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赫斯特自然衰减的地下水污染羽流在河床：控制由低流区混合污染的地下水最终退出地表水，包括溪流，河流和河口，对人类和生态健康构成威胁。事实上，美国环保署发现，一半的已确定的危险废物场地影响地表水。过量的营养物质也经常流入农业地区的河流。随着地下水污染物向河流移动，它们最终穿过河流下方和附近的潜流区，在浅层沉积物中地表水和地下水的混合创造了比上覆地表水或更深层地下水更活跃的条件。在高梯度含水层中几乎没有降解的污染物，一旦到达潜流带，可降解达100%（潜流自然衰减）。然而，上涌的污染物往往需要与来自地表水的反应物在潜流区混合，以利用这种巨大的潜力，为潜流自然衰减。 该项目的结果将改变地下水修复，风险评估和总最大日负荷，以解决生态，人类健康和人类娱乐的风险和损害，由于地下水污染交叉地表水。了解潜流自然衰减潜力如何随水文和地貌条件变化，将允许计算特定地点预期的潜流自然衰减量。拟议的项目还将导致随后的项目，解决具体的污染物和工程方法，以加强潜流自然衰减，如通过河岸重新造林的碳修正。这些实验室实验将作为PI地表水-地下水课程的学生的优秀工具，以其他方式不可能的方式可视化潜流带过程。PI将与工程学院的工程多样性增强中心合作，招募代表性不足的本科生参与项目研究。对这种混合的控制几乎没有得到关注，但最近的工作表明，这种混合对水文条件非常敏感。为了挖掘潜流自然衰减的潜力，有必要更好地理解这种对潜流混合的控制，并更好地区分混合依赖反应与稀释等相关过程。这将允许预测不同水文，气候和地球化学条件的河流之间的潜流自然衰减如何变化;不同类型的污染物之间;跨时间尺度，如风暴和季节;并响应工程增强。这个项目将是第一个研究上涌污染物的行为是如何受到现实复杂的水文流动路径在潜流区。因此，这项研究的示踪剂和地球化学部分都是新颖的。例如，该项目将首次测量当地分散性，并首次估计河流沉积物在现实的潜流区流动条件下的微生物生长参数。这样的参数是需要广泛的地球化学反应模拟的潜流带过程。该项目在方法上也将是开创性的，包括第一次在实验室模拟示踪剂的上涌和与通过潜流区平流的地表水的混合。通过关注广泛相关的过程，如示踪剂，氧气和碳的运输和转化，该项目将揭示潜流区各种污染物的转化，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，石油烃）。这项工作将支持未来的研究，评估其他电子受体（例如，硝酸盐、铁）、特定污染物和夹带的特定碳，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。