Impact Of Reclaimed Water Irrigation On Groundwater In Southern Suburb Of Beijing

Water scarcity is one of the great threat to socioeconomic development.Utilization of Non-conventional water resources such as reclaimed water is a promising way to alleviate water shortages.As agriculture irrigation is the main way to use reclaimed water,many researches have been conducted to study the influences on soil,crop.While the understanding of pollution risk on groundwater by long-term reclaimed water is still poor.The southern suburb of Beijing was selected as the study area in this study.This research focused on the reclaimed water transportation and utilization process,and studied the typical pollutants migration and transformation of reclaimed in soilgroundwater systems in the study area using historical data analysis,filed monitoring,statistical methods,etc.A new evaluation method for the impact of reclaimed water use on ground,zoning model and pollution prevention and control countermeasures have been proposed.Conclusions that be got in this study are presented as follows.The surface water in reclaimed water channels and groundwater are both weakly alkaline in reclaimed water irrigation area of southeastern suburbs of Beijing.The surface water in reclaimed water channels has higher salinity and nitrogen content in relative to the natural surface water upstream.The salinity and nitrogen content of surface and groundwater in the study area are in the following order: surface water > phreatic water > confined water.The infiltration of reclaimed water may pose potential threat to groundwater quality.The chemistry of phreatic water and confined water is mainly controlled by natural water-rock interactions such as minerals(e.g.halite,gypsum,anhydrite)dissolution,sillicated minerals hydrolysis and cation exchange interaction in the study area.Evaporation has rare influence on phreatic water chemistry.While reclaimed water infiltration is an important import way of salinity and nitrogen pollutants for phreatic aquifers.Reclaimed water infiltration only affects the phreatic aquifers within the depth of 80 m,and has limited impact on the confined aquifers below the depth of 80 m.Chloride,nitrate and ammonia in phreatic groundwater are most affected by human activities and can be used as indicators of the influences of reclaimed water infiltration on groundwater chemistry.The maximum influence depth of salinity due to reclaimed water infiltration is 50-80 m,and the maximum influence depth of nitrogen is within 40 m.This is due to the nitrogen pollutants removal effect by the hydrogeological condition of multi thick clay layers in the study area.This study proposed a new method to improve the DRASTIC groundwater vulnerability assessment model.In this new method,cohesive soil thickness was introduced to improve the unsaturation zone scoring,and weighted average method was used to improve the non-uniform media aquifers scoring.This improved method can increase the correlation coefficient between nemero comprehensive pollution index(NI)and groundwater intrinsic vulnerability index(IVI)from 0.185 to 0.772 in contrast to the unimproved model.Based on the improved model and pollution load,the study area has been divided to three types of different pollution risk zones with the high,medium and low risk zones accounting for10.6% ? 59.6% and 29.8% of the total area,respectively.