Spatial variations of trace metals, salinization processes and multivariate analysis in the near surface aquifer systems of Krishna delta, Andhra Pradesh, India.

Krishna delta along the east coast of India presents a complex hydrogeological and hydrogeochemical situation with Holocene marine transgression events marked by paleo strand lines and subsequent evolutionary trends of the delta marked by numerous paleochannels/lobes. These paleochannels/lobes act as huge repositories for groundwater in the near surface aquifer systems with depth levels varying between 10 and 80 m bgl (below ground level) with high recharge potentials and are underlained by brackish water aquifers deposited during the marine transgressional events. These near surface aquifer systems have been subjected to over abstraction of groundwater to meet the irrigation and drinking water demands through multiple shallow well field systems resulting in vertical migration of brackish water and mixing with near surface freshwater aquifers. These processes are dominant in the regions with high abstractions and relatively low or insignificant mixing in the low abstraction and high recharge regions. Sixteen trace metals Beryllium (Be), Cobalt (Co), Strontium (Sr), Boron (B), Nickel (Ni), Molybdenum (Mo), Lead (Pb), Vanadium (V), Copper (Cu), Chromium (Cr), Zircon (Zn), Manganese (Mn), Arsenic (As), Iron (Fe), Selenium (Se) and Barium (Ba) were analyzed from the groundwater of the near surface aquifer systems at 29 sites covering the entire delta complex. Almost all the trace metals incorporated lie within safe and acceptable limits prescribed by WHO/BIS excepting Sr, B, Mo, Pb, V, Mn, As, and Fe located at few isolated sites due to localized pollution impacts prevailing in the low-lying delta regions. The spatial distributional trends, intensity levels and their impacts on natural/ anthropogenic processes are analyzed and presented. Pollution indices related to Contamination Factor (CF) and Pollution Load Index (PLI) are estimated and applied to arrive at different levels of contamination against each element. A number of graphical cross plots are also drawn between TDS and different trace metal levels to assess the trends of each element in relation to fresh and brackish water zones and their impacts on salinization and anthropogenic processes. Multivariate statistical analysis (correlation matrix and factor analysis) are also used to assess the natural/ anthropogenic impacts. The overall analysis indicates dominant brackish water mixing processes and low to moderate impacts due to several automobile units, agro-based fertilizer units, aqua forms, electro chemicals and coal-based industries in addition to municipal wastes and sewerage disposal sites existing in the delta region. [ABSTRACT FROM AUTHOR]