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".

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.

Infiltration areas to stop flooding couldn't be 3m deep – without breaching MWWT

Another major failing.

Aggregate Industries' plans to quarry Straitgate Farm propose infiltration areas along the eastern boundary to control flooding, maintain groundwater recharge for springs and water supplies, and maintain stream flows – all without becoming permanent bodies of water and an airport safeguarding hazard.

We’ve already shown that these areas can’t work as described. Surface water would not infiltrate equally along the length of the eastern boundary given the gradient of the proposed extraction base. 

But with groundwater recorded so close to the surface there are other problems too. To retain surface water run-off, these features are proposed to be 3m deep: 

2.18.3 Quarrying operations will be excavating down to a range of between 3m along the eastern boundary and up to 9m at the western most extremity including the overburden.

In addition, bunds along the eastern boundary would be formed: 

2.18.3 The north-south bunds shown on Figure A2.1/A2.2/A2.3 are not intended to retain water, their main purpose being visual/noise screening. 

It is claimed the bunds would only act to retain surface water during intense rainfall, including:

2.18.4 In the event of an extreme rainfall event filling up void capacity, such that depths exceeded the excavation depth and backed up against the bund. Given a maximum of 1.45m of depth is expected during the design (1 in 100 year + climate change allowance) rainfall event, and the maximum void depth is 3-9m, a significant exceedance event would be required.

However, given the elevated groundwater levels recorded along the eastern boundary, and the newly-submitted maximum winter water table contours – the base of any extraction – it is clear that it would be impossible to dig 3m deep along this boundary without breaching this new MWWT.

The diagram above overlays three plans: the phase 2 infiltration area, the surface contours and the MWWT contours. The numbers indicate the depth from the surface to the MWWT elevation at points where contours from the latter two plans intersect. Clearly, along at least half the length, a depth of 3m is not available for excavation. 

The phase 1 infiltration area would have similar problems too. 

And what's the impact on flooding? The elevated groundwater levels recorded at three locations along the eastern boundary – PZ2017/02, PZ2017/03 and SG1990/21 – may have informed a new base of extraction, but they have not informed the Flood Risk Assessment which was written in 2016.

Without assessment of this new information, who knows what the flooding implications might be? Obviously not Devon County Council, the Environment Agency, or any councillors unlucky enough to determine this mishmash of chaos.  

The issue of how surface water is to be managed has always been recognised as critical if any quarrying were to be permitted at Straitgate Farm. Clearly Aggregate Industries' planning application is still in no fit state to be determined.

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.

 

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.

AI’s infiltration plans can’t work either – with groundwater this close to the surface

The issue of surface water management is critical at Straitgate Farm if any quarrying is to be permitted.

Surface run-off must not increase flooding downstream, it must maintain stream flows and groundwater recharge, and must not create permanent bodies of water that might attract birds and cause a birdstrike issue for planes landing at Exeter Airport. DCC warned in 2015:

The surface water management is inextricably connected to Flood Risk Management/Airport safeguarding and the need to maintain and recharge watercourses. This issue is so important in terms of the likely significant impacts of the proposal the MPA would wish to ensure that a SWM scheme can be designed to meet all of the requirements identified in advance of the determination of this application. 17

And again in 2017:

The MPA will wish to have it demonstrated that the applicant has engaged with the LLFA, the EA and the Airport to design a scheme that can accord with all of their various requirements. 2.18

Over the years countless consultants' reports have been written on the subject; they are not always consistent. Take the Updated Flood Risk Assessment for example:

Flows from the spring line adjacent to the Site may become more responsive to rainfall events as the removal of part of the unsaturated zone will decrease the time taken for water to recharge the aquifer. 3.5.4

Whilst this response a few months later from the same group of consultants said the opposite:

This increase in the proportion of rainfall passing to groundwater recharge will act to slightly flatten the hydrographs of the watercourses during storm events... reducing downstream impact. 2.11.3

It’s bad news when even the consultants are confused.

AI’s current answer to surface water management at Straitgate is to have infiltration areas along the eastern boundary of the proposed extraction area, shown in blue on the maps below:

Quarrying operations will be excavating down to... 3m along the eastern boundary... 2.18.3

The proposed infiltration areas at the Straitgate Quarry [sic] have been designed to meet national guidance on design events (1 in 100 year with climate change). 2.18.5

All runoff can be infiltrated via the provision of the storage volumes specified in the void base for each phase to allow for infiltration into the BSPB. 6.1.9

But from recent posts – in particular AI has ‘forgotten’ one 1990 borehole – that puts groundwater 2.8M ABOVE MWWT – you can see that, as things stand, this can't work.

Surface water would obviously not soak away in these infiltration areas in the way that AI and Amec hope, not if groundwater is as close to the surface along this boundary as these piezometers have recorded: PZ2017/02: 1.72m, PZ2017/03: 0.43m, SG1990/021: 1.26m.

So unless the intention is to flood downstream communities, and have long stretches of ponding along the eastern boundary (meaning a run-in with Exeter Airport), AI’s flooding consultants will need to go back the drawing board.

