Two months on – PZ2017/03 is STILL underwater

On 12 February this year, we posted Water level at borehole PZ2017/03 rises to GROUND LEVEL.

By 18 February, the situation was even worse:

Last week – more than two months on, and now with monitoring equipment finally installed – the top of the piezometer was still underwater:

The sand and gravel that Aggregate Industries wants at Straitgate Farm starts on average 2.3m below ground level. The company’s permission only allows quarrying above the maximum water table.

Clearly this is one area where extraction should not be taking place.

So, how close to this area could extraction be permitted? Aggregate Industries is in no position to say. As we previously posted: 

Piezometer PZ2017/03, at the NE corner of Phase 1 and SE corner of Phase 2, is obviously unable to provide any meaningful information on how far to the west of this point the maximum groundwater levels would allow sufficient depth for mineral extraction, given water levels here have reached ground level. 

Clearly, therefore, there need to be further boreholes drilled at the redrawn eastern boundary of the extraction area – to fulfil Condition 30, ie. so that there are piezometers at "each corner of each working sub-phase".

Groundwater levels continue to rise at Straitgate

This week, the groundwater level at PZ2017/02 – a borehole that sits on the eastern boundary of the proposed extraction area – was 30cm higher than reported here last week.

It now sits just 0.90m below ground level – a new maximum. 

As previously posted, the sand and gravel that Aggregate Industries wants at Straitgate Farm starts on average 2.3m below ground level. 

The company’s permission only permits quarrying above the maximum water table. 

Another borehole showing ZERO depth of available resource

The sand and gravel that Aggregate Industries wants at Straitgate Farm starts on average 2.3m below ground level.

The company’s permission only permits quarrying above the maximum water table. 

Clearly, therefore, in areas where the maximum groundwater level is closer than 2.3m below the ground surface, there is likely to be no sand and gravel available for the company to recover. 

In practice, to make it at all worthwhile – bearing in mind the costs, ecologically or otherwise, involved in stripping, storing, restoring more than 2.3m of 'best and most versatile' topsoil, subsoils and overburden – the maximum groundwater would need to be no nearer than 3.3m below ground level to be able to extract even 1 metre’s worth of sand and gravel. 

Earlier this month we posted how the water level at borehole PZ2017/03 has risen to ground level, and how Aggregate Industries has been pulling the wool over everybody’s eyes – planning inspectors included. 

Obviously, there is no resource available to the company for an indeterminate area around this borehole on the eastern boundary of the extraction area. It's now the same for the area around another borehole. 

Last week, the groundwater level at borehole PZ2017/02 was just 1.19m below ground level. This is again on the eastern boundary - as shown below:

   

This groundwater level is higher, by our estimation, than the borehole’s previously recorded maximum on 18/02/2020. It is notable that levels in this location have only been monitored between 2017 and 2022, and not, like a number of the other locations, during the wet winter of 2013-2014. 

It’s not altogether surprising that the previous maximum has been exceeded, given the recent rainfall:

Last February was one of the driest on record for England & Wales with many locations seeing less than 10% of normal rain.

This February will be one of the wettest, many places will record more than 200%.

Extremes driven by climate change and things will get more extreme. pic.twitter.com/3xPTqh8soj

— Dave Throup (@DaveThroup) February 18, 2024

This all ties in with what we said in 2021, when we posted Depth of available resource at Straitgate is in places ZERO. 

Borehole PZ2017/02 is where Aggregate Industries plans to locate infiltration trenches to stop downslope flooding. Clearly, with water levels this high, those trenches can't work as intended. Again, as we posted in 2021, Infiltration areas to stop flooding couldn't be 3m deep – without breaching MWWT and in 2018, AI’s infiltration plans can’t work either – with groundwater this close to the surface. 

Ordinarily, if Aggregate Industries were monitoring the site, another calculation of the extrapolated maximum winter water table, the MWWT, would now be triggered, the company’s permitted base of extraction would have to be moved upwards and the available tonnage moved downwards. 

For reasons we can all guess, the company is not currently monitoring groundwater levels across the site.

