Soil Stability and Groundwater Chemistry in Urban Areas Covered by Loess (Investigation Site—Galati City, Romania)

摘要

Galati city is located on the left side of the Danube river, close to the Danube Delta (Romania). Local deformation of the soil and of the constructions signalized some instability phenomenon on the geological background. For this reason, in the southern part of the city, in the newly built quarters of block of flats, a large network of shallow boreholes was performed. In this paper, a small (0,75 km 2 ) model area was studied. In the boreholes and on the steep riverside of the Danube, Upper Pliocene, Middle and Upper Pleistocene deposits were identified and analyzed: the Poiana Formation, the Barbosi Formation and the Würmian loess. The variation of the depth and the chemistry of the groundwater were also studied. In our study, we try to distinguish the variation of the natural (geological) components of the soluble salts to the anthropogenic pollutants as K + , NH 4 + Cl - , SO 4 -2 , NO 3 - , NO 2 - , PO 4 and some trace element ions. Note, that some ions as K + , Cl - , SO 4 -2 could have both natural and man made origin. The spatial distribution of the concentration of these components shows a difference between them because of interaction between the groundwater and the mineral components (mainly of the clay minerals) of the deposits: one part of the ions is released, while the others are “braked” in their movement. This way, an anomalous zone was identified in the centre of the model area, which was probably caused by the damaged sewerage network: the “aggressive” components of the slurry reacted with the loess, causing the breakdown of the macroporous structure of them.