Summary

Projected road improvements in south Hampshire included plans to dispose of surface drainage into soakaways to be sited near an area of swallow holes in the Chalk. An experiment was undertaken to establish if there was a direct connection between the swallow holes, located near the junction of the Chalk and the Lower Tertiary strata, and major springs used for water supply in the Havant area. As the swallow holes are dry except in periods of storm rainfall a tracer, the fluorescent dye Rhodamine WT, was injected together with a large volume of water into one of the swallow holes. Water samples were collected from the springs at Havant and analysed for Rhodamine WT using a Turner fluorometer. The tracer was found at both sets of springs sampled and the straight line velocity from input point to spring was in excess of 2 km per day. Computations based on the concentration of dye recovered from the springs show that in the event of a tanker spillage within the proposed drainage scheme severe contamination would be expected to occur at the springs. The experiment and the results obtained make it clear that extreme caution should be exercised to avoid contamination of fissure-flow within the Chalk aquifer.

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