In gravity surveys, many unwanted effects are produced by geological or non-geological sources. These calculable effects have to be removed through the data reduction procedure. Common corrections in gravity measurements are those for the instrument drift, the tide, the Free Air, the Bouguer and the terrain effect. However, when we deal with gravity campaigns carried out in cities, we also have to take into consideration the so-called Building Correction. This concerns the correction of the gravitational effect caused by the existence of buildings and anthropogenic constructions (stadiums, bridges etc.) close to a gravity measurement. This process can become quite demanding sometimes. Because of that, in this paper we discuss a calculation method for the Building Correction of the gravity measurements. Two types of data are crucial in that procedure. The first one is the mean building density and the other one is the volume of the existing buildings, which is related to the spatial distribution and the buildings height. The mean building density has been calculated in this paper, based on percentage contribution of the building materials (concrete, bricks etc.) of the whole building volume. The calculated mean building density was equal to 0.44 g/cm3. A Building Height Map has been produced, based on the Digital Elevation Model and the Digital Surface Model. Taking into account the building volume and their density, a simulation of the terrain correction procedure has been carried out, for the Building Correction calculation. The calculated Building Correction values range from almost zero (in the suburbs) to 0.25 mGal. A comparison for the Residual Anomaly values (affected by the Building Correction) has also been made. Differences up to 0.19 mGal revealed are considered to be quite significant for the credibility of the final data.

River deltas sustain important ecosystems with rich biodiversity and large biomass, as well as human populations via the availability of water and food sources. Anthropogenic activities, such as urbanization, tourism and agriculture, may pose threats to river deltas. The knowledge of the factors controlling the regional water quality regime in these areas is important for planning sustainable use and management of the water resources. Here, hydrochemical methods and multivariate statistical techniques were combined to investigate the shallow aquifer of the Pinios River (Thessaly) deltaic plain with respect to water quality, hydrogeochemical evolution and interactions between groundwater and surface water bodies. Water quality assessment indicated that most of the river and groundwater samples fully comply with the criteria set by the Drinking Water Directive (98/83/EC). The river is recharged mainly from springs of the Tempi valley and the shallow aquifer, and to a lesser degree from precipitation, throughout the year. The hydrogeochemical characteristics indicated a cation (Ca, Mg, and Na) bicarbonate water type, which evolves to calcium-chloride, sodium-bicarbonate and sodium-chloride water type, in the northern part of the delta. Calcite and dolomite dissolution determined the major ion chemistry, but other processes, such as silicate weathering and cation exchange reactions, also contributed. In the northern part of the plain, the interaction with the deeper aquifer enriched the shallow aquifer with Na and Cl ions. Principal Component Analysis showed that five components (PCs) explain 77% of the total variance of water quality parameters; these are: (1) salinity; (2) water-silicate rocks interaction; (3) hardness due to calcite dissolution, and cation exchange processes; (4) nitrogen pollution; and (5) non-N-related artificial fertilizers. This study demonstrated that the variation of water hydrochemistry in the deltaic plain could be attributed to natural and anthropogenic processes. The interpretation of the PCA results dictated the parameters used for the development of a modified Water Quality Index (WQI), to provide a more comprehensive spatial representation of the water quality of the river delta.