USING GROUND-PENETRATING RADAR TO DETECT LAYERS IN A SANDY FIELD SOIL

Pollutant transport in sandy soils can be very complex due to the pres ence of coarse sand lenses. Water flows laterally over the coarse mate rial and, subsequently, breakthrough occurs in concentrated pathways, called fingers, This (funneled) flow process is a form of preferential flow reducing solute travel time and degradation of organic chemicals . In this paper, we test ground-penetrating radar (GPR) as a tool for detecting layers in the soil. Several GPR transects were established o n a fine sandy loam soil throughout the growing season and subsequent fall period to find the best time to reveal layer structures. The effe ct of the spatially varying moisture content on the radar velocity was determined from actual measurements with soil samples and by using th e Common Mid-Point (CMP) technique. The optimal time to find coarse la yers with GPR in this soil was at the end of the fall season when the soil was wetted and evaporation had decreased. The depth of layers, as indicated by GPR, was highly sensitive to the soil moisture content a nd could be in error by as much as +/- 0.4 m on a depth scale of 1.5 t o 2 m if an average propagation velocity was used. A satisfactory dept h prediction of textural interfaces was obtained non-destructively by collecting data in both reflection and CMP mode.