R. A. Monkhouse writes: This paper essentially states that for borehole development, simply to remove the wall-cake (slurry) from a freshly constructed (Chalk) well, very much smaller quantities of hydrochloric acid are required than are generally employed in this form of borehole development. It is also said that, when larger quantities are used, these are to develop fissures in the surrounding aquifer rather than to remove wall-cake. What is not said is what amount of acid should be used (in particular, the borehole depth is not considered) and how to define the circumstances in which the lesser treatment is preferable to the larger. Stow & Renner (1965) recommended an injection of 20 kg (rounded to the nearest kilogram) per square metre of wall face exposed within the saturated chalk in order to remove the wall-cake. This ratio was determined for an acid strength of 30° Twaddell. for treatment of the aquifer, no particular amount of acid was recommended, but there was an implication of some 2 to 2½ times the volume of water contained within the borehole below the plain lining tubes. I have been able to identify in the Geological Survey well record collection five of those boreholes listed in Table 1 as having been acidised commercially (which I call here group A), and all seven of those treated by the Anglian Water staff (Group B). From these records, I obtained additional details of depth, length of lining tubes and depths to rest water level and from these calculate

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