Exposure from groundwater contamination to aquatic receptors residing in receiving surface water is dependent upon the rate of contaminated groundwater discharge. Characterization of groundwater fluxes is challenging, especially in coastal environments where tidal fluctuations result in transient groundwater flows towards these receptors. This can also be further complicated by the high spatial heterogeneity of subsurface deposits enhanced by anthropogenic influences such as the mixing of natural sediments and backfill materials, the presence of subsurface built structures such as sheet pile walls or even occurrence of other sources of contaminant discharge. In this study, the finite volume point dilution method (FVPDM) was successfully used to characterize highly transient groundwater flows and contaminant mass fluxes within a coastal groundwater flow system influenced by marked tides. FVPDM tests were undertaken continuously for more than 48 h at six groundwater monitoring wells, in order to evaluate groundwater flow dynamics during several tide cycles. Contaminant concentrations were measured simultaneously which allowed calculating contaminant mass fluxes. The study highlighted the importance of the aquifer heterogeneity, with groundwater fluxes ranging from 10⁻⁷ to 10⁻³ m/s. Groundwater flux monitoring enabled a significant refinement of the conceptual site model, including the fact that inversion of groundwater fluxes was not observed at high tide. Results indicated that contaminant mass fluxes were particularly higher at a specific monitoring well, by more than three orders of magnitude, than at other wells of the investigated aquifer. This study provided crucial information for optimizing further field investigations and risk mitigation measures.

中文翻译：

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受潮汐影响的含水层中的创新污染物质量通量监测

地下水污染暴露于接收地表水中的水生受体的程度取决于污染的地下水排放速率。地下水通量的表征具有挑战性，特别是在沿海环境中，潮汐波动导致瞬时地下水流向这些受体。由于人为因素（例如天然沉积物和回填材料的混合），地下建筑结构（如板桩墙）的存在，甚至其他污染物排放源的出现，人为影响增强了地下沉积物的高度空间异质性，这也可能使情况进一步复杂化。在这个研究中，有限体积点稀释法（FVPDM）已成功用于表征受潮汐影响的沿海地下水流系统中的高瞬态地下水流和污染物质量通量。FVPDM测试在六个地下水监测井中连续进行了48小时以上，以评估几个潮汐周期中的地下水流动力学。同时测量污染物浓度，从而可以计算污染物质量通量。研究强调了地下水非均质性的重要性，地下水通量范围为10 同时测量污染物浓度，从而可以计算污染物质量通量。研究强调了地下水非均质性的重要性，地下水通量范围为10 同时测量污染物浓度，从而可以计算污染物质量通量。研究强调了地下水非均质性的重要性，地下水通量范围为10^-7至10 ^-3 m / s。地下水通量监测可以对概念站点模型进行重大改进，包括在涨潮时未观察到地下水通量倒置这一事实。结果表明，特定监测井的污染物质量通量比被调查含水层的其他井高三个多数量级。该研究为优化进一步的现场调查和减轻风险措施提供了关键信息。