井群出水量减少原因分析及治理——以北京某应急备用地下水源地为例

Analysis of the causes of the decrease in wellproduction and its remedial measures:exemplified by an urgent standby wellfield in Beijing

近来,为缓解北京市日趋紧张的供水情况,需启用1995年建成的北京某应急备用地下水源地。该水源地建有30眼水井,属第四系河旁非承压含水层,当时静水位埋深为4m,单井平均出水量超过4000m3h。近年来由于各种原因,尤其是2003年该水源井出水量大幅减少的主要原因是含铁碳质化合物附着对井壁的堵塞。针对这一情况,通过试验确定了以强力正反冲洗活塞洗井工艺为核心的复合洗井方案,对17眼水井实施洗井处理,使井群出水量恢复到了建井初期的水平,取得了良好的效果。

In order to relax the austere situation of water supply in Beijing, an urgent standby wellfield, which was set up in 1995, needs to be put into action. There are 30 wells in this wellfield. Groundwater is pumped from a quaternary unconfined aquifer beside a river. In 1995, the depth to water table was about 4 m and the average well yielding was above 4?000m^3/d. In recent years, however, owing to the decrease in water replenishment to the aquifer on the ground surface and to the well silting and clogging, etc, the depth to the water table dropped to 20 m in 2003, and the yielding of the wells reduced considerably. Data of several well tests indicate that the reduction in well production is due mainly to the jam of ferrated charcoal compound attaching to the well screens. With regard to this situation, a multiple well-washing scheme is selected through careful tests, and good effects have been obtained from the practice of this scheme.