Geofísica e morfometria em terrenos de disposição de resíduos sólidos na porção setentrional do Estado de Roraima

Abstract

Population growth and the formation of new urban centers in an accelerated and disordered manner have caused reflexes in the production and management of urban solid waste, since its unplanned disposal can significantly affect the available natural resources, such as water, air, soil and rock. The present research employed indirect methods of investigation, that is, noninvasive, such as remote sensing (morphometry) and geophysics (Vertical Electrical Surveying) to evaluate the signatures on the surface and subsurface, respectively, to identify possible contamination arising from solid waste disposal areas, and how much it impacts surface and subsurface water bodies. The focus areas of study comprise the northern portion of the state of Roraima (municipalities of Alto Alegre, Cantá and Normandia). The physical characterization of each area used as a solid waste deposit revealed that none of them follows the normative prescriptions, since the three municipalities have solid waste disposal through open dumps. The municipality of Alto Alegre is based on crystalline terrain (gneiss from the Rio Urubu Metamorphic Suite) covered by a sandy and permeable material. Located at the edge of the Igarapé Commission drainage basin with predominantly moisture absorption strands, characteristics that provide rapid leachate percolation in saturated and clayey horizons, a fact evidenced by the electroresistant survey that detected conductive areas under the disposal pit and the pile of adjacent waste (110.3 Ω.m <ρa <324.6 Ω.m, with vertical migration up to 18 m deep), which can flow towards SW in the direction of the stream. The Cantá municipality area also includes crystalline rocks (diabase from the Rio Urubu Metamorphic Suite) covered by sandy-clay material. Such characteristics favor the accumulation of the contaminating liquid in the form of a plume of contamination, and that, when considering the topography, there is a tendency of flow in the south direction, up until Quitauaú River, corroborating with the electro resistive survey, which detected conductive zones the 10 m depth (3.6 Ω.m <ρa <261.8 Ω.m) under the waste disposal pit, which starts to percolate laterally towards the old dump and the river. The region of the municipality of Normandia owns sedimentary rocks of the Tacutu Basin (Boa Vista Formation - sandy and floodable terrains). Since the waste allocation area is located on the Passarinho stream drainage basin with low altimetric amplitude (58 meters), it provides high vulnerability to flooding and, consequently, the contamination of surface and groundwater by dilution processes. Conductive zones (94.2 Ω.m <ρa <159.4 Ω.m) up to 2.4 m in depth were detected, these being indicative of contamination, which percolates vertically and spreads laterally in saturated and porous zones nearby to the crystalline basement (55 m deep). In view of the results obtained, there is evidence of the efficiency of indirect methods of investigation for environmental studies and the importance of complying with laws regarding the management of solid waste for environmental preservation.