Chapman Steven W, Parker Beth L, Cherry John A, Aravena Ramon, Hunkeler Daniel
Department of Earth Sciences, University of Waterloo, 200 University Avenue West, Waterloo, Ontario Canada N2L 3G1.
J Contam Hydrol. 2007 May 14;91(3-4):203-32. doi: 10.1016/j.jconhyd.2006.10.006. Epub 2006 Dec 19.
A field investigation of a TCE plume in a surficial sand aquifer shows that groundwater-surface water interactions strongly influence apparent plume attenuation. At the site, a former industrial facility in Connecticut, depth-discrete monitoring along three cross-sections (transects) perpendicular to groundwater flow shows a persistent VOC plume extending 700 m from the DNAPL source zone to a mid-size river. Maximum TCE concentrations along a transect 280 m from the source were in the 1000s of microg/L with minimal degradation products. Beyond this, the land surface drops abruptly to a lower terrace where a shallow pond and small streams occur. Two transects along the lower terrace, one midway between the facility and river just downgradient of the pond and one along the edge of the river, give the appearance that the plume has strongly attenuated. At the river, maximum TCE concentrations in the 10s of microg/L and similar levels of its degradation product cis-DCE show direct plume discharge from groundwater to the river is negligible. Although degradation plays a role in the strong plume attenuation, the major attenuation factor is partial groundwater plume discharge to surface water (i.e. the pond and small streams), where some mass loss occurs via water-air exchange. Groundwater and stream mass discharge estimates show that more than half of the plume mass discharge crossing the first transect, before surface water interactions occur, reaches the river directly via streamflow, although river concentrations were below detection due to dilution. This study shows that groundwater and surface water concentration measurements together provide greater confidence in identifying and quantifying natural attenuation processes at this site, rather than groundwater measurements alone.
对表层砂质含水层中三氯乙烯羽状物的现场调查表明，地下水与地表水的相互作用对羽状物的明显衰减有强烈影响。在康涅狄格州的一个原工业设施所在地，沿垂直于地下水流的三个横截面（样带）进行深度离散监测，结果显示有一个持续存在的挥发性有机化合物羽状物从重质非水相液体源区延伸700米至一条中型河流。在距离源区280米的样带上，三氯乙烯的最高浓度在数千微克/升，降解产物极少。在此之外，地表突然下降到一个较低的阶地，那里有一个浅池塘和一些小溪流。沿着较低阶地的两条样带，一条在设施和河流之间的中途位置，正好在池塘下游梯度处，另一条沿着河边，这使得羽状物看起来有强烈的衰减。在河流处，三氯乙烯的最高浓度在数十微克/升，其降解产物顺式二氯乙烯的浓度水平与之相似，这表明从地下水直接向河流的羽状物排放可以忽略不计。尽管降解在羽状物的强烈衰减中起作用，但主要的衰减因素是部分地下水羽状物排放到地表水（即池塘和小溪流）中，在那里一些物质通过水 - 气交换而损失。地下水和溪流的质量排放估计表明，在与地表水相互作用发生之前，穿过第一条样带的羽状物质量排放中超过一半直接通过溪流流入河流，尽管由于稀释河流中的浓度低于检测限。这项研究表明，地下水和地表水浓度测量相结合，比仅进行地下水测量能更有信心地识别和量化该场地的自然衰减过程。
