Recent evidence suggests that the Eifel Volcanic Fields (EVF) make measurable contributions to the surface deformation in GPS networks, but quantitative assessments of displacement time series and their impacts on long-term rates are lacking. The GPS sites in the EVF indicate anomalously slow uplift (up to 1 mm/yr) which stays at the limit of GPS sensitivity and noise level for monitoring crustal deformation in geophysical applications. Since the primary aim of existing geodetic GNSS networks in west Germany is positioning service for land survey engineering and transportation applications, many sites have been installed on inexpensive and non-geodetic monuments, thus highly vulnerable to disturbances resulting from monument instability and near-field multipath sources. These potential pitfalls have not been fully addressed in previous studies. Here, we reprocess all available GNSS observations (combined GPS and GLONASS observations) using precise point positioning technique and present precise analysis of displacement time series to generate reliable long-term rates and uncertainties. Individual time series is examined to determine local motion, non-linear deformation due to regional and local hydrology and site-specific noise.