Both EPR and XAFS spectroscopy were used to characterize the sorption of Cu(II) on silica surfaces at extremely low surface coverage (0.8 and 9.9% monolayer). The binding structure of Cu(II) on silica surfaces revealed by XAFS experiment was compared to that predicted by EPR spectra. Our XAFS results show that Cu(II) hydroxide clusters form on silica surfaces even at surface coverage as low as 0.8% of a monolayer. However, we observed low EPR intensity and line-broadening which has been assigned to dipole-dipole interactions between isolated Cu(II) ions. The results of our XAFS studies indicate that the loss of EPR intensity and line-broadening can be traced to Cu(OH)(2) clusters on silica surfaces.