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

Composition, concentration and size distribution of the particulate ph ase in saline groundwater from the Laxemar borehole, Sweden, were meas ured 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 s ize distribution analysis were performed on-line in a field laboratory using measurements of light scattering in combination with photon cor relation 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 calcul ations were made with the geochemical code PHREEQE, based on hydrochem ical analysis. The results indicate that the particulate phase consist ed of aluminosilicates, SiO2, CaF, and probably CaCO3. The concentrati on 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 sectio n was 0.5-0.7 mg/litre (depending on the assumed mineral composition), while the highest concentrations were found in the samples from the d eepest level (concentration range 1.4-3.0 mg/litre). The average diame ters increased with increasing depth, (540, 640 and 1840 nm at the dep ths 315.0-321.5, 1090.0-1096.3 and 1420.0-1705.0 m, respectively) whic h probably was related to the increasing salinity and corresponding in crease in the Ca concentration. The study clearly illustrates that lim iting the change; in the activities of CO2 and O-2 during sampling and measurements are of utmost importance in order not to disturb the sol id phase in terms of composition, concentration and size distribution. (C) 1998 Elsevier Science Ltd. All rights reserved.