Geology and hydrogeology ... …
Report No. SRL/FP/004.1 (10/05/2006)
density of compacted PFA slurry in the phase 2 lakes at Radley is consistently lower than they had anticipated39. Possibly the density is just as high as they had expected, where there is compacted PFA slurry, but that also lying beneath the surface of the filled lakes is a water body emanating from a spring beneath the Lakes, or quicksand supported by springs. If this hypothesis is true, then the PFA is not suffering from delayed consolidation; it will never consolidate and will remain unstable and unsafe indefinitely. And fourthly, what is really responsible for the purity of the water in Lake F, namely hard, oligo- mesotrophic water with benthic vegetation of Chara? Why is such water present in a gravel area? The absence of agricultural runoff of substances such as nitrates and phosphates is a major factor. One hypothesis has been that the groundwater feeds Lake E and that Lake F is directly fed from Lake E, but filtered by the gravel in the isthmus between the two. But there's another hypothesis to consider: Such water is frequently associated with limestone country and is rare in the south of the country: might it be the case that Lake F (and possibly Lake E as well) is spring fed from the Corrallian aquifer beneath and that this explains both the properties of the water and the reason why it maintains its water level?
These new pieces of information may at first appear to answer several questions but they raise further questions. From the planning point of view, there is first the question of whether there is sufficient clay to do the job and whether any possible faulting in the Corrallian Rag might be associated with faulting in the Kimmeridge Clay (these questions come on top of the previously asked question about the quality of clay vis-à-vis large fossils and the thickness of the layer of clay). Secondly there is the question of damage to the life in Lake F if Lake E is drained. This question remains an open one with very worrying consequences if we (they) get it wrong. But most important of all is the several lines of evidence that point strongly towards the possible existence of springs beneath some or many of the lakes at Radley40. If this is the case, then none of the lakes are suitable for being bunded, clay-sealed repositories of PFA. No further filling should be done without an answer to the question, do springs exist at Radley? If they do, not only the new proposal to fill Lake E should be refused, but also the continued filling of other lakes at Radley should be stopped until these matters are properly investigated and appropriate future action determined.
APPENDIX 2: ACKNOWLEDGEMENTS
The author would like to thank Basil Crowley and Bob Eeles for their significant contributions to the manuscript, and David Guyoncourt for pointing out several important issues of relevance.
39 ES, page 26 where it states “…the cause of this reduced density is not completely understood.”
40 In the background to the research and thinking that went into this postscript is the niggling question “Why, given that Mr Drysdale said
he removed fish from Lake E in the expectation that it was going to be filled with PFA, was it not filled in the 1990’s?”. A story going the rounds is that it was not geologically suitable. Were springs discovered at the time? Was the poor quality of the Kimmeridge clay noticeable? If it was found to be unsuitable then, why is it any more suitable now? These questions also need to be addressed.
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© SAVE RADLEY LAKES 2006