Long-term Water Balance Monitoring of Engineered Covers for Waste Containment

Abstract: The growing realization that remediation of many contaminated sites is technically infeasible has resulted in a shift in emphasis to containment as an alternative to remediation. Monitoring is required to demonstrate the effectiveness of engineered cover systems in minimizing infiltration into underlying waste. The purpose of this study is to evaluate a variety of monitoring technologies. Monitoring systems were installed in a resistive (GCL/asphalt) barrier at 1.3 m depth and a conductive (capillary) barrier at 2.0 m depth constructed near El Paso, Texas, in 1997. The site is heavily instrumented with both automated and manual monitoring systems designed to quantify the soil water balance and to monitor soil water potential energy. All of the water balance components are being monitored except evapotranspiration. Results indicate that electromagnetic induction (EM), once calibrated with neutron probe and temperature data, can reliably monitor water storage changes. The non-invasive nature of EM measurements could preclude the development of preferential pathways resulting from instrument installation. Neutron probe measurements of water storage are more reliable at this site than time domain reflectometry because of signal attenuation resulting from high conductivity soils. Heat dissipation sensors have proved more reliable than thermocoupl