Relation between pore water chemistry and groundwater flow

Based on the chemical analysis of pore water extracted by three centrifugal forces from sandstone

Abstract

Pore water was extracted from sandstone at different pF values. The samples originate from three locations where sandstone rock cores of 100m length at each location were obtained. Afterwards pore water was extracted from 63 samples by centrifuge at three different values of pF (low: up to pF 2.3, medium: pF 2.3 -3.9, high: pF 3.9-4.3). For each pF range the pore water was analyzed for main anions and cations. Results show that concentrations vary with pF and depth. Based on the distribution of Ca²⁺ concentration, three zones could be defined: (1) Ca²⁺ concentration is independent of pF, (2) Ca²⁺ concentration is increasing with the value of pF, and (3) Ca²⁺ shows the same value for medium and high pF value. We conclude that water chemistry of deep pore water is likely to have reached equilibrium due to almost stagnant flow conditions, whereas shallow water is likely to participate in chemical interactions due to the relatively high flow velocity. The depths of the interfaces of these three zones are almost consistent with geological boundaries of weathered and fine sandstone and there is an evidence of relationship between pore water chemistry and physical rock properties.