PROPERTIES OF THE PARTICULATE PHASE IN DEEP SALINE GROUNDWATER IN LAXEMAR, SWEDEN

Composition, concentration and size distribution of the particulate phase in saline groundwater from the Laxemar borehole, Sweden, were measured at three different sampling sections sealed off by rubber packers (315.0–321.5, 1090.0–1096.3 and 1420.0–1705.0 m). Concentration and size distribution analysis were performed on-line in a field laboratory using measurements of light scattering in combination with photon correlation spectroscopy (PCS). Estimates of the chemical composition of the solid phase were obtained from scanning electron microscopy (SEM) coupled to energy dispersive spectroscopy (EDS), and saturation calculations were made with the geochemical code PHREEQE, based on hydrochemical analysis. The results indicate that the particulate phase consisted of aluminosilicates, SiO2, CaF, and probably CaCO3. The concentration of particulates varied between the different depths with the lowest content at the 1090.0–1096.3 m level, where it was estimated to be <0.5 mg/litre. Estimated concentration range in the 315.0–321.5 m section was 0.5–0.7 mg/litre (depending on the assumed mineral composition), while the highest concentrations were found in the samples from the deepest level (concentration range 1.4–3.0 mg/litre). The average diameters increased with increasing depth, (540, 640 and 1840 nm at the depths 315.0–321.5, 1090.0–1096.3 and 1420.0–1705.0 m, respectively) which probably was related to the increasing salinity and corresponding increase in the Ca concentration. The study clearly illustrates that limiting the changes in the activities of CO2 and O2 during sampling and measurements are of utmost importance in order not to disturb the solid phase in terms of composition, concentration and size distribution. © 1998 Elsevier Science Ltd. All rights reserved