MassDEP issued its long-awaited final policy on how to close LNAPL sites under revised 2014 regulations on February 19, 2016. The final policy, “Light Nonaqueous Phase Liquid and the MCP: Guidance on Site Assessment and Closure,” ends a long period of public comment and revision to the guidance that began in July 2014 with the first public review draft.

The guidance is targeted at Massachusetts Licensed Site Professionals (LSPs) who perform site remediation work under the Massachusetts regulatory scheme and provides an overview of LNAPL – Light Nonaqueous Phase Liquid – behavior in the environment and describes tools that can be used to assess LNAPL, how specific lines of evidence can be utilized to develop a site-specific conceptual site model, and how to use these lines of evidence to comply with the state regulations. The guidance emphasizes that there is inherent complexity and uncertainty in assessing LNAPL sites and recommends a multiple lines of evidence approach. The guidance continues to provide as an option for petroleum sites a simplified approach that is presumptively compliant with the state requirements.

The revised regulations require a deed restriction known as an activity and use limitation (AUL) if NAPL with Micro-Scale Mobility remains in place. “NAPL with Micro-Scale Mobility” refers to NAPL in the environment with a footprint that is not expanding but which is visibly present and has the potential to move short distances, including to pool in an excavation. The guidance clarifies that despite the regulatory language, MassDEP does not expect an AUL to be recorded for those sites with de minimis levels of LNAPL (less than ½ inch). However, because the regulations do not provide for a de minimis exception, MassDEP will exercise “enforcement discretion” in those cases. MassDEP explains that AULs should instead be recorded for those sites with “conditions that are more likely to warrant measures to manage NAPL as the result of future excavation or other activities affecting subsurface conditions.” See Guidance, page 25.