The Great MWWT Hoax – AI’s groundwater model has been sketched by hand

We have long argued – as have others, including Professor Brassington and Dr Rutter – that Aggregate Industries' model of the maximum groundwater levels – the MWWT, the base of any quarry, denoted by the contours below, originally guesstimated across 55 sloping acres from 'maximum' water levels recorded in just 6 boreholes – is not accurate. How on earth could it be?

Meanwhile, in the land of fairy tales, Aggregate Industries’ consultants – Amec Foster Wheeler now Wood – have over many years been peddling the story that the MWWT – the determinant of the recoverable resource and hence the proposal’s monetary worth – was generated by a clever and super accurate computer algorithm, NOT by the hand of some easily persuadable human. 

Lots of people were taken in by this story, including the Environment Agency. 

Documents were produced on the subject, following a meeting we had with the Environment Agency in September 2017, when Aggregate Industries was asked to supply:

A description of the tolerance levels and interpolation method used to produce the ‘Maximum Winter Water Table’ grid 

At this point, consultants had every chance to come back and say we used a sharp pencil and our immense brain power. But they didn’t. Consultants said: 

Four alternative grid interpolation methods were selected: Simple linear Kriging; A Radial Basis Function; Inverse Distance to a Power; Triangulation with linear interpolation. Each of these methods represents an exact interpolator in which the input data point will be preserved and respected by the interpolation algorithm…. The grid determined by Radial Basis Function was therefore adopted as being a more conservative preferred method for estimating the maximum water table distribution. 

Clearly, consultants accepted they were estimating, but no indication of the accuracy of this estimation was supplied, so in February 2018, the Environment Agency asked again. The consultants came back with more nonsense: 

The description of how the MWWT grid was calculated explained that two of the interpolation methods used produced realistic results (in line with expected hydrogeological behaviour and professional judgement). One method, ‘Radial Basis’ produced a grid that was generally higher than the other grid prepared by a Kriging method. As the MWWT was subsequently based on the higher of the two interpolated surfaces (i.e. Radial Basis interpolation) this could be considered to represent the upper limit of interpretation, with the Kriging interpolation representing the lower limit of interpretation and therefore the difference between these two realistic grids could be considered as reflection of the ‘tolerance’. 

It was a bogus argument. The Environment Agency asked more questions, and were told:

The generally higher Radial basis grid is subtracted from the generally lower Kriging basis grid to give an indication of “tolerance”….The Radial grid formed the basis for the final composite MWWT (shown in Figure 5), which also underwent final adjustment (upwards) to take further account of hydrogeological professional judgement. 

More gibberish, but the Environment Agency was satisfied. In June 2018 it wrote: 

We have reviewed the document and we are satisfied that it answers our questions about the derivation of the Maximum Winter Water Table grid.

But all the radial basis and kriging talk was baloney. A mathematician has analysed the MWWT, and has concluded "it is not a radial basis function, per se": 

If a sensible, well conditioned parameter and an appropriate generating function are chosen, a radial basis function will be a well behaved mathematical surface with continuous, smoothly differentiable contours between interpolation points... The only conclusion is that AI have defined their MWWT by hand.

And indeed, if we look through the myriad of documents, we find a map showing "hand contoured groundwater levels for February 2014 (mAOD)" submitted with the 2015 application, and again thereafter:

If we overlay these hand drawn contours over the MWWT (before recent changes) we find miraculous agreement over large areas. Check out the agreement along the 141mAOD contour, the 145m contour, the 148m contour, the 150m contour; the hand drawn contours are grey, the MWWT contours are blue. 

No mathematical model, no matter how clever, radial basis, kriging or otherwise, could produce such agreement from just – as it was originally – 6 numbers. A similar overlay with the MWWT recently supplied (and recently adjusted for elevated groundwater levels along the eastern boundary) shows corresponding agreement – see below – to areas not recently tweaked. 

This means that consultants have not only been spinning a long and convoluted yarn to the Environment Agency, but have used whatever professional judgement they have – which may of course be biased, compromised, subject to errors or simply lacking – to guesstimate the levels that their fee-paying client may dig down to; in other words, deciding exactly how much money Aggregate Industries could lay its hands on. Anybody smell a massive conflict of interest? 

And knowing that the MWWT has been drawn by hand, on the back of a proverbial fag packet for all we know, means there is certainly NO basis for claiming cm accuracy of these contours, and EVERY basis for not trusting them, and EVERY need to add a very large safety margin above them to accommodate "professional judgement". 

Who can trust a single word Aggregate Industries' consultants say any more?

AI’s ‘conservative’ model of the MWWT has been EXCEEDED YET AGAIN

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.

 

‘Note: All models have uncertainty / margin of error’

Over the last year, the pandemic has exposed us all to a variety of sobering forecasts and models. 

Here’s one produced by Sage last year.

 

Even though the four groups were all looking at the same pandemic, there was a range of projections. 

However, the chart came with a warning: 

Note: All models have uncertainty / margin of error 

Which is to be expected when you have limited data. Any expert knows that. 

