Spatiotemporal Evolution Characteristics Study on the Precipitation Infiltration Recharge over the Past 50 Years in the North China Plain

The spatiotemporal evolution characteristics of precipitation infiltration recharge during the past 50 years are discussed in this paper. This research is significant for groundwater resource rational utilization. The distribution of precipitation infiltration recharge coefficients in the 1960 s, 1980 s, and 2000 s can be obtained using unsaturated zone lithology and depth to water table at different times. The amount of precipitation infiltration recharge in the 1960 s, 1980 s, and 2000 s can be calculated using precipitation infiltration recharge coefficients and precipitation data from the Ministry of Water Resources of China. Results show that the change in the precipitation infiltration recharge coefficient is closely related to the water table decrease. From the 1960 s to the 1980 s, the precipitation infiltration recharge coefficient clearly increased in all units. From the 1980 s to the 2000 s, the value slightly increased in the ancient Yellow River alluvial-proluvial and eastern alluvial-marine plains and slightly decreased in the piedmont alluvial-proluvial and central alluvial-lacustrine plains. The piedmont alluvial-proluvial and ancient Yellow River alluvial-proluvial plains exhibited a large precipitation infiltration recharge coefficient for the coarse lithology. The amounts of precipitation infiltration recharges were 16.23×109（1960s）, 19.11×109（1980s）, and 19.42×109 m3/a（2000s）. The amount of precipitation infiltration recharge increased from the 1960 s to the 1980 s then decreased from the 1980 s to the 2000 s in the piedmont alluvial-proluvial and the central alluvial-lacustrine plains. However, this value increased from the 1960 s to the 2000 s in the ancient Yellow River alluvial-proluvial and eastern alluvial-marine plains.

Influence of Rain on Tetrachloroethylene's Multiphase Migration in Soil

For the increasingly serious soil and groundwater pollution by volatile organic compounds, tetrachloroethylene（PCE） was selected as the research object in this study. With the in-situ soil column physical simulation experiments, migration law of PCE in soil under rain conditions was studied by monitoring precipitation and soil parameter as well as sampling and analyzing soil and soil gas, and influence of rain on the multiphase migration process of PCE was preliminarily discussed. Research shows that migrations of PCE and soil moisture were not synchronous, and the rate of the former was speeded up by the latter caused by rain. Preliminary analysis indicates that migration of volatile chlorohydrocarbon in soil was not only driven by soil moisture, but also controlled by the nature of volatility of their own, that is to say, volatilization into gas phase was an important way of migrating and diffusing in pore medium, and the rate of migration and diffusion of gaseous PCE was faster than that of solid, resulting in more abroad distribution of gas phase than that in solid phase.