This study aims to understand the extension of groundwater pollution downstream of a landfill, Andralanitra-Antananarivo-Madagascar. Twenty-one samples, composed of dug well waters, spring waters, river, and lake, were measured in stable isotopes (δ 2 H, δ 18 O) and tritium. Results showed that only two dug well waters, collected at the immediate vicinity of the landfill, have high tritium activities (22.82 TU and 10.43 TU), probably of artificial origin. Both upstream and further downstream of the landfill, tritium activities represent natural source, with values varying from 0.17 TU to 1.46 TU upstream and from 0.88 TU to 1.88 TU further downstream. Stable isotope data suggest that recharge occurs through infiltration of slightly evaporated rainfall. Using the radioactive decay equation, the calculated tracer ages related to two recent ground water samples collected down gradient of the landfill lay between [8-15] years and [4-7] years, taking into account the uncertainty of tritium measurements. For the calculation, a value of 2.36 TU was taken as A o . The latter was estimated based on similarity between stable isotope compositions of nearby spring and dug well waters as well as tritium activities of the local precipitation. Calculation of the tritium activities from the contaminated water point having 22.82 TU to further downstream using the calculated tracer ages showed values of one order of magnitude higher than the measured values. The absence of hydrological connection from the contaminated water point to further downstream the landfill would explain the lower tritium activities measured. Groundwater pollution seems to be limited to the closest proximity of the landfill.

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Knowing the groundwater quality is important for the drinking water supply in the highland area of Madagascar, including Merimandroso Commune insofar that groundwater is the main source of drinking water for a large number of Malagasy people. In this way, this study assessed the shallow groundwater quality with special focus on nitrate occurrence using multivariate statistical techniques such as cluster analysis (CA) and principal component analysis (PCA). That was to determine the similarities among the water samples in terms of hydrochemical features and to identify the different mechanisms involved in the shallow groundwater hydrochemistry. The study was conducted on twenty-one water samples collected from dug wells. Cluster analysis grouped the water-sampling points into two main clusters: a highly nitrate polluted group (concentration greater than 50 mg/l) and a non-nitrate polluted group. The results showed a spatial variation of the groundwater chemistry processes, while no such variability was found temporally for water samples collected at different periods. Principal component analysis extracted three principal components accounted for over 82% of the total variance. It attributed the hydrochemical features of the water samples of high nitrate content to the nitrate pollution mechanisms along with the weathering of feldspar and ferromagnesian minerals. For some of the latter water samples, the water chemistry is likely affected by igneous rock weathering. This study confirmed both the usefulness and powerfulness of multivariate statistical techniques in water quality assessment, since they helped get a proper understanding of processes controlling the shallow groundwater chemistry.

Nitrate contamination of groundwater was assessed in the crowded area of Ambohidrapeto, Antananarivo city-Madagascar using hydrochemistry and multivariate analysis. Seventeen dug well waters and three spring waters were collected and measured in the field for physical parameters and in the laboratory for major ions. The results showed that all water samples have nitrate concentration above the standard value of 50 mg/L-NO3 set by the World Health Organization, with a minimum value of 79.3 mg/L-NO3 and a maximum value of 394.5 mg/L-NO3. Anthropogenic activities, from the surrounding pit latrines are the main sources of the groundwater nitrate contamination and are dominant over natural processes, which contribute to a lower degree to the groundwater mineralization. Ionic ratios indicated the occurrence of mineral dissolution and silicate weathering as the natural sources of magnesium and sodium, respectively. Furthermore, the correlation between calcium and sodium as well as the Piper diagram revealed the occurrence of ion exchange, resulting in sodium being the dominant cation over calcium. Forty percent (40%) of the water samples have the hydrochemical facies Na–Mg–Cl, followed by Na–Mg–Ca–Cl facies for 25% and Na–Mg–Cl–HCO3 facies for 20%. By applying principal component analysis, the influence of anthropogenic activities is confirmed. The first principal component extracted, which explained 52.88% of the total variance showed strong positive loadings on TDS, NO3−, Cl−, Mg2+, Na+, K+ and Ca2+, indicating that these ions contribute as anthropogenic sources, although Mg2+, Na+, K+ and Ca2+ contribute to a lesser extent than NO3−, and Cl−.

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