Planning conditions mean AI must drill more water monitoring boreholes

In order to protect surrounding private water supplies, Condition 30 of Aggregate Industries’ permission to quarry Straitgate Farm stipulates: 

Piezometer coverage across the site shall be, at any time, no less than the proposed one piezometer at each corner of each working sub-phase. Piezometers which are lost through quarry working shall be replaced within seven days. 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 measured groundwater level than 1 metre. 

Our emphasis.

Three working phases have been proposed, with two sub-phases in each.

Even as things currently stand, there is no piezometer on the SE corner of Phase 1. 

Furthermore, it is patently clear – and has been for years – that there are large areas on the eastern boundary that cannot be quarried without breaching the MWWT, given that groundwater has now been recorded just 1.19m, 0m, 1.26m and 1.59m below the surface at PZ2017/02, PZ2017/03, SG1990/021 and SG1990/012 respectively. 

The eastern boundary of Phase 1 and Phase 2 will therefore need to be redrawn.

Piezometer PZ2017/03, at the NE corner of Phase 1 and SE corner of Phase 2, is obviously unable to provide any meaningful information on how far to the west of this point the maximum groundwater levels would allow sufficient depth for mineral extraction, given water levels here have reached ground level. 

Clearly, therefore, there need to be further boreholes drilled at the redrawn eastern boundary of the extraction area – to fulfil Condition 30, ie. so that there are piezometers at "each corner of each working sub-phase". 

At least 12 months of groundwater monitoring in these new boreholes would then be required to provide any meaningful baseline. 

Without new piezometers in these locations there can be no way "to ensure, during working, that the base level to which the quarry is worked is no closer to the measured groundwater level than 1 metre."

Water level at borehole PZ2017/03 rises to GROUND LEVEL

Following the post AI has been pulling the wool over everybody’s eyes – planning inspectors included, the water level in PZ2017/03 was last week found sitting at ground level. 

The water level has no doubt reached ground level in this location before – but is not something that has been disclosed by Aggregate Industries.

Remember, the sand and gravel that Aggregate Industries wants starts about 2.3m on average below this level. 

What are groundwater levels doing in other boreholes across the site? Have maximum levels been exceeded again, given all the recent rainfall? 

No one has any idea because Aggregate Industries is not monitoring them. 

This matters, because the maximum water table across the site – the MWWT, guesstimated using previously recorded levels from this borehole and others – will not only form the base of the permitted excavation, to protect the groundwater supplying nearby private water supplies, but will also determine how surface water is managed, to avoid flooding and maintain stream flows.

Last month, Aggregate Industries made clear that it only intended to monitor the boreholes across the excavation site once a month using manual dipping. 

Groundwater levels can rise quickly at Straitgate Farm. Borehole readings show that even from a low base they can reach maximum levels in just 4 weeks. Continuous data loggers, as Aggregate Industries and its consultants have used in the past, are therefore essential for capturing these movements. Clearly, the company doesn’t want to do any more than the barest minimum. It certainly doesn’t want to discover that the MWWT has been exceeded again.

AI has been pulling the wool over everybody’s eyes – planning inspectors included

Nowhere in the mountain of documentation – either for the planning application to quarry Straitgate Farm, or the subsequent 2-week public inquiry – did Aggregate Industries make known that groundwater on the east of the proposed extraction area – an area designated a soakaway for flood mitigation – can at times sit just 16 cm or less? below the surface. 

Fancy omitting such a crucial piece of information. 

Aggregate Industries has not monitored groundwater at Straitgate Farm since March 2022. A curious lack of inquisitiveness, you might think, given how wet the last few months have been. 

But Aggregate Industries doesn’t want to know about any elevated water levels that might reduce the amount of recoverable material. 

However, curiosity can get the better of some people. 

At borehole PZ2017/03 – shown on this map, on this hydrograph, and below – groundwater was found this week to be sitting just 16 cm below the ground surface. 

16 cm.

We have been warning about this issue on multiple occasions – including here, here, here, here, etc – but even we didn't realise just how close the groundwater actually sits below the ground surface*. 

Aggregate Industries’ consultants, on the other hand – who, in addition to relying on an automatic data logger, have been manually dipping this borehole quarterly since 2017 – would have known. They would have seen with their own eyes how close the water sat below the ground surface, but chose not to share the information more widely – not with Devon County Council, not with the Environment Agency, not with the Planning Inspectors at the Public Inquiry. 

