Archive for July, 2010

Floating Cover Systems

July 29, 2010

Floating Cover Systems are successfully used in several commercial and municipal applications.  Some examples include:

  • evaporation and algae growth prevention
  • potable water protection from pollution and contamination
  • odor and emission control
  • biogas recovery for power generation or flaring
  • protection of birds and waterfowl from contact with hazardous liquids
  • remediation contamination

Why Use Floating Covers?

The best engineered floating cover systems cost 75% to 85% less than most every acceptable rigid roof structure.  A single floating cover can exceed over a million square feet / 93,000 square meters of surface area and be viable.  Saving of natural resources is another large factor that should be considered.

Floating cover systems prevent water loss due to evaporation; greatly reduce algae growth and treatment chemical demand resulting in improved water quality.  They also provide barriers against contamination by dead animals, airborne particles such as pollen and bird droppings.

In potable water contamination applications, another advantage is treatment chemical cost reduction and positive health impact as considerably less chlorine is required in covered reservoirs.  Using less chlorine in potable water enhances safety by reduced production of trihalomethane (TTHM) (a methane-derived compound that contains three halogen atoms, e.g. chloroform, formed especially during the chlorination of drinking water) type compounds like chloroform that result from the combining of organic substances with chlorine.

Floating Cover Systems have been used for about 35 years.  Service lives of 20 years or more have been recorded in potable water applications.  Gas collecting floating cover systems can be expected to perform for about ten years.

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Environmental Containment Systems

July 22, 2010

Liners

Liner systems are containment elements constructed under the waste to control infiltration of contaminated liquids into the subsoil or groundwater.  The contaminated liquid, or leachate, may be part of the waste itself or may originate from water that has infiltrated into the waste.

Liner systems consist of multiple layers which fulfill specific functions.  The description presented below refers specifically to landfill liner systems.  However, the main characteristics of liner systems are similar for other applications.  Landfill liner systems may consist, from top to bottom, of the following functional layers:

Protective layer

This is a layer of soil, or other appropriate material, that separates the refuse from the rest of the liner to prevent damage from large objects.

Leachate collection layer

This is a high-permeability layer, whose function is to collect leachate from the refuse and to convey it to sumps from where it is removed.  Frequently the functions of the protective layer and the leachate collection layer are integrated in one single layer of coarse granular soil.

Primary liner

This is a low-permeability layer (or layers of two different low-permeability materials in direct contact with each other).  Its function is to control the movement of leachate into the subsoil.

Secondary leachate collection layer or leakage detection layer

This is a high-permeability (or high transmissivity, if geosynthetic) layer designed to detect and collect any leachate seeping through the primary liner.  This layer is used only in conjunction with a secondary liner.

Secondary liner

This is a second (or backup) low-permeability layer (or layers of two different low-permeability materials in direct contact with each other).  Not all liner systems include a secondary liner.

Drainage layer

In cases where the liner system is close or below the water table, a high-permeability (or high-transmissivity, if geosynthetic) blanket drainage layer is generally placed under the liner system to control migration of moisture from the foundation to the liner system.

Subbase

This layer is generally of intermediate permeability.  Its function is to separate the liner system from the natural subgrade or structural fill.  These layers are normally separated by geotextiles to prevent migration of particles between layers, or to provide cushioning or protection of geomembranes.

Liner systems may have a primary liner only or may include primary and secondary liners.  In the first case it is called a single-liner system, and if it has a primary and a secondary liner it is called a double-liner system. Further, each of the liners (primary or secondary) may consist of one layer only (low-permeability soil, geomembrane, or GCL) or adjacent layers of two of these materials, in which case it is called a composite liner.  There are multiple combinations of these names, some of which are given below as examples (obviously there are many more combinations):

• Single synthetic liner: primary liner only, consisting of a geomembrane.

• Single soil liner: primary liner only, consisting of a low-permeability soil layer.

Long-term Performance Of HDPE Geomembranes As Landfill Liners

July 20, 2010

Geomembrane Liners are impermeable membranes used widely as cut-offs and liners.  Until recent years, liners were used mostly as pond liners; however, one of the largest current applications is to the containment of hazardous or municipal wastes and their leachates.

High density polyethylene (HDPE) geomembranes are normally used as part of a composite liner for waste containment facilities such as municipal solid waste (MSW) landfills and heap leach pads.  Field conditions, which include physical stresses on the geomembrane, elevated operating temperatures, and contact with leachate constituents, have the potential to affect the service life of the HDPE geomembranes.  This thesis examined the long-term performance of different HDPE geomembranes based on both conventional laboratory accelerated immersion tests and simulated landfill liner tests.  A 1.5mm HDPE geomembrane was immersed in different synthetic leachates at different temperatures in order to evaluate the effects of leachate chemical constituents on the depletion of antioxidants.  The results showed that a basic leachate with trace metals, surfactant, and a reducing agent was the most appropriate for evaluating the potential degradation of HDPE geomembranes.  A similar immersion test was performed to evaluate the effects of thickness on the aging of HDPE geomembranes.