AI has ‘forgotten’ one 1990 borehole – that puts groundwater 2.8M ABOVE MWWT

If you thought 1.6m under water was bad, how about 2.8m – in the middle of summer? If Aggregate Industries' model of the groundwater at Straitgate Farm wasn't laughable before, it is now.

Last week we posted how AI’s water problems at Straitgate go from bad to worse. We posted how AI’s quarry plans are now under water in four places. We posted how water levels in piezometers PZ2017/02 and PZ2017/03 have this spring exceeded AI's maximum winter water table model by 1.3m and 1.6m respectively.

But it’s worse than that. Look at this map of the various boreholes drilled at Straitgate before 2011. Look at SG1990/021, south of where PZ2017/03 is located.

This borehole was drilled in 1990. The map refers to "W 6.7", where W is the depth of the saturated zone above marl in metres. What this means is that water was recorded 1.3m from the ground surface (3.1+4.9-6.7). 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.

But it’s worse than that. Whilst AI’s water consultants Amec (now Wood) have modelled the MWWT – the proposed base to any quarry – to 136m in this location, the data sheet below shows the height of the groundwater here recorded as 138.81m AOD – a full 2.8m above Amec’s guesstimate. Notably, this was recorded in mid June, not in winter or spring when groundwater levels would normally be higher.

Not only does this further undermine Amec’s MWWT model, and any tolerance levels the consultants might produce, but it also means that there is again no winnable sand and gravel from this area or from the – as yet undetermined – surrounding area.

But it’s worse than that. AI was in possession of this data all along, not just in a dusty 1990 report, but on the map above – a map that was also supplied to DCC for preparation of the Devon Minerals Plan. Why therefore has the company proposed to dig in this location? If AI’s water consultants knew about it, why have they proposed the same? Was it just a matter of trying to get away with things?

Because SG1990/021 is exactly where Amec has proposed infiltration areas to control flooding and maintain stream flows; and exactly where Amec has proposed, post restoration, and for evermore:

ephemeral water bodies and species-rich wet grassland to be encouraged in low-lying infiltration areas (in the base of the depressions)

The data for PZ2017/02, PZ2017/03 and now SG1990/021 show however that water bodies in this extended area might not be ephemeral at all – not if these infiltration areas have to cope with surface water run-off from 55 acres, not if there's groundwater sitting here less than 0.5m below the surface. And this is a problem, not only for flooding and stream flows, but also because the MD of Exeter Airport was under the impression that:

For the avoidance of doubt, one of our conditions was that the site will not have any new permanent bodies of water and furthermore we have corresponded with DCC in relation to this matter... if the planning authority approves the application without including the conditions requested by the airport, then the airport has the right to engage the CAA to request that the application be called-in for determination by the Secretary of State.

AI will have to further pull in the extraction boundaries and remodel the MWWT accordingly, which will again reduce the available resource.

AI’s water problems at Straitgate Farm go from bad to worse – quarry plans now UNDER WATER IN FOUR PLACES by up to 1.6M

The depth of proposed extraction is one of the most critical pieces of information for any quarry planning application. Why? Because it determines how much resource can be wrestled from the earth, and how much damage will be caused to the surrounding water regime in the process.

Surely by now, three years on from the company’s first planning application, Aggregate Industries should know how deep it could safely dig at Straitgate Farm? You would have thought so, but no – not judging by the latest groundwater monitoring data.

AI has claimed – contrary to warnings from other hydrogeologists – that it’s safe to dig down to the maximum winter water table, but after five years of groundwater monitoring and 18 boreholes it’s clear that the company still hasn’t discovered exactly where that level is.

Determining the MWWT is important because AI plans to work Straitgate dry. It needs to do this to protect surrounding springs, streams and drinking water supplies. We’ve always said that AI can’t model this MWWT with any sort of accuracy – except at the locations measured. That’s why standardly 1m is left unquarried as a buffer to protect water supplies; a 1m buffer that AI has decided local people can do without, so it can bank the profits instead.

Consultants Amec (now Wood) claimed the MWWT had been "defined with confidence" but were reluctant to say how confident, in +/- m terms. Now we know why. Because the model – which it was claimed "builds in a conservatism" – has already failed, and AI’s seasonal working scheme has been exposed for what it is – a shambles.

In February, we posted New borehole readings put base of planned quarry at Straitgate 1M BELOW WATER. In April, we posted March rainfall will have put AI’s quarry plans even further under water.

But it’s worse than that. AI has now supplied us with groundwater monitoring data for Straitgate for the last quarter – and for the first time it came with a commentary, presumably from Wood:

Turning to the attached spreadsheet; you will see from the most recent data (Feb-April 2018) that groundwater levels in two of the newer piezometers installed in 2017 (PZ2017/02 and PZ2017/03) have shown higher groundwater levels than expected this winter. Groundwater levels in all other piezometers across the site have levels as expected and have remained lower than the gridded maximum winter water table, so this is thought to be a localised effect in an area where data was limited prior to the installation of the 2017 piezometers.

