Hydrogeochemical Characterization And Assessment Of Groundwater Resources In Rohri Canal Command,Sindh,Pakistan

Freshwater is a commodity that is scarce and its higher usage levels are rising worldwidewater scarcity.The problem of watersheds is further exacerbated by contamination from numerous natural reasons,including industrial waste,the overuse of fertilizers,pesticides and heavy metals,particularly arsenic.The second biggest source of irrigated agriculture is groundwater in Pakistan.The degradation and dissimilation of use of water supplies?surface and groundwater?have significant and abominable effects,including the deterioration of water quality,serious health problems,and water level decline.Accommodating the adequate management and identification of associated deteriorating factors,appropriate groundwater management is necessary to ensure the long term sustainable availability of groundwater resources.The Rohri Canal Command aquifer requires the use of groundwater flow models.The main aim of this thesis is the appraisal of hydrogeochemical evolution,assessment ground water quality for drinking and agricultural practices,simulate ground water flow modeling to determine the ground water behavior during steady and transient state identification of the anthropogenic and geo-genic factors for arsenic mobilization and its potential health impacts in the central Sindh Rohri canal command area.The main work and achievements are followings:?1?Hydro-geochemical Characterization of Groundwater:Determination of the mainfactors governing groundwater chemistry by statistical techniques and geochemical modeling is helpful in understating the hydro-geochemical characteristics of groundwater and its evolution and enhancing groundwater quality protection.Statistical analyses demonstrate that the abundance of cations is in the order:Na⁺>Ca²⁺>Mg²⁺>K⁺,while the abundance of anions is in the order:HCO₃^->Cl^->SO₄^2-.The abundance of Na⁺and HCO₃^-proves that silicate weathering is the eminent phenomenon controlling the major ion chemistry of the groundwater in the research area.This is also supported by the correlation analysis and graphical relationships between ions that reveal that ion exchange and rock weathering–like the dissolution of halite,albite,and dissolution of carbonate minerals–are important rock-water interactions,which govern the evolution of groundwater chemistry.Further,rock dominance has been found as the key natural factor governing the groundwater evolution as depicted by the Gibbs diagrams,while few samples falling in the evaporation dominance propose the influence of evaporation in shallow groundwater depth zone.Hydrochemical facies are predominantly of mixed CaMgCl and Na-Cl type with few samples of Ca-HCO₃ type,constituting fresh recharged water.Saturation indices computed by geochemical modeling indicate that the aqueous phase is under-saturated with respect to evaporites like halite and gypsum?negative values?,while equilibrium to over-saturated with respect to carbonates like calcite and dolomite?positive values?.?2?Suitability assessment of drinking and agricultural practices:The study ofhydrochemical data by various methods and the performance work in groundwater helps to determine whether groundwater is suitable for domestic use and irrigation and to identify possible sources of pollution that influence soil quality.These findings can provide significant information for policy makers on groundwater hydrochemistry and quality and help to rationally use and protect groundwater resources and to scientifically manage their resources.The analytical parameters of groundwater were compared with WHO and Pakistan water quality standards.The results show that:majority of the samples were found not potable,the mean values of EC,TDS,and TH are 1570.97?S/cm,993.92 mg/l,and 421.12 mg/l respectively.Dissolution of minerals and soluble salts,and evaporation of shallow groundwater can very well be the leading contributing factors of elevated salinity across the study area.The concentration of Na⁺and K⁺ranges from 17 mg/l to 638 mg/l and 0 to 25 mg/l,with average values of 165.20 mg/l and 3.53mg/l respectively.Continuous exposure and contact of groundwater along with the dissolution of minerals containing Na⁺and K⁺with surrounding rocks lead to having higher concentrations.Ca²⁺and Mg²⁺vary from 14 mg/l to 220 mg/l and 10 mg/l to 175 mg/l respectively,with mean corresponding values of 76.46 mg/l and 55.41 mg/l,which are mainly attributed to the contribution of carbonate minerals.The concentration of HCO₃^-ranges from 59 mg/l to 950 mg/l,with an average concentration of 308.90 mg/l.SO₄^2-and Cl^-varies from 20 mg/l to 600 mg/l and 16 mg/l to 779 mg/l respectively,giving mean corresponding values of 169.88 mg/l and 209.76 mg/l.Dissolution of gypsum,and other sulfate-bearing minerals and halite give rise the values of such minerals in groundwater.Hydrochemical facies depict the overall scenario of the interaction of groundwater solutions within a lithological structure.Most of the samples fall in Zone 4?mixed CaMgCl type?and Zone 2?NaCl type?,where the rock-water interaction significantly interprets hydrochemical behavior,anthropogenic activities,interaction with the unsaturated zone,increased resident time,ion exchange and reverse ion exchange.Few samples lie in Zone 1?CaHCO₃ type?,constituting fresh recharged water.?3?Factor influencing Arsenic mobilization:For the identification of influencing factorson arsenic mobilization,single factor models of water level?WL?model-30 and population