Sampling and characterization of colloids in groundwaters from the El Berrocal Site, Spain

This report represents a study of colloids and suspended particles in groundwaters from boreholes S7,S13,S15,S16,S17 and S18 at the El Berrocal site. The two sampling campaigns which took place in November 1991 by the AEA Technology group and in december 1992 by the CIEMAT group, were carried out under different conditions and have yielded water samples from slightly different horizons in borehole S7. The third sampling campaign was carried out jointly in June/July 1994 in S13,S15 and S17. Therefore CIEMAT group carried out the sampling of boreholes S16 and S18 CIEMAT used a flat-bed membrane system in the range of 450-1000 MWCL to isolate natural groundwater colloids while AEA group's colloid samples were based on the tangential ultrafiltration principle. Electron microscopy coupled with EDAX established that the S7 samples contained approximately 10''12 colloid particles/litre and that these colloids were predominantly feldspar weathering products such as silica-rich clays and quartz with some minor presence of Fe oxyhydroxides and Al gels. The mean colloidal size using TEM was approximately 100 nm. The PCS technique, sensitive to particle sizes above some 50-80 nm only, has yielded a mean colloidal size of approximately 270 nm. Trace elements have been found mostly in solution (<1 nm) and virtually none were associated with the colloids. This is also true of U and Th isotopes, suggesting that the inorganic colloids found in groundwater samples form borehole S7 do not appear to play a significant role in the transport of radionuclides in that part of the El Berrocal rock/water system. (Author)