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Geology and hydrogeology ... …

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

concerning the existing phase 2 disposal site (most notably Lakes H/I) and possible explanations of several hitherto unexplained phenomena.


The author was an Associate Lecturer for 33 years with the Open University. One of the duties undertaken was to lecture in Earth Sciences and from time to time to take students on geological field trips into quarries near Durham and Newbury.


The in situ clay (Kimmeridge Clay), which RWE npower propose to use to seal the bunds around and under Lake E at Radley, may not be of sufficient quantity or quality to retain the impurities, heavy metals and other dangerous substances, which are dissolved from the fly-ash. The Environment Agency has required PFA waste tips, if they lie below the water table, to be so sealed. The lakes that were filled first were not lined with clay before filling, the recent ones were lined. The principle of lining is to retain potentially dangerous substances for a long period of time, even indefinitely.

Those which were not lined must have increased the amount of pollution in the surrounding water table by a significant amount at the time they were filled, due to r a p i d l e a c h i n g , b u t , b y n o w , o n e m i g h t s u p p o s e t h a t t h e l e a c h r a t e w o u l d b e significantly reduced. However data from borehole 13a and the Pumney Ditch 4 i n d i c a t e t h a t t h e r e i s a n o n g o i n g p r o b l e m . T h i s i s a c t u a l l y n o t s u r p r i s i n g w h e n o n e c o n s i d e r s t h e a m o u n t o f s o l u b l e m a t e r i a l t h a t i s p r e s e n t . N p o w e r s t a t e 5 t h a t o n l y to 3% of the ash solid matrix is soluble”, as if this was somehow reassuring. They propose to dump 500,000 tonnes into Lake E. This represents 10,000 to 15,000 tonnes of soluble material. If this dissolved at a rate of say 1kg per cubic metre of 2 w a t e r , t h e n t h i s w o u l d b e s u f f i c i e n t t o p o l l u t e 1 0 t o 1 5 m i l l i o n c u b i c m e t r e s o f g r o u n d w a t e r a s i t f l o w s a c r o s s t h e l a k e 6 . H o w e v e r g r o u n d w a t e r f l o w s a r e q u i t slow, and the flow intercepting a lake of the size of Lake E would, on the basis of e t h e g r o u n d w a t e r d a t a g i v e n 7 , b e i n t h e r e g i o n o f 4 × 1 0 - 4 c u m / s o r ~ 1 2 , 0 0 0 c u m / y e a r 8 . T h u s t h e t i m e s c a l e f o r l e a c h i n g a l l t h e s o l u b l e m a t e r i a l , b y g r o u n d w a t e advection, out of an unbunded lake is estimated to be ~1000 years, possibly longer. The unbunded phase 1 lakes, A-D, have only been in existence for a small fraction of that time, which is not long enough for all the pollutants contained in them to have been washed out. So, it’s a case of very bad for a time, not so bad later, where “later” means in perhaps 1000 or more years time! r

Those which were lined should, in principle, have leached very little by comparison9. However, if the clay is not perfect, leaching can occur. And that is the subject of this objection to the County Council.

Very slow leach rates are unimportant, if they can be maintained in the long term.

5 ES, page 11.

6 The ~1.5 cu m of polluted water that would be discharged into the outflow during the filling period can be ignored for the purposes of

this calculation..

7 ES, Appendix 7. See also comments relating to hydraulic gradients later in this report.

8 The hydraulic permeability has been taken to be 10-4 m/s (ie similar to the surrounding gravel, If the PFA were compacted, this figure

could be much smaller.) and the hydraulic gradient to be 2.6×10-3. The estimated flow rate (33 cu m/day) is within the range given in Table 3 on page 2-15 of Appendix 7 of the ES, where the opinion is expressed that the flow rate is more likely to be in the range 5-10 cu m/day, ie 3 to 6 times smaller. If so, this would increase the timescale estimate by the same factor.

9 Containment times, assuming perfect sealing, would be of the order of 200 times greater than for unbunded lakes. See page 14.

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