Natural Attenuation of Groundwater Contaminant Plumes in Riverbeds: Control of Hyporheic Zone Mixing

河床中地下水污染物羽流的自然衰减：潜流带混合的控制

• 批准号: 1437021
• 负责人: Erich Hester
• 金额: $ 33万
• 依托单位: Virginia Polytechnic Institute and State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-08-01 至 2020-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1437021&HistoricalAwards=false
• 关键词: Natural; Attenuation; Groundwater; Contaminant; Plumes

1437021HesterNatural Attenuation of Groundwater Contaminant Plumes in Riverbeds: Control by Hyporheic Zone MixingContaminated groundwater eventually exits to surface water including streams, rivers, and estuaries, posing a threat to human and ecological health. In fact, the US EPA found that half of identified hazardous waste sites impact surface water. Excess nutrients also frequently well-up into rivers in agricultural areas. As groundwater contaminants move toward rivers, they eventually cross through the hyporheic zone beneath and adjacent to rivers, where mixing of surface water and groundwater in shallow sediments creates conditions that are often far more reactive than in overlying surface water or deeper groundwater. Contaminants that have degraded little in up-gradient aquifers can degrade up to 100 % once they reach the hyporheic zone (hyporheic natural attenuation). Yet upwelling contaminants often require mixing with reactants from surface water in the hyporheic zone in order to capitalize on this great potential for hyporheic natural attenuation. The results of this project will transform groundwater remediation, risk assessment, and total maximum daily loads to address ecological, human health, and human recreational risks and impairments due to groundwater contamination intersecting surface water. Knowing how hyporheic natural attenuation potential varies with hydrologic and geomorphic conditions will allow calculating the amount of hyporheic natural attenuation expected at specific sites. The proposed project will also lead to subsequent projects addressing specific contaminants and engineering approaches to enhance hyporheic natural attenuation, such as carbon amendment by riparian reforestation. These lab experiments will serve as excellent tools for students in the PI's surface water-groundwater class to visualize hyporheic zone processes in ways that are otherwise not possible. The PI will work with the School of Engineering's Center for the Enhancement of Engineering Diversity to recruit under-represented undergraduates to participate in project research.Controls on such mixing have received almost no attention, yet recent work shows that such mixing is highly sensitive to hydrologic conditions. To tap the potential for hyporheic natural attenuation, it is necessary to better understand such controls on hyporheic mixing, and better distinguish mixing-dependent reactions from related processes such as dilution. This will allow prediction of how hyporheic natural attenuation varies among rivers of differing hydrologic, climatic, and biogeochemical conditions; among different types of contaminants; across time scales such as storms and seasons; and in response to engineered enhancements. This project will be the first to examine how the behavior of upwelling contaminants is affected by realistically complex hydrologic flow paths in the hyporheic zone. Both the tracer and biogeochemical portions of this study are therefore fundamentally novel. For example, this project will produce the first measurements of local dispersivities and first estimates of microbial growth parameters for riverine sediment subject to realistic hyporheic zone flow conditions. Such parameters are required for a wide range of biogeochemical reaction modeling of hyporheic zone processes. This project will also be groundbreaking methodologically, including the first laboratory simulation of upwelling of tracer and mixing with surface water advecting through the hyporheic zone. By focusing on broadly relevant processes like transport and transformation of tracers, oxygen, and carbon, this project will shed light on transformations of a wide range of pollutants in the hyporheic zone, including metals, organic contaminants that act as electron acceptors (e.g., chlorinated solvents), and organic contaminants that act as electron donors (e.g., petroleum hydrocarbons). This work will support future studies that evaluate other electron acceptors (e.g., nitrate, iron), specific contaminants, and entrained particular carbon, as well as extension of these experiments to larger lab experiments (flowing flume) and field sites.

1437021地下水污染羽流在河床中的自然衰减：由地下水位带混合控制受污染的地下水最终进入地表水，包括小溪、河流和河口，对人类和生态健康构成威胁。事实上，美国环保局发现，在已确定的危险废物场地中，有一半会影响地表水。过量的营养物质也经常流入农业区的河流。当地下水污染物向河流移动时，它们最终会穿过河流下方和邻近的地下潜流带，在那里，浅层沉积物中的地表水和地下水混合产生的条件往往比上覆地表水或更深的地下水更具反应性。在上坡含水层中几乎没有降解的污染物，一旦到达潜水带(潜水自然衰减)，最高可降解100%。然而，上升的污染物通常需要与潜流带地表水中的反应物混合，以利用潜流自然衰减的巨大潜力。该项目的成果将改变地下水修复、风险评估和总最大日负荷，以解决由于地下水污染与地表水交叉造成的生态、人类健康和人类娱乐风险和损害。了解潜水自然衰减势如何随水文和地貌条件变化，将有助于计算特定地点预期的潜水自然衰减量。拟议的项目还将导致针对特定污染物的后续项目，以及加强水下自然衰减的工程方法，例如通过河岸重新造林来修正碳。这些实验室实验将为PI地表水-地下水课程的学生提供极好的工具，让他们以其他方式无法实现的方式可视化潜流带过程。PI将与工程学院的工程多样性促进中心合作，招募代表不足的本科生参加项目研究。对这种混合的控制几乎没有受到关注，但最近的研究表明，这种混合对水文条件高度敏感。为了挖掘低渗透自然衰减的潜力，有必要更好地了解这种对低渗透混合的控制，并更好地区分混合依赖反应和相关过程，如稀释。这将允许预测不同水文、气候和生物地球化学条件的河流、不同类型的污染物、不同时间尺度(如风暴和季节)的地下自然衰减如何变化，以及对工程增强的响应。该项目将首次研究潜流带中实际复杂的水文流动路径如何影响上升流污染物的行为。因此，这项研究的示踪剂和生物地球化学部分从根本上来说都是新颖的。例如，该项目将首次测量河流沉积物的局部分散性，并首次估计受现实潜流带水流条件制约的河流沉积物的微生物生长参数。这样的参数对于对潜流带过程进行广泛的生物地球化学反应建模是必需的。该项目还将在方法上具有开创性，包括首次在实验室模拟示踪剂上升流并与流经潜流带的地表水混合。通过关注广泛相关的过程，如示踪剂、氧和碳的传输和转化，该项目将阐明各种污染物在潜流带中的转化，包括金属、作为电子受体的有机污染物(例如氯化溶剂)和作为电子供体的有机污染物(例如石油碳氢化合物)。这项工作将支持未来评估其他电子受体(如硝酸盐、铁)、特定污染物和夹带特定碳的研究，以及将这些实验扩展到更大的实验室实验(流动水槽)和现场。