Using radon-222 in soil gas as an indicator of subsurface contamination by non-aqueous phase-liquids (NAPLs)

Abstract

The dependence of the soil gas radon concentration on ground contamination by non-aqueous phase-liquids (NAPLs) was studied. Subsurface NAPL contamination is known as one of the major problems concerning the clean-up of polluted industrial sites. One reason is the mostly limited number of soil sampling locations, which makes adequate tracing of the extent of contamination difficult. With the aim to enable a more detailed assessment of NAPL plumes a new indirect method for NAPL detection has been developed. The method uses the good solubility of radon in NAPLs which enables the NAPLs to partly accumulate the radon available in the soil pores. Radon enrichment in the NAPL causes a local decrease of the soil gas radon concentration in the vicinity of the NAPL contamination. Thus radon minima can be used to localize NAPL plumes indirectly. The results of the present investigation suggest that the radon concentration in soil gas may be used as a complementary tool for the detection of sub-surface NAPL contamination together with conventional investigation methods.