GROUNDWATER QUALITY WITH SPECIAL REFERENCE TO FLUORIDE IN UNNAO DISTRICT, UTTAR PRADESH, INDIA: A HYDRO-GEOCHEMICAL AND MULTIVARIATE STATISTICAL APPROACH

An assessment of groundwater quality with special reference to fluoride (F) contamination was carried out systematically on extensive basis using hydrogeochemical and multivariate statistical approach to delineate the factors governing the chemistry of groundwaters in Unnao district of Uttar Pradesh (India). The water samples (n=84) were collected randomly at a random intersection of 2.6 km x 2.6 km of a square grid from both shallow (n=42) and deep (n=42) hand-pumps from the study area. The results revealed higher concentration of F in shallow hand-pumps which ranged between 0.19 to 4.33 mg L-1. The F level in the shallow hand-pumps exceeded the desirable limit of 1.0 mg L-1 in 28.57% of sampled water whereas it was only 7.14% in case of deep hand-pumps. The hydro-geochemical analysis revealed that, besides pH, weathering of silicates, carbonates, and ion exchange processes were responsible for the geochemistry of the groundwater. The F had a significant positive correlation with pH (r=+0.63, p<0.05) in shallow hand-pumps. The water type of majority of the samples of groundwater was found to be Na-HCO3 type. The spatial distribution of F concentration in deep hand-pumps was determined by geo-statistical method using semi-variogram analysis and F map was generated by using Kriging. The inverse distance weighting method was applied for mapping of F in shallow hand-pumps, where no valid semi-variogram was obtained. The present study may be helpful for public health departments for carrying out epidemiological surveillance to reduce the F exposure risk in the delineated areas.