Monday, 5 August 2013

SLR's water report - Hydrological Position Statement

Can DCC rely on Straitgate Farm for its Minerals Plan? A lot hinges on SLR's report which outlines the impact a quarry would have on water - to people, to ancient woodland and on flooding. SLR has put forward a hydrological model and various mitigation measures. It will be up to the Environment Agency to decide whether it all makes sense or not.

The report is a more thorough affair than the last one, the Hydrological Baseline Report of 2012 - it had to be. That report was scant and inaccurate on detail, concluding there were no "significant constraints to site development", that "any encountered groundwater would be pumped and discharged to the local watercourses" and "local water supplies would be monitored and mitigation in the form of an alternative supply would be available if required". That's all changed.

SLR recognises that there are now constraints to development. "Additional monitoring data have been collected and revisions made to the working proposals to limit the potential constraints to development and to answer the concerns and comments raised by the Environment Agency. An updated hydrological impact assessment has been undertaken in light of the additional data and revised working proposals".

SLR recognises that "the ecological site most at risk from the proposals is Cadhay Bog, as it includes significant water dependant habitats" and that "such woods are now scarce nationally and this is a good example of wet woodland". SLR also recognises that there are a large number of properties and farms at risk, and that a detailed field survey is required over an area to be agreed with the Environment Agency. On the positive side, SLR is of the view that "the development offers the opportunity to reduce the current flood risk downstream of the site by the provision of areas within the quarry that can be designed to hold back flood waters during a storm event".

SLR considers that mitigation of the negative impacts may be possible. This would rely on "maintaining the current groundwater flow regime" by leaving 1m of pebble bed on the base of any quarry, creating cut gradients on the eastern side to promote infiltration, and operating no "active dewatering". However, working below the water table is still proposed - "extraction in the more saturated eastern areas of the site takes place when groundwater levels are at their lowest (in the late summer to autumn) and that winter working is restricted to the relatively dry eastern part of the site". It will of course be the EA and DCC who decide on the wisdom of such a measure with 100 people dependent on the area for their drinking water supplies, not AI or SLR.

SLR is of the view - and bear in mind who its customer is - that although Straitgate Farm is a "hydrologically sensitive" site, it "can be worked so that the current groundwater infiltration and flow directions are maintained and storage is provided to mitigate the loss of storage in the aquifer".

The EA will now need to decide whether the mitigation measures put forward stand a chance of working. DCC will need to decide on whether to rely on a report where, as SLR emphasises, "a definitive assessment of the impacts cannot be provided [until] further data is collected on the seasonal variation of groundwater levels and surface water discharge rates".