A joint programme of research by the British Geological Survey and the Environment Agency
Groundwater issuing from springs has been regarded since the earliest recorded history as something pure, even sacred (Figure 1). In its natural state it is generally of excellent quality.
The properties of groundwater are overwhelmingly determined by geochemical processes taking place as rain or surface water enter the ground and react with rock-forming minerals.
This natural baseline quality will vary from one rock type to another, seen at its simplest in the different areas of hard and soft water across the country. Each area will, therefore, be underlain by an almost unique groundwater quality resulting from the influence of the local geology. The baseline may vary spatially within aquifers of the same type due to variations in the original sediments known as lithofacies. The chemistry also evolves with time as the water moves along flow lines. A number of geochemical processes ? for example oxidation and reduction (controlling natural levels of Fe, Mn, As and Cr), mineral solubility (controlling F and Ba concentrations), and sorption and exchange with mineral surfaces (affecting the concentrations of many metals and ionic constituents) ? may help shape the unique natural characteristics of groundwater.
Baseline concentrations of a substance in groundwater may be defined in several different ways. For present purposes the definition is given as the concentration of a given element, species or chemical substance present in solution which is derived naturally from geological, biological or atmospheric sources.
It is impossible to decide if a water is polluted unless the baseline is known. An ideal starting point is to locate waters where there are no traces of human impact, essentially those from the pre-industrial era.
Newly drilled boreholes provide a good opportunity to monitor the initial conditions (Figure 2). The high natural purity of groundwater is also essential in providing baseflow to rivers and streams to maintain their good quality status.
The activities of the Baseline project are as follows: