Groundwater levels and spot flow measurements have been recorded by AMEC on behalf of AI at Straitgate since January 2013 in order to help to refine the understanding of the baseline water environment. This work has enabled an appreciation of the local groundwater regime and the establishment of the seasonal range in flows at springs and in watercourses that flow off the site. This is proving useful in giving a stronger understanding of the flow of water in and out of the area under investigation and the catchments served. For example measurements show that a large proportion of the downstream streamflow is derived from baseflow to the east of the site, although more work is needed to quantify the effect of any potential reductions in spring flow. Using the groundwater level data some initial interpretation can also be made about the effect of geological faulting east of the proposed extraction area on the groundwater regime. This faulting appears to act as a partial barrier to groundwater flow, with groundwater from the site partially emerging from headwater springs, and partially flowing across the faulted zone. The hydrometric data are very useful in preliminary impact assessments which are informing the engineering design for the site to ensure that suitable methods and mitigation measures are proposed. For example, wet working below the water table would remove the need for active dewatering of the aquifer, reducing the potential impact.
With 100 people relying on the aquifer at Straitgate for their drinking water, we remain dumbfounded that "wet working below the water table" is still being considered.
