square feet and the concentrations were relatively low, the responsible party implemented an aggressive remediation plan to meet a pending closing and post-transaction development plan. The environmental consultant chose to excavate the contaminated soil. The residual ground water contamination was treated with a combined pump and treat recirculation system and in-situ bioaugmentation to accelerate remediation to meet the development schedule and to beat the coming cold weather.

Geology

The contaminated soil was mainly silty clay till overlying shallow bedrock. The top of bedrock was at approximately 8 to 10 feet deep. Due to the low permeability of the silty clay till, the soil was excavated for off-property treatment and disposal to meet the project schedule. While it was possible to excavate the contaminated soil relatively easily, the contamination had leached from the soil to the ground water.

Hydrogeology

The impacted ground water was a perched zone at the top of bedrock. Because the permeability of the till was very low, saturated conditions were found only at the till/bedrock interface. After the excavation of contaminated soil, the water table rose in the excavation and saturated the fill material sufficiently to support ground water extraction by pumping and aeration by sparging.

Ground Water Contamination

The contaminants were a mix of more than 20 organic chemicals, which were mainly volatile hydrocarbons. The main contaminants were tetrachloroethylene, cis-1,2-dichloroethylene, toluene, and benzene. CL-Out was selected for the treatment because its capability to metabolize aromatic compounds and cometabolize halogenated aliphatic compounds. One of the additional benefits of CL-Out is that the organisms are aerobic, which means that the metabolism in not hindered, but increased by the introduction of oxygenated water and sparging.

Remediation Application and Monitoring

CL-Out was added to the excavation pit, which acted as an infiltration and treatment gallery. Initially, five drums of the CL-Out slurry were added after the soil excavation. After the recirculation system was added, three drums of CL-Out were added to the effluent into the recirculation gallery through 10 recirculation wells.

Six additional sparge wells were installed to increase the volatilization of the contaminants and to supplement oxygen for the bioremediation.

The ground water treatment results were monitored by sampling the combined influent from the extraction system. The monitoring results show an immediate decrease in the contaminant concentrations. After less than one month, the main contaminants were decreased by 90 to 99%.

The site construction began on schedule after the ground water treatment.

All concentrations shown in µg/L (ppb). 

Conclusions

This project demonstrates one of the benefits of aerobic bioaugmentation. The metabolic diversity of the organisms in CL-Out allows it to degrade a wide range of organic chemicals found on this and other sites. Furthermore, the compatibility of CL-Out aerobic cometabolism may be used in combination with other technologies to accelerate site closure.