- Billy Nichols of the Philadelphia Water Department (PWD) attended and discussed proposed regulations for geomembranes used in stormwater containment applications.
- Billy is in the water resources team & working on green infrastructure systems that intercepts storm water before water reaches storm water system
- Stormwater Detention System is a system that retains stormwater until stormwater system can handle the flow
- Detention Systems are fully-lined with a geomembrane - The geomembrane liner system is installed to protect nearby basements, prevent sinkholes, etc.
- Use of geomembranes is new to PWD
- PWD tested completed systems since 2020 and some of the systems are not holding water => the test involves filling the completed system with fire hydrant water before placing it in service
- PWD is running leak test after stone installation – to reflect stone placement and stone weight on geomembrane with full weight of water
- However, it is difficult to find leak with stone in-place = must vacuum out stone to locate and fix the leaks
- Old Allowable Leakage rate = 1 inch/hour = f(size) = ?
- Moving to new Allowable Leakage rate of < 0.5 inch/hour
- 143 systems and 216 tests performedso far and 73 systems failed on first filling or testing
- 70% of systems pass initial leakage test (see figure below)
- Leakage mostly occurring at:(1) Pipe penetrations, (2) failed extrusion welds in a tight space, and (3)holes or tears in the geomembrane
- Extrusion Welds = common failure points
- PWD thinking thicker material is better because more material to weld to
- PWD Specification says use fusion welds where possible to minimize extrusion welds
- PWD considering requiring cushion geotextiles on side walls as well as bottom on storage chamber
- Applications: storm trench (PWD and public projects) v. storage chambers (private projects)
- Storm trench used within roadway Right-of-Way = public system not private system
- Primarily 40 mil and 60 mil thick HDPE geomembranes have been used for storm trenches
- PWD Weld Testing = ?
- spark, vacuum box, and air channel testing specified but tests may not be performed
- Suggestions:
- A 12 ounce/yd cushion geotextile is a cost-effective protection for the geomembrane
- Field fabrication should be considered to minimize field extrusion welds
- Atlantic Lining Company(ALCO) has installed many of these systems– Tim Rafter of ALCO shared his experiences with Philly contractors, different geomembrane polymers, and system water testing
- PWD Testing = ? PWD water test not ASTM but developed to test final product
- PVC tube installed in stormwater trench to measure water level every five minutes and filled system sits overnight to measure leakage rate
- Tim Rafter thought a 30 mil GM could not stand up to Philly contractors and thus thought a thicker geomembrane was a good idea
- Terry Sheridan of Geo-Storage described some of his geomembrane experiences designing subsurface storage chambers
- Terry is only working on private projects so new PWD regs don’t impact his private projects
- Terry thinks 40 mil PVC Geomembrane and a thick cushion geotextile are adequate for stormwater containment systems
- Terry suggested using more flexible geomembrane due to better puncture resistance, pipe boot welding, andlarger tensile elongation, which is good with a rising groundwater level
Suggestions for Specification of CQA and Welding Certifications
- Add certifications to FGI Material Specifications
- FGI Members add to your specifications
- For example, make it similar to electrical certifications for construction
- How do we get regulators involved in the certification process?
