Estudo da acumulação e caracterização de sedimentos em sarjetas de vias urbanas

Abstract

The urbanization process has consequences as the introduction of new sources of pollution and changes in the natural environment, as the increase of impervious areas that accumulate pollutants between rainfall events. The pollution caused by washing of accumulated sediment on the gutters which will be carried to water bodies through the stormwater drainage system, stands out in this process. In this study dried sediments collected in the gutters of a new housing development in the city of Poços de Caldas (state of Minas Gerais, Brazil) were analysed. Field work took place during the period of 21.05.2013 to 27.08.2013. Main goal of this study was to investigate the process of accumulation of dry sediments on impervious surfaces, characterize the sediments and find how this process relates with the urban occupation. More specific goals were to quantify the average mass and characterize the granulometric distribution of accumulated sediments and identify the occurrence of trace metals Zn, Cu, Ni, Cd, Cu and Pb in the fraction of sediments with diameter smaller or equal to 63μm. The sediments were collected by dry-sweeping in areas of 1m2. The samples were weighed to find the aggregate mass and then sieved through meshes of 63μm, 125μm, 250μm, 600μm, 1180μm, and 2000μm for the granulometric analysis. Samples of the sediment fraction smaller than 63mm of diameter were subjected to analysis by Energy Dispersive X-Ray Fluorescence (EDXRF) and Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) for the identification of trace metals. It was found that the aggregate mass of accumulated sediments varies in time and space and is particularly influenced by the land use of the sampling areas. It was concluded that the dry-sweeping method allowed to obtain samples which were able to be analysed. Areas with the largest area of construction showed to have the highest accumulation of dry sediments while unoccupied areas had the lower values. The granulometric curves showed that the average particle size (d50) is in the “average sand” particle size range. The metals analysis allowed to identify the presence of trace metals in the studied area: Cr (735.2 μg.m-2), Cd (137.9 μg.m-2); Pb (3676 μg.m-2); Zn (2297.5 μg.m-2); Ni (1072.5 μg.m-2) Cu (495 μg.m-2); As (2722.5 μg.m-2) and Sn (825 μg.m-2).