Groundwater abstraction quantity from the Chalk is limited to what is sustainable. Water quality data collected in the 1970s and 1980s have been compared with modern water quality monitoring data for 25 public supply abstraction sites. This comparison has established that there has been both substantial (magnitude) and significant (statistical) change in composition at all sites. Identified changes generally represent real changes in groundwater composition. At some sites in the south of the area considered, water that is not the result of present-day recharge processes is being replaced by water from present-day recharge. It is also clear that at those sites where ancient brackish water is known to be present at depth, it is generally not being mobilized by pumping. In the north of the area, changes are more subtle but there is a tendency of groundwater composition to approach the regional average, apart from calcium which is trending higher. Nitrate has not increased here, suggesting that reduction is a still-active process. Thus, although quantity has been sustained, quality is changing but not to a degree that impacts potable use.

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