By now you might be thinking that Aggregate Industries’ model of groundwater at Straitgate Farm couldn’t get any worse. You’d be wrong.
The contour map below was supplied by Amec last year to back up AI’s seasonal working scheme and satisfy concerns from the Environment Agency. It is a work of fiction.
The map has been given the Amec Foster Wheeler seal, but the contours started life on the AI map below: "Isopachs of average summer unsaturated mineral". It was one of the reasons why we questioned whether these things were being put together by competent experts – because:
To ensure the completeness and quality of the Environmental Statement, the developer must ensure that it is prepared by competent experts.
Anyway, AI would have us believe that the contours show the difference between the maximum winter water table and the average summer low groundwater levels. It was supplied to the EA to show that AI can be trusted to dig down to the MWWT during the summer months without affecting surrounding drinking water supplies or wetland habitats in ancient woodland; to show that in the drier months there would always be 1m separating its excavators from groundwater levels.
You may not believe it, but the contours were derived from just 6 locations. You have to admire the creativity; local people have referred to these contours as "The Himalayas".
But, yes, you’ve already spotted the problem: the average summer low is not the summer maximum. AI is looking at the best case summer water levels – the best case for the company that is: the very lowest levels recorded that would allow its seasonal scheme to succeed. The contours are meaningless as an indicator of the validity and safety of AI's scheme. If maximum summer water levels had been used, AI's model would fall apart; we have already posted on the subject:
... if instead of looking at average summer low groundwater levels we look at maximum summer groundwater levels (MSWT), AI’s model falls apart completely, with half of the piezometers around the site showing significantly less than a metre difference between maximum winter and summer levels. It makes a mockery of this statement:
...the working method ensures that the floor of the excavation will always have at least 1.0m of unsaturated gravels beneath. 2.4.7
Anyway, it's worse than that.
Boreholes from this year and 1990 have really put the boot in and exposed the contours across large areas of the site for what they really are – fiction.
Take SG1990/021 – subject of the last post – as an example. Amec has modelled the MWWT in this location to be 136m AOD. AI's isopachs claim that the difference between the MWWT and the average summer low in this location is 4.0m; here is an enlarged screenshot from the map below, the crosshairs mark the position of SG1990/021:
AI is therefore claiming (taking 4 from 136) that the average summer low groundwater level in this location is 132m AOD. The trouble is that borehole SG1990/021 recorded the groundwater level in mid June to be 138.81m AOD – 6.8m higher, or about the height of a house.
Three other locations – indicated below – also show significant discrepancies.
What's laughable is that, if you look at the top contour map, you’ll find AI’s consultants making predictions to the nearest centimetre:
At the nearest point to PZ01 within the excavation, difference is 1.17 mAt the nearest point to PZ03 within the excavation, difference is 4.78 mAt the nearest point to PZ04 within the excavation, difference is 5.83 mAt the nearest point to PZ06 within the excavation, difference is 2.34 m
The reality is that AI and its consultants can’t even make predictions to the nearest metre. Competent experts?? GCSE maths students would make a better job.
We’ve reminded people many times before, but in Dr Helen Rutter’s words:
The steep hydraulic gradient combined with limited monitoring, in my opinion, is likely to result in errors in the actual depth to maximum groundwater across the site.
Here are some of those errors:
