Completed Project

Approximately 16,000 cubic yards of soil were contaminated with about 15,000 pounds of MeCl. The highest soil concentration observed was 42,928 mg/kg. The remediation goal was to reduce the 95th percentile upper confidence limit for the soil samples to less than 24 mg/kg MeCl. To achieve this goal would require a 99% reduction in average MeCl concentrations. Post-treatment soil sampling showed that the cleanup goal was exceeded and that a 99.8% reduction of MeCl in soil was achieved after 10 months of remediation system operations. All soil samples were remediated to below 24 mg/kg; the 95th percentile upper confidence limit was reduced from 2,453 mg/kg to 3 mg/kg.

A network of 95 electrodes was installed for power delivery to the subsurface. Each electrode was installed with hollow-stem augers using common drilling techniques. The majority of the electrodes were completed above grade. Six electrodes were installed below grade in an active street. Sixteen electrodes were installed inside the existing building. All drill cuttings were placed on the surface beneath insulating covers for simultaneous treatment in the remedial area.

Thirty-four vapor recovery (VR) wells were installed for extraction of in-situ generated steam and MeCl. The VR wells were installed to a depth of 20 feet bgs. To monitor the progress of the remediation system, 41 thermocouples were installed at 20 locations throughout the remediation area - one thermocouple location in each treatment cell.

While the Illinois EPA did not require vapor treatment, vapor samples were collected throughout operations and analyzed by EPA Method TO-18. By May 2000, approximately 1,000 pounds of MeCl had been recovered and discharged to the atmosphere. This extracted mass was anomalously low in comparison to the estimated MeCl loss of 15,000 pounds. To resolve the discrepancy, soil samples were collected in late May 2000 to determine the fate of the MeCl. The samples were analyzed for total MeCl concentration, MeCl microbiological degrader populations, and chloride ion concentrations.

Soil samples were collected from the area of highest concentrations of MeCl, from MeCl regions that had not yet been heated, and from background non-contaminated regions. Most soil samples from the heated region were found to have less than 0.05 mg/kg of MeCl and contained a reciprocal amount of chloride ion. Moderate microbiological activity was identified in soil that was below 70°C.

From the results, it was determined that the majority of the MeCl was being degraded in situ by heat-enhanced hydrolysis reactions. A letter of No Further Action (NFA) was issued by the Illinois EPA in 2001. The site is now closed.