The problems of water – whether it’s to do with flooding, ponding, or maintaining the quality and flow-rates of springs, streams, and private water supplies – has been, and still is, one of the biggest issues for Aggregate Industries to resolve in its planning application to quarry Straitgate Farm.
AI maintains that any quarry would be worked dry, that it would have:
a working base that coincides with, and never drops below the maximum recorded winter water table XD28
So it was therefore necessary for its consultants:
to determine what the maximum winter groundwater level would be, so as to ensure that all working under normal operating conditions would be above this level. 6.1.13
But this obviously leaves no margin for safety, no margin for inaccuracies in AI’s model, no margin for errors in digging, no margin for future land-use pollutants, and no margin for climate change. Leaving 1 metre unquarried above the maximum water table – typical elsewhere where groundwater is at risk – would go some way to resolve this, but AI wants it all.
AI’s problem, however, is that it doesn’t know where the highest winter water table is with any degree of accuracy, even less so with all the problems highlighted in the posts last month – here, here, here, here, here and here. The more time goes on, the more AI and its groundwater model seems to fall apart – out by up to 6.8m in one place!
For AI’s experts this must be embarrassing. It must also reflect on their professional competence; because if they can be wrong by as much as 6.8m in one area, how wrong could they be elsewhere?
You have to also ask: if these measurements had not come to light, and AI’s unorthodox scheme had already been given the nod, what problems would we now be looking at?
Plainly, the proposed depths and extraction area will have to be modified – but without new boreholes, new piezometers, and years of further groundwater level monitoring, AI and its consultants are just groping in the dark.
There are simply too many unknowns for groundwater levels along the eastern side to be extrapolated, or for 'localised adjustments' to be made. AI's consultants will have to produce something more robust – something which can only come from more measurements, not more guesswork.
Why is the maximum groundwater level so difficult to model? Well, it doesn't help that AI drilled insufficient boreholes back in 2013. It doesn't help that only 6 locations were used to model the proposed extraction area – 6 data points is hardly enough to model a handkerchief, let alone 60 acres. It doesn't help that the site is on the side of a hill. It doesn't help that, in Amec’s words, the site has "unmapped local faulting" and "steps in the water table related to faulting". There are now 13 boreholes around the proposed extraction area – but clearly that doesn't help enough either.
The issue of water at Straitgate is so important to private water users, flood-prone communities, ancient woodland, listed mediaeval fishponds and Exeter Airport, that the matter needs to be resolved before determination – as DCC has already made clear:
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
Why is the issue so important?
Flooding is one reason: Readers may remember the flooding in 2008, when the four watercourses from Straitgate caused flooding downstream; one flooded more than 50 properties, prompting the EA to build a flood defence scheme – 11/2338/FUL. The EA's FRA wrote:
The aim of the proposed relief channel is to reduce fluvial flood risk to properties at Thorne Farm Way which was last flooded from the Thorne Farm Stream in October 2008. This event resulted in the flooding of 55 properties in Thorne Farm Way.
But the EA recognised that if the scheme suffered "an over design event" this still:
may result in flooding to Thorne Farm Way
What would increase the risk of an over design event? Well, having a quarry upstream – with ineffective infiltration areas, heavy machinery causing soil compaction, and removing a million tonnes of groundwater storage capacity for evermore – is hardly going to help. As AI has previously admitted:
One of the potential consequences of climate change is the increasing number of heavy rainfall events; our sites cover large catchment areas and there is an increasing risk of sites breaking permitted discharge consent limits...
And in 2012, after discussions with the EA, DCC had to concede in email correspondence that:
... the scheme for Thorne Farm does not take account of any increased surface water flows that may occur as a result of quarrying upstream of that site.
Later that year, unaware of what was being planned upstream, the Environment Secretary, Caroline Spelman paid the scheme a visit – after another bout of flooding.
Hugo Swire MP followed and felt it important "that we double our efforts" to prevent a repeat, having commented earlier on the Straitgate proposal:
It would seem somewhat regressive having spent a large amount of public money on flood prevention to then allow for a scheme which may contribute to future flooding.
AI of course didn't want to remind people about all this. Despite the relief scheme, despite visits from the Environment Secretary and MP, despite being on the EA's Historic Flood Map, the historic flooding section of its Flood Risk Assessment 'forgot' to mention it was a watercourse from Straitgate that flooded 55 properties in 2008. Funny that.
But it’s not just flooding. Exeter Airport has had things to say about AI’s plans too. In 2012:
Under the Air Navigation Law, it is a criminal offence to endanger an aircraft or its occupants by any means.... To ensure aviation safety it is suggested that no ponds or body of water be allowed as part of this development.
The Environment Agency has also previously expressed concern that:
A possible change in recharge and runoff patterns (e.g. an increase in runoff and decrease in aquifer recharge during high intensity rainfall events ) as a result of removal of part of the unsaturated zone, with the potential to impact on: eastward flowing groundwater; the flow of springs; local private water supplies; the volume of groundwater draining to Cadhay Wood CWS and Cadhay Bog CWS. An increase in the possible risk of contamination of groundwater as a result of the removal of part of the unsaturated zone. 7.104
What problems can councils have if this type of thing isn’t sorted out before determination? Look at what happened in Cheshire a few weeks ago, where – with less than 24 hours notice – a council pulled a planning meeting to determine an application by Sibelco for a sand quarry – due to newly presented groundwater concerns:
The applications have been deferred due to a late representation which raises issues with respect to hydrology and hydrogeology.
After waiting years for AI to get its act together with Straitgate Farm, DCC is unlikely to want that.
