Physical-chemical and microbiological analysis of water from shallow wells in Imperatriz (MA), Brazil

The quality of groundwater from Imperatriz (MA) is little known. This work investigated microbiological contaminants (total coliforms and Escherichia coli ) and the levels of 10 physicochemical parameters in 10 wells located in the urban periphery of the municipality of Imperatriz. The counts of E. coli and total coliforms were ≥ 1600 CFU mL -1 in all the wells. Levels of chloride, sulfate, hardness and turbidity levels were below the maximum allowed for drinking water. However, levels of iron (0.46 – 1.75 mg L -1 ) and pH (5.02 – 5.92) were not in compliance with drinking water standards in all the wells investigated. The same was observed in relation to oil and grease in water (0.0 – 6.8 mg L -1 ), which were detected in 40% of the wells. Levels of nitrite (0.71 – 3.84 mg L -1 ), nitrate (4.16 – 13.52 mg L -1 ) and total dissolved solids (810 – 2060 mg L -1 ) were above the highest limit in 50%, 60% and 70% of wells, respectively. The acidic pH observed in all the wells makes them also unsuitable for animal intake and irrigation. The acidity and the high level of iron in all wells suggest that they are natural characteristics of the soil and the groundwater of the region. Contamination with nitrite and nitrate in some wells, as well as high counts of coliforms, may be related to deficiencies in basic sanitation in the area. The origin of oil and grease in the wells should be better investigated to avoid contamination of the water table.