Site-specific reduction factors using the PFT-method
The passive tracer gas technology called PerFlourcarbon Tracer (PFT) has been tested for estimating site specific attenuation factors between sub-slab soil gas and indoor air at sites with slab on grade. As a part of the study, the installation procedure and the speed of diffusive tracer gas migration in the sub surface has been investigated.
With regard to the installation procedure and choice of materials for installing the tracer gas sources directly under the concrete slab (after core-drilling through the slab), satisfying results have been obtained. Hence, the developed installation procedure has been proven not to open up new preferential migration pathways through the concrete slab. The procedure can be used when a high quality seal is desired, after performing environmental investigations, where perforation of the concrete slab is involved.
Unfortunately, we did not succeed in our efforts to propose and document a method that can be used for estimating site specific attenuation factors between sub-slab soil gas and indoor air at sites with slab on grade. We do, however, think that there is a basis for establishment of a procedure/methodology that will enable estimation of site specific attenuation factors at sites with more permeable sub-slab soil types or at sites with a capillary barrier layer of e.g. Leca® or with a layer of insulation material. At such sites it will be much easier to ensure a satisfactory sub-slab distribution of the tracer gas.
Published as Danish EPA project no. 1898, 2016.
Project type: Investigation
Project target: Vapor intrusion
Former dry cleaning facility
PCE in clay till and sand aquifer, P&T plant
Meeting room and office spaces.