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:

• In fact, it is easier to “leak locate” flexible geomembranes because they usually exhibit a greater amount of intimate contact with the subgrade, i.e., they lay flat, and exhibit smaller wrinkles that do not have to be removed as HDPE geomembranes do.  
• In general, it is difficult to perform a ELLS with wrinkles greater than 3 inches high because they cannot be “walked out” and there is no intimate contact with the subgrade.
• ELLSs are independent of geomembrane polymer type, the main limitations are wrinkles and the geomembrane being a good insulator.
• However, ELLSs cannot be performed on two types of geomembranes; conductive geomembranes and EPDM geomembranes because of the large amount of carbon black.

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Best Practices for Dealing with Temperature Fluctuations include:

• 50-degree temperature swings can cause  significant changes in GM dimensions  
• never backfill anchor trench until GM has experienced two or three days of temperature cycles
• install wrinkle across the toe on short slopes and then cut it out if needed on long slopes, place wrinkle further upslope because wrinkle will not move upslope
• fill containment with water or other material to stabilize GM as soon as possible
• include 3 to 3.5% extra unreinforced GM material (slack) for thermal contraction when large temperature fluctuations are anticipated
• calculate the wrinkle height using the equation from Giroud and Wallace (2016) so the coefficient of thermal expansion for each GM type, interface friction angle, e.g., smooth v. textured, bending modulus, and material type, are important parameters in the calculation

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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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• ASTM D6182-00 (2015) – Standard test method for flexibility and adhesion of finish on leather 
 
• ISO 32100: 2018 Rubber- or plastics-coated fabrics — Physical and mechanical tests — Determination of flex resistance by the flexometer method
 
• AS 4878.9-2001- Methods of Testing For Coated Fabrics - Determination Of Resistance To Damage By Flexing
 
• ISO 7854:1995 - Rubber- or plastics-coated fabrics — Determination of resistance to damage by flexing
 
• ASTM D2097 – Standard Test Method for Flex Testing of Finish on Upholstery Leather
 
• ASTM D882 – test method for testing tensile properties of thin plastic sheeting.
 
• ASTM 5323-19a - Standard Practice for Determination of 2 % Secant Modulus for Polyethylene Geomembranes
 

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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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