潮白河再生水补给河道对周边浅层地下水影响的数值模拟研究

再生水在北京被广泛用于补给河道，2007年底至2017年共有2.3×108 m3再生水补给至潮白河顺义段。其污染物本底值较高（Cl?浓度约62~122 mg/L），通过河床入渗补给到周边的含水层中，对周边地下水产生一定影响，尤其是浅层地下水。为了定量评价再生水补给河道对周边浅层地下水的影响，基于10年（2007—2017）的地下水监测数据，建立了再生水补给河道周边的地下水水流和溶质运移模型，模拟了受水区浅层地下水的水位和Cl?浓度的变化，分析了浅层地下水水量、Cl?负荷和NO₃-N负荷的变化。结果表明，再生水补给河道后的前2年（2007—2009），河道周边浅层地下水水位迅速抬升了3~4 m，之后在再生水的持续补给下保持稳定。但受深层地下水开采影响，2007—2014年研究区整体浅层地下水的水量仍在下降。2014年底实施地下水压采措施后，浅层地下水水量从2014年底的3.76×108 m3恢复到了2017年底的3.85×108 m3。周边浅层地下水中的Cl?浓度从再生水补给前的5~75 mg/L变化到了补给后的50~130 mg/L，之后保持稳定。浅层地下水水质受再生水影响的范围从2008年底的11.7 km2扩大到2017年的26.7 km2，影响区内的Cl?负荷从2008年底的1.8×103 t增加到2017年底的3.8×103 t，NO₃-N负荷从2008年的29.8 t下降到2017年的11.9 t。尽管研究显示影响范围外的浅层地下水质受再生水影响不明显，但潜在的咸化和污染的隐患不容忽视，需要在后续研究中进一步明确。

Numerical modeling of the impacts of reclaimed water recharge to the Chaobai River channel on the ambient shallow groundwater

Reclaimed water has been widely used to recharge river channels in Beijing, with 2.3×108 m3 of reclaimed water recharge to the Shunyi section of the Chaobai River from the end of 2007 to 2017. It has a high background value of pollutants (Cl? concentration ranging from 62 to 122 mg/L) and recharges the ambient aquifers, which has an impact on the ambient groundwater through riverbank filtration, particularly on the shallow groundwater. Based on 10-year series groundwater monitoring data (2007?2017), we conducte a 3D groundwater flow and solute transport model to simulate the variations of the shallow groundwater table and chloride concentrations, and analyze the variations in groundwater storage, Cl? loads, and NO₃-N loads in the shallow aquifers near the Chaobai River receiving reclaimed water. The results demonstrate that the ambient groundwater table swiftly rose by about 3?4 m following the reclaimed water replenishment from 2007 to 2009, and stayed steady under the condition of continuous replenishment of reclaimed water. However, affected by the exploitation of deep groundwater, the groundwater storage in the unconfined aquifer still decreased overall from 2007 to 2014. After reducing the groundwater extraction since 2014, the shallow groundwater storage recovered from 3.76×108 m3 at the end of 2014 to 3.85×108 m3 at the end of 2017. Cl? concentrations in the ambient shallow groundwater changed from a range of 5?75 mg/L before the recharge to 50?130 mg/L after the recharge (2007?2009), and then remained stable. The areas of shallow groundwater quality affected by reclaimed water infiltration expanded from 11.7 km2 in 2008 to 26.7 km2 in 2017. The Cl? loads in the affected areas increased from 1.8×103 t in 2008 to 3.8×103 t in 2017. The NO₃-N loads decreased from 29.8 t in 2008 to 11.9 t in 2017. Although the results show that the shallow groundwater quality outside the affected area is not significantly affected by the reclaimed water, the potential salinization and pollution cannot be ignored and need to be further clarified in the subsequent studies.