Any expert except the ones working for Aggregate Industries, who have for years failed to answer the simple question: How accurate is your model of the Maximum Winter Water Table – when it has been guesstimated with just 6 numbers? 

As we said in this post last year, AI still won’t come clean on accuracy of MWWT: 

The MWWT – the maximum winter water table – would be the base elevation of any quarry at Straitgate Farm. It is a model, a prediction of what might be happening across some 55 acres, based on water levels recorded in just 6 piezometers. The accuracy of this prediction would matter less if Aggregate Industries were planning to leave a safety margin, an unquarried buffer, above this surface – but it is not.

Aggregate Industries’ consultants, Amec Foster Wheeler now Wood*, clearly needed the help of a dictionary to understand tolerance. As we posted: 

All AFW was attempting to do was to obfuscate, to confuse, to muddle the EA. All AFW was doing was showing the difference between how two techniques (kriging and radial basis) have interpolated 6 measurements to predict groundwater levels across 55 sloping acres. All AFW was showing was the difference between one inaccurate model and another inaccurate model. This is not a tolerance, it is a difference. What AFW has NOT done, for very obvious reasons, is to consider – at least in public, for the benefit of locals, the Council and the EA alike – the inherent inaccuracies of each of those techniques. 

But muddle the Environment Agency it did. The Agency clearly didn’t grasp that all models have uncertainty / margin of error and subsequently wrote in an email in June 2018: 

We have reviewed the document and we are satisfied that it answers our questions about the derivation of the Maximum Winter Water Table grid.

However, some experts do get it. Professor Brassington warned: 

The MWWT for this site has been defined by using a computer model as the number of piezometers (six) are insufficient to cover the quarry area in sufficient detail. Computer models of groundwater systems are good at showing changes in groundwater levels although they are poor at showing the actual amount of such changes. As a result, the computer model derived MWWT surface is unlikely to provide an accurate representation of the real maximum groundwater levels... 

Dr Rutter also warned: 

I am concerned that there is a very steep hydraulic gradient across the site, from around 152m in the west to less than 135 m in the east, and the limited number of piezometers used to grid the water table surface. Variations in the shape of the water table cannot be contoured based on the number of piezometers used in the application... 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. 

Prof Brassington was sufficiently concerned to recommend: 

an unquarried buffer of at least 3 m is left above the maximum water table to minimise the negative impacts.

It's all a matter of which experts Devon County Council should trust: consultants who whitewash reports to help clients win as much material as possible, or an award-winning Professor who has made "an outstanding contribution to hydrogeology." Tough call.

* In other news, Aggregate Industries' water consultants Wood have sets aside an extra $151 million to settle corruption and bribery probes at Amec Foster Wheeler, reports the FT. The Serious Fraud Office launched an investigation into Amec Foster Wheeler in 2017, as we posted at the time.

 

Wood sets aside extra $151m to settle corruption probes https://t.co/jBOpol0roY

— FT Energy (@ftenergy) March 16, 2021

AI’s quarry plan for Straitgate likely to be UNDER WATER AGAIN

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.

Boreholes at Straitgate ‘will have groundwater levels lower than local water table’

The impact on surrounding private drinking water supplies – be they wells, springs or boreholes – is one of the most contentious aspects of the proposal by Aggregate Industries to quarry Straitgate Farm.

Over the years, we have posted about how the maximum winter water table – the MWWT, the base of any quarry at Straitgate – can not be predicted accurately. The elevation of the MWWT put forward by Aggregate Industries’ consultants Amec (now Wood) is just a model, a prediction, a guesstimate of what might be happening across some 55 acres, based on water levels recorded over a limited time from just 6 piezometers across that area. The accuracy of this model would matter less if Aggregate Industries were planning to leave a safety margin, an unquarried buffer, above this surface to protect surrounding drinking water supplies – but it is not. After all this time, AI still won’t come clean on the accuracy of the MWWT – which for most people would be warning enough.

Last May, Professor Rick Brassington Eur Geol Eur Ing BSc MSc CGeol FGS CEng MICE FCIWEM, recent winner of the Whitaker Medal "in recognition of an outstanding contribution to hydrogeology", produced an extensive and damning report which warned that "any proposals to quarry at Straitgate Farm will impact on the fragile groundwater system and cause the flows of springs to decrease and the quality of the water also to deteriorate".

As readers may remember, this report was largely ignored by the Environment Agency, which in its wisdom decided early this year that it "will not be providing further responses" in relation to Aggregate Industries’ application – before then going on to do just that, as we posted in Alternative water supplies: EA’s remit is 'objectives and outcomes, not solutions', EA "consolidates and revises" conditions – but still fails to justify position, and Another response from the EA – and a swipe at SAG.

In his report, Prof Brassington recommended that "an unquarried buffer of at least 3 m is left above the maximum water table to minimise the negative impacts", in part because "the MWWT surface cannot be modelled accurately".

