Standard Guide for NAPL Mobility and Migration in Sediments—Use of Ebullition Flux Chambers

Importancia y uso:

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

 

Subcomité:

E50.04

Volúmen:

11.05

Palabras clave:

field survey; gas quantification; gas trap; hydrocarbon degradation; methane; remediation; risk assessment; sediment capping; sediment contamination; surface water;