Smarter Site Cleanup with LNAPL Transmissivity Assessments
Authored by: Rebecca Graustein, LSRP & Martin J. Hamper, PG
When a site is contaminated with light non-aqueous phase liquids (LNAPL), like oil, deciding how to clean it up, or whether cleanup is even feasible, can be complex. Transmissivity testing offers a science-based approach to guide these decisions. Rather than relying on outdated methods or simply measuring how thick the LNAPL appears in a monitoring well, LNAPL transmissivity testing helps determine how easily LNAPL can realistically be recovered.
Regulatory agencies increasingly recognize transmissivity as a key metric, especially when testing shows that remaining contamination is no longer recoverable. This makes transmissivity testing a powerful tool for evaluating cleanup options and satisfying site closure requirements, ultimately saving time, reducing costs, and avoiding unnecessary cleanup.
What is LNAPL Transmissivity?
LNAPL transmissivity measures how easily LNAPL flows through an aquifer. It reflects the combined influence of:
- The soil or rock stratigraphy
- The physical characteristics of the liquid (like density and viscosity)
- How much LNAPL is present in the subsurface (i.e., saturation profile)
Generally, higher transmissivity means the liquid is more mobile and easier to recover. Unlike in-well LNAPL thickness measurements, which can be misleading, transmissivity provides a more accurate picture of whether cleanup is feasible.
Why it Matters for Site Closure
Across the US, state regulatory agencies are increasingly allowing the use of transmissivity testing as a tool to help determine whether a site can be closed. The Interstate Technology Regulatory Council (ITRC) notes that transmissivity values between 0.1 and 0.8 ft²/day typically indicate that LNAPL is no longer recoverable even if some product remains in the well. Demonstrating LNAPL transmissivity reduction through field testing can satisfy closure requirements and help transition a site from active remediation to long-term monitoring.
How Transmissivity Testing Supports Smarter Decisions
Transmissivity testing can be used to:
- Establish baseline conditions before remediation
- Estimate potential LNAPL recovery rates
- Evaluate whether a recovery system or alternative method is appropriate
- Support system optimization or shutdown
- Build a strong case for site closure or transition to natural attenuation
How Roux Can Help
The Roux team brings extensive expertise in designing and executing transmissivity assessment programs that have been incorporated into approved regulatory documents, achieving closure, or establishing a framework to achieve closure with LNAPL still present. With the right data, you can move confidently from ongoing remediation to a successful site end point. Through employing Roux’s experts to utilize transmissivity testing, you can make more well-informed decisions on a quicker path to site closure. Reach out to us for more information below.
