Field and laboratory investigations of solute transport through soil

Abstract

<p>Two single tracer methods (basic and variance) and one multiple tracer method were developed to simultaneously estimate soil hydraulic properties and mobile/immobile solute transport parameters in situ. In this study, immobile water contents (thetaim) and mass exchange coefficients (alpha) were estimated with the multiple tracer method and the single tracer methods on the same five field sites. The theta im values estimated by the basic single tracer method were consistently lower than the multiple tracer method values. This was attributed to the assumption that alpha = 0 for the basic single tracer method. Furthermore, alpha values estimated by multiple tracer method were more realistic and easier to obtain than the variance single tracer method;A novel miscible-displacement system with on-line high performance liquid chromatograph (HPLC) was developed to study the fate and transport of volatile organic compounds. This system was capable of simultaneous detection of multiple compounds at low concentrations. This system was automated and could operate for long time periods (several days to weeks) with minimal flow rate fluctuations and stable chemical detections;Lastly, zero-valent metals were used to reduce chlorinated solvents in contaminated groundwater by flowing it through zero-valent metals. Previous zero-valent metal research included batch or resident concentration column experiments to study degradation processes and to design remediation systems; however, difficulties were associated with these methods such as determination of sorbed concentrations and estimation of effluent concentrations from resident concentrations. In this study miscible-displacement experiments were used as an alternative to study trichloroethylene (TCE) fate and transport through zero-valent metals. Dissolved TCE was passed through columns filled with sand, iron, or copper-platted iron filings (Cu-Fe) at three velocities and effluent breakthrough curves were determined with an on-line HPLC. There was no detectable TCE degradation in the sand column experiments. More TCE was reduced in the presence of Cu-Fe than iron. The reduction of TCE produced ethylene which resulted in simultaneous breakthrough curves of these compounds. These simultaneous breakthrough curves were described with a two-site partial nonequilibrium sorption model with degradation and production. Based upon the experimental results sorption should be a consideration when designing flow through remediation systems.</p>