Comprehensive Quality And Safety Assessment Of Drinking Pore-Groundwater Based On Fuzzy Mathematics And Numerical Simulation Methods

Groundwater is a major water resource of drinking water,irrigation,and industrial use in Longqiao town of the North Chengdu Plain,China.However,unreasonable urbanization and the rapid development of industry,among other factors,have led to severe environmental issues,such as drinking-water contamination.The research objective is to assess the quality and management of drinking-groundwater within the vicinity of a shallow,unconsolidated aquifer of Quaternary age,and providing a scientific basis for groundwater resource management in the region.To achieve this objective,nineteen groundwater samples(Q1,Q2,Q3,Q4,Q5,Q6,S1,S2,S3,S4,S5,S6,J1,J2,J3,J4,J5,J6 and J7)were selected in the study area.These samples were analyzed for 20 different physicochemical water quality parameters,which included(p H,EC,TH,TDS,Na⁺,K⁺,Ca²⁺,Mg²⁺HCO₃^–,Cl^–,SO₄^2–,NH₄⁺,COD_Mn,NO₂^–,NO₃^–,Fe,Mn,As,Cr⁶⁺,Pb to assess groundwater quality.In order to define the hydrochemical characteristics that controlled the quality of groundwater,a detailed investigation was conducted based on traditional methods.Considering the uncertainties linked with water resources and environmental complications,the fuzzy mathematics method was used in the determination of groundwater quality for more precise findings that support decision-making.The results stability of fuzzy mathematics method was compared with comprehensive evaluation method(CEM)and water quality index(WQI),which are the most common methods for assessing the quality of groundwater for drinking.The Health risks of NH₄⁺and Fe contaminants for adults and children also were assessed through the different exposure pathways for drinking water intake and dermal contact.In this research,a three-dimensional finite-difference groundwater model was constructed based on proper calculation and calibration of major hydraulic parameters for the best management strategy was proposed for different modelling scenarios.Sixteen hydraulic head observation wells were used for flow-model calibration.Based on groundwater sampling test results,the ammonia(NH₄⁺)was selected as a pollution indicator with a high concentration for the solute-transport model calibration and prediction.The results of physicochemical data revealed that groundwater in the basin was slightly alkaline in nature according to p H for most groundwater samples.Total hardness(TH)and total dissolved solid(TDS)values showed that the investigated water was classified as very hard and fresh water,respectively.The study took the results of the fuzzy logic evaluation method into consideration and classified samples into five groups according to the Chinese groundwater quality standard(GB/T 14848-2017)for their suitability for domestic use(grade I=most suitable to grade V=least suitable).The fuzzy method results demonstrated that the quality of groundwater in most of the wells was within grade II and III,and was suitable for drinking purposes except wells(Q1 and S2)were found to be in class V,which meant very poor quality and cannot be used for drinking.Based on the results of assessment obtained from all compared methods(Fuzzy,CEM and WQI),the groundwater quality in the study area was suitable for drinking at ratio 89.5,78.9%and 94.7 respectively.This confirms that the holistic picture of groundwater quality within the study area is satisfactory and consistent with the actual situation of the study area under the prevailing conditions.However,the fuzzy indicator is recommended as a more practical indicator for assessing groundwater quality owing to the introduction of membership degree and weight of each factor to the models.Referring to health risk assessment,the results show that the children are more at risk than adults.The evaluation results show that the risks through pathways of exposure to dermal contact is low and acceptable for children and adults,which can be ignored.However,the risks through drinking water intake is high and unacceptable for both children and adults.The results also revealed that the risk of children through both exposure pathways(drinking water intake and dermal contact)is significantly higher than that of adults.Through the results of numerical modelling,the computed vs.observed hydraulic heads at16 observation wells were found matching closely.The solute-transport model showed that industrial pollution sources were the main factors that led to the deterioration of water quality.To analyze the necessity and effectiveness of remediation measures for the safety of drinking-water sources,two scenarios were predicted of NH₄⁺concentration in this study over 20 years.Based on the results of scenario I in which no precautions and remediation measures were taken,the NH₄⁺concentration in the wells(S2,Q1 and Q4)increased to 0.83,2.19 and 0.56mg/L until the end of the prediction(2035)respectively.This indicates that the water quality would be significantly affected and not suitable for drinking,as it was worse than Class-III(0.5 mg/L)of the Chinese Groundwater Quality Standards(GB/T 14848–2017).Regarding the prediction of Scenario II,some remedial measures have been taken into account such as construction of treatment station for industrial wastewater and anti-seepage system of domestic wastewater treatment facilities.As a result,the peak value of NH₄⁺concentration was at the end of the forecast period(2035)of wells(S2,Q1 and Q4)are 0.14,0.33 and 0.26mg/L respectively,which did not exceed the Class-III(0.5 mg/L)of(GB/T 14848–2017)standards,and thus the drinking function was unaffected.This study can provide an important framework of reference for decision making on improving groundwater quality which in turn can be applied to safety management practices in the study area and nearby surrounding.