Aquifer properties of the Chalk of England

Aquifer properties data from 2100 pumping tests carried out in the Chalk aq uifer have been collated as part of a joint British Geological Survey/Envir onment Agency project. The dataset is highly biased: most pumping tests hav e been undertaken in valley areas where the yield of the Chalk is highest. Transmissivity values from measured sites give the appearance of log-normal ity, but are not truly lognormal. The median of available data is 540 m(2)/ d and the 25th and 75th percentiles 190 m(2)/d and 1500 m(2)/d respectively . Estimates of storage coefficient from unconfined tests have a median of 0 .008 and from confined tests, 0.0006. The data indicate several trends and relationships in Chalk aquifer propert ies. Transmissivity is highest in the harder Chalk of Yorkshire and Lincoln shire (median 1800 m(2)/d). Throughout much of the Chalk aquifer a direct r elation is observed between transmissivity and storage coefficient, reflect ing the importance of fractures in governing both storage and transmissivit y. Pumping tests undertaken in unconfined conditions give consistently high er measurements of transmissivity than in confined areas, probably as a res ult of increased dissolution enhancement of fractures in unconfined areas. At a catchment scale the data illustrate a relation between transmissivity and winter flowing streams.