Strategies for groundwater prospecting in hard rocks: a probabilistic approach

Private wells in fractured, Precambrian, crystalline rocks are important for rural areas and small communities in Sweden. Since well yields normally are small, systematic approaches to groundwater prospecting are required in order to predict how to site the wells and what costs to expect. The proposed approach is to minimise the sum of investigation and exploitation costs under the assumption of a lognormal distribution of well yields. The strategy involves the drilling of a fair number of exploratory wells, of which the best are connected to the supply system. Statistical data on well yields, in this case from the Swedish Well Archive, are required to support the decisions of pre-investigations and exploratory well drilling programmes that are suggested for small groundwater users and larger supply schemes using this probabilistic approach.