ABSTRACT
For many decades, per- and polyfluoroalkyl substances (PFAS) were used in firefighting foams at airports and military sites. Today, large amounts of soil and consequently groundwater are contaminated with PFAS. Upon reuse of sites, there must be a definite plan on how the contaminated excavated soil will be addressed. Typically, present waste disposal regulations require the soil to be landfilled. However, transport and disposal of enormous amounts of soil make projects expensive and unecological. For storage or reuse of contaminated soil in the vicinity of the excavation innovative contaminant filters are developed. The target is to treat the soil passively, i.e., without labor, energy, or fresh water. Natural precipitation is used to dissolve PFAS from the soil body and transport downwards through the structure. A permeable contaminant filter is placed at the bottom of the stockpile area. This geocomposite consists of a highly effective amendment sandwiched between two layers of geotextiles. The selective agent extracts PFAS from leachate. To develop a long-life contaminant filter, four performance factors must be considered: affinity, kinetics, capacity, and irreversibility. Affinity describes the tendency of the sorbent to uptake particular pollutants. Regarding PFAS, it is essential that long- and short-chain PFAS are included. The kinetics of the amendment determines whether it is possible to reduce contaminant concentrations below the specified permissible threshold while the seepage percolates through the filter at a natural flow rate. The capacity must be greater than the product of the leachate concentration, the total amount of seepage over a defined period, and an appropriate safety factor. Irreversibility precludes subsequent desorption and thus enables long-term safety of the impoundment. Additionally, there are interdependencies between these factors. The determination of the performance factors and their influence on the design concept are presented and discussed in this paper.
