Monday, 14 August 2017

‘Drillers were really surprised they struck water so quickly’

That's what one local was told, after Aggregate Industries’ latest round of drilling at Straitgate Farm in June this year, for one of the boreholes.

It was surprising, after such a dry winter, and in the middle of the summer too, but Aggregate Industries’ Technical note: Straitgate Farm Unsaturated Zone Infiltration Tests June 2017 confirms it.

Infiltration testing was performed in five locations. This is where "Test Hole 4" lies:

And this is what AI’s report says about "Test Hole 4":
It is possible that a hydraulic connection to the water table was achieved at this test holes due to the closeness of the water table to ground level in this area.
You can see where "Test Hole 4" is located on AI’s work of fiction below.

Those contours apparently show the difference between the maximum winter water table (MWWT) and average summer low groundwater levels. AI is using this to show it can be trusted to dig to the MWWT during the summer months without affecting surrounding drinking water supplies or wetland habitats in ancient woodland.

Essentially AI's 'model' has been derived from just 6 locations. As Dr Rutter says in her report:
This surface is only a model of reality, and may not represent actual groundwater levels across the site...
AI has extrapolated data from these 6 locations across some 60 acres and pretended that measurements can be deduced to the nearest cm: "At the nearest point to PZ01 within the excavation, difference is 1.17 m", etc, etc. Here's AI's maths:

Guesstimate (in metres) minus Wilder Guesstimate (in metres) = Who Knows (in centimetres)

Of course, it's utter nonsense; you don't need to be a mathematician to see that.

In reality, for a site this sloping, AI can’t make predictions to the nearest metre; that's why 1m is normally left above the MWWT when sensitive groundwater receptors are at risk. As Dr Rutter says again:
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.
We’ve already exposed the lie at PZ05, where the difference is supposedly and very conveniently shown as 0.99m. In reality the groundwater movement here is next to nothing - as the water record - and Amec's report shows:

Now "Test Hole 4" exposes the lie at another location too.

AI’s contours at the location of "Test Hole 4" pretend that 4m separates the MWWT and the summer groundwater levels. In AI’s world, summer water levels should be about 6.5m below ground level. However, in the land of reality, "Test Hole 4" demonstrates "the closeness of the water table to ground level in this area".

In fact, 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

It all goes to show that for the majority of the site - except where boreholes have actually been drilled - AI and their merry band of consultants haven’t got a clue where the water is.