The Use of Geostatistics in the Assessment of Hydrogeological Parameters to Map the Composition of the Intrinsic Vulnerability of Aquifers.

ABSTRACT The aim of this study is to perform a geostatistical estimation of hydrogeological parameters to compose the intrinsic vulnerability map for an aquifer. The study presents an exploratory analysis of well data extracted from the Groundwater Information System (SIAGAS), which refer to parameters such as degree of confining, lithology and static level. Therefore, initially, among other procedures, we look for inconsistent data, we produce descriptive statistics and we also apply a normality test to the dataset. The following steps were to make up the primary space description of the respective parameters based on the corresponding identified patterns, randomness and grouping of well data in addition to exploring the existence of a tendency along certain directions. After the preliminary steps, the geostatistical methodology is then applied divided into three phases. The first refers to the variogram study, characterized by the construction of the experimental variograms. In the second phase, automatic adjustment is made to these variograms for three mathematical models: spherical, exponential and gaussian. Then, by cross validation, the performance is estimated for the different models adjusted using statistical indicators. After validation of these models, the last phase takes place, in which we perform the geostatistical estimation by kriging. The estimated values of hydrogeological parameters, when jointly multiplied, composes the estimation of the intrinsic vulnerability index illustrated in the form of a map. This proposal was applied in an area partially covering the city of Belém. The results showed that the methodological approach represents an excellent planning and management tool for the protection of groundwater aquifers.