再生水回灌地下水环境安全风险评价技术方法研究

Risk Assessment Technology Method on Groundwater Environment Safety of Reclaimed Water Injection

再生水回灌是水资源管理的一条有效途径，也是污水再生利用的重要发展方向。然而，当再生水以农灌、土壤含水层处理（SAT）、河湖入渗和井灌等方式进行地下水回灌时，不可避免的会在回补地下水的过程中造成对地下水环境的污染风险。针对不同回灌方式建立适用于我国的再生水回灌地下水环境安全风险评价技术体系至关重要。借鉴国内外地下水污染风险评价方法，综合分析再生水回灌对地下水产生风险的关键环节，采用层析分析法，从回灌水特征污染物特性、回灌区地下水固有脆弱性以及回灌工程布设方式3个方面，针对地表灌溉、河湖入渗和井灌3种回灌方式，建立了包含污染物浓度水平、分配系数、溶解度、半衰期、半致死剂量、地下水埋深、降雨入渗补给量、地形坡度、土壤介质、包气带介质、含水层介质、含水层厚度、回灌强度、回灌周期、回灌水停留时间以及取水点与回灌点水平距离16个指标在内的风险评价指标体系。在此基础上，结合地下水使用功能，以20个典型再生水回灌场地调研结果和160种再生水回灌地下水污染风险因子物化特性为数据基础，对各指标进行了风险水平的划分，基于聚类分析法，采用各指标风险指数相乘的风险表征方法计算总风险指数，构建了再生水回灌地下水环境安全风险评价技术方法。该方法有效的避免了指标权重计算的主观性，并且能够直观的找出导致风险的主要因素。结果表明：利用建立的风险评价技术方法可将我国再生水回灌地下水环境安全风险划分为3级，风险值〈5为一级，风险值在5-15之间为二级，风险值〉15为三级。在某再生水回灌场地的应用表明，该回灌区地下水环境安全风险为二级，同时得出回灌水特征污染物特性指标是造成该回灌区地下水环境风险的主要因素。

Groundwater recharge using reclaimed wastewater is an important aspect of water resource management. Nevertheless, when reclaimed wastewater percolates to groundwater via agricultural irrigation, the soil aquifer treatment （SAT）, infiltration of lakes and well irrigation, it will inevitably carry pollutants to groundwater which increases the risk of groundwater pollution. Therefore, it is vital to establish risk assessment guidelines for reclaimed wastewater recharge by various injection methods to protect groundwater quality in China. This study developed a risk assessment index system through comprehensive analysis of risk assessment methodology and the key processes of reclaimed water injection. The system was established based on three aspects including the characteristics of pollutants in recharge water, the inherent vulnerability of groundwater in the irrigation area, and the layout of the recharge engineering by applying analytic hierarchy process. The risk assessment index system consists of 16 indicators, including the pollutant concentration level, distribution coefficient, solubility, half-life, half lethal dose, groundwater table, rainfall infiltration recharge, the land surface slope, top soil medium, vadose medium, aquifer medium, thickness of aquifer, recharge intensity, recharge cycle, residence time of reclaimed wastewater, and horizontal distance between the water intake point and inject point. The system can be used to protect groundwater environment when reclaimed wastewater is injected through surface irrigation, infiltration of lakes, and well injection. Based on the survey on 20 typical reclaimed wastewater injection fields and the physical and chemical properties of 160 groundwater pollution risk factors, combined with the groundwater function, the level of risk for each indicator was ranked. The total risk index was calculated by multiplying the individual risk indicators, and the method of groundwater environment safety risk assessment was established by applying the clustering analysis. The method can effectively avoid the subjectivity of index weight calculation, and identify the main factors that lead to the risk. Our results showed that in China the risk of groundwater environment safety due to reclaimed water injection could be divided into 3 levels from high to low：the risk values of Level 1 were less than 5, of Level 2 were between 5 and 15, and of Level 3 were greater than 15. We applied this risk assessment system in a test reclaimed water injection field, and it showed that this operation had a potential risk of Level 2, and the characteristic of the pollutants in the reclaimed wastewater was the main factor that caused the relatively high groundwater environmental risk.