Why so? There are many reasons – as we have posted about in the past – but there’s another reason too, which we have not previously highlighted, and which has obviously not been picked up by the EA either. It’s based on work by this renowned scientist almost 80 years ago:

Prof Brassington outlined the relevance of M.K.Hubbert’s work with regards to Straitgate in his report:

3.16 Hubbert (1940) produced a ground-breaking demonstration of how groundwater flows through aquifer systems based on Darcy’s law. In essence, he showed that groundwater flow is three-dimensional with a vertical component of flow. Both the depth of a borehole and its location within an aquifer have a significant influence on the water level within it. Figure 3.5 below shows how these factors impact on groundwater levels.

3.17 The figure shows groundwater flowing through an idealised aquifer from recharge areas to discharge areas in valley bottoms. Flow lines are shown as solid lines, while equipotential lines (contours of equal pressure) are hatched. The effect of this flow system on the water levels in wells gives decreasing elevations with depth in recharge areas and increasing elevations with depth in discharge areas. As a consequence, the water level in adjacent boreholes will not be the same if the depths are different.

3.18 As a result of the above, it is important to take account of the depth of the monitoring borehole or piezometer and its location in respect of the groundwater flow pattern when interpreting the elevation of a water table. This will not always be significant when looking at regional flow over an aquifer. However, in the small area of an aquifer such as being considered in this report these differences are likely to be significant. For example, fully penetrating boreholes in recharge areas will have a lower groundwater level than the local water table.

Our emphasis. Wikipedia confirms:

In an unconfined aquifer, the water level in the piezometer would not be exactly coincident with the water table, especially when the vertical component of flow velocity is significant.

How much is not exactly? According to this paper:

In the case where groundwater shows a significant vertical flow component (Fig. 4), the water level measured in a well can vary considerably (from a few centimetres to decimetres, and locally to a few metres) from the depth to the top of the saturated zone of the aquifer. This difference depends on the vertical hydraulic gradient, thus on the location of the observation well along a flow line, but also on the depth and length of the piezometer screen.

A number of boreholes have been drilled across the Straitgate site over the years. Eighteen have now been installed with piezometers. As Wikipedia also confirms, a piezometer – like the ones at Straitgate – will typically have:

a solid casing down to the depth of interest, and a slotted or screened casing within the zone where water pressure is being measured

Back in April 2015, Aggregate Industries' Hydrogeological Assessment was telling us:

To date, 11 piezometers have been installed by AI to monitor groundwater levels in the BSPB across the Straitgate site... All piezometers have been drilled into the underlying Aylesbeare Mudstone but are installed with a 3 m screened section in the BSPB... In some cases the screened section is now partially filled with sediment and it is unknown what effect this may have.

In other words, all these boreholes fully penetrate the aquifer.

That was 5 years ago. The latest HA has, for whatever reason, removed the above information.

But to confirm: Straitgate Farm is in a recharge area: rain falling on the ground surface slowly percolates through the sand and gravel to the unconfined aquifer below, to emerge many years later in springs and wells. The land is sloping, as is the water table. Dr Helen 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.

Here’s Amec’s conceptual cross section of the site:

And here's another representation of Hubbert’s work. It shows that water will flow from regions of higher pressure to regions of lower pressure. In areas of recharge – like at Straitgate – where there is a vertical and horizontal component to the groundwater flow, the lower pressure at the open or screened section of deeper piezometers will only be able to support a column of water (the black columns) in the borehole to an elevation lower than the immediate water table. In the example below, boreholes D and E have been drilled in the same location to different depths. The lower pressure at the bottom of piezometer E supports a column of water to a lower elevation than D. Boreholes C,E and F have been drilled to depths of equal pressure and thereby support columns of water to the same elevation.

It can therefore be seen that using water levels recorded in piezometers in recharge areas would produce a model of the water table at a lower elevation than in reality.

Aggregate Industries’ proposal to quarry down to the MWWT – modelled from groundwater levels in an area of recharge – would therefore in reality be a proposal to quarry below the level of the maximum water table. This would be unlike other operators that maintain a freeboard above the water table, where water sources are at risk.

Not only would quarrying below the water table at Straitgate risk derogating drinking water supplies for more than 100 people, including a Grade I listed manor house, and three livestock farms, it would also be contrary to the Devon Minerals Plan.

Of course, over all these many years, Aggregate Industries’ consultants have not mentioned Hubbert. They have not mentioned that the depth of a borehole and its location in respect of the groundwater flow pattern is important. They have not mentioned it, even though any hydrogeologist worth their pay grade would know about it. These consultants have not mentioned it, because it’s not in their interest, or that of their paymasters.

But why hasn't the EA – given that groundwater is one of our most precious raw materials?

💧Groundwater plays a major role in the water cycle supporting baseflows to #rivers, #wetlands & its also one of our most precious of earth's raw materials used in #drinkingwater supply, #industry & #agriculture in #food production

💧#Groundwater 'It truly is our hidden asset' pic.twitter.com/FFcvhD5bKK

— Geoscience EnvAgency (@GeoscienceEA) March 20, 2020

It turns out that the EA – or at least, the one person overseeing this project – would rather side with consultants representing an operator hell-bent on extracting as much material as possible, over the warnings from an independent Professor responsible for writing textbooks on the subject.

