A former chemical manufacturing company in Brazil had a historical use of chlorinated solvents as raw materials. Chlorinated solvents are useful for degreasing fats, oils, waxes, and resins. They are used widely and have been manufactured in large quantities. However, they are harmful to human and ecological health. At the subject site, these chlorinated volatile organic compounds (CVOCs) had entered the soil and groundwater. The contaminant plume migrated to four neighboring properties and extended to a depth of 20 meters below ground surface. Concentrations of CVOCs were high and approached DNAPL (Dense Non-Aqueous Phase Liquid) levels, although no DNAPL had been identified in the source area.
First, a detailed conceptual site model (CSM) using conventional and high resolution site characterization tools was developed. Then a focused feasibility study was prepared, the purpose of which was to identify a technology that would be cost-effective, acceptable to the regulatory agency (CETESB), and impact off-site properties to the least extent possible.
Antea Group's environmental site remediation experts completed a focused feasibility study that screened biological, chemical, physical, and thermal technologies as well as monitored natural attenuation (MNA) with no action.
The focused feasibility study included these considerations:
- overall protection of public and environmental health
- effective reduction of toxicity, mobility and volume of the contaminant mass
- long-term and short-term effectiveness of the remedy
- potential consequences of the remediation process itself
- implementation and technical reliability
- regulatory compliance
- public opinion
The list of technologies was reduced to three remedial options and a selection of in situ chemical reduction (ISCR) was made to address gross contaminant mass reduction. MNA was considered for polishing to regulatory standards. Microbial testing was completed during the feasibility study and was instrumental in the remedy decision.
An ISCR remedy for the source area and distal plume was implemented for both shallow and deep impacts in groundwater and was further verified through pilot testing. The focused feasibility study was key to selecting a technology that could address the high concentrations of CVOCs, while initially taking advantage of the favorable microbial conditions and then limiting daughter product production through the reduction process. It also enabled the selection of a remedy that was acceptable to the regulator and adjacent property owners. The project is ongoing and after substantial reduction in contaminant mass and plume footprint, a polishing round of injection is planned.