If Aggregate Industries thought it had the hydrogeology part of its planning application to quarry Straitgate Farm finally sown up it will be disappointed; the Environment Agency wants more answers.
Last October, the EA requested further information on a number of issues - one of which was:
A description of the tolerance levels and interpolation method used to produce the ‘Maximum Winter Water Table’ grid.
Whilst AI’s consultants were happy to talk about interpolation methods, they refused to tell the EA about tolerance levels. It was the same story two years ago, when we first asked DCC - who in turn asked AI, but never got an answer to - the question:
Since AI now intends to dig right down to the maximum water table, perhaps you could ask Amec to confirm the specific level of accuracy (in +/- m) to which their maximum groundwater contours are mapped?
Why is this question important? In the same post we wrote:
The MWWT is the surface that AI wants to quarry down to at Straitgate Farm. It would be the floor to any quarry. As AI does not intend to leave 1m unquarried above the MWWT to protect drinking water supplies - the typical requirement elsewhere - it is quite appropriate to ask what level of confidence AI or its consultants Amec have in this surface, and how this tolerance level has been derived. When essentially only 6 data points have been used to model this surface across almost 60 acres, the MWWT obviously cannot be exact. So, is it +/-1m, +/-2m or more? It's important to know because it could have a dramatic bearing on any working method employed.
It’s obviously not a question that AI or its consultants want to answer. But you only have to read the post above to see how inaccurate the MWWT model is already proving.
Last week the EA requested the information again, writing to DCC:
Straitgate Action Group has highlighted to us the incompleteness of the response provided by Aggregate Industries (via AMEC) to our letter of [9 October 2017] with regard to them providing a ‘description of tolerance levels’.
Section 2.1 of AMEC’s response makes no reference to tolerance levels, the relevance of tolerance levels, or the level of accuracy in the interpolated maximum winter water table (MWWT).
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.
The EA also used the opportunity to raise this point:
We would also like to seek additional clarification on the infiltration tests carried out on the proposed backfill material. The report, ‘Aggregate Industries UK Ltd, Straitgate Farm hydrogeological assessment’ – AFW, December 2016, states that infiltration trials have shown the disturbed, proposed backfill material to have a similar infiltration capacity to the in-situ BSPB. However, the report, ‘Aggregate Industries UK Ltd, Straitgate Farm hydrogeology/drainage – Regulation 22 responses’, AFW, July 2017, Table 2.2, shows the disturbed overburden material to have a ‘much enhanced infiltration rate’. The applicant should clarify how the infiltration rate of the proposed backfill material compares to that of the in-situ material, and what effect the change between in-situ and disturbed overburden material might have on groundwater levels beneath the site.
Has Amec (Amec Foster Wheeler, AFW, now Wood) been found out? Telling one story to one party and a different story to a different party? The answer in 2016 was provided to satisfy concerns of the EA (4.1.3); the one in 2017 to satisfy concerns of the Lead Local Flood Authority after its objection (2.10).
AI’s unorthodox scheme proposes that the quarry base would be:
backfilled with at least a minimum of 1m of material derived from the upper uneconomic BSPB, in order to create an infiltration layer 4.1.3
Anyone worried that the future hydrological landscape for drinking water, wetland habitats in ancient woodland, or flooding in this part of the Budleigh Salterton Pebble Beds would be irreparably changed - as a result of undisturbed in-situ BSPB being replaced with backfilled and disturbed overburden material - is unlikely to find comfort in Table 2.2, the table referred to by the EA in the point above.
Because much enhanced infiltration rates might not only affect groundwater levels, as alluded to by the EA, but also the speed at which future pollutants - from farming or whatever - would reach drinking water supplies. As Dr Rutter's report made clear:
the restored soil (and possibly overburden) will not have the same structure as the original, and will have less capacity to attenuate any contaminants infiltrating from the surface
Plainly AI and its consultants have some explaining to do.
