Aggregate Industries' unorthodox scheme to work Straitgate relies on groundwater levels falling by at least 1m during the summer months to allow extraction down to the maximum winter water table – the MWWT. Professor Brassington says "the EA should object strongly to this proposal":
The method of working that is proposed is untried anywhere else in the country and is designed to maximize the sand and gravel dug with no regard to the changes it will inevitably bring to both the quantity and the quality of the groundwater and the springs it discharges through.
Aggregate Industries' Supporting Statement claims:
2.4.7 The resource declared assumes a working base that coincides with, and never drops below the Maximum Winter Water Table (MWWT)... Moreover, the working method ensures that the floor of the excavation will always have at least 1.0m of unsaturated gravels beneath.
However, in July 2017, we raised the issue that the Seasonal working scheme for Straitgate can't work as AI describes. We pointed to PZ05 where it showed that groundwater levels do not fall by 1m over the year. PZ05 shows seasonal movements of only 0.2m. It would therefore be impossible to quarry down to the MWWT in these areas and "always have at least 1.0m of unsaturated gravels beneath".
In August 2017, Aggregate Industries held a meeting with the Environment Agency. The issue was discussed. The Agency said:
If, at PZ05, the MWWT grid and actual maximum levels are the same then the summer water level cannot be 1m below the MWWT grid because groundwater levels here only vary by 0.2m.
Aggregate Industries pushed back:
The level at PZ05 and, hence, the ‘MWWT grid’ in its vicinity recognises this and the summer working base is ruled in this instance by the need to maintain the 1m unsaturated buffer between the MWWT and the summer water level.
But the MWWT in the vicinity of PZ05 recognised no such thing. By October 2017, Aggregate Industries finally conceded that the MWWT contours would need to be changed:
The base of the quarry working during summer months will be the MWWT with slight adjustments in the vicinity of PZ05 in order that the summer working base remains standing 1 m above the summer water level around this piezometer
A revised MWWT was duly produced "... with small adjustments around PZ05 to retain 1m of BSPB above the summer water level." And the adjustments were indeed small, unreliably small, and given the absence of nearby piezometers, complete guesswork.
A revised MWWT has now been submitted. It would be the base of any quarry. The Environment Agency proposes the conditions:
No working shall be undertaken below the ‘Maximum Winter Water Table (MWWT) grid’ .
...the base level to which the quarry is worked is no closer to the contemporaneous measured groundwater level than 1m.
So, why has the adjustment to the MWWT around PZ05 been removed? Did Aggregate Industries hope no one would notice?
