Applied NAPL Science Review

Sediment Sample Collection and Field Screening to Inform NAPL Mobility and Migration Evaluations 

Editor: Lisa Reyenga, PE

ANSR Scientific Advisory Board
J. Michael Hawthorne, PG, Board Chairman, GEI Consultants, Inc.
Andrew J. Kirkman, PE, BP Corporation North America
Robert Frank, RG, Jacobs
Paul Cho, PG, CA Regional Water Quality Control Board-LA
Randy St. Germain, Dakota Technologies, Inc.
Dr. Terrence Johnson, USEPA
Brent Stafford, Shell Oil Co.
Douglas Blue, Ph.D., Imperial Oil Environmental & Property Solutions
Natasha Sihota, Ph.D., Chevron
Kyle Waldron, Marathon Petroleum
Danny D. Reible, Professor at Texas Tech University

Applied NAPL Science Review (ANSR) is a scientific ejournal that provides insight into the science behind the characterization and remediation of Non-Aqueous Phase Liquids (NAPLs) using plain English. We welcome feedback, suggestions for future topics, questions, and recommended links to NAPL resources. All submittals should be sent to the editor.

DISCLAIMER: This article was prepared by the author(s) in their personal capacity. The opinions expressed in this article are the author’s own and do not necessarily reflect the views of Applied NAPL Science Review (ANSR) or of the ANSR Review Board members.

Sediment Sample Collection and Field Screening to Inform NAPL Mobility and Migration Evaluations 

Marcus Byker, PE and Kim Groff, PE – Ramboll 

The technical defensibility of an evaluation of NAPL mobility and migration in sediment hinges on the integrity of sample collection and field screening processes. Procedures to maximize the integrity of these sample collection and field screening phases are provided in this article. 

Introduction 
Non-aqueous phase liquid (NAPL) mobility and migration evaluations have been increasingly used to assess the need for active remediation at NAPL-affected sediment sites. The technical defensibility of a NAPL mobility and migration evaluation hinges on the integrity of sample collection and field screening processes that are integral to providing the required foundational data.  This article describes processes and procedures to maximize the integrity of sediment sample collection and field screening when characterizing NAPL-affected sediment. This approach is summarized by the flow chart provided in Figure 1.  

Figure 1 – Sediment Sample Collection and Field Screening Flow Chart 

Sample Collection
Pre-investigation planning activities should be completed consistent with ASTM E3268 to obtain available site data to inform selection of sample collection methodologies. Sediment sample collection methodologies may vary during different phases of NAPL mobility and migration evaluations. Initial characterization focuses on the collection of sediment samples to screen for NAPL presence. Accordingly, sampling methods such as Vibracore™ or sonic drilling that provide one continuous lined sample of the entire interval of interest are typically preferred. Subsequent characterization often focuses on the collection of undisturbed samples for pore-scale mobility assessments.  During this phase of investigation, sampling approaches prioritize the maximization of core recovery while minimizing pore structure disturbance (e.g., thin-walled samplers or modified operations of traditional sampling methods). ASTM E3268 provides additional insights on typical sediment coring methods for NAPL-affected sediment.

Field Screening

Field screening for the presence of NAPL in a sediment core is time-intensive and is best completed on a horizontal surface at a dedicated location in the field. Field screening begins by removing the liner  (cutting liner in two locations parallel to the core axis) with tools that minimally contact sediment (e.g., electric router or shears). 

Core Logging and Photography
Photographs are taken to document core condition prior to core logging. Best practices are to include a tape measure for scale, to ensure photographs document a consistent interval (e.g., two feet) and to photograph directly above the core at a consistent height, angle, and lighting condition.  Following photography, sediment classification and logging is completed in accordance with ASTM D2487/D2488 prior to assessing NAPL presence. 

NAPL Presence
Assessing presence and relative magnitude of NAPL in sediment may be challenging due to sediment heterogeneity, lack of visual contrast between NAPL and sediment, and presence of non-NAPL sheens.  Accordingly, visual observations should only be used to identify intervals of potential NAPL presence. NAPL presence is confirmed using secondary assessments. Similarly, elevated headspace results via photo-ionization detector (PID) should not be interpreted as an indicator of NAPL presence. PID results should solely be used to identify intervals of potential NAPL presence for further assessment.

