At Straitgate Farm, Aggregate Industries proposes to quarry down to the maximum winter water table – wherever that might be.
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.
... groundwater resources of this area are very sensitive and fragile [but] if Devon County Council are minded to grant permission for these proposals, despite the evidence given in this report, they are asked to ensure that an unquarried buffer of at least 3 m is left above the maximum water table to minimise the negative impacts.
It’s standard to leave an unquarried buffer or safety margin in a quarry where nearby groundwater supplies are at risk from pollution or degradation.
Quarries on sites less sloping, or where’s there’s less at stake, might leave less than 3m. Some leave 2m or more. At Town Farm Quarry – a quarry that has the same geology that underlies Straitgate, but where only two properties were reliant on private water – Hanson left 1m. Hanson recognised:
The unsaturated zone above the water table affords protection of the aquifer from surface pollution, allowing adsorption, attenuation and degradation of contaminants prior to reaching the water table. Removal of lower permeability clay layers from within the Pebble Beds could also remove some protection from the groundwater. During the operation of the site pollution may arise from the extraction and restoration activities. The pollution may be in the form of fuel, lubricants and other fluids associated with the operator’s machinery. C3.1
Once upon a time, AI also said it was going to leave 1m unquarried above the MWWT. AI confirmed this to the EA and DCC. The EA said:
Aggregate Industries have proposed to stop quarrying a metre above the water-table. We expect DCC to make this a condition of any permission that is granted.
It was a lie. Resource figures put forward by the company showed that AI intended to leave 0m. It took months before the company came clean on the matter.
But it’s not just that. AI claims it knows where the MWWT is to cm accuracy, and furthermore that it could dig to this. That’s also a lie, not least because water levels have already exceeded AI’s guesstimate by almost 3m in places.
But the truth is, quarry companies find it difficult digging in the right direction, let alone to the nearest cm.
Recent site inspections have highlighted that parts of the site are not being worked in accordance with those approved plans in terms of the directionality of the working.
restoration was not in accordance with the approved plans and failed to achieve a natural slope, leading to some areas becoming waterlogged while the ponds had reduced water levels
Unfortunately, AI is no better. At Houndaller in Devon – the site with 4 million tonnes of permitted sand and gravel reserves that the company is currently working – DCC’s monitoring report of 2016 reported:
The site is in contravention with the requirements of Condition B2 and Condition B6. The requirements of these conditions relate to the order of development in defined phases. The working of phase 4 should not have commenced until the "majority of the restoration, seeding and planting of the following Phases has been completed". 4.3
To "regularise the situation", agricultural land was lost – as DCC's monitoring report 2017 made clear:
To regularise the situation on site the operator submitted an interim restoration plan and a biodiversity statement. The statement provided evidence that the area which had previously been left to naturally regenerate had now developed valuable areas for ecological habitats. It was concluded that it would not be appropriate to regrade this area and return to the approved restoration of agricultural land given that this would then harm established habitats of value. 4.9
The point is, once quarry companies are left to their own devices, anything can happen. We posted examples in What’s the chance that AI would stop digging when it gets to the water table? of how much notice the industry takes of planning conditions and water tables, saying:
To be fair, it’s not just Aggregate Industries that breaches planning conditions – the whole industry is at it.
But what of AI's unorthodox scheme? According to Prof Brassington such a scheme is "untried anywhere else in the country", and:
It is suggested that this operational procedure is too difficult for typical machine operators and so the application should be refused unless there is a much thicker layer of unquarried rock left in place stipulated in the application. 4.20
Clearly, if quarry companies find it difficult to work in the right direction, or in the right phase order, or to the right depth, Prof Brassington has a very valid point.
