t a former gasoline/petrol station known as Smile in Kaohsiung, a 2005 site investigation detected high levels of contamination in the clayey soil, including total petroleum hydrocarbons (TPH) at as much as 42 times greater than the soil quality standard. Various remediation approaches and activities were conducted between 2009 and 2016, yet contaminants of concern (mainly benzene and TPH) in the soil remained far above the targeted standards.
Given the lack of progress and the uncertainty as to if and when the site might achieve acceptable remediation standards, the owner investigated excavation and disposal options, but the costs were deemed too high.
Golder took on the challenge of resolving the stubborn contamination problems using a novel on-site soil treatment approach known as TEVET (Thermally Enhanced Vapour Extraction Technology), trailblazing its use in Taiwan.
The TEVET system removes and destroys volatile organic compounds (VOC), polyaromatic hydrocarbons (PAH) and TPH through heat treatment and vapour extraction. Engineered piles of excavated contaminated soil (up to 25 x 12 m in area and 2 to 2.5 m high l containing approximately 1000 tonnes of soil) are interconnected with a hot air distribution piping system, and then wrapped in a low permeability geomembrane bottom liner and top cover. Propane fuel is supplied to a burner that heats the air, which is then injected and circulated via the piping system throughout the soil piles. The contaminants in the soil are converted to vapour by the heat and are captured by a vapour extraction system. The contaminants in the extracted vapours are destroyed by heat in the burner, and the clean airstream is recirculated back into the soil pile. The process continues until target concentrations in the soil are achieved – leaving the soil clean enough to be re-used safely.
Between December 2016 and June 2018, 16 contaminated soil piles were treated with the TEVET system for between approximately 6 and 10 days each. Multiple soil samples from each pile were first field tested by an independent third party using a photoionization detector and TPH test kits, followed by the submittal of selected soil samples to an accredited laboratory for confirmatory analysis. Laboratory analytical results indicated that contaminants of concern had reduced strikingly to well below the regulatory standards.
TEVET proved itself to be a far more effective, reliable, quick and cost-effective treatment solution than those approaches attempted during the previous 7 years. Remediation of 14,500 tonnes of soil was achieved within 18 months without any health and safety incidents. This successful result gave stakeholders many reasons to smile and enabled the client to reach its goal for re-use of the site.
Editors’ note: TEVET was patented by Quality Recycling, Inc. and all rights were acquired by TEVET Environmental, LLC, which is currently operated as a subsidiary of Hilltop Enterprises. Golder signed an agreement with Hilltop to use TEVET in Taiwan (as well as other countries in Asia).
* This work was performed by Golder professionals who joined WSP in an acquisition completed in 2021.