Theme: 06. Petroleum and Heavy Hydrocarbon Site Strategies

Topic Area: 6c. LNAPL Recovery/Remediation Technology Transitions

Formatted Title:

Insights from 100 Baildown Tests: Pace of Progress toward LNAPL Transmissivity Metrics

Background/Objectives:

LNAPL transmissivity measurements have become part of standard practice for remediation project managers. However, transmissivity testing is often done toward the end of a long-term project's active life-cycle, after LNAPL recovery measures have reached a probable endpoint. When used deliberately from the start of a project onward, transmissivity measurements can add significant value as both a threshold metric (providing an indication of where to begin or target removal efforts) and as an endpoint (providing an indication of when to stop removal efforts at a given location). This value will be illustrated through discussion of LNAPL assessment and recovery efforts conducted by CN at a rail yard site in Illinois.

Approach/Activities:

The data set developed for this LNAPL project is extensive, including a series of 20 baildown tests per well at five (5) wells – 100 tests total – conducted two to four times yearly from 2015 to 2022. Two automated LNAPL skimming systems were also maintained at these wells over this period. The skimming systems were used to reduce LNAPL mass, track LNAPL transmissivity/recoverability, and meet regulatory requirements for site closure. Trends observed in the data set, including the ranges of fluctuation over time, rates of change, and correlations of baildown test results to recovery efforts, will be discussed.

Results/Lessons Learned:

This discussion will focus on the following aspects of the data set. First, from a technical standpoint, the volume of data, particularly of repeat tests at specific locations, will be used to address common questions that are raised around transmissivity measurements; these include repeatability, variation among different calculation methods, and ranges of seasonal fluctuations. The pace of progress that can be expected from skimming (i.e., relationship between cumulative LNAPL removal and transmssivity reduction) will be discussed, along with the role of NSZD. Additionally, from a more general and strategic standpoint, the data will be discussed as an example of how transmissivity bears a strong real-world correlation to actual LNAPL recovery potential, and how a detailed data set collected on a single project can help improve outcomes on other sites with more limited resources and less opportunity for detailed study.

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Andy Pennington