Sandia National Laboratories has developed sensors allowing real-time, continuous measurement of hydrogeologic parameters for use in contaminant transport modeling, risk assessments, and the optimization of remedial alternatives (e.g., soil venting, bioremediation). These sensor packages have been engineered into a cone penetrometer push technology, in addition to their stand-alone deployment. The sensor packages include a time domain reflectometry (TDR) sensor to quantify volumetric soil moisture content and a fiber optic relative humidity (RH) sensor to quantify capillary pore pressure in unsaturated soils. Results indicate that TDR probes having optimal specifications yield measurements representative of the formation. TDR probes show better accuracy than neutron and capacitance probes. RH sensors responded quickly in the laboratory, but redesign will be necessary to make the housing suitable for 'real-time' cone penetrometer applications. Sandia deployed the TDR and RH probes along with geotechnical sensors on a cone penetrometer rig. Data allowed three- dimensional analysis of lithologic control of soil water migration at a level of detail greater than possible using conventional methods. In addition, the TDR design has been employed in a down-hole logging configuration for routine monitoring in access tubes, as a non-nuclear alternative to a neutron probe. The cone penetrometer with the TDR probe represents a significant technological advance in site assessment capabilities.