ASTM E3447 : 24

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.