IWRA Proceedings

ABSTRACT

GROUNDWATER QUALITY INDEX

Nowadays, the groundwater sources are very important to supply population water uses, considering the water scarcity resulted from surface water pollution and others human impacts. Then, the present study develops a Groundwater Quality Index for human consumption (GWQIHC) for use in areas of crystalline aquifers with agricultural use, taking as case study the São Domingos River Basin in the Northwest of Rio de Janeiro State, Brazil. For this, shallow and deep well were sampled from São Domingos River Basin in 2004. Many parameters were analyzed to each sample. The results were compared to groundwater quality limits established by environmental lows. After they were applied to the GWQIHC and this Index was compared to others. The main steps to build the index were: 1) selection of parameters to specify the index; 2) normalization of data by boolean logic; 3) establishment of water type classes. From the sum of each equivalent class, wells were distributed in water quality categories: Excellent, Good and Requires treatment, (grouping samples with some inconformity related to potability standards) and Not suitable for drinking (grouping samples with some toxic parameter). The GWQIHC grouped most samples in Requires treatment category, about 80%. Few samples were classified as Not suitable for drinking for human consumption, only 15%. No samples, however, was classified as Excellent, and this absence of a direct effect of this class definition, which is rigorous. That is, in all sampling points at least one parameter had values above the guide level. Only 2,5% were classified as Good. The GWQIHC proved to be restrictive and coherent with previous results, since various parameters were found to be in unconformity with the adopted legal standards.

Key words: agriculture, crystalline aquifer, water quality index.