Theme: 01. Remediation Technology Innovations

Topic Area: 1d2. Combined Remedies and Treatment Train Technologies for Chlorinated Contamination

Formatted Title:

ISCO-ISS for Remediation of TCE Source Area: Achieving Cleanup Goals within One Week of Application

Background/Objectives:

During the development of a former industrial area located in Västerås, Sweden, elevated concentrations of TCE were found in dense clay near the planned housing development. Prior to the construction of new residential buildings could proceed, remediation of the contaminated soil was required. Site-specific challenges included high levels of TCE (>500 mg/kg), poor soil stability, low permeability soil, nearby infrastructure, and a short 6-month timeframe to complete the remediation. The contamination occurred from 2 to 7 meters below ground surface.

Approach/Activities:

Following a review of potential remedial options an in situ remedial approach combining in situ chemical oxidation (ISCO) with in situ stabilization (ISS) was selected for treating the impacted soil. Justification for the choice of remedial approach included rapid results (fast acting), cost savings (relative excavation and disposal), minimal risk of degradation products being formed (DCE / VC), large reduction of soil-bound contamination, reduced potential for leaching and improved soil stability. In total, 600 m³ of contaminated clay was treated. The work was carried out over the course of one week; 8 tonnes of Klozur® SP sodium persulfate and 70 tonnes of Portland cement were blended into the soil using large diameter (60 cm) augers.

Results/Lessons Learned:

Sampling one and five weeks after the ISCO-ISS application showed a reduction in the average TCE concentrations by 90%, which was confirmed with a large number of soil samples collected before and after the remedial action. Maximum TCE concentrations were reduced by 97%, from a high of 542 mg/kg measured prior to treatment to a maximum of 16.5 mg/kg measured after the ISCO-ISS application. The overall TCE mass was reduced by an estimated 80%, which exceeded the remedial goal of at least 50% reduction.

The stability of the soil was improved, infrastructure was minimally affected, and the method provided significant (~70%) cost savings relative a more traditional remedial approach involving excavation and disposal in this case, due to the need for sheet piling. The method also aligns with Sweden’s Environmental Agency’s aspiration to reduce energy consumption and promote more sustainable remedial approaches.

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Petter Wetterholm