Changes in the chemistry of groundwater in the chalk of the London Basin
1 The current investigation involved sampling and analysing six sites to measure changes in groundwater chemistry. 2 The sites were selected from the London Basin area, which is located in the south-east of England and has been frequently used to interpret groundwater evolution.2, 3, 4
3 A total of 18 samples was collected and then analysed for the isotopes mentioned earlier. 4 Samples 1–9 were collected in thoroughly-rinsed 25 ml brown glass bottles which were filled to the top and then sealed tightly to prevent contamination. 5 The filled bottles were shipped directly to two separate laboratories at Reading University, where they were analysed using standard methods suitably miniaturised to handle small quantities of water. 5
6 Samples 10–18 were prepared in our laboratory using a revised version of the precipitation method established by the ISF Institute in Germany.6 7 This method obtains a precipitate through the addition of BaCl2.2H2O; the resulting precipitate can be washed and stored easily. 8 The samples were subsequently shipped to ISF for analysis by accelerator mass spectrometry (AMS).
9 All tubing used was stainless steel, and although two samples were at risk of CFC contamination as a result of brief contact with plastic, variation among samples was negligible.