- OEPA Landfill Rules – IAGI CWT was considered but couldn’t require IAGI over another provider – so specified a minimum level of experience = 1 M sq ft of liner experience for Junior Seamer &over 5 M sq ft for Master Seamer
- Fracking industry has limited requirements and many problems
- Most military and government specs require a minimum square footage of liner experience
- In PA they require training by DemTech or the installer = orientation classes not a certification class and exam
- Iowa DNR – including another entity's rule into Iowa’s Rule is difficult because it could change = hard to stay current so leave it to consultants to specify the certification
- Certification could result in liability
- FGI Create Drop-In Specifications for Consultants to download from FGI website and include list appropriate lab and field ASTM Test Methods
- Detail specification is at engineering level not regulatory level so target engineering firms
- How do we contact all state regulators? Instead contact ASTWMO, SWANA, AWWA, etc. and inquire about including specification
- CQA Course and Certification is do able but inspection is more difficult & probably requires regulatory involvement – certification does increase cost but inspection increases cost much more, especially for full-time inspection – have regulators consider requiring or recommending certification and/or inspection, especially full-time inspection
- OEPA – has required 3rdparty CQA for a long time – right now CQA firm is hired by the landfill; future may have CQA paid by landfill but CQA firm reports to OEPA directly; another option is having CQA firm report to the contractor not the landfill owner
- Another option is landfill provides a pool of 3rd party CQA firms and OEPA selects the firm or firm is randomly selected so same company cannot keep doing the CQA for the same landfill
- It may need a national requirement – USEPA – White Paper on Subtitle D updating and clarifications recommends adding CQA requirement to Subtitle D; Ed Silva will contact GMA about the status of presenting the White Paper to the USEPA
Each month Tim Stark introduces a new technical topic for discussion and possible action. This month’s topic is: “Terminology and Applications for Used Geomembrane Polymers”. This topic generated significant discussion with the main “take-aways” listed below:
Terminology for Thermo-Plastics and not Thermo-Set Plastics:
- Thermo-Set Plastics can’t be reworked or recycled due to reinforcement so repurpose them
- Reworked = material from like product internal to the manufacturing process but not after field/external usage; could be wrong formulation or scarp material so a “prime product”
- Reground = edge trimmings, startup scraps that from manufacturing process and has not left the factory
- Recycled = material from like product after field/external usage, melted and reformed thermos-plastics but properties degrade with every re-use
- Repurposed = after field application – same product cleaned and using it in a different application, e.g., billboard film being used as a wood pile cover
- Reprocessed = after field application - cleaned, reground, and remanufactured for less critical application - landfill geomembrane reprocessed for a less critical application, e.g., use in an agricultural application, e.g., wee control film
- Post-Consumer Products – plastic bottles are usually polyester (PET) and are not typically used for engineered geomembranes, but could be used for other geosynthetics
- IGS website has information on sustainability: https://www.geosyntheticssociety.org/sustainability/; https://www.geosyntheticssociety.org/wp-content/uploads/2022/10/Fontana-Bologna-2022.pdf
Applications
- Short-term applications due to changes in applications
- Not permanent applications
- Applications driving amount of reworked material
- Agricultural applications
- Old billboards used for tarps
- Non-critical applications
- If the reprocessed material meets GM-17 for LLDPE, it may be suitable
- Water v. potable water – not viable for potable water unless it meets NSF specifications
- PFAS applications=? Probably not viable and must prove chemical resistance with new formulation
- Use for core of multi-layer materials
Amount of Rework Material
- Usually 5 to 10% for new geomembranes
- Can be as high as 50% for repurposed applications, i.e., less critical applications
Each month Tim Stark introduces a new technical topic for discussion and possible action. This month’s topic is: “Hydropower Applications”. This topic generated significant discussion with the main “take-aways” listed below:
Hydropower Reservoir Applications
- Industry want a Geomembrane (GM) that will last 50 years, a 75 to 100 year life-cycle, and/or aa 75 year warranty
- Mt. Elbert Reservoir – GM is covered with 18 to 24” of soil and rockfill on the upstream slop
- Only GM lined hydropower reservoir in public us in the U.S.A.
