Department of Geology and Environmental Geosciences, College of Charleston, 66 George St., Charleston, SC 29424, USA.
Y-12 National Security Complex, US Department of Energy, Oak Ridge, TN 37831, USA.
Sci Total Environ. 2017 Jan 1;575:247-257. doi: 10.1016/j.scitotenv.2016.09.222. Epub 2016 Oct 12.
We assessed whether coal tar present in contaminated streambed sediments can be mobilized by flood events and be re-deposited in an adjacent floodplain. The study was conducted within a contaminated urban stream where coal tar wastes were released into a 4-km reach from a coke plant in Chattanooga, Tennessee, USA. Sediments containing visible amounts of coal tar were dredged from the streambed in 1997-98 and 2007 as part of a cleanup effort. However, post-dredging sampling indicated that very high concentrations of polycyclic aromatic hydrocarbons (PAHs) remained in streambed sediments. Sampling of sediments in the floodplain at two sites downstream of the coke plant indicated that high concentrations of PAHs were also present in the floodplain, even though no coal tar was observed in the samples. Age-dating of the floodplain sediments using Cs indicated that peak PAH concentrations were contemporary with coke plant operations. While there was little or any direct contamination of the floodplain sediments by coal tar, sediment contamination was likely a result of deposition of suspended streambed sediments containing sorbed PAHs. A flood model developed to delineate the extent of flooding in various flood recurrence scenarios confirmed the potential for contaminated streambed sediments to be transported into the adjacent floodplain. It was hypothesized that coal tar, which was visibly "sticky" during dredging-based stream cleanup, may act as a binding agent for streambed sediments, decreasing mobility and transport in the stream. Therefore, coal tar is likely to remain a persistent contaminant source for downstream reaches of the stream and the adjacent floodplain during flood events. This study also showed that even after excavation of tar-rich streambed sediments, PAH contaminated non-tarry sediments may be a source of flood-related contamination in the adjacent flood plain. A conceptual framework was developed to delineate specific mechanisms that can mobilize contamination from stream sources.
我们评估了受污染河床沉积物中的煤焦油是否会在洪水事件中被迁移，并重新沉积在相邻的洪泛区。该研究在美国田纳西州查塔努加市的一家炼焦厂将煤焦油废物排放到 4 公里长的一段受污染城市溪流中进行。1997-98 年和 2007 年，作为清理工作的一部分，从河床中疏浚了含有可见量煤焦油的沉积物。然而，疏浚后的采样表明，河床沉积物中仍然存在非常高浓度的多环芳烃（PAHs）。在炼焦厂下游的两个洪泛区地点对沉积物进行采样表明，即使在样本中未观察到煤焦油，洪泛区也存在高浓度的 PAHs。使用 Cs 对洪泛区沉积物进行年龄测定表明，PAH 的峰值浓度与炼焦厂的运营同期。虽然洪泛区沉积物几乎没有或没有直接受到煤焦油的污染，但沉积物的污染可能是由于含有吸附 PAHs 的悬浮河床沉积物的沉积所致。为描绘各种洪水重现情景下的洪水范围而开发的洪水模型证实，受污染的河床沉积物有可能被输送到相邻的洪泛区。假设在基于疏浚的溪流清理过程中可见的“粘性”煤焦油可能充当河床沉积物的结合剂，从而降低其在溪流中的流动性和迁移性。因此，在洪水事件期间，煤焦油很可能仍然是溪流下游和相邻洪泛区的持久性污染源。这项研究还表明，即使挖掘了富含焦油的河床沉积物，受 PAH 污染的非焦油沉积物也可能成为相邻洪泛区与洪水相关的污染源。提出了一个概念框架，以划定可以从溪流源中迁移污染的具体机制。
