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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Each month Tim Stark introduces a new technical topic for discussion and possible action. This month’s topic is: “Use of Geomembranes and Geosynthetics in Energy Applications”. This topic generated significant discussion with the main “take-aways” being listed below:
1. Use of Geomembranes and Geosynthetics in Energy Applications
Hydropower
Solar Power – white reflective geomembranes below solar panels increase solar capture
o San Antonio Landfill – fPP-R cap and acres of solar panels – TVA 300 acres site
o Closure turf – solar panels on artificial turf instead of on the ground – sure grip geomembrane from AGRU holds panels inplace
o Solar panels on rails so they can be placed on 3:1 slopes – flat panels only on crest - https://watershedgeo.com/products/powercap/
Pumped Storage Hydropower (PSH) projects –
o Use geomembrane for bottom liner system but flow velocities are difficult
o Use floating cover to reduce evaporation
o Mt. Elbert PSH project = bottom liner system with18” soil cover to project geomembrane from high flow velocities– 240 acres – installedin 1980 - chlorinated polyethylene (CSPE) geomembrane
o Traditional pumped storage liner system =asphalt and concrete
o Research topic – conduct 40-year costanalysis for Mt. Elbert PSH project – initial cost v. decrease loss of water &no seepage into old landslide in hillside b/c of slope instability concerns
o Forebay/water conveyance projects – typically use asphalt or concrete liner system, which will eventually crack and leak –geomembrane installed to replace cracked compacted clay liner
Gas collection in landfills – near surface gas collection to capture methane
Coalfired powerplants – bottom liner systems – single composite bottom liner system– GM & clay
Oil and gas applications – geomembranes
Secondary containment – oil and gas
Wind Power = application uncertain for geosynthetics
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Electrical Leak Location Surveys with Flexible Geomembranes
Electrical Leak Location Surveys (ELLSs) can be performed with flexible geomembranes, i.e., non-HDPE geomembranes; if an HDPE geomembrane is used, it should be white to reduce wrinkling, which is discussed below:
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Best Practices for Dealing with Temperature Fluctuations include:
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Each month Tim Stark introduces a new technical topic for discussion and possible action. This month’s topic is: “Longevity of Geonets and Geotextiles”. This topic generated significant discussion with the main “take-aways” being listed below:
1. Longevity of Geonets
· Little performance specifications
· No longer using an AOS requirement; no FOS
· Civil v. Environmental grade geotextiles -
· What is happening under the geomembrane?
· Research – check embedment of geonet on GM without a cushion GT – when to transition to a composite
· Industry moving to composites from sands and gravels – so check compatibility of nets with flexible GMs – Brian and Rohit webinar on net and 40 mil GM
2. Longevity of Geotextiles
· Little performance specifications
· No longer using an AOS requirement; no FOS
· Civil v. Environmental grade geotextiles -
· Are geotextiles chemically resistant to liquidsbeing contained?
· Kerry Rowe – double composite liner system – GCLgeotextile decomposed
· No specs to excavate and check the geonet andgeotextile
· Intercell berm excavations look good –
· Compatibility b/t net and GTs – Polyester & Polypropylene GTs -
· Compatibility b/t net and GMs – use same resin for both – no spec requiring same resin as GM
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Leak Testing Mechanical Attachments
- Cannot conduct electronic leak locate survey near metalattachments because of interference so need some other type of testing ofattachments
- Place ballast tubes around penetration, inject airbelow geomembrane, soap the attachment, and watch for bubbles along or aroundattachment
- Thermal imaging – not tried yet but possibly effective onsunny day to measure cooler air being pumped below geomembrane and exiting atleak(s) along attachment
- Vacuum below the geomembrane in tank or attachment and listen for vacuum sound along attachment
- Vacuum Acoustic Leak Identification (VALID) method – apply vacuum between primary and secondary geomembranes and listen for vacuum soundalong attachments; tests both geomembranes; the top surface of the geomembrane is scanned with ultrasonic microphones that can detect distinctive sounds of a vacuum leak.
- Smoke Test – smoke exits at attachment surrounded by ballast tubes
- Spark test with material embed but cannot be used at landfills and oil and gas sites
- Vacuum boxes for strips and corners but limited because not straight segments for box
- Dye test – divers places dye along attachment or concrete joint and see if dye disappears into attachment or crack (see video)
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- Changes in liquid/water level but must show that change in level is not due to evaporation
- Seepage around pond/containment facility
- Contaminant detection in groundwater monitoring well(s)
- Pressure transducer – placed in stilling well on opposite sides or in LDZ sump show different liquid pressures
- Add chloride to liquid and conduct subsequent geophysical testing to detect chloride outside of facility
- Add dye to liquid and monitor adjacent wells
- Measure flow in Leak Detection Zone (LDZ) if present
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