Abstract
The Lower Mersey Basin Permo-Triassic Sandstone Aquifer lies in a heavily urbanised and industrial area of NW England. Extensive pumping has lowered the piezometric surface considerably, causing the sandstone aquifer, which is overlain by a variable sequence of glacial deposits, to become extensively unconfined. The groundwater chemistry of the system appears to be controlled by the geometry of the sandstones, faulting, the variable distribution and permeability of the Quaternary deposits, and by the pumping. The water in the present-day recharge areas is affected by pollution, with high NO 3, SO 4, and Cl concentrations; it has pH values as low as 4.3. The oldest fresh waters in the area (age less than a few thousand years) are strongly ion exchanged as a result of the flushing of saline water from the system: these waters grade into similar but much less ion exchanged waters, with zero NO 3, very low SO 4, and high HCO 3. A fourth group of waters appears to be the result of mixing between the latter waters and pumping-induced leakage through the Quaternary deposits. A final group of waters is characterised by very low alkalinity and is strongly associated with particular geological units poor in carbonates. Minor-ion distributions confirm the patterns suggested by the major ions. The distribution of the water chemistry preserves some of the features of the pre-pumping system in this low-transmissivity-high-storage system, and reconstruction of the pre-pumping chemical distributions is attempted, to highlight the effects of industrial man on the system.
Published Version
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