Groundwater levels from Straitgate Farm’s network of piezometers, which were read this week by Aggregate Industries’ water consultants, are back up to 2014 levels. This spells more problems for AI.
AI is now in its 6th year of groundwater monitoring at Straitgate. Long enough for AI’s water consultants, who started off as AMEC, and then Amec Foster Wheeler, to now be part of the Wood Group.
This extended monitoring programme is not of AI’s choosing. Both the company and its consultants have found the hydrogeology in and around Straitgate Farm much more complicated than initially expected. Monitoring started with just 6 piezometers, and now there are 18. This is all before the winning of any sand and gravel, and all before the monitoring that would have to continue for the lifetime of any quarry.
Anyway, even in this 6th year, AI still has problems.
Groundwater levels were last read in February. Since then "An average of 192.5mm of rain fell in Devon in March 2018 making it the wettest county in the UK".
It’s hardly surprising therefore that water levels around Straitgate have bounced back up to 2014 levels.
It was in 2014 that the maximum groundwater levels were recorded at 6 locations around Straitgate Farm. Consultants extrapolated these levels across nearly 60 acres to produce a guesstimate of a maximum winter water table (MWWT) and - because AI’s plan is to quarry dry, not to quarry below the MWWT - the proposed base to any quarry at Straitgate Farm; a proposed base that does not incorporate the typical 1m unquarried buffer above the MWWT to protect surrounding water supplies.
We say a guesstimate - because no-one knows whether we’ve yet seen the highest rainfall since monitoring started, in our increasingly changeable climate, and no-one knows the accuracy of AFW’s 60 acre prediction; the 1m buffer would ordinarily have allowed for such matters. AI has done away with this safety margin because, of course, it’s in the company’s interest to have the MWWT as low as possible, since it defines how much resource is recoverable and how much money it can make.
AFW has claimed that the current MWWT "builds in a conservatism" and has been "defined with confidence" - but to date AFW has refused to indicate how much conservatism or what that level of confidence is, in number terms, in +/- m terms. In February, the EA asked yet again:
We recommend that a description of tolerance levels is therefore requested again from the applicant to support the planning application and to provide clarity in advance of the Planning Committee.
It’s an important subject - when so many private drinking water supplies are at risk, when water to wetland habitats in ancient woodland is at risk, when water to a number of livestock farms is at risk, and when water to mediaeval fishponds at Grade I Cadhay is at risk.
AFW - now Wood - will analyse the borehole readings in due course.
The results may hold more interest than usual. In February, and even though AFW’s MWWT had supposedly been "defined with confidence", we posted that New borehole readings put base of planned quarry at Straitgate 1M BELOW WATER, specifically that PZ2017/02 was already at a level close to the modelled MWWT, and:
the MWWT at PZ2017/03 has been modelled ONE METRE BELOW current levels.
Embarrassing.
Since then "Devon had its fourth wettest March since 1910" and one of the boreholes read this week has risen 2.8m.
Elevated readings from these two piezometers have the capacity to significantly lift the guesstimated MWWT across a large portion of the proposed quarry, thereby again reducing the potential resource.
With modified boundaries and elevated floors, it’s about time AI told people how many tonnes it now expects for all this fuss; in other words, the ever decreasing benefit to weigh against the ever lengthening list of problems.
