Baseline quality variations in space and time

Photograph showing an overflow of 50,000 gallons per hour (65 litres per second) from the Pinchbeck West borehole in South Lincolnshire in the early 30's

The quality of groundwater varies spatially in relation to changes in residence time, aquifer mineralogy and chemical environment (e.g. redox conditions). Large differences may also exist with depth in the aquifer with older, more evolved waters often being present at depth.

A three dimensional interpretation of water quality in the Triassic sandstone of Nottinghamshire has been developed. The diagram shows modern groundwater, with pollution indicators (NO3, SO4), migrating downgradient. High quality natural fresh water occurs in this aquifer although some natural high salinity is present at depth.

The monitoring of boreholes is essential to understand the temporal changes taking place in groundwater both with regard to pollution and natural processes. The water first struck under artesian conditions may represent a good example of water untouched by humans (Figure 1).

It is important to have knowledge on the behaviour of key indicators and be able to predict the rate and extent of any natural or anthropogenic change imposed on the baseline.

Aquifer materials generally have a strong buffering effect on many incoming contaminants, but small changes in key mobile indicator elements (e.g. Cl) may herald more significant problems upstream.

The distribution of various elements in the confined chalk groundwaters of Berkshire has been determined and is provided in graphical form. This shows that most trace elements are enriched relative to sea water. The natural baseline for any element may have a considerable range of concentrations.