THE SALINE WATERS OF LLANDRINDOD AND BUILTH, CENTRAL WALES

Saline or brackish mineral waters have been recorded at several locati ons in mid-Wales and the Welsh borderlands. The main groups are center ed on Llandrindod Wells and Builth Wells where maximum salinities of 5 340 and 16380 mg l(-1) respectively are found. The total discharge fro m these springs is very low (combined 21 s(-1)) yet their flow remains almost constant. Residence times of several thousand years are derive d using C-14 analysis, and delta(13)O and delta(2)H results suggest th at the waters at Llandrindod (although not at Builth) contain a compon ent of Late Pleistocene water. Evidence from the Br/Cl ratios and trac e elements indicates that the origin of the salinity lies within the L ower Palaeozoic formations and has not been derived from evaporites. T he mineral waters have undergone complete reduction of sulphate which has led to high concentrations of Pa (maximum 53.2 mg l(-1)) at Llanga mmarch Wells. The most likely origin of these waters is the deep circu lation of meteoric water over a residence time of several thousand yea rs which has risen slowly along minor fracture systems to the points o f outlet. The interconnected fracture storage of these waters implied from the various lines of evidence must be of the order >30 Mm(3).