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This easy-to-read brochure offers answers to practical and technical questions about cost-effective management, cleanup or closure of sites with groundwater impacted by light non-aqueous phase liquids (LNAPL), such as petroleum hydrocarbons.

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Bulletin 18: Managing Risk at LNAPL Sites - Frequently Asked Questions, 2nd Edition, May 2018

Frequently Asked Questions, 2nd Edition - File Size: 4 MB (updated May 8, 2019 to correct the figure on page 48)

Frequently Asked Questions, 2nd Edition - File Size: 5 MB (Chinese)

Frequently Asked Questions, 2nd Edition - File Size: 40 MB (Español)

Bulletin 18: Answers to Frequently Asked Questions About Managing Risk at LNAPL Sites, 1st Edition, May 2003

Low Resolution - File Size: 316 KB
High Resolution - File Size: 5.2 MB

The Questions (2nd Ed.):


  • What is LNAPL?
  • What is the biggest new idea that will affect LNAPL management in the future?
  • Why is it important to recognize that LNAPL releases evolve with time?
  • Are we making progress with LNAPL releases?

Critical Concepts

  • What happens when LNAPL is released?
  • How is LNAPL distributed in the subsurface, and why is it important? Why do changes in water levels complicate matters?
  • What can we learn from LNAPL thicknesses in wells?
  • What causes the complex behavior of LNAPL observed in wells? What can we learn from water quality in wells?
  • What can be achieved with hydraulic recovery?
  • What can be achieved with soil vapor extraction?
  • When are LNAPL bodies stable?
  • What makes cleanup of LNAPL releases so challenging?

Emerging Ideas

  • What drives natural source zone depletion?
  • What is the best way to measure natural source zone depletion rates?
  • What is LNAPL recovery to the extent practicable?
  • When is vapor intrusion an issue?
  • Why are sheens a big issue?
  • What causes sheens?

Current Research

  • Can we enhance NSZD rates?
  • How long will LNAPL and LNAPL-related impacts to groundwater persist?
  • Can temperature be used to monitor LNAPL sites?
  • Are there viable alternatives to dredging of hydrocarbon impacted sediments?
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