Formatted Title

Pilot Testing: Stabilization of PFAS in Unsaturated Zone with Activated Carbon

Background/Objectives

Per- and polyfluorinated alkyl substances (PFAS) are persistent substances that are hazardous to the environment and health even in low concentrations. Swedish Geotechnical Institute (SGI), together with Swedish Geological Survey (SGU), has received a government assignment to contribute to increased rate of action regarding PFAS-contaminated areas. SGI shall work with research and dissemination of knowledge regarding investigation, and remedial methods of PFAS-contaminated areas. This presentation focuses on a pilot project within the government assignment where PFAS-contaminated soil has been stabilized in situ. The method is based on mixing a sorbent, which has a high affinity for PFAS, into the soil with the aim of reducing the leaching of PFAS and thus reducing the spread of PFAS.

Current project within the government assignment aims to increase knowledge of the applicability and challenges of in situ methods for PFAS. Dissemination of knowledge about the possibility of using new remedial methods such as stabilization of PFAS in the unsaturated zone can promote an increased rate of remediation of PFAS-contaminated areas.

Approach/Activities

A pilot project is being carried out at Sundsvall-Timrå airport where PFAS-contaminated soil has been excavated, homogenized and placed in nine HDPE containers (with a volume of approx. 2 cbm of soil). In six of the containers, PFAS-contaminated soil has been mixed with 2% by weight of activated carbon (AC). The other three containers constitute controls in the experiment. Two different types of ACs have been used, one based on wood and the other on coal. Initial leaching trials (L/S 10) were conducted to determine optimal percentage of AC.

In each test container, two suction lysimeters in stainless steel have been installed at three depths for continuous sampling of pore water in the unsaturated zone. The test containers have a bottom with a drain 20 cm from the bottom, creating a fictitious saturated zone. Sampling from the saturated zone takes place through a groundwater well. Water from unsaturated and saturated zones is analyzed for 32 PFAS substances and TOP. In addition to studying the possibility of determining PFAS in unsaturated and saturated zone with two different AC, one aim of the project is to obtain data to better understand transport of PFAS in the unsaturated zone. Moisture and temperature are measured at the same depth as the pore water sampling, which makes it possible to study the leaching of PFAS in the unsaturated zone as a function of soil moisture. The drainage at the bottom of the container creates a fictitious groundwater level where PFAS levels in pore water in the interface between air and water can be investigated.

Results/Lessons Learned

This presentation will describe the implementation of the pilot project, practical considerations, and precautions. It will report results and experience from the first six months and discuss the possibilities of implementing in situ stabilization on a larger scale.