废水排放所引起的污染问题一直以来备受国际社会的广泛关注。废水的不达标排放，不仅会造成地面污染，而且会对地下环境造成一定的影响。废水中较高的污染物质是影响地下环境的主要因素，但目前对高COD、高氨氮废水排放对地下水质量的影响及其机理尚未取得系统认识。本文以某企业由于废水排放所产生的污染场地为研究对象，利用野外监测、控制试验与多元统计分析相结合的手段，探讨含高COD和氨氮的废水排放对该地区地下水质量的影响情况，分析地下水中污染物随时间的变化规律和机理，并预测了未来地下水质量的演变趋势。研究成果不仅有利于更好地利用和处理废水，从而更好的实现地下水质量保护，还可以提高我们对污染场地地下水水化学演化规律的认识。主要研究成果如下：

（1）基于实测数据确定了废水排放与地下水质量演化之间的因果关系，并据此量化了废水排放对地下水质量的影响。含高COD、氨氮的废水排放渗入地下，在非饱和带的过滤、阻滞、硝化和反硝化作用后，进入地下水中污染物的浓度已大大衰减，但是仍远高于该地区的地下水背景值。废水的排放引起了地下水中三氮含量的明显改变，在一定程度上影响了水体的质量。个别受污染的点位，在废水停排较长时间后，其地下水中的COD_Mn、NH₄⁺-N浓度仍然呈现明显上升的现象，废水排放对地下水质量的影响是长期的、滞后的。

（2）基于控制试验证实了含高COD和氨氮废水的入渗对含水介质中典型氧化还原敏感组分的激活作用，并据此识别了地下水中浓度异常组分的来源。受废水排放影响的地下水中的NO₃^--N浓度普遍减小，废水中的NH₄⁺-N作为还原性物质进入地下水后改变了氧化还原环境。受COD和NH₄⁺-N的作用，地下环境中的大量氧气被消耗，长期处于还原条件，含水介质中的铁锰物质释放，使得地下水中Fe、Mn浓度升高。

（3）基于实测数据，应用统计学模拟计算模型对未来地下水质量的变化趋势进行了预测，为污染场地未来的污染风险管控工作提供了科学依据。废水排放较长时间后，地下水中的污染物浓度开始大幅度降低，各监测井中的水质参数均趋于平缓。经过长时间的自然衰减作用，地下水质量逐渐向地下水背景值的浓度方向恢复。但是，废水排放确实使得研究区的地下水质量发生了变化，改变了最初的氧化还原条件，使得地下水中长期含有Mn。污染物质COD_Mn、NH₄⁺-N和Mn仍是需要我们长期关注的。

The pollution caused by wastewater discharge has been widely concerned by the international community. The unqualified discharge of wastewater will not only cause surface pollution, but also have a certain impact on the underground environment. The higher pollutants in the wastewater are the main factors affecting the underground environment, but at present, the impact of high COD and high ammonia nitrogen wastewater discharge on the quality of groundwater and its mechanism have not been systematically understood. In this paper, the pollution site caused by wastewater discharge of an enterprise is taken as the research object. By means of field monitoring, control test and multivariate statistical analysis, the impact of wastewater discharge containing high COD and ammonia nitrogen on the groundwater quality in this area is discussed, the change law and mechanism of groundwater pollutants with time are analyzed, and the evolution trend of groundwater quality in the future is predicted. The research results are not only conducive to the better utilization and treatment of wastewater, so as to better realize the protection of groundwater quality, but also improve our understanding of the hydrochemical evolution law of groundwater in polluted sites. The main research results are as follows:

(1) Based on the measured data, the causal relationship between wastewater discharge and groundwater quality evolution is determined, and the impact of wastewater discharge on groundwater quality is quantified. The wastewater containing high COD and ammonia nitrogen seeps into the ground. After the filtration, retardation, nitrification and denitrification in the unsaturated zone, the concentration of pollutants in the groundwater has been greatly attenuated, but it is still far higher than the groundwater background value in this area. The discharge of wastewater caused the obvious change of three nitrogen content in groundwater, which affected the quality of water body to a certain extent. At some polluted points, after the wastewater is stopped for a long time, the concentration of COD_Mn and NH₄⁺-N in the groundwater still shows an obvious rise, and the impact of wastewater discharge on the groundwater quality is long-term and lagging.

(2) Based on the control test, the activation of typical redox sensitive components in aqueous media by the infiltration of wastewater containing high COD and ammonia nitrogen was confirmed, and the source of abnormal concentration components in groundwater was identified. The concentration of NO₃^--N in groundwater affected by wastewater discharge generally decreases, and NH+ 4-N in wastewater enters groundwater as a reducing substance, which changes the redox environment. Due to the effect of COD and NH₄⁺-N, a large amount of oxygen in the underground environment is consumed, and it is in the reduction condition for a long time. Iron and manganese substances in the aqueous medium are released, which increases the concentration of Fe and Mn in the underground water.

(3) Based on the measured data, the statistical simulation calculation model is applied to predict the change trend of groundwater quality in the future, which provides a scientific basis for the future pollution risk management and control of contaminated sites. After the wastewater is discharged for a long time, the pollutant concentration in the groundwater begins to decrease significantly, and the water quality parameters in each monitoring well tend to be flat. After a long period of natural attenuation, the groundwater quality gradually recovers to the concentration of groundwater background value. However, wastewater discharge does change the quality of groundwater in the study area, change the initial oxidation-reduction conditions, and make the groundwater contain Mn for a long time. Pollutants COD_Mn, NH₄⁺-N and Mn still need our long-term attention.