Another response from the EA – and a swipe at SAG

This week, there was more correspondence from the Environment Agency in relation to Aggregate Industries' planning application to quarry Straitgate Farm, this time in response to a planning lawyer saying the EA's position statement was ‘insufficient to enable DCC to determine Straitgate application lawfully’. The EA said it was all a mixup:

With regard to the position statement we previously sent you, there appears to be some confusion about what the document represents.

But there was no confusion when on 20 December 2019, in its response to Professor Brassington’s concerns, the EA wrote :

Thank you for your email (15 November 2019) and your patience while we have worked to bring together all the information needed to respond to you enquiry.

Please find attached a position statement regarding the proposed quarry at Straitgate Farm, Ottery St Mary. If you have any questions regarding the content of this document, please contact us at DCISEnquiries@environment-agency.gov.uk.

Thank you and goodbye. Ok, so there was no thank you, and no attempt to explain why the EA disagreed with Professor Brassington. This week, the EA had another go, regurgitating a lot of worn out arguments, disparaging the views of a Professor of Hydrogeology responsible for textbooks on the subject:

There’s little point in going over the same old ground here, save for one thing. The EA, the protector and guardian of our precious groundwater, says:

the boreholes making up our groundwater level network in the Straitgate area all show that 2013/14 groundwater levels were the highest on record (with some records going back to the late 1960s).

By coincidence, this was the very same time Aggregate Industries started groundwater monitoring at Straitgate Farm. That's right. What are the chances?

However, the EA relies upon the 2013/14 levels to underpin Aggregate Industries' model of the maximum water table – the MWWT, the base of any quarry – despite knowing that 1990 groundwater levels were 2.8m higher than the MWWT in one location, despite knowing that 2018 groundwater levels then exceeded the MWWT in four locations, despite knowing that stream flows from the site indicate higher groundwater levels in other years too.

The EA relies upon the 2013/14 levels to write off the need for an unquarried buffer, the sort typically employed elsewhere, despite knowing the above, and despite having no idea of the accuracy of Aggregate Industries' model.

For clarity, when the EA talks about the "Straitgate area", it means East Devon. One of the handful of boreholes the EA relies upon in the "Straitgate area" is Bussels No 7A, many miles away. Dr Rutter says "I don’t consider it relevant… this well is over 90m deep and unlikely to respond to recharge in the same way as the shallow groundwater." Prof Brassington agrees, saying "a competition between observation boreholes has little meaning" and instead bases his conclusions on stream flows originating directly from the site:

The only conclusion that can be drawn from this hydrograph is that the groundwater levels on the Straitgate Farm site would have been at a higher elevation than those in 2013/14 during the winters of 1976/77 and 2000/01.

The EA has at last grudgingly accepted that the elevated 1990 figure should now be taken into account – which puts groundwater 2.8m above Aggregate Industries’ guesstimate in one area – but then they take a swipe at us:

The 1990 groundwater level information that Straitgate Action Group previously provided to us was one spot reading with no provenance given. Professor Brassington’s report gave the provenance as: SJ Parkhouse, 1990, ‘Report on the reserves of pebble beds at Straitgate Farm near Rockbeare’. We requested this report from Aggregate Industries and agreed with Professor Brassington that the data within it should be used to update the grid.

But the allegation that we supplied "no provenance" is bunk. Not one, but three documents were attached to our email to the EA in June 2018, to provide provenance for the 1990 figure:

Attachments: Straitgate_Geology_Plan_a.pdf (667K), R0001 SJP Dec 1990 Report on reserves of Pebble Beds at Straitgate Farm (dragged).pdf (520K), R0001 Appendix 6 (dragged).pdf (557K)

In other words, not only the relevant data from the said report, but also a map from Aggregate Industries – annotated below – showing groundwater data from 1990. The EA would have had this map from at least 2012, when the Minerals Plan was being put together. If they had bothered to look, the EA could have seen for themselves that at SG1990/021, groundwater in June 1990 was just 1.3m below the ground surface – indicating no resource would be available around this location.

On the same day we sent the email to the EA, we also sent an email to DCC, and posted AI has ‘forgotten’ one 1990 borehole – that puts groundwater 2.8M ABOVE MWWT – the modelled maximum winter water table – writing:

This is clarified in "Report on the reserves of Pebble Beds at Straitgate Farm, near Rockbeare", supplied to us by AI some years ago; a report that was based on analysis of 24 boreholes. The full borehole logs show that on 12/6/90 the water level in borehole 21 was 1.26m below the surface.

Both links went directly to that provenance. On the same day, DCC wrote back:

I have already been in communication with the EA asking for them to address the issues in your recent blogs in their final comments to ensure that my Committee is aware of all the issues at Straitgate.

But if the EA is really looking for someone else to blame for any shortcomings, perhaps it should point the finger at Aggregate Industries and its merry band of consultants. Perhaps the EA should ask them why the 2.8m higher 1990 figure was not included in Aggregate Industries' model of the water table, why it didn’t inform extraction boundaries and infiltration areas, why it didn’t influence resource calculations.