Having been alerted to the elevated groundwater levels in this location, Devon County Council raised the issue with the company back in 2018, when PZ2017/03 recorded its maximum height of water of 138.68 mAOD on 27/04/2018. In a now superseded document, Aggregate Industries wrote:

Results from routine quarterly monitoring in April 2018 identified groundwater levels in localised piezometers on the eastern extraction area boundary higher than those depicted by the existing MWWT contour plot. Consequently, Devon County Council has determined this to be a material matter in that it has requested that the effects of these results be assessed to determine the effects on the quantity of mineral resource. Its position is defined in the following extract from an email dated 1st August 2018 (S Penaluna, Devon CC) as a: “......need to know exactly which areas might be excluded for reasons of groundwater protection and these would need to be indicated on a plan.” 

But the Council was misled, fobbed off, or lied to, when the company claimed: 

1. The extraction area, as shown on the Wood E&IS plan, remains unchanged... 

4. The change [in mineral resource], moreover, results in no area being “excluded for reasons of groundwater protection” but merely a localised effect on the depth of working in a localised (eastern) part of the site. 

What’s the big deal? Condition 28 of the permission allows the design of the base of the quarry to be changed to reflect revised estimations of the maximum water table: 

Prior to the commencement of any soil stripping on any phase of the development, a review of the Maximum Winter Water Table (MWWT) grid (being the hydrogeologically modelled surface of the maximum winter water table based on the highest recorded winter groundwater levels) shall be submitted to the Mineral Planning Authority for its approval in writing.

In Aggregate Industries' latest resource assessment for the site: 

The MWWT will ultimately form the base of the workable deposit, and any variation will impact the potential resource. 

But what’s most concerning is that borehole PZ2017/03 is in an area designated for flood mitigation, an area where it is intended to dig a trench, with a 1m buffer above the maximum groundwater level, to hold back surface water runoff and allow it to soak away.

   

Surface water will not soak away as designed with groundwater sitting just 16 cm below the surface. 

Why is it important to get the management of surface water right? You only have to look at the ponding problems at Aggregate Industries' Houndaller site for the answer.

There can therefore be no confidence that the planned trenches to stop downslope flooding will act as intended, and every confidence a water body will be created. 

As we have already posted, quarrying at Straitgate can only be permitted if: 

25. No water body shall be created within the site other than the approved weigh bridge lagoon.   

Without drilling another borehole further into the site, and implementing another period of monitoring, no one has any idea where the maximum groundwater levels are in the area surrounding PZ2017/03 – Aggregate Industries’ MWWT is at best a guesstimate. 

What should be done? 

In 1967 they knew exactly what to do – they left this area alone. Aggregate Industries should be forced to do the same.

*The exact depth to water from the ground surface could not previously be calculated using piezometer groundwater level data in mAOD, because a precise surface elevation figure for the borehole had not been supplied by Aggregate Industries.

AI’s MWWT ‘adjustment’ has been fudged

Aggregate Industries' model of the maximum winter water table – the MWWT, denoted by the contours below – would define the base of any quarry at Straitgate Farm.

Professor Brassington says it can’t be trusted. We have already shown that the MWWT is nothing more than a hand-drawn guesstimate. The MWWT makes no allowance for errors, no allowance for climate change, no allowance for an unorthodox working scheme not used anywhere else. It may give the illusion of being precise, but time has demonstrated it is anything but. 

To indicate this, let's show what journey these contours have been on. Let's superimpose Aggregate Industries' first stab at estimating groundwater levels in 2013 over the latest MWWT. 

In places, the latest MWWT – in blue – is now 5m higher than that initial 2013 estimate. How very fortunate that estimate wasn’t used. The next guesstimate in 2015 was based on levels which we were told "are likely to reflect the highest groundwater levels that may occur at Straitgate". These levels have since been exceeded in numerous locations on numerous occasions. As we recently posted: 

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. 

In time, the MWWT will be exceeded again. A maximum is not a maximum if it keeps being exceeded. 

