Establishment And Application Of Evaluation System For Site Selection Of Surface Infiltration Of Reclaimed Water

Reclaimed water recharge is a viable and effective way to alleviate groundwaterresources crisis. Successful surface infiltration project depends critically on suitablesite selection. Consequently, evaluation of site suitability has an important practicalsignificance. Depending on analysis of researches and projects of site selection ofsurface infiltration recharge, a new evaluation system of site selection of surfaceinfiltration, which is based on characteristic of North China Plain, is developed. Inorder to verify reliability and practicability of this system, the system was used inBeijing plain. Main conclusions obtained from this study are as follows:（1） There are two main surface infiltration methods of surface infiltration, i.e.,farmland irrigation and soil aquifer treatment system （SAT）. Influencing factors onsite selection of the two recharge methods are the same, but influencing intensity ofeach factor are different. Therefore, a criteria system with different quantificationmethod and weights information of each criterion was developed for site evaluation ofthese two recharge methods.（2） There are two types criteria in this evaluation system, i.e., constraint criteriaand suitability criteria. The environmental, economic, social and sites characteristicfactors are included in constraint criteria. The main objective of constraint criteria isto screen out alternatives, which have been deemed as being non-feasible. The surfaceand ground characteristic, and groundwater quality are included in suitability criteria.Its objective is ranking the feasible areas in order to choose best suitable site forrecharge. The standardization functions are used for quantification of criteria.Analytic Hierarchy Process is used for giving weights information to criteria, andaccumulative frequency is used for ranking the results. Three methods are used inorder to weaken the influence of subjective factors.（3） This system was used in Beijing plain for site selection of surface infiltration.The results in this study are coincident with previous works, which means that thesystem is available and reliable. However, the number of criteria needed in thissystem are less and the quantification methods are more simple., The evaluation results showed that the most suitable area of farmland irrigation and SAT are locatedin middle north of Beijing plain. According to sensitivity analysis, the ground criteria（ground water and stabilized aquiclude depth） index weights are more sensitive inirrigation area, the ground and surface criteria （types of soil and soil texture） indexweights are more sensitive in SAT region.（4） According to risk assessment of reclaimed water from sewage treatmentplants in Daxing, Miyun, and Huairou, it was found that the recharge risk ofreclaimed water from the last two sewage treatment plants is low. The Simulationresults of PHREEQC indicates that the groundwater quality is mainly influenced bymixing, dissolution and precipitation processes. During the recharging process, theconcentration of TDS, Ca²⁺, Mg²⁺, Na⁺, HCO₃^-increases, and the concentration ofK⁺decreases.