Three commercially available HDPE geomembranes having nominal thicknesses of 1.5, 2.0, and 2.5mm were immersed in a synthetic leachate at four different temperatures in this experiment.  The results showed that a thicker geomembrane may have a longer service life if other things are similar.  The depletion of antioxidants from a 1.5mm thick HDPE geomembrane was examined by conducting accelerated aging tests at 55, 70, and 85oC under simulated landfill liner conditions.  The results showed that the antioxidant depletion rate was consistently lower for the simulated landfill liner tests compared to the leachate immersion tests.

The effectiveness of the aged HDPE geomembrane on the migration of volatile organic compounds (VOCs) was examined by conducting diffusion and partitioning tests using both unaged and aged HDPE geomembranes.  The results showed that the aging of HDPE geomembranes did not increase diffusive migration of organic contaminants, provided that the geomembrane remained intact.  A new method was developed to estimate the service life of the HDPE geomembrane based on the landfill liner temperature history.  The service lives of the HDPE geomembranes were calculated to be between 20 and 4700 years, depending on the geomembrane type, exposure conditions, and the time-temperature history examined.

Floating Covers For Airport Glycol Containment

July 15, 2010

Floating Covers for airport glycol containment

Floating covers are designed to provide many years of lasting service in a variety of environments and applications.

After more being used in the most difficult applications around the world, XR-5 is recognized as the first choice material in a countless number of projects.  Airports utilize XR-5 geomembrane technology because of its resistance to jet fuel, glycols and acetate de-icers.  Because the XR-5 has low thermal expansion-contraction properties, it does not require soil cover and can be left UV exposed.

Geomembrane Liners Using XR-5 Technology

July 13, 2010

Geomembrane Liners can be installed for the following applications:

  • High Density Polyethylene (HDPE), PVC, EPDM, Reinforce
  • polypropylene (RPP) & XR-5 liners
  • secondary containment systems
  • tank liners
  • landfill liners
  • pond/lagoon liners
  • stud liner systems
  • golf course pond liners
  • pipe liners


XR Geomembranes
are the most durable and strongest geomembranes in use today.  They are specified worldwide for projects including wastewater impoundments, landfill liners, floating covers, tank farms, and potable water applications.  Each XR Geomembrane is capable of performing in the hardest, most difficult environments.  XR-5 grade geomembranes are high-strength, chemically resistant membranes that are best suited for high temperatures, and broad chemical resistance applications, including acids, oils and methane.  XR-5 geomembrane is UV resistant, has a coefficient of thermal expansion 1/20th of polyethylene, and has an extremely high yield tensile strength.  After being used in the most difficult applications around the world, XR-5 is recognized as the first choice material in a countless number of projects.

Patented Design Floating Covers, Tank Systems, Storage Lagoon Covers and Liners

July 6, 2010

IEC, a company with 16 years experience designing, fabricating, and installing industrial cover and liner systems, designs its products to provide many years of lasting service in a variety of environments and applications.  Since 1993, the company has designed, fabricated and installed more than 250 projects involving odor control, gas collection, pond liner systems and tank liner systems.

IEC’s Odor Control & Gas Collection Covers are specifically designed for each client utilizing a variety of material options.  Cover applications can be used with any type of gas collection from water basin and keep rain and snowmelt water separate from wastewater under the cover. Advantages of a cover include installation without site interruption, use on tanks or lagoons, elimination of rainwater ponding problems, elimination of gas ballooning, provides high buoyancy and rigidity, hatches can provide access to in-basin equipment, improved quality with pre-manufactured panels and are fabricated at IEC’s plant, so field welding is not required.

IEC also has a patented Modular Cover System comprised of a series of individual casings connected together to form a complete floating cover system.  Each individual casing consists of a panel of closed cell insulation encapsulated between two sheets of durable geomembrane.  The result is a unique floating cover system that provides insulation values ranging from R-2 to R-30; and is engineered and manufactured to specific dimensions/basin requirements.

The Modular Cover System offers the following advantages over conventional covers systems:
• maintenance free
• can be installed on tanks or lagoons
• adepts to varying water levels
• individual casings are removable,
• installed without site interruption
• shorter installation time, no field welding required
• installation requires less heavy equipment
• eliminates rainwater ponding problems
• eliminates gas ballooning
• high buoyancy and rigidity
• hatches can provide access to in-basin equipment