The latest MWWT is found in the recently submitted document Collation of post Regulation 22 discussions and clarifications, which says: 

...as requested by DCC, this document includes a revised version of the Maximum Winter Water Table (MWWT) grid which incorporates any recently recorded groundwater water levels higher than the previous MMWT (including ‘spot’ groundwater level measurements recorded in 1990).

The revised MWWT is included in this pack of correspondence and includes additional adjustment for slightly higher groundwater levels recorded close to the eastern boundary (PZ06, 2017/02 and 2017/03) in April 2018 and February 2020. The following are noted from the revised MWWT: The method used for determining the MWWT is slightly conservative and means that the extent to which the grid is raised propagates from the eastern boundary to the centre of the excavation area. In reality, the higher recorded groundwater levels most likely represent more localized effects close to the eastern boundary.

But knowing these contours are drawn by hand – a potentially biased and persuadable hand, not some clever computer algorithm – let's look at the revised MWWT against the previous version. Let’s see what allowance Aggregate Industries’ consultants have made for the elevated water levels recorded on the eastern boundary. Superimposing the new MWWT over the previous MWWT – blue for new, grey for previous – this is what we find: 

It's immediately clear "that the extent to which the grid is raised" is minor. 

It's also clear that, far from being "slightly conservative", the MWWT should in fact be raised more widely – given the elevated levels recorded at PZ06, PZ2017/02, PZ2017/03 and SG21/90, given that the MWWT is an interpolated surface, and given the lack of any other contradictory data in the vicinity of these piezometers to demonstrate otherwise. The Environment Agency's proposed conditions state:

If any of the maximum recorded groundwater levels exceed the height of the MWWT grid then the MWWT grid shall be updated using that data... 

Continuous (daily) monitoring of all site piezometers, and interpolation between them, shall be used...  

Our emphasis. So – in the areas indicated – what's happened to the interpolation? In fact, why was the entire MWWT not re-interpolated, in the same way it would have been had all these new maximums been available in 2015? Why have we instead been left with a tweak, an "adjustment", a fudge?

Note that when Aggregate Industries’ consultants talk about "slightly higher groundwater levels" we’re talking about 1.6m in one location, 1.75m in another and 2.8m in another – so not slightly at all. 

Note that when Aggregate Industries’ consultants talk about "most likely more localized effects close to the eastern boundary", they don’t have a watery clue – given the lack of other boreholes between the eastern boundary and the centre of the site. 

So, why has the MWWT not been raised more extensively, based on all the data, based on reason and logic? Easy. These consultants are trying to wrestle from the ground as much material as possible for their paymasters – irrespective of the permanent harm it would cause to surrounding water supplies.

Oh look, yet ANOTHER location where AI’s seasonal working scheme can’t work

Crikey, everywhere you look you find problems with this planning application.

Aggregate Industries' unorthodox untried unproven seasonal working scheme to quarry Straitgate relies on groundwater levels falling by at least 1 metre during the summer months to allow extraction down to the maximum winter water table – the MWWT. Aggregate Industries’ Regulation 22 document claims: 

2.2.8 By working only to the MWWT then during the summer months the water table will be lower. Therefore across the areas being worked the zone of water level fluctuation is undisturbed. This zone is at least 1m thick. Appendix C includes a plot showing the contours of average summer unsaturated mineral thickness, derived from the MWWT (i.e. the final proposed depth of working) and the Average Summer Low Water Table from piezometer readings.

There’s one big mistake right there. Because contours of "average summer unsaturated mineral thickness" will not be generated by using average summer lows. That only shows – in Aggregate Industries' favour of course – the average summer maximum unsaturated thickness. Those dependent on drinking water from the site should instead be concerned about the minimum unsaturated thickness below the MWWT in summer, which can only be derived using maximum summer groundwater levels. You can guess why Aggregate Industries didn’t do that. 

In fact, only by using maximum summer groundwater levels would the ability to reliably comply with planning conditions be demonstrated, knowing that groundwater levels can rise by up to "1m in 5 days", and given that the Environment Agency states:

our recommended condition requires that the base of the excavation is no closer to groundwater level than 1m at any time.

But this post is about more than that. 

