Numerical Modeling on Fate and Transport of Pollutants in the Vadose Zone

Abstract

Soil contamination is an issue of paramount importance to assess human health (HHRA) as well as ecological (ERA) risk assessment. To analyze risk scenarios related to contaminated soils, the identification of sources, either of primary or secondary type, as well as the assessment of propagation and fate processes is needed. Although many studies refer to the transport of pollutants in fully saturated porous media, little efforts have been made concerning the case of partially saturated soils so far. The matter is of interest as the contamination in the fully saturated region may take place as a result of the percolation in the vadose zone. Governing equations ruling fate and transport processes in partially saturated soils are here solved numerically by means of a finite element method approach. Richards equations are adopted to describe flow dynamics through the hydraulic conductivity coefficient Ks, while contaminant fate is mainly described by the sorption coefficient Kp. As for the boundary conditions, we consider a local and continuous spill of contaminant at the upper ground of variable thickness. Precipitations are given as step functions whose intensity is derived by considering pluviometric data at the station of Gròmola, Campania Region, Italy. Benzene and tetrachloroethylene (PCE) are taken into account. A comparative analysis is carried out for permeability Ks and distribution Kd coefficients in the range [10−6, 10−4] m/s and [10−5, 10−3] m3/kg. Results are then compared and discussed.

Reciprocal Interactions of Abiotic and Biotic Dechlorination of Chloroethenes in Soil

“…As a sink of various organic contaminants, soil could affect the fate of organic pollutants (e.g., organohalides) and their subsequent transport to other environmental matrices, including groundwater and atmosphere. , The fate of organic pollutants in soil was synergistically determined by combined biophysiochemical processes, including accumulation and transformation through sorption/desorption, abiotic degradation, and biotransformation, which highly depended on the soil compositions and physiochemical properties as well as soil microbiomes. , In China, according to the National Soil Contamination Survey Bulletin published in 2014, around 16% of surveyed soil samples had at least one organic pollutant exceeding standard values, particularly the organohalide pollutants . Similarly, an agricultural soil survey reported that volatile organohalides were present in all tested samples.…”

Modeling of Transport of Loose Products with the Use of the Non-Grid Method of Discrete Elements (DEM)

“…The available numerical methods to investigate the behavior of particles make it possible for machine constructors to track the forces acting on a transported material. The most important ones are normal forces and tangential forces resulting from the collision of particles with the walls of transport equipment [7][8][9]. They affect mainly the quality of the transported material.…”