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.
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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 In a now superseded document, Aggregate Industries wrote: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.