We have in the past pointed out that AI's seasonal working scheme for Straitgate can't work as described, that groundwater levels do not fall by 1m around the piezometer location PZ05, a fact that Aggregate Industries recently tried to bury. Groundwater levels do not fall by more than 1m at PZ01 either, but the company argues that at the extraction boundary this would conveniently increase to 1.17m. It’s an absurd claim; Aggregate Industries can’t make predictions to the nearest metre, let alone the nearest centimetre. 

But now, lo and behold, another location has come to light where Aggregate Industries’ seasonal working scheme can’t work. 

The Environment Agency, after a protracted struggle – both by Professor Brassington and us, posted here, here and here – finally accepted that groundwater levels recorded in 1990 should, together with other borehole data, be used to define the MWWT. This was reflected in the Environment Agency’s revised conditions and Position Statement which reads: 

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. 

Aggregate Industries’ consultants subsequently produced a revised MWWT to accommodate groundwater levels recorded in borehole SG21/90 (also known as SG1990/021). 

But crucially, those 1990 groundwater levels were recorded in summer. The MWWT at location SG21/90 therefore now reflects a summer level. The MWWT and the summer level at SG21/90 are one and the same; the difference is ZERO. Clearly, groundwater levels do not fall by 1m from the MWWT here in the summer. Only by adding 1m to the MWWT in this area could Aggregate Industries' seasonal scheme even begin to work as described.

Appendix C – referred to above, shown below – and its Himalayan-style contours "of average summer unsaturated mineral thickness" is one of the documents Aggregate Industries is relying upon for its planning application.

  

We have already posted that it contains errors the height of houses. That was before the Environment Agency recommended the MWWT be updated using 1990 data. What that means is that around SG21/90 there is not 4m of summer unsaturated thickness as shown above, and here, there is in fact ZERO.

Given that those lines of fiction were interpolated, this figure will obviously have a knock-on effect on the surrounding area, and on the amount of resource available. Obviously, extraction down to the MWWT would never be possible – if planning conditions were complied with – in areas where the groundwater does not fall by 1m in summer.

Lines of fiction? Not only were those amazing patterns derived from just a handful of data points, but in some areas those claimed "contours of average summer unsaturated mineral thickness" even exceed the depth of mineral between the MWWT and underlying mudstone. Sense-checking is not Aggregate Industries' strongest suit.

But it doesn’t stop there, because those Himalayan contours above were generated in July 2017. At that time, only 8 piezometers had been recording groundwater levels for longer than 12 months. The above contours have therefore NOT been updated by the summer groundwater levels recorded over the almost 4 years since then – not just from those 8 piezometers, but also from piezometers PZ2017/01, PZ2017/02, PZ2017/03, PZ2017/04 and PZ2017/05 installed in 2017. 

Neither have those contours been updated using the summer 1990 levels. 

Without using ALL the available summer groundwater data for the site, without using maximum summer groundwater levels, no-one can know what might be revealed, no-one can make an informed decision. 

As things stand, therefore, the Environment Agency's condition could not be met: there would not always be 1m or more of unsaturated material below the level where Aggregate Industries would be working. It's yet another fail.

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 to drill boreholes at Penslade for ‘monitoring of the watertable’

Last week, Aggregate Industries was granted permission, DCC/4235/2021, to drill nine boreholes at Penslade, a site adjacent to Hillhead near Uffculme, that – like Straitgate Farm – is designated a Preferred Area for sand and gravel extraction in the Devon Minerals Plan, but – unlike Straitgate Farm – has 8 million tonnes and is 23 miles closer to the company's processing plant. 

In fact, where Straitgate would yield less than 1 million tonnes of material – if the company ever works out how to design effective infiltration areas – the area around Penslade Farm would give Aggregate Industries access to some 23 million tonnes – more than 70 years' worth based on sales of 300k tonnes per year. The statement below, from the Minerals Plan, hardly needed saying:

Policy M12 proposes two new locations for mineral working... In the event that Straitgate Farm proved to be incapable of being delivered, then the other site, West of Penslade Cross, would have adequate resources to enable sand and gravel supply to be maintained for the Plan period.

