School of Geography Earth and Environmental Sciences, University of Birmingham, Birmingham B15 2TT, UK; Mott MacDonald, 2 Brewery Wharf, Kendall St, Leeds LS10 1JR, UK.
GroundH(2)O Plus Ltd, Quinton, Birmingham B32 1DY, UK; Department of Civil and Environmental Engineering, University of Strathclyde, Glasgow G1 1XJ, UK.
J Contam Hydrol. 2018 Mar;210:15-30. doi: 10.1016/j.jconhyd.2018.02.001. Epub 2018 Feb 9.
Groundwater-quality assessment at contaminated sites often involves the use of short-screen (1.5 to 3 m) monitoring wells. However, even over these intervals considerable variation may occur in contaminant concentrations in groundwater adjacent to the well screen. This is especially true in heterogeneous dense non-aqueous phase liquid (DNAPL) source zones, where cm-scale contamination variability may call into question the effectiveness of monitoring wells to deliver representative data. The utility of monitoring wells in such settings is evaluated by reference to high-resolution multilevel sampler (MLS) wells located proximally to short-screen wells, together with sampling capture-zone modelling to explore controls upon well sample provenance and sensitivity to monitoring protocols. Field data are analysed from the highly instrumented SABRE research site that contained an old trichloroethene source zone within a shallow alluvial aquifer at a UK industrial facility. With increased purging, monitoring-well samples tend to a flow-weighted average concentration but may exhibit sensitivity to the implemented protocol and degree of purging. Formation heterogeneity adjacent to the well-screen particularly, alongside pump-intake position and water level, influence this sensitivity. Purging of low volumes is vulnerable to poor reproducibility arising from concentration variability predicted over the initial 1 to 2 screen volumes purged. Marked heterogeneity may also result in limited long-term sample concentration stabilization. Development of bespoke monitoring protocols, that consider screen volumes purged, alongside water-quality indicator parameter stabilization, is recommended to validate and reduce uncertainty when interpreting monitoring-well data within source zone areas. Generalised recommendations on monitoring well based protocols are also developed. A key monitoring well utility is their proportionately greater sample draw from permeable horizons constituting a significant contaminant flux pathway and hence representative fraction of source mass flux. Acquisition of complementary, high-resolution, site monitoring data, however, vitally underpins optimal interpretation of monitoring-well datasets and appropriate advancement of a site conceptual model and remedial implementation.
在受污染场地进行地下水质量评估时，通常需要使用短筛（1.5 至 3 米）监测井。然而，即使在这些间隔内，靠近井筛的地下水中污染物浓度也可能会发生相当大的变化。在非均相致密非水相液体（DNAPL）污染源区域，这种情况尤为明显，厘米级的污染变异性可能会质疑监测井提供代表性数据的有效性。通过参考靠近短筛监测井的高分辨率多层采样器（MLS）井，以及采样捕获区建模来探索对井样来源和对监测方案的敏感性的控制，可以评估这种情况下监测井的实用性。从高度仪器化的 SABRE 研究现场收集了现场数据，该研究场所在英国工业设施的浅层冲积含水层中包含一个旧的三氯乙烯污染源区域。随着冲洗量的增加，监测井样品趋于流量加权平均浓度，但可能对实施的方案和冲洗程度表现出敏感性。井筛附近的地层非均质性，以及泵的吸入位置和水位，都会影响这种敏感性。由于冲洗初始 1 至 2 个筛体积时预测的浓度变化，低体积冲洗容易出现重现性差的问题。显著的非均质性也可能导致长期样品浓度稳定化有限。建议制定专门的监测方案，考虑冲洗的筛体积以及水质指标参数的稳定化，以验证和减少在解释源区范围内监测井数据时的不确定性。还制定了一般性的监测井基于协议的建议。监测井的一个关键用途是，它们从构成重要污染物通量途径的渗透层中抽取相对较大比例的样本，因此代表了源质量通量的重要部分。然而，获取补充的高分辨率现场监测数据对于最佳解释监测井数据集以及适当推进场地概念模型和补救实施至关重要。
