Evaluation of hydrogeochemical characteristics and the impact of weathering in seepage water collected within the sedimentary formation

A study was conducted by collecting eight seepage water samples that drain through the sedimentary rocks,mainly sandstone and shale,to evaluate the hydrogeochemical characteristics.The collected samples were analyzed for physico-chemical parameters using standard procedures.Three water types were identified in the Piper plot and the hydrogeochemical evolution starts from a CaCl facies(type 1) via mixed Ca-Mg-Cl and Ca-Na-HCO_3 facies(type 2) to Na-Cl facies(type 3).Increasing trend of electrical conductivity(EC) values were observed from type 1 water to type 3 water.Lower ionic concentrations with an average EC value of 35.7(is/cm in Ca-Cl facies indicate the recharge water by monsoonal rainfall,and ion exchange/weathering process is reflected in the mixing zone.Higher ionic concentration with an average EC value of 399(is/cm is noted in Na-Cl facies,which indicates the ion exchange during water-rock interaction.Higher log PCO_2 values are also found in this facies,revealing the longer residence time of seepage water in the rock matrix,which release more ions into the water.The relative mobility of elements during weathering suggest that the order of mobility in both sandstone and shale is Na > Ca > Mg > K.It was observed that the hydrogeochemistry of seepage water is mainly controlled by the bedrock geology.

Determination of the major geochemical processes of groundwater along the Cretaceous-Tertiary boundary of Trichinopoly,Tamilnadu,India

The hydrogeochemical variations in groundwater are mainly influenced by lithology,residence time of water in the aquifer matrix,and anthropogenic activities.This study was focused on the geochemical variations of groundwater in different lithological units(Archaean,Cretaceous,Tertiary,and Quaternary)by understanding the major factors governing the geochemical variations in each lithology.The 71 groundwater samples were collected from these rock types,namely,Archaean(14),Cretaceous(37),Tertiary(11),Quaternary(9).The collected samples were measured for major ions and they were used for preparation of standard geochemical plots and ionic ratios.Factor analysis and factor score were used to identify the major factors controlling the hydrochemistry and their spatial distribution in the study area.In addition,geochemical model,WATEQ 4 F was used to determine the saturation condition of carbonate and sulphate minerals in the groundwater.Na–Cl and mixed Ca–Na–HCO3 were the dominant hydrochemical facies irrespective of lithological units.The overall interpretation of geochemical data revealed that leaching of secondary salts,weathering and ion exchange reaction along the groundwater flow path through various lithological units,and anthropogenic influence from domestic sewages and agricultural activities constitute the major geochemical processes in the study area.Hence,this study brings out the multiple hydrogeochemical process in the complex geological terrain along the Cretaceous-Tertiary boundary.