Estudo da qualidade física, química e bacteriológica das águas subterrâneas em aquífero freático : Região do bairro Pedra Noventa, Cuiabá-MT

Abstract

This study aimed to assess the impacts on physical, chemical and bacteriological quality of groundwater from the unconfined aquifer in the region of the Pedra Noventa neighborhood in Cuiabá-MT, as well as to evaluate the direction of groundwater flow through the construction of a potentiometric map. To this aim, 31 wells were evenly distributed throughout the neighborhood Pedra Noventa, Cuiabá-MT. Samples were collected following the instructions indicated by the Guide for Collecting Water Samples CETESB (2011), using manual type bailer sampler. The physical and chemical parameters were evaluated in the following periods: July 2011 (dry season) and November 2011 (early rain), however for bacteriological evaluation periods were November 2011 (early rain) and February 2012 (rain). The results of this study allow the following conclusions: 1 - the region has a divisor of groundwater in NW-SE direction cutting across the study area, showing two directions of groundwater flow, with one preferential flow heading northeastern and the other southwestern. This occurs both during the rainy period as well as during the drought period. 2 - the physical-chemical parameters studied did not show very high concentrations, only the manganese, iron, lead, ammonia and nitrate concentrations were above the Maximum Allowable Values for human consumption. 3 - high concentrations of manganese, iron and lead, probably originated from the geological formation, possibly indicating a relationship with the composition of soil and weathered rock. 4 - high concentrations of ammonia and nitrate, probably originate from septic tanks, which are disseminated in the area and decomposing organic matter that fall into open wells. 5 - the concentration of chemical elements between the periods of drought and rain changed for a few parameters evaluated. This indicates that there were seasonal fluctuations in quality, with higher concentrations during the rainy period and lower in the dry period, probably due to leaching processes to be more intense than the processes of dilution and. 6 - the bacteriological (total coliform, Escherichia coli and heterotrophic bacteria) had concentrations above the Maximum Allowable Values for human consumption, probably due to the large number of septic tanks distributed in the region. 7 - Through the study of Mann-Whitney statistical well as through the box plots, there is significant evidence that the median parameters: sodium, potassium, calcium, magnesium, sulfate, pH and water temperature presented with medians which differ seasonality.