Open borehole wells in fractured crystalline rock are commonly used for domestic water supply. Concentrations of contaminants present in the well water, typically collected from the tap after some degree of purging, are weighted average concentrations. In this study, factors which influence sample concentrations collected from domestic wells are evaluated through the use of conceptual models and confirmatory field tests. Focus is on the extent of drawdown during sampling, distance between the pump inlet and contaminated fractures, relative fracture transmissivity, fracture discharge rate into the borehole, and the hydraulic head distribution of the fractures. Simplified spreadsheet models were developed to assess the relation between these factors and sample concentrations. The models show that in addition to fracture transmissivities, drawdown in relation to fracture head plays a significant role in how much water recharges a well from each fracture, yet it is rarely measured when sampling domestic wells. To evaluate the extent of drawdown that may occur under typical household usage, water levels were monitored in three domestic wells. Pumping tests were conducted in three wells to measure changes in concentration as a function of pumping duration. Downhole profiling was conducted to examine how pumping induces changes to water quality within the wellbore. The results indicate that these factors can have a strong influence on contaminant concentrations in samples collected from these wells. As such, the weighted averaging factors should be considered in sample collection, in data interpretation, in assessing exposure risk and in mapping contaminant distributions.

中文翻译：

---

对影响从生活井水样品中确定的污染物浓度的水文因素的评估

裂缝性结晶岩中的裸眼井通常用于家庭供水。通常在一定程度的吹扫后从水龙头收集的井水中存在的污染物的浓度是加权平均浓度。在这项研究中，通过使用概念模型和验证性现场测试来评估影响从家庭井中采集的样品浓度的因素。重点在于采样期间的回缩程度，泵入口与受污染裂缝之间的距离，相对裂缝透射率，裂缝向井筒中的排放速率以及裂缝的水力压头分布。开发了简化的电子表格模型来评估这些因素与样品浓度之间的关系。这些模型表明，除了裂缝的透射率，相对于压裂头的回缩对每口裂缝补给一口井的水量起着重要的作用，但是在对家用井进行采样时却很少进行测量。为了评估在典型的家庭使用情况下可能发生的用水量下降，对三口家庭用水井中的水位进行了监测。在三口井中进行了抽水测试，以测量浓度随抽水时间的变化。进行了井下剖析，以检查抽水如何引起井筒内水质的变化。结果表明，这些因素可能会对从这些孔中收集的样品中的污染物浓度产生强烈影响。因此，应在样品采集，数据解释，评估接触风险和绘制污染物分布图时考虑加权平均因子。