There could be a number of reasons for the higher than expected groundwater levels in this location such as:
* localised effects caused by temporary backing up behind the BGS fault (where BSPB is faulted against BSPB) which could be of lower permeability (reduction in transmissivity) than envisaged or positioned further west than mapped.
* localised clayey horizons giving rise to confined/semi-confined conditions.

In other words:

Whoops. We’ve got things wrong. We don’t really know why. We have a number of ideas. We hope the problem is localised but without drilling more boreholes we’re just guessing. We say it’s just these two points - but to tell you the truth, we haven’t properly checked the others yet. We’re now not even sure where the BGS fault is.

Hardly instills confidence does it?

How much 'higher than expected' has the groundwater risen in these two locations?

In February, we posted that groundwater levels at PZ2017/02 and PZ2017/03 had reached 134.62m and 138.06m, compared with the modelled MWWT in these locations of 135m and 137m respectively.

The latest data shows these levels have now risen further, and on 3/4 and 10/4/18 reached 136.28m and 138.57m – a difference compared with AI’s MWWT model of 1.3m and 1.6m respectively.

But it’s worse than that. The surface elevation at these positions is 138m and 139m AOD respectively.

There is therefore NO winnable sand and gravel from this area or from the – as yet undetermined – surrounding area. Even plans in 1967 recognised that much.

But it’s worse than that. Even overlooking the 1967 plans, AI has had 12 months warning about all this. PZ2017/03 is next to "Test Hole 4". We posted on this subject last year, how in June 2017 ‘Drillers were really surprised they struck water so quickly’. Given that in April this year, groundwater at this location reached less than 0.5m below ground level (139 - 138.57), it’s not so surprising now.

But it’s worse than that. Two other locations, PZ06 and PZ05a, also exceeded the MWWT model with new maximums of 132.43m and 146.78m reached on 15/3/18. On PZ05a, AI’s consultants hope that:

Water level thought to be below borehole screen and within sump as indicated by 'flatline' hydrograph. Hydrograph not representative of BSPB [groundwater levels]

But thinking so and knowing so is quite different. In any case, PZ05 in the same location has been flatlining for 5 years now. Was that not "representative" either? Does anyone trust these consultants to recognise "representative" groundwater levels based on previous errors?

So, Wood’s assertion that "Groundwater levels in all other piezometers across the site have levels as expected and have remained lower than the gridded maximum winter water table" is obviously incorrect.

But it’s worse than that. These elevated groundwater levels this year were not reached during a particularly wet winter and spring, according to Met Office data, and nothing like the winter of 2014 when the other ‘maximum’ groundwater levels were recorded elsewhere across the site. In fact, in the South West, total rainfall in the winter and spring of 2014 was 35% higher than the same period in 2018. These maps put things in perspective:

Any piezometer installed after 2014 (7 out of the 18) is therefore unlikely to have yet logged a maximum.

But it’s worse than that. These problems occur in and around the Environment Agency’s Source Protection Zone for the water supply for Grade I Cadhay. Furthermore, these elevated levels have plainly only been recorded where boreholes have actually been drilled. For all AI, Wood, or anybody else knows, they could be higher elsewhere. This is why – with more than 100 people reliant on the site for drinking water – precaution should obviously prevail.

But it’s worse than that. This puts a huge question mark over a large area of the proposed quarry. Look at the area around PZ05a, PZ06, PZ2017/02 and PZ2017/03. The MWWT will have to be remodelled to a higher level, and the proposed extraction area reduced. Last year we posted that AI’s extraction plans are now down to 6 fields and 1.1 million tonnes. These changes will reduce the available resource still further – to less than 5% the company thought it had in the 1960s. As it is, the proposed quarry base will have to be lifted across an extended area because the groundwater does not fall by 1m during the summer at PZ05, now PZ05a – and the undetermined area surrounding it – to allow AI’s seasonal working scheme to succeed.

No wonder DCC asked AI "to provide information on other sites either in their control or operated by another company where the proposed working technique is used successfully" in order "to consider whether the proposed working technique is a "novel approach" as set out in the NPPF" that would need financial guarantees. As we said at the time, how telling that AI could not point to a single other site where its unorthodox seasonal working scheme has been tried before.

It’s all a giant mess. How prescient hydrogeologist Dr Rutter was when she warned that at Straitgate:

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.

Because errors are what we’ve got. And without many more boreholes and many more years of monitoring to give a fuller picture of what’s going on at Straitgate, errors are what we will keep on getting.

Who knows, if AI hadn’t been greedy for the last 1m of gravel above the MWWT perhaps none of the above problems would have been revealed? But then we could have been staring at large lagoons of water – and associated birdlife – directly under the flight path of Exeter Airport. We could have been staring at flooding downstream in Ottery St Mary. We could have been staring at all sorts of problems with surrounding water supplies. It doesn’t bear thinking about.

AI and its band of partisan consultants will now have to go back to their drawing boards and get their facts right, or, with the resource reduced still further, give it all up as a bad job.