Significance and Use
4.1 Ebullition in sediment is a concern primarily when it causes EFT of NAPL/contaminants, resulting in potential risk to humans or ecological receptors; a perceptible water quality issue such as sheening, known as narrative water quality standards in some US states; or combinations thereof. Ebullition is also a key design consideration when capping has been selected as part of a site remedy. It is important to quantify the transport of gas and EFT of NAPL/contaminants from sediment to surface water to support decision making regarding risks, remedy selection, and remedy design.
4.2 Ebullition is common in the natural environment; however, when ebullition occurs in areas collocated with NAPL/contaminants, hydrophobic contaminants in the sediment matrix may adhere to the surface of gas bubbles. Additionally, petroleum hydrocarbons (PHCs) can contribute to methanogenesis through anaerobic degradation of PHCs (1). The upward migration of the bubbles may also result in redistribution of NAPL/contaminants from deeper sediment. NAPL/contaminant-coated gas bubbles released from the sediment may create sheen blossoms at the water surface, thereby enhancing contaminant transport to the surface water column from the sediments. In addition, the gas bubbles may resuspend contaminated surficial sediment in the water column (see Fig. 1).
4.3 Using flux chambers for measuring EFT of NAPL/contaminants is the primary activity addressed by this guide.
4.4 There are varying equipment options, deployment strategies, and data collection techniques available depending on the conditions of the sediment site. This guide provides instruction and considerations for addressing these conditions most appropriately.
4.5 This guide assumes that a CSM (Guide E3240) has been developed that includes the characterization of the nature and extent of NAPL/contaminants in sediment. This CSM would include an understanding of (1) the hydrological setting, (2) the physical and chemical characteristics of the sediment and water body, (3) the physical and chemical characteristics of the NAPL/contaminants, (4) mechanism(s) of NAPL/contaminant emplacement, (5) the physical extent of the NAPL/contaminant zone, and (6) the potential for human and ecological receptor exposure to NAPL/contaminants in sediment, or via NAPL/contaminant release to overlying surface water. The means and methods for collecting this information are not addressed in this guide.
4.5.1 This guide assumes that the CSM developed establishes that ebullition and the EFT of NAPL/contaminants occur at a magnitude and prevalence that warrants further evaluation. This is typically accomplished by performing ebullition surveys at the sediment site (Guide E3300). The CSM should be updated and refined as more information becomes available.
4.6 This guide is intended to be used as a reference for the design of, deployment of, and data collection from ebullition flux chambers. This guide is not intended to provide specific guidance on sediment site investigation, risk assessment, monitoring, or remedial action.
4.7 This guide may be used by various parties involved in a sediment site, including regulatory agencies, project sponsors, environmental consultants, site remediation professionals, environmental contractors, analytical testing laboratories, data reviewers and users, and other stakeholders.
4.8 This guide does not replace the need for engaging competent project planning and field personnel to evaluate ebullition and EFT of NAPL/contaminant fluxes from sediments. Activities necessary to design, build, and use flux chambers should be conducted by persons familiar with NAPL/contaminant-impacted sediment site characterization techniques, physical and chemical properties of NAPL/contaminants in sediments, fate and transport processes, remediation technologies, and sediment evaluation protocols. The users of this guide should consider assembling a team of experienced project professionals with the expertise to scope, plan, and execute data acquisition activities.
4.9 This guide is intended to be applicable at a broad range of local, state, tribal, federal (such as the Comprehensive Environmental Response, Compensation and Liability Act), or international jurisdictions, each with its own regulatory framework. As such, this guide does not provide a detailed discussion of the requirements or guidance associated with any of these regulatory frameworks, nor is it intended to supplant applicable regulations and guidance. The user of this guide will need to be aware of the regulatory requirements and guidance in the jurisdiction where the work is being performed.
4.10 The user of this guide should review the overall structure and components of this guide before proceeding with use, including:
| Section 1 | Scope |
| Section 2 | Referenced Documents |
| Section 3 | Terminology |
| Section 4 | Significance and Use |
| Section 5 | Flux Chamber Sampling Locations and Timing |
| Section 6 | Flux Chamber Design |
| Section 7 | General Procedures |
| Section 8 | Keywords |
| Annex A1 | Example Flux Chamber Design for Shallower Environments |
| Annex A2 | Example Flux Chamber Design for Deeper Environments |
| Annex A3 | Example Automated Flux Chamber Design for Deeper Environments |
| References |
|
Scope
1.1 This guide addresses the use of flux chambers for quantifying the transport of gas and non-aqueous phase liquids (NAPL)/contaminants from sediment to surface water by ebullition. Degradation of labile organic compounds in the sediment can generate biogenic gas that can migrate through the sediment into the overlying water column. Sediments that contain hydrophobic contaminants (such as NAPL) may adhere to the surface of the gas bubble resulting in ebullition-facilitated transport (EFT) and migration of NAPL/contaminants to the surface water or air–water interface. Ebullition can also result in resuspension of surficial sediment, enhancing contaminant transport to the water column. A detailed summary of biogeochemical and environmental factors that influence biogenic gas production and ebullition rate in sediments is presented in Guide E3300 and Zamanpour et al (1).2
1.2 Ebullition can be quantitatively measured by direct or indirect methods. Indirect measurement methods such as hydroacoustic equipment measure the density of gas bubbles in the water column to estimate ebullition rates. Indirect methods have the advantage of collecting data over large areas and provide better resolution on spatial variability of ebullition fluxes. Direct methods primarily employ a device to capture gas bubbles at the air-water interface, or within the water column.
1.3 In field studies, near-bottom measurements using anchored flux chambers have proven to better represent gas and NAPL/contaminant flux (2, 3, 4, 5) than have surface-based measurements. Although other methods can be utilized to measure ebullition and EFT of NAPL/contaminant fluxes, this guide focuses on the use of cone sampler style flux chambers. This guide describes the configurations and use of three types of flux chambers used in various environmental settings. However, other flux chamber designs have been successfully used, and the general principles presented in this guide may be applicable to the other designs (for example, 3, 6, 7, 8, 9).
1.4 Flux chambers can be advantageous in understanding sediment site rates for both ebullition and EFT of NAPL/contaminants by monitoring over time. Flux chambers can be deployed for several days or tide cycles to account for temporal variability. Measuring NAPL/contaminant flux near the sediment bed reduces water column impacts on the data. Flux measurements at the air–water interface can be impacted by factors such as wind, waves, and potential sources of contamination within the water column, while near-bottom measurements are less affected by these factors. Use of flux chambers as near-bottom samplers reduces the potential for degradation of NAPL/contaminant mass in the water column or at the water surface (or both) and allows for more precise deployment to a specific location with a defined area for calculating gas or NAPL/contaminant flux (or both). In contrast, sampling devices placed at the water surface may move around during deployment, resulting in flux data that are less representative of a defined area.
1.5 Units—The values are presented in SI units. Imperial units are provided parenthetically, as appropriate. Units in the annexes are provided in Imperial and metric units when commonly associated with standard materials.
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.7 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