- Tesla Reservoir– Original Design - exposed GM - 1995 & 2017
- Concern with a soil or rock cover is the soil or rock could get into turbines so industry is interested in exposed GM applications
- A bituminous geomembrane (BGM) might be suitable
- Taum Sauk Pumped Storage Hydropower (PSH) Facility leaking upper reservoir was repaired with exposed GM – subsequently embankment was overtopped because no spillway was present; should have initially lined the upper reservoir with a geomembrane
- Luddington PSH –leaking upper reservoir was repaired with exposed GM
- Asphalt concrete(AC) liners appear to be currently preferred to a GM – advantages are waterproof barrier & durable wear surface – a hydraulic grade of asphalt is used but overtime cracks develop & have to be sealed – in addition, subjected to seismic cracking
- FGI should research cost of AC liner system per square foot – probably cost is $15 to $20/ft2
- Could install four or five GMs for the cost of an AC liner
- A better liner system in seismic areas could be a dual system of GM over lain by AC liner due to cracking
- Concrete facing is too expensive for a reservoir so not considered
- In non-seismic areas could use GM as a secondary liner under the AC liner to provide containment after AC starts cracking due to exposure
- GM under an asphalt liner system – hot asphalt (1700F) placed on top of fPP-R has been effective and can be installed with no wrinkles to facilitate AC liner placement
- Flexible geomembranes make more sense because few wrinkles and good elongation and ductility
- If there is a short-term application, e.g., line a spillway or a storage tank, a flexible geomembrane makes more sense
- AC Pavement design – asphalt pavements have exposure issues with time, e.g., reflective and shrinkage cracking; flexible geomembranes would be a good secondary barrier or use GM exposed and forego AC liner
Conveyance Structures
- Emergency spillways can be protected with a geotextile and then covered with rockfill
Each month Tim Stark introduces a new technical topic for discussion and possible action. This month’s topic is: “Surface Repair of Thin Geomembranes”. This topic generated significant discussion with the main “take-aways” listed below:
Geomembrane Thickness
- Thin geomembranes are usually (< 30 mil thickness) for temporary and non-critical containment applications
- Examples of thin geomembranes = Woven Coated Polyethylene (WCPE) & linear low density polyethylene (LLDPE)
- Thin geomembranes can be welded in a factory but difficulties in field
- Thin geomembranes are preferred to create large factory fabricated factory panels
- IAGI CWT Program could be expanded to include thin geomembranes
Temporary Repair/Welding Techniques
- Solid Wedge weld– 12 to 20 mil is possible for thin geomembranes
- Hot air wedge weld – 12 to 20 mil is possible for thin geomembranes
- Hot air gun –Patches – 12 to 20 mil is possible for thin geomembranes
- Tapes –available but not preferred unless for cap strip over a patch
- Available tapes– Tapecoat/Chase Adhesives is a tape and primer supplier
- Tape may be stable for a temporary small patch until crew arrives to install proper patch
- Tape is available single-sided and double-sided tape
- Tape may be useful for underwater applications
- Can use tape to help seal penetrations
- Tape is not preferred for long-term applications
- No good adhesive for polyethylene based materials
- Do you require trial welds for patches? Not for heat guns
- Need some documentation/guideline to improve quality of field welding thin geomembranes - ASTM D8468-23 Practice for Data Recording Procedure may be a useful reference
Repair Testing
- Air lance testing is preferred – ASTM D4437
- Vacuum box testing preferred but limited with WCPE geomembranes b/c air can pass through patch with a thin geomembrane
- Electrical leak surveys can be used with thin geomembranes
CQA of Thin Geomembranes
- Can field test seams in shear
- Peel testing of seams is limited
- Same seam test procedures as thick geomembranes including documentation
- No warranty on patching old thin geomembranes – case by case determination – only warranty repair was made “with good workmanship
Each month Tim Stark introduces a new technical topic for discussion and possible action. This month’s topic is: “Methane Containment and Detection”. This topic generated significant discussion with the main “take-aways” listed below:
Methane Detection Applications
- Landfills
- Biodigesters
- Oil and gasproduction
- Common in Europe
Methane Detection
- Unmanned Aerial Vehicles (UAVs) – Attend May, 2024 FGI Webinar by Art Mohr
- Hand-held gas meter – FLIR GF320
- Neighbors are best detectors – of other gases b/c methane is odorless but usually accompanies landfill odors
- Larger issue in eastern portion of USA than western portion, e.g., Colorado
- Newer drones detecting other contaminants besides Methane
- Satellites also being used to detect methane–
- Safety issues –H2S gas
- Infrared gas meters in Europe – FLIRGF320 in Europe - https://www.flir.com/discover/instruments/gas-detection/biogas-facilities/ or Gas Detection Cameras | FLIR Industrial | Teledyne FLIR
Methane Containment
- Manufacturers investigating geomembrane durability subjected to Methane and other factors – see GRI GM-35 material specification
- Use temporary geomembrane covers to control methane release – significant leakage around gas wells, i.e., final cover penetrations
- Also use temporary geomembrane covers for leachate control as well as methane capture
- Methane capture is proving lucrative, so temporary covers are gaining interest
- Should FGI develop test method and criterion for methane/odor transmission through flexible geomembranes? Decided that methane geomembrane transmission is small compared to current leakage points so focus on leakage points - https://www.fabricatedgeomembrane.com/articles/methane-gas-migration-through-geomembranes
- EVOH based geomembrane appear more effective than HDPE based geomembranes in containing landfill odors and methane
- European regulations on methane control are available at https://energy.ec.europa.eu/topics/oil-gas-and-coal/methane-emissions_en
Each month Tim Stark introduces a new technical topic for discussion and possible action. This month’s topic is: “Update PFAS and PFOS Regulations & Compliance”. This topic generated significant discussion with the main “take-aways” being listed below:
PFAS Regulations
- No regulations promulgated yet so no compliance activities yet
- Proposed PFAS/PFOS rules released on 1/31/2024 – see excerpts below and full document at: prepublication_version_of_definition_of_hazardous_waste_proposal.pdf (epa.gov)
- Proposed rules released on 1/31/2024 do not classify PFAS/PFOS as a hazardous waste for disposal so they can be disposed in a Subtitle D facility (see pasted text below)
- See recent article on PFAS/PFOS regulations HERE.
