Aggregate Industries may have made its "final submission of additional information" for its planning application to quarry Straitgate Farm, but it's clear that one of the most important pieces of information is still not known with any certainty.
We're referring to the maximum winter water table, the MWWT, the base elevation of any quarry, critical in determining how deep to dig, critical in determining the amount of material available, critical in determining the impacts on water supplies and stream flows.
We have warned for years that the maximum water table could not be accurately predicted. So too have two independent hydrogeology experts. Professor Brassington warned:
...the computer model derived MWWT surface is unlikely to provide an accurate representation of the real maximum groundwater levels
What proof do we have? Simple. The MWWT keeps being exceeded.
Last year, we posted AI’s quarry plan for Straitgate likely to be UNDER WATER AGAIN. We wrote:
In 2018, Aggregate Industries put a stop to public scrutiny of groundwater data for the Straitgate site – after groundwater levels embarrassingly exceeded the company’s guesstimate of the maximum winter water table, the MWWT, in four locations by up to 1.6m. The MWWT is intended to be the base of any quarry. It’s important to get it right, if no buffer or margin of error is to be left to protect surrounding water supplies. It had apparently been "defined with confidence", but the company still won’t come clean on its accuracy. It was shown to be wrong by a staggering 2.8m in one location.
Aggregate Industries' guesstimate of the maximum water table at Straitgate Farm – which consultants had claimed "builds in a conservatism" – has been found wanting ever since it was produced.
No realistic margin of error – in terms of +/- metres – has ever been provided for this prediction. All consultants eventually did – having avoided the question for years – was consider the difference between one inaccurate model and another inaccurate model, pretended it was a "reflection of the ‘tolerance’", and claimed:
a negative tolerance represents conservatism and contingency which is incorporated in the selection of the MWWT
It sounds like bullshit, and it is. For obvious reasons, consultants did not address the inherent inaccuracies of the interpolation method itself, of estimating groundwater levels across 55 sloping acres with just a handful of numbers.
So for all that confidence, conservatism and contingency, what do we now find? Just as we thought likely last year, when we said:
Aggregate Industries' realistic assessment will no doubt have been breached YET AGAIN. Earlier this year, PZ10 reached 102.4 mAOD – 70cm higher than in 2018. It’s virtually certain that a number of the newer piezometers – PZ2017/02 and PZ2017/03 in particular – will have recorded new maximums.
And hey presto, water levels did indeed exceed Aggregate Industries' guesstimate AGAIN. The maximum water level in PZ2017/02, which exceeded the MWWT back in 2018, went nearly 50cm higher in 2020. The groundwater level in this location has now exceeded the company's original guess by a whopping 1.75m. Water levels in PZ06 – installed back in 2013 – also reached a new maximum, as did three other piezometers. So much for the promise from Aggregate Industries' consultants – and backed up by the Environment Agency – that 2014 groundwater levels "are likely to reflect the highest groundwater levels that may occur at Straitgate."
How could consultants get it so wrong? Was it by erring not on the side of caution, but on the side of its profit-hungry client?
Consultants Wood have had another go and have re-guesstimated the MWWT contours. Who knows whether they're right this time? Certainly not Aggregate Industries, Devon County Council or the Environment Agency. In 2017, Dr Rutter warned:
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.
As we finished by saying last year:
The MWWT is never going to be an accurate prediction of the maximum water table. There needs to be a margin of safety, a freeboard, an unquarried buffer retained above the MWWT – like EVERY OTHER QUARRY where drinking water supplies are at risk.
