Soil and vadose zone profiles are used as an archive of changes in groundwater recharge and water quality following changes in land use in an area of the Loess Plateau of China. A typical rain-fed loess-terrace agriculture region in Hequan, Guyuan, is taken as an example, and multiple tracers (chloride mass balance, stable isotopes, tritium and water chemistry) are used to examine groundwater r...

Subsurface fate and transport models are utilized to predict concentrations of chemicals leaching from wastes into downgradient receptor wells. The contaminant concentrations in groundwater provide a measure of the risk to human health and the environment. The level of potential risk is currently used by the U.S. Environmental Protection Agency to determine whether management of the wastes shou...

Problems involving capillary barriers along sloping, layered unsaturated soils were first addressed by ZaslavThis study presents a systematic approach to analyze the flow sky and Sinai (1981a, 1981b). In the last few decades, diversion and flow focusing caused by the natural flow-barrier system several quantitative analyses of lateral water flow in in the unsaturated zone (UZ) of Yucca Mountain...

Agrochemical contamination in groundwater poses a significant long term threat to water quality and is of concern for legislators, water utilities and consumers alike. In the dual porosity, dual permeability aquifers such as the Chalk aquifer, movement of pesticides and their metabolites through the unsaturated zone to groundwater is generally considered to be through one of two pathways; a rap...

Characterizing percolation patterns in unsaturated fractured rock has posed a greater challenge to modeling investigations than comparable saturated zone studies due to the heterogeneous nature of unsaturated media and the great number of variables impacting unsaturated flow. An integrated modeling methodology has been developed for quantitatively characterizing percolation patterns in the unsa...

This paper summarizes the progression of modeling efforts of infiltration, percolation, and seepage conducted between 1984 and 2008 to evaluate feasibility, viability, and assess compliance of a repository in the unsaturated zone for spent nuclear fuel and high-level radioactive waste at Yucca Mountain, Nevada. Scientific understanding of infiltration in a desert environment, unsaturated percol...

We consider a radial elliptic-parabolic initial boundary value problem with ux conditions at the lateral boundary. This problem arises as a model for saturated-unsaturated ow in a porous medium. Using formal methods we describe the non-uniform behaviour of the solutions near the extinction time, which is the time at which the unsaturated zone disappears. Borderline cases are particularly delica...

A substantial reservoir (up to 1 kg ha(-1)) of natural perchlorate is present in diverse unsaturated zones of the arid and semi-arid southwestern United States. The perchlorate co-occurs with meteoric chloride that has accumulated in these soils throughout the Holocene [0 to 10-15 ka (thousand years ago)] and possibly longer periods. Previously, natural perchlorate widely believed to be limited...

In accordance with the migration and transformation laws of pollutants in soil groundwater, research progress chemical fertilizers, pesticides, sewage irrigation is reviewed systematically from three perspectives: topsoil layer, underground aquifer, unsaturated zone. The results study various water layers soils illuminate current research's problems future directions.

[1] The air pressures in coastal unsaturated zones fluctuate in response to tidal fluctuations. Two-phase air-water flow induced by sea tides in a coastal two-layered subsurface system is investigated through numerical simulations. The system consists of upper and lower layers with permeabilities of kU and kL, respectively. A water table exists in the lower layer. The study demonstrates that ai...