Each month Tim Stark introduces a new technical topic for discussion and possible action. This month’s topic is: “Discussion of Subtitle D”. This topic generated significant discussion with the main “take-aways” being listed below:

1.       Discussion Topics for Subtitle D

·        Subtitle D became effective in the late 1990s and thus is over thirty years old.

·        Subtitle D is followed in Canada but some of Europe has more stringent requirements than Subtitle D, e.g., Germany

·        A discussion of Subtitle D was convened to identify various requirements that might be clarified or updated

·        States can implement their own requirements if they are equally or more stringent than Subtitle D, i.e., Federal = minimum level – states can have different requirements, e.g., CA, PA, NY

·        As a result, clarifications and/or modifications can be initiated at the state level

·        Only major change in Subtitle D since its promulgation is inclusion of: Project XL Bioreactor Landfill Projects as are search and development initiative

 ·        First requirement discussed involved the Flexible Membrane Liner component of a composite liner system – under “Design Criteria”, the requirement is: “the upper component must consist of a minimum 30-mil flexible membrane liner (FML).” FML components consisting of high density polyethylene (HDPE) shall be at least 60-mil thick. The FML component must be installed in direct and uniform contact with the compacted soil component.”

Some of the suggestions for clarification and/or updating of this requirement include:

-      Replace 60 mil HDPE with at least 40 mil thick unreinforced or reinforced LLDPE b/c better dimensional stability, i.e., “direct and uniform contact”

-      Change requirement to be engineering property based instead of polymer and thickness based, e.g., make FML requirement to be a performance specification like compacted soil component, i.e., saturated hydraulic conductivity “of no more than 1x10^-7 cm/sec”

-      Main advantage of HDPE = chemical resistance so require FML performance based on 9090 US EPA testing - immersion test with SW846 - https://www.epa.gov/hw-sw846/sw-846-test-method-9090a-compatibility-test-wastes-and-membrane-liners- Use landfill gas condensate for 9090 testing because more aggressive than bottom leachate

-       Can use different types of FMLs for the primary and secondary composite liner systems, e.g., 60 mil HDPE or 40 mil LLDPE for primary liner system and 30 mil or 40 mil thick FML (PVC, EIA, PP,LLDPE, WCPE, etc.) for secondary liner system

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