Most of this area is owned by Aggregate Industries. In relation to the boreholes, the company says: 

The boreholes will be between 23m and 38m in depth and piezometers will be installed to enable the monitoring of the watertable as required by the Devon Minerals Local Plan.

The Minerals Plan specifies "groundwater monitoring for a minimum 12 month period." 

This has been in the pipeline some time. In 2017, we posted Plans to install piezometers at Penslade: 

at a meeting last week, AI's Head of Geological Services confirmed that budgets are now in place to install piezometers at Penslade… 

You might ask, however, why these plans were only submitted in the middle of a consultation to quarry Straitgate Farm, a proposal that would see minerals worked "over a period of between 10 and 12 years" and would not start until 2023? Was it coincidence, or did Aggregate Industries sense things going pear-shaped with the Straitgate application again? 

In 2017, on being questioned about Penslade by Devon County Council, Aggregate Industries reckoned: 

It is envisaged that groundwater monitoring will be undertaken for a minimum of 3 years prior to submission of a planning application in some 5 years hence.

but went on to say that the site "subject to planning, would come on stream approximately 2030."

Aggregate Industries will obviously be hoping for more success with Penslade than with Straitgate, where boreholes were first drilled in 2013, and where 8 years later, in 2021, the company is still floundering. In its first application for Straitgate back in 2015, Aggregate Industries had been hoping on the site "being available from early 2016". It wasn't to be. The application was pulled following a complete fiasco. In March 2017, another application was submitted with the hope that mineral would start being imported from Straitgate into Hillhead Quarry by "mid 2018". 

The fact that Aggregate Industries has been able to function quite happily for the last 5 years with just the sand and gravel from Houndaller – a reserve of some 2.9 million tonnes at the last count, enough to last for 10 years – clearly means it can survive quite happily without Straitgate.

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.

Prof warns DCC – quarry at Straitgate would ‘irreversibly damage’ water sources

Unsaturated zone flow times of 8 YEARS – not the 1 to 3 days consultants claimed...

Drinking water sources suffering PERMANENT acidity increases – due to the LOSS OF 7 YEARS of rock/water interaction times, a 50% CUT...

Piezometers recording lower groundwater levels than reality – enabling extraction DEEPER THAN THE MAXIMUM WATER TABLE...

These are some of the damning conclusions from a new report by Professor Rick Brassington in response to Aggregate Industries’ planning application to quarry Straitgate Farm.

Prof Brassington wrote his new report specifically for Devon County Council – "to ensure that they have a clear view" – given that the Environment Agency "will not be providing further responses", and given the EA's request that "further concerns... should be directed to Devon County Council". The report landed with DCC at the start of this week, but despite Prof Brassington's request, the Council batted the report straight off to the EA, presumably without a second glance, and responded:

If your report raises any new issues which the EA consider to be material then I will ask the applicant to clarify.

However, clearly the report does raise new material issues, which will need much more than clarification to sort out. This would have become immediately apparent if the Council had bothered to read it.

Because, what’s abundantly clear from Prof Brassington’s report is that Aggregate Industries’ so-called hydrogeology experts – Amec Foster Wheeler now Wood – have not been very expert at all. They have either been guilty of intentionally misleading, or have completely misunderstood groundwater behaviour at Straitgate, such as the length of time water takes to permeate down to the aquifer. Either intentionally or otherwise, they have dismissed the role that the unsaturated zone – the resource above the water table that Aggregate Industries wants to quarry – plays in determining the groundwater chemistry.

Prof Brassington warns:

the application for the proposed quarry should be refused because of the irreversible damage that it will cause to the local groundwater system that both supports local habitats and forms the water supplies for Cadhay House with its medieval fishponds and tearooms, more than 100 people plus three livestock farms. 80

By the way, Prof Brassington is not just any expert on hydrogeology; that's obvious from his CV which stretches across pages 32 to 40 of the new report. He clearly has more experience, knowledge and independence than any consultants engaged by Aggregate Industries, a company hell-bent on extracting as much material as possible. He is a recognised authority on hydrogeology, recent winner of the Whitaker Medal, and author of various textbooks on the subject.

