Many years ago, in a spirit of glasnost, Aggregate Industries decided to share the groundwater data it recorded in and around Straitgate Farm. With so many private water supplies at risk, it did so to show it had nothing to hide.
Not any more. 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 stopped public scrutiny of groundwater levels despite the risk that mineral working poses to surrounding drinking water supplies – as so starkly outlined by Professor Brassington, who also warned:
The MWWT grid will therefore be modelled from levels lower than reality, which will enable AI to excavate below the maximum water table.
Fortunately, however, we still have access to the data from one borehole, PZ10, adjacent to Straitgate Farm. Water levels in this borehole closely trend with those recorded at Straitgate.
For example, in Winter 2013/2014, when PZ10 recorded groundwater at a high level of 103.0 mAOD, high groundwater levels were also recorded across the then 6 piezometers across Straitgate Farm. These levels were then used by Aggregate Industries’ consultants to predict the MWWT across the proposed excavation site.
Following that, the Environment Agency requested further boreholes be drilled and groundwater monitoring piezometers installed to provide a fuller picture of what was going on across the site. There are now 18 piezometers monitoring groundwater levels. A fuller picture was indeed provided.
In Spring 2018, when PZ10 reached 101.7 mAOD, groundwater levels in a number of these new boreholes exceeded the MWWT guesstimate by as much as 1.6m. We posted about it. We alerted Devon County Council and the Environment Agency – who had no access to this data.
What then happened? Aggregate Industries’ consultants, instead of remodelling the entire MWWT, made a trivial finger-in-the-air localised fudge to the modelled surface, which in their so-often-shown-to-be-mistaken view, represented:
a realistic assessment of the change in MWWT arising from the readings in April 2018
Since then the EA has requested the MWWT be adjusted again.
But 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.
Someone needs to get-a-grip of this nonsense. There needs to be public scrutiny of the groundwater data for Straitgate. 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.
