Archive for August, 2010

Leachate Collection Systems Part 1

August 27, 2010

Components Of Leachate Collection Systems

There are many components to a collection system including pumps, manholes, discharge lines and liquid level monitors.  However, there are four main components which govern the overall efficiency of the system.  These four elements are liners, filters, pumps and sumps

Liners

Natural and synthetic liners may be utilized as both a collection device, and as a means for isolating leachate within the fill to protect the soil and groundwater below.  The chief concern is a liners ability to maintain integrity and impermeability over the life of the landfill.  Subsurface water monitoring, leachate collection, and clay liners are commonly included in the design and construction of a waste landfill.  To effectively serve the purpose of containing leachate in a landfill, a liner system must possess a number of physical properties.  The liner must have high tensile strength, flexibility, and elongation without failure.  It is also important that the liner resists abrasion, puncture, and chemical degradation by leachate.  Lastly the liner must withstand temperature variation, be black (to resist UV light), easily installed, and economical.

There are several types of liners used in leachate control and collection.  These types include geomembranes, geosynthetic clay liners, geotextiles, geogrids, geonets, and geocomposites.  Each style of liner has specific uses and abilities.  Geomembranes, are used to provide a barrier between mobile polluting substances released from wastes, and the groundwater.  In the closing of landfills, geomembranes are used to provide a low-permeability cover barrier to prevent the intrusion of rain water.

Shown here is a leachate evaporation pond in a landfill site 

Leachate Collection Systems Part 2

Geosynthetic clay liners (GCLs) are fabricated by distributing sodium bentonite in a uniform thickness between woven and non-woven geotextiles.  Sodium bentonite has a low permeability which makes GCLs a suitable alternative to clay liners in a composite liner system.  Geotextiles are used as separation between two different types of soils to prevent contamination of the lower layer by the upper layer.  Geotextiles also act as a cushion to protect synthetic layers against puncture from underlying and overlaying rocks.  Geogrids are structural synthetic materials used in slope veneer stability to create stability for cover soils over synthetic liners or as soil reinforcement in steep slopes.  Geonets are synthetic drainage materials, which are often used in lieu of sand and gravel.  Geonets can replace 12 inches of drainage sand, thus increasing the landfill space for waste.  Geocomposites are a combination of synthetic materials ordinarily used singly.  A common type of geocomposite is a geonet heat bonded to two layers of geotextile, one on each side.  The geocomposite serves as a filter and drainage medium.

Geosynthetic clay liners are a type of combination liner.  One advantage to using a geosynthetic clay liner (GCL) is the ability to order exact amounts of the liner.  Ordering precise amounts from the manufacturer prevents surplus and over-spending.  Another advantage to GCL’s is the liner can serve appropriately in areas without an adequate clay source.  Conversely, GCL’s are heavy, cumbersome, and installation is very labor intensive.  In addition to be arduous and difficult under normal conditions, installation can be cancelled during damp conditions because the bentonite absorbs the water making it even more burdensome and tedious.

Geosynthetics – Geomembrane Liners

August 24, 2010

Geomembrane Liners

Geomembrane liners are impermeable sheets of polymer that are utilized in containment applications.  They are available in large custom panels or rolled goods that can be field seamed to form a barrier system.

Applications

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

High Density Polyethylene Liners

August 19, 2010

HDPE- High Density Polyethylene Liners

HDPE is the most widely used geomembrane today.  It has been the choice of many for large critical containment applications.

  • Resistant to a wide range of chemicals on account of density >.94/cm3
  • Reliable in exposed environment due to high UV protection against degrading and low temperature brittleness
  • Typically delivered to the site in large rolls manufactured smooth or textured on one or both sided
  • Panels are heat welded in the field by certified technicians providing a high quality, test certified installation.

LLDPE – Linear Low Density Polyethylene Liners

LLDPE is a flexible membrane liner that can conform to any surface even in cold temperature.

  • High elongation, tear resistance and burst strength properties
  • Contains carbon black and UV stabilizers to enhance longevity and outdoor performance
  • Available in large rolled goods manufactured to be either smooth or textured on one or both sided to improve friction.
  • Custom size factory welded panels that are accordion folded and rolled for economical deployment in the field.

Reinforced Geomembrane Liners

Reinforced geomembrane liners are produced by extrusion laminating multiple layers of high strength polyethylene with tear resistant polyester scrim.

  • Scrim reinforcement enhances strength and resistance to tear
  • Excellent longevity in outdoor applications – UV inhibitors and carbon black
  • Manufactured and factory welded into large manageable panels
  • Panels are accordion folded and rolled for economical deployment in the field
  • Easy to install

PVC -Poly Vinyl Chloride Liners

PVC liners are extremely contractor friendly and offer many advantages over other liners.

