TESTES DE BOMBEAMENTO E COM TRAÇADOR PARA DETERMINAR CONFINAMENTO E PARÂMETROS HIDRÁULICOS DO AQUÍFERO ALTER DO CHÃO EM MANAUS

Pumping and tracer tests to determine confinement and hydraulic parameters of the Alter do Chão Aquifer in Manaus

Abstract

The Alter do Chão Aquifer (ACA) is located in the national territory. It has an estimated water reserve of 14,4 km³. In Manaus, there are approximately 27.000 wells, with a strong predominance of private owners. There is no precise data about groundwater use, since obligatory wellbore authorization began only six years ago, but the strong lowering of the water level caused in several neighborhoods indicate that it is intense. In terms of contamination vulnerability in the urban area, there is a predominance of low to moderate intrinsic vulnerability, granted mainly by the presence of silt and clay layers in the unsaturated zone. Clay layers also occur in the unsaturated and saturated zones, and despite their importance in terms of water recharge, contaminant access and hydraulic characteristics of the aquifer, specific tests to define the degree of confinement were never executed in ACA. Thus, the general objective of this work is to determine the hydraulic parameters and to infer the degree of confinement that occurs in the ACA in Manaus. A constant flow pumping test and a tracer test were used to determine these parameters. The results show that the AAC is completely confined in the test site, has a hydraulic conductivity of 3.1x10^-5 m/s, storativity of 5.4x10^-5 and transmissivity of 8.0x10^-4 m²/s. Its effective porosity is 9.9%, the longitudinal dispersivity (aL) is 1.2 m, and the retardation coefficient is 1.2. The average real groundwater velocity during the test was 1.3x10^-5 m/s, and the Uranin tracer decay constant was 1.3x10^-6 1/s.