- 27th April 2018
- Posted by: Sophie Bunker
- Category: Projects
The Magnesian Limestone Aquifer extends from Sunderland in the north, along the coast to Hartlepool and southwest towards Darlington, underlying the River Skerne catchment. The aquifer is classified as part of the Water Framework Directive (WFD) as being at ‘poor status’. This is due to saline intrusion, reflected in the widespread elevated concentrations of sulphate and chloride.
Aquifer behaviour and history here is complex and affected by:
- Historical mine dewatering from the Coal Measures, which underlie the Magnesian Limestone. This has had a significant impact on water levels and aquifer flows which, in turn, are responsible for some of the chemical signatures seen in the aquifer.
- Historically high levels of public water supply abstraction near the coast are also likely to have affected the flows and chemistry within the aquifer. Persistent lowering of water levels can induce saline water to be drawn in from the coast.
- The presence of evaporite minerals in the Magnesian Limestone may also contribute to the water chemistry profile, while fracture flow in the aquifer makes predicting flow paths difficult.
These factors affect the current behaviour of the aquifer today, because historical changes in chemistry within the aquifer are likely to propagate through the aquifer at a fairly slow rate.
Part of the work in understanding the behaviour of the aquifer requires a better appreciation of whether current groundwater abstractions contribute to the ongoing saline intrusion issues. Commissioned by the Environment Agency’s Groundwater, Hydrology and Contaminated Land Team, we carried out a pumping test at Camerons Brewery groundwater abstraction boreholes in Hartlepool, close to the coast.
This abstraction is in constant use for a large brewery site in a historic building and the logistics of the operational demands posed a challenge to carrying out an industry-standard pumping test. This is further complicated by the current water supply storage and infrastructure, meaning that pumping to waste was dictated by storage tank levels.
Initial investigations were required to determine the normal operational pumping regime before designing a pumping test that would best test the boreholes and wider aquifer. Outcomes from the testing revealed that transmissivities local to the Brewery may be exceptionally high and likely to be impacted by fracture flow. Whilst estimates of the likely catchment to the abstractions highlighted that saline intrusion may be possible, records of electrical conductivity as a proxy for measuring salinity in the water did not indicate evidence for saline water as a result of pumping.
Tests showed that there is no clear evidence that abstraction from Camerons Brewery boreholes is currently causing saline intrusion. Nonetheless, due to the complexity of the aquifer conditions, neither is it possible to provide clear evidence from this pumping test that elevated salinity levels are entirely natural or caused by historic abstraction across the wider aquifer.
Our study provided an insight into the functioning of the brewery abstraction, which was previously unavailable, and has provided key baseline information on which the Environment Agency can expand their studies into wider aquifer water quality issues, in order to address WFD failures for this important water body.
For the Brewery, who rely on the borehole supplies as a source of water for brewing, the outcomes from the study mean that there is not sufficiently clear evidence that their abstractions are the cause of saline intrusion within the aquifer. As such, there is no requirement on them to make changes to their current abstraction licence.
We have also been able to help improve the current efficiency of the borehole operations, which will allow them to have greater confidence about how they manage potential impacts to the aquifer.