Last month, the EA revised its conditions in relation to the Aggregate Industries' application. On the issue of the EA’s revised conditions still allow AI to dig below MWWT, the EA doesn’t care:

on annual update of the MWWT grid, we draw your attention to the following recommended condition:

Continuous (daily) monitoring of all site piezometers, and interpolation between them, shall be used to ensure, during working, that the base level to which the quarry is worked is no closer to the contemporaneous measured groundwater level than 1m.

We feel this sufficiently addresses this issue.

But of course it doesn’t address the issue. If groundwater levels surpass the MWWT – as they have before – so long as water levels recede during the summer by more than 1m, as they invariably do, the EA are effectively saying it’s fine to continue to quarry to the breached MWWT levels (i.e. below the level of the maximum water table) until such time that Aggregate Industries gets around to adjusting its model, maybe never judging by previous water reports.

Even the condition above isn’t clear. As someone pointed out: "Continuous (daily) monitoring" is not the same as "Continuous daily interpolation". Does the EA therefore mean "... quarry is worked no closer to the contemporaneous interpolated groundwater level than 1m"? Who knows? Perhaps not even the EA.

And while digger drivers try to work to contemporaneous interpolations, groundwater levels across the site can rise by up to "1m in 5 days". What an earth could go wrong?

The EA of course doesn’t want to trouble itself with knowing how any of this unorthodox untested untried seasonal scheme is going to work:

It is not for the Environment Agency to advise on the precise methods by which the operatives will work. DCC should agree this with the quarry operator.

EA ‘will not be providing further responses’ – but now accepts base of any quarry at Straitgate will have to be raised again, this time to reflect 1990 groundwater levels

Professor of Hydrogeology, Rick Brassington, recent winner of the Geological Society's Whitaker Medal, has sent three substantive responses to the Environment Agency – all objecting to Aggregate Industries’ plans to quarry Straitgate Farm. We have posted about them here, here and here. His latest response warns:

It is my view that this application should be turned down and that no quarrying be permitted as to allow it will threaten these water resources for many years to come.

It is clear however that the Environment Agency has had enough. Haven’t we all? At the end of last year, in its reply to Prof Brassington’s latest response, the EA set out its position:

We have concluded that the applicant has undertaken appropriate risk assessment and proposed appropriate mitigation measures to protect water resources. We therefore do not have any objections to this planning proposal. We have provided SAG and other stakeholders the opportunity to give their views on our advice to DCC. Where appropriate we have incorporated their views and requested additional information from the applicant. Whilst we are happy to continue to receive additional information from stakeholders, we will not be providing further responses over-and-above the information contained within this position statement.

So there. No attempt to explain why the EA disagrees with Prof Brassington, and clearly little thanks to stakeholders for all their help. But plainly the EA is tired of hearing about Straitgate Farm and tired of modifying its conditions based on new information fed to them by stakeholders; information that has not been supplied by the applicants, information they had not uncovered for themselves.

But whilst the EA may be tired of Straitgate, and may not be providing any further responses, only last month it was forced to recommend yet another change to Aggregate Industries' plans.

Readers may remember that in June 2018, we posted AI has ‘forgotten’ one 1990 borehole – that puts groundwater 2.8M ABOVE MWWT, 2.8m above the base of a quarry that was proposed to be worked dry. Previously, the EA had dismissed data from this borehole. In an email to us in July 2018:

The data you highlight in your email of 12 June 2018 is one ‘spot reading’ of groundwater level from 1990. As such, it is difficult to judge its significance.

A year later, the EA provided exactly the same response to Prof Brassington’s report:

We note the groundwater level reading from 1990. However, because this is just one spot reading it is difficult to judge its significance.

Aggregate Industries’ consultants agreed with the EA. In September, Wood wrote a letter responding to Prof Brassington and was adamant this measurement should have no significance. This despite this measurement being undertaken by ECC Quarries (Aggregate Industries’ predecessor), and despite this and other measurements forming part of a report used to support the site’s inclusion in the Devon Minerals Plan. Previously, Aggregate Industries’ consultants had argued "A comprehensive review of the geology across the site was undertaken in 1990… to confirm the local geological characteristics and groundwater levels". These same consultants have now changed their tune, being at pains to argue that "the reliability of this record is, at best, questionable":

The isolated (in time) water level measurement recorded at SG1990/021 cannot be considered reliable because there is insufficient context provided regarding the circumstances under which it was recorded.

Prof Brassington was having none of it:

Wood’s arguments dismissing the water level reading recorded in borehole SG1990/021 have been shown to be untrue.

I am surprised that the Environment Agency has accepted that this water level should be ignored particularly in the absence of any contradictory evidence.

The Environment Agency has now been forced to admit:

Based on further information received from SAG we recommended to Devon County Council that the applicant updates the Maximum Winter Water Table grid with groundwater levels recorded at the site in 1990.

Why is this important? As we previously posted, the measurement in question showed groundwater 2.8m higher than the base of the proposed quarry, 2.8m higher than the MWWT – Aggregate Industries’ prediction of the maximum winter water table – the surface its consultants had merrily claimed:

Monitoring over the exceptionally wet winters of 2013 and 2014 allow this surface to be defined with confidence. 6.2.2


The groundwater level recorded in 1990 should now be used to create a new interpolated surface of the maximum water table. 