Prof Brassington says his new report "should be read in conjunction with the conclusions and recommendations reached in my earlier reports" on Aggregate Industries’ planning application. We posted about these in: Professor of Hydrogeology says ‘ANY quarrying at Straitgate would cause problems’, Professor rebuts EA’s response to his report. Has the EA got it all wrong?, and Another damning response from Professor of Hydrogeology on AI’s Straitgate plans.

This time, Prof Brassington focuses on the permanent change to groundwater chemistry that would result if all but 1m of the unsaturated zone were removed.

Last year, the company’s consultants Wood tried to claim – although clearly they weren’t too sure – that a reduced unsaturated zone thickness would "not necessarily" make any difference:

The moderately low pH, alkalinity and dissolved solids in groundwater in this area is, therefore, not necessarily a function of the time it takes for water to pass through the unsaturated zone, but a function of the variable and limited presence of soluble material within the sub-surface materials. A reduction of the unsaturated zone therefore will not necessarily give rise to a reduction in the pH, alkalinity or dissolved solids concentration of groundwater. With respect to the topsoil, subsoil and overburden that will be replaced once extraction of an area is completed, the replaced material will then be subject to water/rock interaction processes as water percolates through the replaced unsaturated zone material. As is shown by the leach test data, the soluble content of the unsaturated zone is low across much of the site or is mostly influenced by the shallow deposits which will be replaced after mineral extraction. Therefore, again, this implies that removal of the deeper unsaturated material will not necessarily result in a noticeable change in groundwater quality beneath the site or, more categorically, not at downgradient receptor. p10

Prof Brassington, however, is having none of that:

The length of the travel time involved is critical in determining the development of the chemistry of the water that discharges from the springs. 35

Let’s repeat that for the benefit of those championing Aggregate Industries’ scheme – be they consultants, the EA or Devon County Council – who seem so hard of understanding:

The length of the travel time involved is critical in determining the development of the chemistry of the water that discharges from the springs. 35

In fact:

...the whole of the flow path from the ground surface where recharge water starts its journey downwards through the unsaturated zone to the water table where it becomes groundwater which then flows through the saturated zone to emerge at the springs is essential in the development of the water chemistry. The removal of part of the unsaturated zone where flow velocities are far less than in the saturated zone will result in the greatest impact on the water chemistry. 21

It makes you wonder how knowledgeable Aggregate Industries’ experts really are. Or indeed, the EA for being taken in by their tales.

In 2015, Amec was trying to convince people that:

transit of water through the unsaturated zone is considered to be fairly rapid due to the intergrannular and fractured nature of the BSPB and therefore the thickness of the unsaturated zone may not be as important. 2.5

Again in 2017, in response to DCC’s Reg 22 request – that raised questions over unsaturated zone storage and flood risk – Amec argued:

...recharge reaches the water table in the BSPB through unsaturated thicknesses of between approximately 3 and 10 m within between 1 and 3 days. This is consistent with the conceptual model for relatively rapid recharge occurring in the BSPB (i.e. days rather than weeks or months). 2.7.3

This is rubbished by Prof Brassington, who reminds Wood’s so-called experts that groundwater flow through the unsaturated zone occurs as a "piston flow resulting in an equal volume of water entering at the top of the unsaturated zone being released from the bottom to enter the saturated zone beneath the water table" and that:

It is important not to confuse this type of flow with one that suggests that the recharge from any rainfall event reaches the water table rapidly through fracture flow 60

Prof Brassington says the time groundwater takes to travel through the unsaturated zone should not be measured in days, weeks or months – but in YEARS:

According to Wang et al (2012) the unsaturated zone velocity for the Sherwood Sandstone Group falls in the range 0.6 – 2.3 m/year with a mean of 1.06 m/year (these values were summarized by Chilton and Foster (1991)). The values for unsaturated zone flow rates are several orders of magnitude (three to five) lower than flow velocities in the saturated zone. 59

In the case of Straitgate:

... the lack of cement means that the rock is basically a pebbly sand with layers of silt and clay; consequently there are no fractures and so there will be no bypass flows. 59

It is simple to calculate the loss in groundwater travel time caused by the loss of some 7 m of the unsaturated zone as it is 7 × 1.06 years = 7.42 years. 62

YEARS, NOT DAYS. Much as indicated below – and widely elsewhere:

That’s an amazing, fundamental mistake for Amec to have made, and for the EA to have overlooked. It makes you wonder how many other things these parties have got wrong about Straitgate's groundwater.

