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Geology and hydrogeology ... …

Report No. SRL/FP/004.1 (10/05/2006)

  • Very high leach rates are equivalent to having no bund, with associated disadvantages, which the Groundwater Regulations are supposed to prevent and which prompted the Environment Agency to specify a clay lining.

  • Intermediate leach rates may be worse than any other, permitting a sufficiently high rate of leaching to occur that precautions have to be taken, and ill-consequences suffered, but retaining the toxins in the lake for a very long time. The precautions and ill-consequences might have to continue for a much longer period than has been allowed for.

  • Leaching, ie pollutants being carried, or advected, in water seeping through the lake linings is not the only mechanism whereby pollution can escape. Pollutants, particularly when they exist in the form of single atoms or ions, can diffuse through wet clay independently of any flow of water. This process, which occurs in addition to leaching, can be accelerated by various physical and chemical mechanisms and can result in significantly faster migration of some chemical species than by leaching alone.

Some housing is within about 100 metres of Lake E; a substantial amount of Abingdon housing is within 500 metres. This housing is to the West of Lake E, the very direction which will be followed by the ground-water10, after it has been deflected by the new clay bund around Lake E and by the already constructed bund around Lake H/I. Deflection of contaminated ground-water towards housing presents a serious problem. A recent resident of one of the cottages at Thrupp Farm used to draw drinking water from a shallow well in the garden, drawing water from the terrace gravel deposits, which are now allegedly contaminated by leachate emitted from the Lakes. But that historic reference is only the tip of the iceberg. The movement to eat natural foods has promoted a great

interest in home-grown vegetables and

development

of

garden

ponds.

Both

fruit. There is of these are

also a movement occurring in the

to encourage the context of water

shortage in the South-East of learn that there is a growing

the country, hose pipe bans number of boreholes being

and so on. It is drilled by those

not surprising to who want to be

sure of shallow

their water supply. boreholes for their

Those living on housing built gardens. They will draw water

on terrace gravels will deflected by the bunds

only drill from the

Radley Lake (E, H, I) chromium and arsenic

and will draw with it the dangerous substances, for example, which occur in the leachate.

such

as

barium,

KIMMERIDGE CLAY AND ITS SUITABILITY FOR SEALING The quantity of Kimmeridge Clay and the underlying Corallian Rag

RWE npower are working on the assumption that the Kimmeridge Clay which underlies the Radley lakes is 30 m thick. They also suggest that the Corallian Rag may be 100 m thick. These figures are pure fiction, not even educated guesses.

The

writer

is

aware

of

the

thickness

of

the

Kimmeridge

Clay

under

his

garden

in

North

Abingdon, having dug over 40 m of trenching for foundations, foul drainage, water mains and soakaways with his own hands. Generally, in this location, the Kimmeridge Clay presents itself in isolated patches, separated by sections of boulder clay and terrace gravels, but surprisingly also containing pockets of Oxford clay, Greensand and another unidentified layer (possibly Gault). That this mixture can occur within a metre of the surface of ground, otherwise undisturbed, sounds a serious warning to anyone planning to

10

ES, page 2-8 of Appendix 7, 6 lines from end of page.

Page 7 of 23

© SAVE RADLEY LAKES 2006

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