Mr. R. C. Walker enquired whether the author had evaluated the extent of any structural instability the removal of such a large volume would have, and whether any researches had been conducted to consider the effect of solution of the large volume of evaporites, given that extensive fracturing associated with the proposed extraction techniques in an aquifer area might tend to increase solubility effects.
In reply, the Author stated: Research is being conducted on potential subsidence problems. In many cases there will be as much as 2000 ft (610m) of overburden covering the mined-out area, and, as a result, subsidence problems are not expected to be very severe. In terms of evaporites, most extraction will be in zones where soluble minerals have already been leached out, thus this problem should not be severe either. However, there are likely to be localized problems where shallow, unleached deposits are developed.