Guest Editorial — God Didn’t Make Those Little DNAPLS Andrew W. Stone
Risk-Based Evaluation of Ground-Water Contamination by Agricultural Pesticides    P. Varshney, U. S. Tim & С. E. Anderson
Agrotechnically Induced Salinization in the Unsaturated Zone of Loessial Soils, N.W. Negev, Israel    M. Magaritz & A. Nadler
A Simple Analytical Approach for Predicting Nitrate Concentrations in Pumped Ground Water    D. N. Lerner & К. T Papatolios

In the field of groundwater numerical flow modelling has become a standard tool for scientific and also for most of the practical problems. The modelling software has matured during the past 10 years from being user-unfriendly with complex interfaces to a powerful, easy-to-use, windows-based system. For porous media flow in the saturated zone, the basic principle pertinent to all common programmes like MODLFOW, FEFLOW etc. is the solution of the linear DARCY- and continuity-equations. The numerical problems associated with the limitations in discretisation known in earlier days are not a serious burden any more because of the high-speed PCs with hundreds of Mbytes memory available nowadays.

The main aim of this book is to provide an introduction to the most relevant investigation methods and techniques that can be used to study karst hydrogeological systems, including modern approaches to interpreting and modelling the data obtained. Studying karst aquifers is not only scientifically challenging, but it is also important for humanity. Ford & Williams (1989) estimated that 25% of the world’s population drink water from such resources. Although this number is probably an over-estimate, karst groundwater constitutes a crucial freshwater resource for many countries, regions and cities around the world.

Hydrogeology is now considered to be a core course in the curriculum of undergraduate geology programs as well as many fields of engineering. There is ongoing de- ; mand for persons with training in hydrogeology by consulting organizations, state and federal regulatory agencies, and industrial firms. Most of the employment in hydrogeology is in the environmental area. This is a book that will help prepare students for either a career in hydrogeology or in other areas of environmental science and engineering where a strong background in hydrogeology is needed.

In 1803, when Alexander von Humboldt arrived in Mexico, the colonial site of Guanajuato represented the third largest town in “Spanish” America, just overwhelmed in population by Mexico City and Havana. During the 18th century, the Guanajuato Mining District was reportedly producing one-third of the world´s silver. Estimates of historic production range from 700 million to 1.5 billion ounces of silver, as well as 4 to 7 million ounces of gold. Remarkably, some areas are still today under exploitation. Geomorphological and environmental consequences from hundreds of years of mining activity can still be observed in the surroundings of this charming UNESCO World Heritage community.

The demand for freshwater is increasing as the world’s population continues to grow and expects higher standards of living. Water conservation, better systems’ operation, higher end use, and water allocation efficiencies have not been able to offset the growing demand. Many societies are struggling to bring supply and demand to a sustainable level. Although water is abundant on earth, freshwater accounts only for about 2.5% of global water reserves. Out of this amount, approximately 30% is stored as groundwater and the same amount is on the surface as rivers and lakes; the remaining reserves are held in glaciers, ice caps, soil moisture, and atmospheric water vapor. Groundwater is a source of vital natural flow.