density?PD?model-28 were found the best matching with arsenic concentration having matching frequencies of 30.96%and 29.28%.This matching shows that WL and PD affect more than the other factors in the arsenic concentration in the Rohri canal command.The single factor model of SE?model-29?shows the least matching frequency?19.29%?with arsenic concentration.The matching frequency for LU and PR was found to be 27.20%and 20.60%respectively.Since the two factors?WL and PD?showed highest matching frequency with arsenic?30.96%and 29.28%respectively?.Among multi-factor models model-21?two factors;PD+WL?showed the highest matching frequency of 29.11%succeeded by model-8?three factors;PD+LU+WL?28.41%,model-4?four factors;PR+PD+WL+LU?25.14%and model-1?five factors;PR+PD+SE+WL+LU?23.17%.?4?Human health risk assessment:The potential hazard and arsenic origin in the RohriCanal Command Area should be measured to effectively monitor contaminant and reduce risks for protection.This study examines the frequency and spatial distribution of groundwater arsenic,human health risks and evaluates the variables regulating groundwater arsenic concentration and risk assessment for groundwater arsenic research.Research can be a valuable reference point for comparative studies.For the identification of influencing factors on arsenic mobilization,141samples of groundwater were taken.Single and multi-factor models of depth to water table,elevation,pumping rate,population density and land use maps were developed in GIS environment and matching frequency operation were employed to fid best matching with arsenic.Furthermore,potential human health risk was estimated by calculating chronic daily intake?CRI?,hazard quotient?HQ?and cancer risk probability?CR?.For health risk assessment,the predominant regions of high arsenic are located in southernpart of RCC in tehsil Matiari,Hala,Hyderabad and Tando Allahyar.The percentage of the region surpassing the WHO permissible threshold?0.01 mg/l?is 74.42%.The average daily dose of arsenic is higher in adults?mean=0.0065?than in children?mean=0.00075?.The average non-carcinogenic risk of arsenic for adults is higher than children.The standard shows that non-carcinogenic risk for children varies from 0 to 2.5 with an average value of 0.33,while non-carcinogenic risk for adult's variates from 0 to 13.67 with a mean value of 2.89.On the other side,average daily dose of arsenic for carcinogenic risk is higher in children?mean=0.011?than in adults?mean=0.0065?.The average carcinogenic risk is higher in children than in adults.Carcinogenic risk for children varies from 0 to 0.016 with an average value of 0.002,while carcinogenic risk for adult's variates from 0 to 0.0098 with a mean value of 0.0001.?5?Development of Numerical Model:The concept of safe yield and mining also focusedon sustainable groundwater reservoir development and yields.Many concepts of healthy yield are found in literature.Any useful definition of a safe return would allow quantitative return values to be set and specify exactly to what degree adverse and undesirable events are accepted in the scope of a main principle of stability.The safe performance of any aquifer,therefore,is not a single fixed extraction level,but a variable rate that is dependent on many complex interconnected variables,many of which may have hydrological condition.Visual MODFLOW 4.5 The Waterloo software has been used to establish the Rohri Canal Command Aquifer ground water flow model.Water and power development agency and other departments obtained the requested information.The model was calibrated manually for steady conditions 1984,considered to be no pumping period and temporary?pumping period?.Stressed periods were defined for which the model is calibrated manually,i.e.1984 through 1991,1991 through 1996,1996 through 2004,2009 and 2009 through2015.The results show that the model can be used to predict flood fluctuations in various rainfall and exploration conditions.The provision of groundwater for the supply of freshwater is increasingly important.The contradictory demands for fresh groundwater for human consumption,for food production,electricity and the environment as well as physical threats and cross-border flood conflicts should be resolved.Over the previous 50 years,the focus has been on the combination of simulation and optimization methods for groundwater quality management to inspect major problems ranging from pollutant remediation to land-subsidence management irrigations,soil-water-driven ecosystems,marine intrusion,anthropological and geogenic contamination,vulnerabilities in supply and long-term sugaring.The model was used for predictive period until 2025.The simulation of flow model indicated that most of the area in Rohri canal command remained under water logged condition.The evapotranspiration is very high and is biggest water balance component in Rohri Canal Command Aquifer.This is due to high temperature,wind speed and high water table in area.The scenario-1 of 10,20 and 30%increment of pumping for predictive years 2020 and 2025 resulted a minimal drop of heads which can be helpful in rationalized exploiting the resources to cope-up the prevalence of water-logging and salinity under conditions.On the other side,scenario-2 reveals a significant drop of heads under100%pumping increment develop a drop which can be considered as a sink that can persuade the up-coning of saline water from the underlying saline aquifer.Such situation is alarming and need a serious attention for better managing the resources to have a safe yield.