- New drinking water standard lowers allowable level of PFAS/PFOS to 4 parts per trillion, which is hard to detect
- Kerry Rowe’s testing at Queens University shows many geomembranes exhibit good chemical resistance to PFAS/PFOS compounds (see FGI webinar that Kerry Rowe gave at this LINK.
- However, Kerry Rowe’s testing shows lower concentrations of PFOS exhibit higher diffusion rates than higher concentrations of PFAS through the geomembranes that he has tested
- Need long-term testing of geomembranes chemical resistance to PFAS/PFOS chemicals
- PFAS/PFOS somewhat new and predate geomembranes so PFAS/PFOS may be in prior chemical resistance testing that used actual leachate instead of synthetic leachate
- Some water agencies are asking if any geomembrane component is extractable PFAS/PFOS material over the service life of the geomembrane
- Manufacturers are being asked if PFAS/PFOS chemicals were used in geomembrane manufacturing? Manufacturers are reviewing their supply chain to confirm no traces of PFAS/PFOS due to requests of customers and regulators – manufacturers are issuing “to the best of our knowledge” letters about no PFAS/PFOS components
- National Sanitation Foundation (NSF) is pursuing extractable constituents and may include PFAS/PFOS – NSF 61
- NSF 61 is having training class in Michigan on April 24, 2024, which my address PFAS/PFOS
- Would be good to investigate water standards in Europe and Australia and how they are handling PFAS/PFOS
- Would be good to investigate municipal solid waste standards and compare them to water standards
- Military will be exempt from PFAS/PFOS regulations initially
- Any changes in geomembrane formulations to deal with PFAS/PFOS, none available yet
- Lots of litigation over PFAS/PFOS are underway
- Health impacts of PFAS/PFOS are starting to become understood
- No new placement restrictions at Subtitle D facilities for PFAS/PFOS compounds but a lot of Not In My Backyard (NIMBY) opinions because leachate will go to local treatment facility
- It is believed that PFAS/PFOS could have a large impact on waste and water industries
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Each month Tim Stark introduces a new technical topic for discussion and possible action. This month’s topic is: “Determining Lining/Floating Cover Systems for Critical and Non-Critical Applications”. This topic generated significant discussion with the main “take-aways” being listed below:
Non-Critical Applications
· Relevant Factors/Questions:
- Site Specific Determination – Activate ancient landslide or fault system? If so, critical application
- Does the owner accept some leakage?
- Regulations don’t require zero leakage?
- What is the cost of a leak (environmentally or economically)?
- What is allowable (regulation)/acceptable (owner) leakage rate?
- What is subgrade condition? Soft, hard, existing asphalt, existing concrete, does it need remediation? If so, may be critical application
- What is geomembrane being selected?
