Johnston C D, Davis G B, Bastow T P, Woodbury R J, Rao P S C, Annable M D, Rhodes S
CSIRO Land and Water, Private Bag No. 5 PO, Wembley, WA 6913, Australia; School of Earth and Environment, University of Western Australia, Nedlands, WA 6009, Australia.
CSIRO Land and Water, Private Bag No. 5 PO, Wembley, WA 6913, Australia; School of Earth and Environment, University of Western Australia, Nedlands, WA 6009, Australia.
J Contam Hydrol. 2014 Aug;164:100-13. doi: 10.1016/j.jconhyd.2014.05.016. Epub 2014 Jun 14.
Management and closure of contaminated sites is increasingly being proposed on the basis of mass flux of dissolved contaminants in groundwater. Better understanding of the links between source mass removal and contaminant mass fluxes in groundwater would allow greater acceptance of this metric in dealing with contaminated sites. Our objectives here were to show how measurements of the distribution of contaminant mass flux and the overall mass discharge emanating from the source under undisturbed groundwater conditions could be related to the processes and extent of source mass depletion. In addition, these estimates of mass discharge were sought in the application of agreed remediation targets set in terms of pumped groundwater quality from offsite wells. Results are reported from field studies conducted over a 5-year period at a brominated DNAPL (tetrabromoethane, TBA; and tribromoethene, TriBE) site located in suburban Perth, Western Australia. Groundwater fluxes (qw; L(3)/L(2)/T) and mass fluxes (Jc; M/L(2)/T) of dissolved brominated compounds were simultaneously estimated by deploying Passive Flux Meters (PFMs) in wells in a heterogeneous layered aquifer. PFMs were deployed in control plane (CP) wells immediately down-gradient of the source zone, before (2006) and after (2011) 69-85% of the source mass was removed, mainly by groundwater pumping from the source zone. The high-resolution (26-cm depth interval) measures of qw and Jc along the source CP allowed investigation of the DNAPL source-zone architecture and impacts of source mass removal. Comparable estimates of total mass discharge (MD; M/T) across the source zone CP reduced from 104gday(-1) to 24-31gday(-1) (70-77% reductions). Importantly, this mass discharge reduction was consistent with the estimated proportion of source mass remaining at the site (15-31%). That is, a linear relationship between mass discharge and source mass is suggested. The spatial detail of groundwater and mass flux distributions also provided further evidence of the source zone architecture and DNAPL mass depletion processes. This was especially apparent in different mass-depletion rates from distinct parts of the CP. High mass fluxes and groundwater fluxes located near the base of the aquifer dominated in terms of the dissolved mass flux in the profile, although not in terms of concentrations. Reductions observed in Jc and MD were used to better target future remedial efforts. Integration of the observations from the PFM deployments and the source mass depletion provided a basis for establishing flux-based management criteria for the site.
基于地下水中溶解污染物的质量通量，越来越多地有人提议对受污染场地进行管理和封闭。更好地理解源质量去除与地下水中污染物质量通量之间的联系，将使这一指标在处理受污染场地时更容易被接受。我们在此的目标是展示在未受干扰的地下水条件下，如何将污染物质量通量分布的测量结果以及源自源区的总质量排放与源质量消耗的过程和程度联系起来。此外，这些质量排放的估计值是在应用根据场外井抽取的地下水水质设定的商定修复目标时得出的。本文报告了在西澳大利亚珀斯郊区一个溴化重质非水相液体（四溴乙烷，TBA；和三溴乙烯，TriBE）场地进行的为期5年的现场研究结果。通过在非均质层状含水层的井中部署被动通量计（PFM），同时估算了溶解溴化化合物的地下水通量（qw；L³/L²/T）和质量通量（Jc；M/L²/T）。在源区质量的69 - 85%主要通过从源区抽水去除之前（2006年）和之后（2011年），PFM被部署在源区正下游的控制平面（CP）井中。沿源区CP对qw和Jc进行的高分辨率（26厘米深度间隔）测量，使得能够研究重质非水相液体源区结构以及源质量去除的影响。源区CP上总质量排放（MD；M/T）的可比估计值从104克/天降至24 - 31克/天（减少了70 - 77%）。重要的是，这种质量排放的减少与该场地剩余源质量的估计比例（15 - 31%）一致。也就是说，质量排放与源质量之间存在线性关系。地下水和质量通量分布的空间细节也为源区结构和重质非水相液体质量消耗过程提供了进一步证据。这在CP不同部分不同的质量消耗率中尤为明显。尽管就浓度而言并非如此，但在剖面中，位于含水层底部附近的高质量通量和地下水通量在溶解质量通量方面占主导地位。观察到的Jc和MD的减少被用于更好地确定未来的修复工作目标。将PFM部署的观测结果与源质量消耗相结合，为建立基于通量的场地管理标准提供了依据。
