A case study on effect of reclaimed water on underground water quality based on numerical simulation

This study aimed to explore the effect of reclaimed water on the changes of ammonia and main salinity concentration in groundwater. Qinghe reclaimed water wetland park was chosen as a case, ammonia nitrogen and Cl-ion are the main research object, using Hydrus-1D solute transport model and coupling groundwater model of Modflow and MT3DMS, the change of ammonia nitrogen and Cl^- index after the long-term utilization of reclaimed water was simulated. At the bottom of vadose zone, the content of nitrogen ammonia and Cl^- ion in reclaimed water was higher than that of phreatic groundwater in the research area, ammonia nitrogen was beyond groundwater quality Ⅲ class standard. The coupling model prediction results suggested that concentration area of ammonia nitrogen exceeding the groundwater quality standard would has expanded constantly 5~20 years later in the horizontal direction, and has extended vertically to the first layer of weak permeable layer; the Cl^- ion concentration would not exceeding the quality standard but has increased in phreatic groundwater surrounding the wetland park. So the long-term reinjection of the reclaimed water in wetland park will have a negative impact on the local groundwater quality.