Given that water was recorded at 1.26m below ground level, there will be no recoverable resource in the area surrounding this location.

As we’ve posted below, Aggregate Industries was asked to provide a level of accuracy, "a description of tolerance levels", for the MWWT. The company’s consultants were reluctant to provide an answer, but eventually claimed the MWWT was "based on the higher of the two interpolated surfaces", that the MWWT was the "upper limit of interpretation". They claimed the difference between those two surfaces provided a "reflection of the ‘tolerance’". The claim is nonsense.

If proof were needed, the 1990 figure shows that the interpolated surface, the claimed "upper limit of interpretation", is inaccurate in one location to the tune of 2.8m. There are four other locations where it has become apparent that the MWWT model has been guesstimated wrongly. Across some 55 acres, there are likely to be other areas. As Dr Rutter made clear, the MWWT:

is only a model of reality, and may not represent actual groundwater levels across the site.

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 have in the past posted that without more boreholes, and years of further groundwater monitoring, AI and its band of consultants are just groping in the dark.

It all underlines the need for a tolerance, a safeguard, a margin of error, to be built into the MWWT across the whole site. The 2.8m figure gives an indication of the scale of safeguard needed. Many quarries leave 1m unquarried above groundwater levels for this very reason. Aggregate Industries is trying to be clever, trying to be greedy.

The company claims, by only working the mineral when groundwater levels recede during the summer and autumn months, there will always be at least 1m between where extraction is taking place and groundwater levels. The EA conditions:

Continuous monitoring of all site piezometers (and interpolation between them) shall be used to ensure, during working, that the base level to which the quarry is worked is no closer to the contemporaneous groundwater level than 1m.

If the base of proposed extraction is inaccurate by as much as 2.8m, this condition is plainly insufficient.

Remember: Aggregate Industries is proposing to leave a 0m unquarried safeguard above the MWWT to protect surrounding drinking water sources, surrounding farms, wetland habitats in ancient woodlands and mediaeval fishponds. The 1990 figure was recorded in the middle of June, when groundwater levels would have already declined significantly from their spring maximums. The 1990 figure was recorded in the same location where AI has proposed infiltration areas to control flooding, an area where there is clearly insufficient depth of material to perform such a task.

A new MWWT prediction should now be produced using all of the available maximum data – the 1990 level, plus the four levels that exceeded the MWWT in 2018 – in exactly the same way it would have been produced originally, had these values been available then. In addition, a tolerance level, a margin of error, should be built in, particularly in areas distant from piezometers.

The MWWT should not be a fudged. There should not be some trivial finger-in-the-air localised adjustments, not some trivial lifting of contours, not some fiddle as there has been in this document – where changes to the MWWT to reflect the higher 2018 figures are not based on interpolation between other site piezometers, but rather an opinion from Aggregate Industries' consultants:

In the specialist opinion of Wood E&IS, the revised contours represent a realistic assessment of the change in MWWT arising from the readings in April 2018.

The problem is, this so-called specialist opinion has been found lacking at every turn. This specialist opinion has no rational basis for tweaking the MWWT as they have – other than to recover the maximum resource for their paymasters. The higher figures now available should be used to reinterpret the whole surface, the whole of the proposed quarry base, as indeed the EA’s condition – "interpolation between them" – calls for.

AI still won’t come clean on accuracy of MWWT – the base of any quarry at Straitgate

The MWWT – the maximum winter water table – would be the base elevation of any quarry at Straitgate Farm. It is a model, a prediction of what might be happening across some 55 acres, based on water levels recorded in just 6 piezometers. The accuracy of this prediction would matter less if Aggregate Industries were planning to leave a safety margin, an unquarried buffer, above this surface – but it is not.

In July, Professor Brassington warned:

The MWWT for this site has been defined by using a computer model as the number of piezometers (six) are insufficient to cover the quarry area in sufficient detail. Computer models of groundwater systems are good at showing changes in groundwater levels although they are poor at showing the actual amount of such changes. As a result, the computer model derived MWWT surface is unlikely to provide an accurate representation of the real maximum groundwater levels...

Dr Helen Rutter has also warned:

I am concerned that there is a very steep hydraulic gradient across the site, from around 152m in the west to less than 135 m in the east, and the limited number of piezometers used to grid the water table surface. Variations in the shape of the water table cannot be contoured based on the number of piezometers used in the application... 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.

Even Aggregate Industries’ own consultants – before they whitewashed their reports – warned:

It should be recognised that a variety of possible grid generation algorithms and parameters exist for discrete point data and that each of these can be supplemented to varying degrees by supporting interpretative data and conceptual understanding. The two grids therefore represent just two of many possible interpretations of the data which themselves are based on an incomplete parameterisation of the detailed groundwater dynamics of the Site.

