http://www.enviroflux.com/PFM_JCH_article.pdf

A direct passive method for measuring water and contaminant fluxes in porous media

Controlled release, blind tests of DNAPL characterization using partitioning tracers.

Summary

Risk assessment of groundwater pollution requires quantitative information on the release kinetics of pollutants and organic matter from contaminated soil. We applied a new experimental design for column outflow experiments to investigate the release of polycyclic aromatic hydrocarbons (PAHs) and dissolved organic matter under water-saturated flow conditions. We used materials originating from a soil contaminated with non-aqueous phase liquids. To distinguish between release at equilibrium and release limited by mass transfer, we used two flow velocities and multiple interruptions to the flow. We quantified release and transport parameters by inverse numerical simulation of the individual breakthrough curves, applying a model based on the advection–dispersion equation including non-equilibrium and non-linear sorption. Release of the dissolved organic C takes place in two steps. Initially, a large amount of readily available organic matter is released. This first flush is followed by an outflow with typical characteristics of rate-limited release: larger concentrations in slower flow and increased concentrations after interruptions. The breakthrough of PAHs responds neither to the different flow velocities nor to the interruptions. We hypothesize that release of PAHs from the contaminated material is governed by dissolution at equilibrium according to Raoult's law. The boundary conditions of the experimental design, i.e. the flow velocities and multiple interruptions, enable us to distinguish between release at equilibrium and that which is rate-limited. Also, the response of the breakthrough behaviour to the boundary conditions can be used to estimate inversely effective release parameters.

Determination of effective release rates of polycyclic aromatic hydrocarbons and dissolved organic carbon by column outflow experiments

Pesticides in the Soil Environment

In the course of industrialization in the 19th century, manufactured gas plant sites were built in almost every larger town in Europe and the United States. Organic and inorganic contaminations pose a continuing threat to groundwater resources at these locations even though the operations were terminated decades ago. The different coal tars and tar oils present in the subsurface are composed of a huge variety of organic compounds often possessing a high toxic potential, such as monocyclic, polycyclic, and heterocyclic aromatic hydrocarbons. In addition to these inorganic contaminants, cyanides and heavy metals can be found due to dumping of by-products and wastes. A multitude of factors influence the fate of these compounds and an increasing number of studies deal with this subject. However, key processes are still not well understood. One example is the mobilization of colloid associated contaminants by extreme single events, which can be responsible for the bulk contaminant load in the seepage water. An...

Contaminants at Former Manufactured Gas Plants: Sources, Properties, and Processes

We examine similarities in constraints to mass transfer of hydrophobic organic compounds (HOCs) between the aqueous and various organic phases in porous media at the grain scale. Published research and data are reviewed regarding equilibrium coefficients and first-order rate constants for mass transfer of HOCs between water and natural organic matter present in various geosorbents (e.g., soils, sediments, and aquifer solids), and several oils (petroleum products, decane, and coal tar). We propose how these equilibrium and mass-transfer coefficients can be estimated by methods common to all organic phases. Equilibrium coefficients can be reliably estimated using Raoult's law. First-order rate constants obtained from extensive literature data appear to be dependent on aqueous-phase diffusion and duration of exposure (or contact). The aqueous diffusion domain may be either an interfacial film (for low viscosity oil ganglia) or a retarded immobile water zone (for geosorbents).

C. Rao

Papers

Nonaqueous Phase Liquid Dissolution and Soil Organic Matter Sorption in Porous Media: Review of System Similarities