Visual Observations of Potential NAPL
Historically, no industry-wide standards have been developed to visually log NAPL presence in sediments. Recently, ASTM E3281 developed a standardized methodology. Practitioners should consider ASTM E3281 when developing a clear, site-specific procedure for visually assessing NAPL presence. A site-specific procedure should, at a minimum, include categorizing a range of visual NAPL observations from least notable to most notable (e.g., none, sheen, blebs, oil-coated, oil-saturated).

NAPL may be difficult to identify visually in dark-colored sediment. A high-intensity light may aid in differentiating NAPL from sediment.  Additionally, ultraviolet (UV) light can cause NAPL containing polycyclic aromatic hydrocarbons (PAHs) to fluoresce, resulting in improved color contrast and can be useful as a supplement white light photography (Figure 2). Certain minerals and organic materials can fluoresce similarly to PAH-containing NAPLs and high molecular weight NAPLs may not fluorescence notably, so practitioners should validate fluorescence observations.

Figure 2 – Comparison of White and UV Light Field Photography

Secondary Assessment of NAPL Presence 
If potential NAPL is observed visually, a secondary assessment should be completed to confirm presence. Prior to selecting a preferred secondary assessment method for the duration of the project, it may be necessary to test a variety of approaches on initial cores to evaluate site-specific viability. Three common approaches are noted below and photos of each are provided in Figure 3:

• Glove Test – Firmly apply a nitrile gloved finger to the sediment interval of interest. Gently wipe the glove dry with a disposable towel. If NAPL is present, the glove will typically either be stained or remain coated with an oily film.
• NAPL FLUTe^TM – NAPL FLUTe^TM paper is a color-reactive, hydrophobic fabric. Press the FLUTe^TM paper against the sediment. If present, NAPL will sorb into the fabric and, depending on the type of NAPL, may release a dye that wicks through to the opposite side of the paper.
• Sediment-Water Shake Test – Place an aliquot of sediment in a clear, plastic sample jar with water. Close and shake the sample jar to release potential NAPL from the sediment matrix. If present, NAPL will typically form blebs, coat the sides of the jar or form a layer at the air-water interface. ASTM E3281 provides details on the implementation and evaluation of this test. Although not typically necessary for petroleum NAPLs, oil-soluble dyes can be added to the sediment-water shake test to aid in differentiating NAPL from suspended sediment.

Figure 3 – Examples of Secondary Assessments  of NAPL Presence

The secondary assessment results are documented in photos and field logs. The relative magnitude of NAPL observed in secondary assessments is categorized from least to most notable. Relative magnitude in secondary assessments is typically categorized by coverage of NAPL on the surface for each test method. Surface area observations can generally be grouped as 0-25%, 26-50%, 51-75% and 76-100% coverage. If potential NAPL presence is identified during visual assessments and confirmed during secondary assessments, it is reasonable to conclude that NAPL is present in the sediment in the interval of interest. 

Relationship of NAPL with Lithology
If NAPL presence is confirmed, the relationship of NAPL with lithology should be noted to inform emplacement evaluations (how NAPL may have originally migrated into the sediment), as described in ASTM E3248 and Johnson and Blue 2020. For example, discontinuous NAPL blebs may be a line of evidence for oil-particle aggregate emplacement. A distinct interval of oil-coated material within a comparatively coarse-grained material near the shoreline may indicate advective emplacement, with NAPL originating from an adjacent upland site. An oil-saturated observation independent of sediment structure may be a line of evidence for NAPL surface flow emplacement.

Next Steps

The project stakeholders evaluate the results of the initial characterization and field screening to determine if pore-scale NAPL mobility evaluations are warranted, or if sufficient characterization has been completed to proceed to risk assessment and feasibility study evaluations. Additional detail on a NAPL mobility and migration decision framework for NAPL-affected sediment sites is provided in ASTM E3248.

