Box 5 Use of Well Record Data to Compare Yield Distributions

Using available well record data from Finland (Central Finland Regional Environment Centre, 2007), Norway (Morland, 1997; Geological Survey of Norway, 2008) and Sweden (Gustafson, 2002), Banks and others (2010) compared the distribution of short-term yields from crystalline bedrock types. Despite differences in lithologies, climate and tectonic history between the countries, the yields in the datasets showed a remarkably similar distribution (Figure Box 5-1). In addition, although wells drilled in crystalline bedrock can exhibit a wide range of yields, the median well yield of all three datasets was in the 600 to 700 L/h range. Based on these results, the apparent bulk transmissivity based on an observed empirical relationship between short-term specific capacity and apparent transmissivity in crystalline rocks of the upper 70 to 80 m of crystalline bedrock aquifers in this region was estimated to be about 0.56±0.3 m²/d. An understanding of the statistical distribution of hydraulic properties of crystalline bedrock aquifers is needed to inform cost-effective drilling strategies in these types of aquifers.

Figure Box 5–1 – Comparison of the distribution of short-term well yield in crystalline bedrock aquifers of Central Finland (n=1297), Norway (Caledonian metasediments, n=2098; all crystalline rock, n=26,811) and Sweden (n=59,000). Note the probability scale on the y-axis and the logarithmic scale on the x-axis (from Banks et al., 2010).

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