CHAPTER ONE

Introduction

1.0 BACKGROUND OF STUDY

Groundwater is commonly understood to mean water occupying all the voids within a geologic stratum. Groundwater is one of the nation’s most valuable natural resources; it is the source of about 40 percent of the water used for all purposes exclusive of hydropower generation and electric power plant cooling. Surprisingly for a resource that is so widely used and so important to health and to the economy of the country, the occurrence of ground water is not only poorly understood but is also, in fact , the subject of many widespread misconceptions. Common misconception includes the belief that ground water occurs in underground rivers resembling surface streams whose presence can be detected by certain individuals. These misconceptions and others have hampered the development and conservations of ground water and have adversely affected the protection of its quality.Groundwater occurs everywhere but sometimes its availability in economic quantity depends solely on the distribution of the subsurface geomaterials that are referred to as the aquifers. This implies that where groundwater is not potentially endowed enough, there may be either complete lack or inadequacy due to increasing industrial and domestic needs.

Pollution occurs when the concentration of various chemical or biological constituents exceed a level at which a negative impact on amenities, the ecosystem, resources and human health can occur. Pollution results primarily from human activities. There are different sources of pollution. When they are chemical or biological constituents creating pollution they are known as contaminants. Contaminants degrade the natural quality of a substance or medium. It can either be organic or inorganic.

Surface resistivity methods have been employed successfully for detecting and mapping ground-water contamination under a variety of conditions. The method is based on the fact that formation resistivity depends on the conductivity of the pore fluid as well as the properties of the porous medium. Under favorable conditions, contrasts in resistivity may be attributed to mineralized groundwater with a higher than normal specific conductance originating at a contamination source. Success with surface resistivity methods depends to a large extent on a good knowledge of subsurface conditions. Conditions favorable for delineating zones of contamination include uniform subsurface conditions, a shallow groundwater table, and good electrical contrast between mineralized and natural water.

One of the primary problems in field investigations of groundwater pollution is locating the contaminant plume. In most cases, the goal is to positively locate the pollutant and its movement by test holes and direct monitoring. In the interest of efficiency the investigative areas should be as focused as possible. In many cases a general knowledge of local hydrogeology allows a reasonable initial estimate of pollutant direction; in other instances even this may be lacking. Drilling of sampling holes on a hit-or-miss basis is both time-consuming and expensive. It can also be destructive to the property involved. Under certain subsurface conditions, surface geoelectrical profiling can quickly and cheaply locate the general location of the plume and identify areas most feasible for sampling and monitoring.

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