Conclusion

Following a well-defined framework like the one described in this article will provide consistent and reliable documentation of the presence and relative magnitude of NAPL, which allows for comparison of data from various phases of investigations. If site conditions and objectives warrant, this framework facilitates identification of representative sample intervals to undergo pore-scale NAPL mobility testing. Assurances on the representative nature of samples subjected to pore-scale mobility testing increases confidence in both the results of pore-scale mobility testing and the findings of the NAPL mobility and migration evaluation.  

A Word of Caution

Sampling sediment and completing field screening for NAPL presence is a time-intensive effort.  Successful implementation requires a clear understanding of project objectives, well-developed field procedures, and experienced field staff.  Depending on investigation size and site constraints, select activities discussed may need to be completed in a laboratory setting rather than in the field. Best practices shared are general recommendations and project-specific considerations may warrant modifications to methods discussed or consideration of alternate methods.

References

ASTM D2487 Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System), ASTM International, 100 Barr Harbor Drive, West Conshohocken, PA 19428. 

ASTM D2488 Standard Practice for Description and Identification of Soils (Visual-Manual Procedures), ASTM International, 100 Barr Harbor Drive, West Conshohocken, PA 19428. 

ASTM E3248 Standard Guide for NAPL Mobility and Migration in Sediment – Conceptual Models for Emplacement and Advection, ASTM International, 100 Barr Harbor Drive, West Conshohocken, PA 19428. 

ASTM E3268 Standard Guide for NAPL Mobility and Migration in Sediment—Sample Collection, Field Screening, and Sample Handling, ASTM International, 100 Barr Harbor Drive, West Conshohocken, PA 19428. 

ASTM E3281 Standard Guide for NAPL Mobility and Migration in Sediments – Screening Process to Categorize Samples for Laboratory NAPL Mobility Testing, ASTM International, 100 Barr Harbor Drive, West Conshohocken, PA 19428. 

Johnson, Jeffery and Blue, Doug. 2020. NAPL Mobility and Migration in Water Body Sediments – Contrasts with Land-Based Soils. Applied NAPL Science Review. Vol 8, Issue 4, December.

Research Corner

Preliminary Assessment of Chlorobenzenes Fate and Transport in Sediment Environment 

Sheik Mohammad Nomaan
Master of Science 
Texas Tech University 

Abstract:

Chlorobenzenes are omnipresent environmental pollutants due to their widespread use as a chemical intermediate and solvent. Sediment from a specific site was characterized for monochlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene and 1,2,4-trichlorobenzene contamination. Adsorption of Chlorobenzenes on commercially available sorbents such as activated carbon (AC), biochar, and organophilic clay were investigated for their potential use for in-situ management and active capping of Chlorobenzene-contaminated sediment. The results show that sorption on AC follows the Freundlich isotherm model whereas, organophilic clay, and biochar exhibit linear sorption properties. AC was found the most sorbing compared to biochar and organophilic clay by about two and four orders of magnitude, respectively. In addition, AC was most affected by natural organic matter (NOM) fouling; the effect of NOM on biochar and organophilic clay was minimal. Data from these studies were used to simulate Chlorobenzenes flux under existing field conditions, as well as, the performance of caps amended with AC, biochar, and organophilic clay. The modeling was done for diffusion control, diffusion-advection (Darcy’s velocity 1 cm/day) and tidal flow system (tidal cycle 12 hours 25 minutes with maximum tidal flow of 100 cm/yr). The effect of bioturbation was also considered. Simulation results suggest that the system with the presence of diffusion-advection is the most critical in terms of flux breakthrough from caps. Only AC amended caps were found to be effective to contain the contaminants for considerable amount of time. The breakthrough time for 15 cm AC layer with 15 cm sand on top and 50% AC amended sand cap is simulated to be about 100 years.

 The primary objective of ANSR is the dissemination of technical information on the science behind the characterization and remediation of Light and Dense Non-Aqueous Phase Liquids (NAPLs). Expanding on this goal, the Research Corner has been established to provide research information on advances in NAPL science from academia and similar research institutions. Each issue will provide a brief synopsis of a research topic and link to the thesis/dissertation/report, wherever available.

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