Theme: 02. Assessing Remediation Effectiveness

Topic Area: 02b. Remedy Implementation: Assessing Performance and Costs

Formatted Title:

Trialling Three Parallel Remediation Options to Select One Strategy for the Entire Site

Background/Objectives:

Background/Objectives: In the city of Varberg, in southwest Sweden, the mechanical industry has caused extensive chlorinated solvent contamination, impacting superficial deposits and superficial groundwater, bedrock and bedrock groundwater. The contamination has migrated under the Kattegatt Sea, and is currently impacting the construction of a train tunnel built beneath the city. The remediation of the site is being performed in three phases. The first phase was to excavate the contaminated soil from the industrial area. Once completed, thermal treatment commenced, targeting the source area in bedrock to 50 m bgl. This presentation covers the third and last remediation phase, to remediate the soil groundwater to a level of 0.1 mg/l CVOC (TCE, TCA, DCE, DCA, VC).

Approach/Activities:

Approach/Activities: As the remediation area consists of 12,000 m², it was decided to start by trialling possible technologies in an area with relatively high contaminant concentrations. The contaminant levels in the trial area were up to 6,300 µg/L for TCE, 6,800 µg/L for DCE and 1,800 µg/L for VC. Ethene and ethane were also present, indicating that reductive dechlorination is ongoing. The superficial geology is heterogeneous, comprising a mixture of sands, silts, gravels and clays in alternating layers down to 6 m bgl. This overlies the fractured granite bedrock, with the superficial groundwater level at 2 m bgl.

The 300 m² pilot trial area was divided into three 100 m² subareas. Each subarea was utilized for a unique pilot test, where two competing remediation product suppliers were tested against each other. All testing was performed using direct push injection, and the results were monitored for approximately 29 weeks.

Results/Lessons Learned:

Results/Lessons Learned: After 29 weeks, sampling in the two monitoring wells per pilot area showed that the contaminant levels of TCE and DCE had decreased. Carbon adsorption was evident from the start, with a faster contaminant reduction where zero-valent iron had been used, and biological degradation has increased over time.

The pilot trials have provided the project with important information about the different remediation options available for the site. While the remediation results are important, other factors play a crucial role in deciding remediation methodology, including injectability, handling and storage on site, H&S, effectivity, cost, and estimated time to reach the targets. Also, the experiences of the site crew are very important in designing the best remediation option that will provide effective site work.

This study proves the benefits of trialling different remediation methods on a site to obtain valuable data to aid selection of the preferred strategy. The presentation will also include practical lessons learned from the site works. By the time of the presentation, the methodology chosen for the remediation of the whole site hopefully will be selected and shared.

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Jenny Ryden