Ground-Penetrating Radar Survey of Residual Ground Pollution by Acid Tars

In this chapter, we mapped the residual pollution near the southern Inčukalns Acid Tar Lagoon (ATL) in Latvia, Northern Europe using Ground-penetrating Radar (GPR). The southern Inčukalns ATL is now remediated, and Acid Tars (AT) are excavated; however, the moving pollution plume has been identified from the borehole data. Due to the considerable variations in the GPR signal properties in the study area, we were able to interpret the differences in Quaternary sediments as well and correlate them with the borehole data. We have found that the lack of glacial till in places could be the main factor in facilitating the migration of pollution originated from ATL trough the sandy sediments towards the Devonian aquifers. Further, we distinguished a distinct area with increased losses of the GPR signal inside the sandy sediment layer appearing as the sharp lateral discontinuity of the deepest prominent GPR signal. We ascribe it to the enhanced electrical conductivity of groundwater that is related to the contamination by ATs. We have demonstrated that GPR is an effective method for the mapping of soil and groundwater pollution created by ATL and can substantially supplement the conservative monitoring methods.