Abstract

Sustainable groundwater management is founded on the sound understanding of the effects of water extraction on the aquifer water level and the springs and streams receiving groundwater discharge. Pumping test data are commonly used in extraction licence applications to evaluate aquifer properties and assess the magnitude of storage depletion resulting from pumping. However, a short duration (eg 48 hours) pumping test can fail to detect the presence of aquifer boundaries, as the cone of depression is not large enough to reach the boundaries. This may cause an underestimation of long-term drawdown and an overestimation of permissible extraction rate (ie safe yield). In the rural town of Irricana in Alberta, groundwater extraction licences for municipal water supply wells were issued in the early 1980s based on the analysis of 48-hour pumping tests. Actual water extraction rates were substantially below the licensed rates, but the unanticipated and excessive drawdown in the aquifer forced the town to discontinue pumping and switch to surface water supply after 25 years. To examine the cause of overallocation, a new 48-hour pumping test was conducted in the same aquifer, which included an extended drawdown analysis using 26 days of recovery data. Geological formation logs for existing wells in the area surrounding Irricana were used to infer the extent of sandstone aquifer units within the heterogeneous bedrock formation. The new data analysis showed that the aquifer is semi-closed, contrary to the infinite-aquifer assumption used in the original pumping test, which caused additional drawdown due to the aquifer boundary effects. This study suggests an improved procedure for estimation of storage depletion using standard hydrogeological methods and readily available data. The new procedure provides a useful tool as part of adaptive groundwater management, in which water levels and other relevant variables are monitored and licensed extraction rates are adjusted accordingly.

摘要

可持续的地下水管理建立在对水抽取对含水层水位以及接收地下水的泉水和溪流的影响的充分理解之上。抽水测试数据通常用于提取许可证申请中，以评估含水层特性并评估抽水导致的存储枯竭程度。然而，持续时间短（例如 48 小时）的抽水测试可能无法检测到含水层边界的存在，因为洼地锥体不够大，无法到达边界。这可能导致低估长期回撤和高估允许开采率（即安全产量）。在艾伯塔省的伊里卡纳（Irricana）乡村小镇，根据对 48 小时抽水试验的分析，于 1980 年代初颁发了市政供水井的地下水开采许可证。实际取水率大大低于许可率，但蓄水层意外和过度抽取迫使该镇在 25 年后停止抽水并改用地表水供应。为了检查过度分配的原因，在同一个含水层中进行了一项新的 48 小时抽水测试，其中包括使用 26 天的采收率数据进行的扩展水位分析。Irricana 周围地区现有井的地质地层测井用于推断非均质基岩地层内砂岩含水层单元的范围。新的数据分析表明，含水层是半封闭的，与原始抽水试验中使用的无限含水层假设相反，由于含水层边界效应导致了额外的水位下降。这项研究提出了一种使用标准水文地质方法和现成数据来估计储存枯竭的改进程序。作为自适应地下水管理的一部分，新程序提供了一个有用的工具，其中监测水位和其他相关变量，并相应地调整许可提取率。