Geophysical verification of subsurface barriers

We have developed a robust, six step methodology for the verification and monitoring of a subsurface containment barrier using geophysical (GP) techniques. First, site characterization data are used to determine in-situ host properties, then laboratory measurements are performed to estimate physical properties of the of soil and grout mixtures for numerical simulations. Based on site characterization and lab data numerical models are computed for survey design and interpretation. Finally field data are acquired, reduced, and interpreted. Representative data and discussion for are presented for a thin-wall diaphragm barrier. The methodology was also successfully demonstrated on a viscous liquid barrier. Results indicate that ground penetrating radar (GPR) and the electrical resistivity (ER) methods were successful at imaging the areal extent of the barrier and assist with leak detection through ER monitoring of a salt water flood test. Seismic and electromagnetic (EM) induction techniques were also demonstrated. All of the geophysical instruments were deployed from boreholes or permanently emplaced vertical electrode arrays (VEAs). To increase resolution, data were acquired prior to and after the grout injection and then differenced.