Removing much of the unsaturated zone – and its capacity to store large amounts of slowly moving water – will naturally have huge impacts on spring flows and flood risk. It is however the change in groundwater chemistry that Prof Brassington has focused on. Indeed, in his original report a year ago he warned:

…the proposals will cause a large reduction in the thickness of the unsaturated zone that will reduce the time for the recharge to percolate through this zone. This reduced period will mean less time for rock/water interaction and will result in a less chemically mature groundwater that is more acidic than it is at the moment. These are reasons why the application should be refused by Devon County Council. 5.13

Given the EA’s dismissive attitude – Prof Brassington has raised those warnings again in his new report:

The water chemistry develops as the water percolates through the unsaturated zone and then, once it has reached the water table, it flows through the aquifer. A series of rock/water interactions takes place along this flow path causing the chemistry of the water to change as it moves along. These interactions are slow and so the time taken for the water to reach the springs will determine the concentration of the dissolved minerals, the balance between the dissolved minerals, the pH and the electrical conductivity of the water. 35

Prof Brassington shows that for Cadhay the period for rock/water interactions would be HALVED if Aggregate Industries’ proposal went ahead:

The EA calculated the Source Protection zone (Walford, 2013) using a similar method to the one adopted here. The map they have produced is shown below in Figure 11. The distance of the flow path from the recharge area in the proposed quarry to the Cadhay spring has been marked on the map. 64

Calculations of the time that groundwater takes from rainfall percolating into the ground to the groundwater emerging from a spring have been carried out for the Cadhay spring that supplies Cadhay House and estate. The water takes almost 15 years to make this journey and if all but 1 m of the unsaturated zone is removed this reduces some 50% of the total travel time. 76

Not only that. Whatever Section 106 conditions are made – and a leading planning lawyer has already shown that draft legal assurances for alternative water supplies are “unfit for purpose” – Aggregate Industries would be long gone:

It shows that the time taken can be expected to be sufficiently long for the quarrying to have been completed by some years by the time that the water quality changes have occurred. This will provide scope for AI to deny causing the problem. 77

No wonder Aggregate Industries had 'no objection' to including Cadhay and its mediaeval fishponds and its ancient woodlands in a Section 106 last year.

Prof Brassington warns:

The impact on the travel time also means that the deterioration of the groundwater chemistry will be a permanent change and it will not be possible to reverse it. 77

The concern for the 100 people or so who obtain their water supply from these springs is that the water make up will substantially change and a reduction in the pH will mean that the water is too acidic for drinking without treatment and it will dissolve metal pipework and storage tanks. It will affect the chemistry of the water in the streams that will impact on the Cadhay Bog and Cadhay Wood wetland habitats in the ancient woodland as these depend on the stream flows. 56

Furthermore, Prof Brassington warned in his original report that Aggregate Industries' model of the maximum water table – the base of any quarry – is not correct, as we posted in Boreholes at Straitgate ‘will have groundwater levels lower than local water table’.

In his new report, Prof Brassington is again at pains to remind us – or at least remind Aggregate Industries’ consultants and the EA who should know about these things: "the depth of a borehole and its location within an aquifer have a significant influence on the water level within it":

The use of fully penetrating piezometers to monitor the elevation of the water table as is the case at the Straitgate Farm site, means that it can be expected that the water levels in the piezometers will reflect a lower water level than the correct water table due to the three-dimensional aspect of groundwater flow. The MWWT grid will therefore be modelled from levels lower than reality, which will enable AI to excavate below the maximum water table. 73

Quite how this planning application can go any further forward – as it currently stands – with so many errors in the environmental information, and with so many warnings from such an eminent independent expert in hydrogeology, is anybody’s guess. An invasive sand and gravel quarry at Straitgate Farm, is – as Prof Brassington so clearly points out – no way to treat "a fragile groundwater system" and no way to treat a water source depended on by so many, including an important Grade I listed house and gardens.