- Site specific CQA/CQC requirements – depends on GM selected but usually less than critical applications
- Is site specific Leak Location Testing necessary? – depends on site
- Choice of material depends on availability, e.g., available soil v. GM
· Non-Critical Applications:
- Canal liners
- Temporary remediation
- Decorative ponds
- Landscape ponds
- Detention basins – control flow
- Stormwater collection – depends on level of contamination – natural and man-made
- Wetland mitigation
- Dewatering
- Freshwater containment if water is readily available
- Final cover systems
- Floating cover system for non-potable water – site specific
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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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1. Estimating remaining service life is important for owner’s replacement and budgeting purposes. This is gaining popularity in Australia, South America, and west and southwestern portions of the United States. As a result, a main objective of this White Paper is to educate engineers and owners on how to design, specify, and include sample coupons in their designs and installations, respectively. Most of this White Paper focuses on new projects except for the last section which focuses on old projects.
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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
To see full document, please click on Download button.
1. Estimating remaining service life is important for owner’s replacement and budgeting purposes. This is gaining popularity in Australia, South America, and west and southwestern portions of the United States. As a result, a main objective of this White Paper is to educate engineers and owners on how to design, specify, and include sample coupons in their designs and installations, respectively. Most of this White Paper focuses on new projects except for the last section which focuses on old projects.
To see full document, please click on Download button.
- Billy Nichols of the Philadelphia Water Department (PWD) attended and discussed proposed regulations for geomembranes used in stormwater containment applications.
- Billy is in the water resources team & working on green infrastructure systems that intercepts storm water before water reaches storm water system
- Stormwater Detention System is a system that retains stormwater until stormwater system can handle the flow
- Detention Systems are fully-lined with a geomembrane - The geomembrane liner system is installed to protect nearby basements, prevent sinkholes, etc.
- Use of geomembranes is new to PWD
- PWD tested completed systems since 2020 and some of the systems are not holding water => the test involves filling the completed system with fire hydrant water before placing it in service
- PWD is running leak test after stone installation – to reflect stone placement and stone weight on geomembrane with full weight of water
- However, it is difficult to find leak with stone in-place = must vacuum out stone to locate and fix the leaks
- Old Allowable Leakage rate = 1 inch/hour = f(size) = ?
- Moving to new Allowable Leakage rate of < 0.5 inch/hour
- 143 systems and 216 tests performedso far and 73 systems failed on first filling or testing
- 70% of systems pass initial leakage test (see figure below)
- Leakage mostly occurring at:(1) Pipe penetrations, (2) failed extrusion welds in a tight space, and (3)holes or tears in the geomembrane
- Extrusion Welds = common failure points
- PWD thinking thicker material is better because more material to weld to
- PWD Specification says use fusion welds where possible to minimize extrusion welds
- PWD considering requiring cushion geotextiles on side walls as well as bottom on storage chamber
- Applications: storm trench (PWD and public projects) v. storage chambers (private projects)
- Storm trench used within roadway Right-of-Way = public system not private system
- Primarily 40 mil and 60 mil thick HDPE geomembranes have been used for storm trenches
- PWD Weld Testing = ?
- spark, vacuum box, and air channel testing specified but tests may not be performed
- Suggestions:
- A 12 ounce/yd cushion geotextile is a cost-effective protection for the geomembrane
- Field fabrication should be considered to minimize field extrusion welds
- Atlantic Lining Company(ALCO) has installed many of these systems– Tim Rafter of ALCO shared his experiences with Philly contractors, different geomembrane polymers, and system water testing
- PWD Testing = ? PWD water test not ASTM but developed to test final product
- PVC tube installed in stormwater trench to measure water level every five minutes and filled system sits overnight to measure leakage rate
- Tim Rafter thought a 30 mil GM could not stand up to Philly contractors and thus thought a thicker geomembrane was a good idea
- Terry Sheridan of Geo-Storage described some of his geomembrane experiences designing subsurface storage chambers
- Terry is only working on private projects so new PWD regs don’t impact his private projects
- Terry thinks 40 mil PVC Geomembrane and a thick cushion geotextile are adequate for stormwater containment systems
- Terry suggested using more flexible geomembrane due to better puncture resistance, pipe boot welding, andlarger tensile elongation, which is good with a rising groundwater level
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
To see full document, please click on Download button
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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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Best Practices for Dealing with Temperature Fluctuations include:
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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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