摘要
Through a wide-spread groundwater sampling mainly at nested monitoring wells in the Beijing Plain area, combined with data collection, the study analyzes water level, hydrochemistry, temperature, tritium, deuterium, 18O, 14C and other aspects, and indicates that there exits an obvious stratification phenomenon of the groundwater in the alluvial plain area down in the middle part of alluvial-pluvial fans, and the hydraulic connection between layers is very weak. The analysis of the tritium concentration suggests that the average influence depth of the modern precipitation is approximately 120 m. Based on the analysis of the 22 paleowater samples through the D-18O method and 14C isotopic dating, the deep groundwater circulation in the fine sediments area of Beijing Plain down in the fringe part of alluvial-pluvial fans is relatively slow. On average the paleowater point occurs approximately below the 180 m at these points. The main reasons for the formation of stratification and paleowater points are the water-blocking effect of the clay type strata and the compaction effect during the sedimentary process, especially the differential compaction, which could form closed or relatively closed stagnant aquifers. Groundwater in this kind of stagnant aquifers to some degree belongs to non-renewable resource, and should be reconsidered and re-arranged in the water resources management strategy.