Nevertheless, it has been a struggle to get Aggregate Industries to say anything on the accuracy – or inaccuracy – of its prediction of maximum groundwater levels at Straitgate. The company has continually refused to provide an answer. What could it want to hide? In 2016, we asked Devon County Council:

Since AI now intends to dig right down to the maximum water table, perhaps you could ask Amec to confirm the specific level of accuracy (in +/- m) to which their maximum groundwater contours are mapped?

Aggregate Industries was asked. Silence. In October 2017, the Environment Agency tried again:

Whilst our position remains unchanged from that which we set out in our letter of 01 September 2017 we agreed with the Straitgate Action Group that further information should be requested from the applicant... In particular we agreed that the following information should be requested: ... • A description of the tolerance levels and interpolation method used to produce the ‘Maximum Winter Water Table’ grid;

Again, as we posted at the time, on the matter of tolerances – silence. In November 2017, we wrote to the EA, pointing out that:

Amec have now responded to your letter of 9 October, but unfortunately they still fail to address a number of the fundamental concerns we raised. Your letter specifically asked for "A description of the tolerance levels...". This has not been provided.

Amec say "Four alternative grid interpolation methods were selected... Each of these methods represents an exact interpolator". In this case, all "exact" means is that the derived MWWT surface passes through each of the six maximum recorded points. It does not mean that the interpolation surface is exact anywhere else across the site. In fact, given that two of the interpolation methods were found not to be suitable, and that for the one chosen, Radial Basis Function, "There are five different basis functions... Each basis function has a different shape and results in a different interpolation surface" there is obviously a very high chance that the MWWT surface provided by AI does not reflect reality.

As you are well aware, this would matter less if any quarrying went down no further than 1m above the maximum winter water table. Since this is not what’s proposed, it is crucial to know the tolerance or error levels of the MWWT - as we agreed at the meeting.

For Radial Basis Functions "2.3 ...the error goes to zero when the data samples are getting dense", but in this case the data samples are not "dense"; far from it. Amec has essentially used 6 data points to model almost 60 acres. If the error or level of tolerance is +/- 1m or more, this could have a dramatic bearing on the working method employed.

In response, writing to us in February the following year, the person responsible for the EA’s technical position on Straitgate weighed in to defend the cement conglomerate and its silent consultants:

Your email questions [sic] the term 'exact interpolator'. Exact interpolator here means that the modelled surface will use the values measured at the piezometers. These will not be changed by the interpolation method. The values in between the points for which values are known will of course have to be interpolated, as is the nature of interpolation. It is not possible to drill boreholes at every point across this quarry (or any other). Therefore it is not possible to know, everywhere, what the difference is between the modelled surface and actual groundwater levels. Interpolation and contouring are very commonly used methods in hydrogeology and geology. They are used because it is not possible to see the groundwater surface or underlying geology. Therefore the best that can be done is to obtain information at set points (boreholes) and interpolate between them. We are satisfied that this addresses the issue of 'tolerance levels'.

But clearly that reply didn’t address, or even understand, the issue of 'tolerance levels', and later that month the EA were persuaded as much, and wrote to DCC again:

...the Straitgate Action Group has highlighted to us the incompleteness of the response provided by Aggregate Industries (via AMEC) to our letter of 18 September 2017 with regard to them providing a 'description of tolerance levels'... Section 2.1 of AMEC’s response makes no reference to tolerance levels, the relevance of tolerance levels, or the level of accuracy in the interpolated maximum winter water table (MWWT). We recommend that a description of tolerance levels is therefore requested again from the applicant to support the planning application and to provide clarity in advance of the Planning Committee.

In March 2018, a response was finally provided by Aggregate Industries’ consultants (Amec Foster Wheeler, previously AMEC, now Wood). Now – at the end of 2019, and only through a Freedom of Information request – that response has finally been provided to us. Unfortunately, however, Aggregate Industries and its consultants still haven't come clean on the accuracy of their prediction. Surprised?

Perhaps they were unsure what 'tolerance' meant. AFW said:

We assume that in this context tolerance is used to mean an allowable amount of variation of a specified quantity (for example in the dimensions of a machine or part) or the level of "uncertainly" around the MWWT.

for which they obviously needed help from a dictionary:

But here’s the thing: Aggregate Industries’ consultants do accept that the MWWT contours are not accurate. We’ll say that again for anyone drifting off at this point: Aggregate Industries’ consultants accept that the MWWT contours are not accurate:

...the MWWT grid is faithful to the actual water levels measured at the piezometers which existed on the site when the historically high levels of winter 2013/14 were experienced. Therefore, at these locations the uncertainty is zero and the grid is accurate to the measured data.

At all other locations – i.e. virtually the whole 55-acre site where there is not one of the 6 piezometers – we can therefore infer that the uncertainty is not zero. Hallelujah. Are we getting somewhere now? The question is, if the uncertainty is not zero, what is the scale of the uncertainty, and how does it vary across the site? Uncertainties will be less in locations close to piezometers, and greater further away. Here are the locations of the 6 piezometers used in 2015, and the MWWT contours interpolated from the maximum groundwater levels recorded by them:

But if the uncertainty is not zero, why have Aggregate Industries’ consultants not built a margin of error, a margin of safety into the company's prediction of the MWWT contours, the base of any quarry? Oh, but we have, AFW argued:

As the MWWT was subsequently based on the higher of the two interpolated surfaces (i.e. Radial Basis interpolation) this could be considered to represent the upper limit of interpretation, with the Kriging interpolation representing the lower limit of interpretation and therefore the difference between these two realistic grids could be considered as reflection of the ‘tolerance’.

However, even AFW doesn't sound convinced: it could be considered a reflection. Really? Is that the best they can come up with? Aggregate Industries’ consultants are no doubt clever people. They will know the reasoning behind that statement is flawed. They will know that just because radial basis interpolation has resulted in a slightly higher surface than kriging for these 6 points, does not mean it is accurate. Likewise, they will know that there is no mathematical textbook that says the lower limit of interpretation of radial basis can be determined by kriging. The argument is hokum.

All AFW was attempting to do was to obfuscate, to confuse, to muddle the EA. All AFW was doing was showing the difference between how two techniques (kriging and radial basis) have interpolated 6 measurements to predict groundwater levels across 55 sloping acres. All AFW was showing was the difference between one inaccurate model and another inaccurate model. This is not a tolerance, it is a difference.

What AFW has NOT done, for very obvious reasons, is to consider – at least in public, for the benefit of locals, the Council and the EA alike – the inherent inaccuracies of each of those techniques.

And there will be interpolation errors in both radial basis and kriging. Our email to the EA above looked at radial basis, and the fact that the error only goes to zero when the data samples are getting dense. But Aggregate Industries’ consultants also claim to have employed kriging. They will therefore know that kriging comes with an advantage, an advantage widely known about. Here are four sources – all saying much the same thing:

An advantage of kriging is that it allows the estimation of the interpolation error at unmeasured points (Deutsch and Journel 1992).

A unique feature of Kriging is that it provides an estimation of the error at each interpolated point, providing a measure of confidence in the modeled surface

Ordinary kriging provides a standard error map that shows the uncertainty related to the predicted values.

Kriging can generate the prediction surfaces and surfaces that describe how well your model predicts

For example:

The figure below, created in 3D analyst, illustrates variation in kriging predictions, showing the range of prediction error (sticks) over kriging predictions (surface). A stick’s color changes according to the prediction error value. As a rule, prediction errors are larger in areas with a small number of samples.

So why, given that Aggregate Industries’ consultants would have known the scale of the potential errors across the site, did they chose not to provide this information to the EA when asked? Why instead, did they chose to mislead, by just comparing the results of two different modelling methods? What are we to infer? That the kriging errors are of such a magnitude to make the MWWT contours look absurd?

But there’s more. Modelling – despite the impression given by Aggregate Industries’ consultants – is not an exact science. For kriging:

Because the output is a geostatistical layer, it’s dynamic, meaning you can change its output type as prediction, errors of prediction, probability or quantile. Or you can even go back into the geostatistical layer and change the parameters if you don’t like the optimized output.

There is a science and art to kriging.

Is "change the parameters if you don’t like the optimized output" ringing any warning bells?

In other words, not only would Aggregate Industries’ consultants have seen where their predictions were poor, they would have also produced a variety of interpolated surfaces with a range of different predictions. And yet what do we have? We have supposedly bright people quoting differences between one guesstimated surface and another guesstimated surface to cm precision, e.g.

the largest positive value (at the northeast boundary of the extraction area) is 0.08m

This is clearly nonsense. Beyond the locations of the piezometers, these models can hardly predict reality to the nearest metre, let alone cm. And of course, to prove this, in 2018 the MWWT failed in four locations, by almost 1.6 m in one location and almost 1.3 m in another.

Has the EA been persuaded by the arguments put forward by Aggregate Industries’ consultants, following their earlier (mis)understanding of tolerances? It would appear so. In an email from the EA in June 2018:

We have reviewed the document and we are satisfied that it answers our questions about the derivation of the Maximum Winter Water Table grid.

However, the EA has been spurred into calling for daily groundwater monitoring – not weekly as previously suggested by Aggregate Industries. The EA has also now requested:

that groundwater levels in the piezometers constructed in 2016 and 2017 are estimated for the 'high water table' period in 2013/14. This 'hindcasting' will provide an indication of groundwater levels in these piezometers prior to their construction and improve confidence in the MWWT grid in this area of the proposed quarry. Correlation of the contemporaneous datasets from 2016 to the present should assist in this process.

Can anybody trust Aggregate Industries’ consultants to do that properly – based on their reluctance to come clean on tolerance levels? Any upwards movement of the MWWT loses sand and gravel resource – aka profit – for its client. As far as Aggregate Industries is concerned:

AIUK would be willing to do this if permission is granted.

In other words, after determination, away from prying eyes. We shouldn't be surprised by Aggregate Industries' attitude anymore, not after AI put a stop to public scrutiny of groundwater data for Straitgate application.

In summary, it's simple: To allow for the uncertainty in Aggregate Industries' predictions, an unquarried buffer should remain above the guesstimated MWWT. Prof Brassington argued "an unquarried buffer of at least 3 m is left above the maximum water table to minimise the negative impacts."