  • Highly flexible so it easily conforms to sub grade contours.
  • Excellent interface friction properties without being textured
  • Excellent puncture and abrasion resistance
  • Superior chemical resistance to acids, alkalis, and alcohols
  • Excellent choice for buried applications to protect from exposure to sunlight.
  • Excellent material for complex sub grades common in smaller application.
  • Available in a variety of formulations including fish grade and oil resistant.
  • Can be contractor installed using PVC glue or Solvent

Maintenance Free Patented Design Floating Covers

August 17, 2010

Maintenance Free Floating Covers

Floating covers are a very economical method of protecting precious water.  The cost can be 20% of that for other cover options.  Industry-recognized guidelines exist for the design, installation and maintenance of floating cover systems.  An example is the American Waterworks Association (AWWA) standard D130-87, which contains the most current standard practices observed for system compliance to US national health and safety regulations.

The California-Nevada Section American Water Works Reservoir Floating Cover Guidelines dated March 1999 offers an excellent source of design, operations and maintenance guidelines.

Floating Covers are customized for each client’s lagoon or tank size and shape.  A series of lateral floats provide pathways for gas to flow underneath to the perimeter collection pipe and on to a single collection point.  The lateral floats keep the entire cover floating on the waters’ surface, and eliminate cover inflation, and exposure to wind damage.

Floating covers that inflate (without lateral floats) expose the geomembrane cover to vibration and geomembrane fatigue from wind constantly blowing over the inflated cover.  This significantly reduces the life span of the cover.  Ballast weights on top of the floating cover channel rainwater and snow melt to sumps to remove all rainwater from the surface of the floating cover.

Properly designed reservoir-floating cover systems prevent fluid loss due to evaporation, reduce chemical demand and improve water quality by preventing contamination from bird droppings, airborne particulates, dead animals, pollen and other pollutants.  Floating covers block off sunlight preventing algae bloom.  They also reduce the production of trialomethane (THM) type compounds such as chloroform from forming that result from the combining of organic substances with chlorine due to reductions in chlorine demand.

Floating cover systems were introduced over 30 years ago.  Many have provided a service life beyond 20 years.  When first introduced, materials and designs were not developed and in some cases had limited success. Today, with advancements in design and materials, floating covers offer the low cost quality solution of choice where water quality standards require potable water reservoirs be covered.

Floating Covers Eliminate Algae Growth and Reduce Odors

August 5, 2010

Floating covers eliminate algae growth and airborne contamination, and reduce odors, evaporation and thermal losses.  Covers may be modular or all-encapsulating.  The latter covers fully encapsulate the upper surface of the reservoir by being mechanically fixed and sealed around the perimeter.  They can be designed to allow for fluctuating water levels, rainwater drainage and routine access.

Floating Covers

Floating covers use flexible geomembranes to enclose the top of a pond.  Floating covers are commonly used for odor control, dilution and evaporation control, and in the containment of treated potable water.  A floating cover is an economical alternative to tanks and concrete vaults for water storage and is one of the few techniques available to cover very large volumes of water.

Floating covers are a unique use for geomembranes where an engineered membrane system is placed on top of the liquid in a pond.  This cover needs to move with changes in water level, resist movement in wind, collect precipitation, and resist damage from ice.

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

Geosynthetics In Agricultural Applications

August 3, 2010

Agricultural Use Of Geosynthetics

Agricultural use of geosynthetics is one of the fastest growing market segments worldwide.  The earliest geosynthetics applications were for on farm use and some of the earliest specifications were directed at agricultural use of pond linings.  These early uses included the lining of ditches to help save valuable water as well as the lining of farm ponds and water harvesting catchments in the arid regions of the world.

Today, there is a wide variety of applications ranging from covered and uncovered ditch linings and ponds to protection of the groundwater and surface waters that are being polluted by animal waste.  The use of geosynthetics and in particular geomembranes on the farm has come a long way and has grown significantly in recent years, especially with more stringent governmental legislation as well as public awareness through programs such as those developed by the USDA/NRCS, U.S. EPA and governmental agencies in other countries.

Containment As A Requirement

Potable water sources are becoming more and more scarce and water is becoming more costly.  The requirement to provide a barrier against high rates of water seepage loss is already a reality in many more areas than just the arid and semiarid regions of the world.  And, just as water is important to conserve, it is even more important to environmentally protect surface and groundwater sources from pollution due to animal waste and the air we breathe from noxious gases and odors.  Again, containment with a reliable time proven method is a requirement, not just an option due to  environmental legislation in many parts of the world.

Shown here: Anaerobic digesters with waste lagoon

Geosynthetics will provide a reliable cost effective alternative to traditional compacted soil and clay liners that provide much less in seepage control, are highly variable in quality and may not be acceptable for design and regulatory compliance.  Although geomembranes are the primary type for use as a barrier or odor control cover, other geosynthetics are used in conjunction with geomembranes and include geotextiles, geo-composites, and geonets.

Animal Waste Lagoon Liners

Animal waste lagoons contribute to the pollution of ground and surface waters worldwide.  To control waste seepage, compacted earth linings as well as geosynthetics are utilized.  However, with the increasing concern over pollution and governmental legislation, the use of geosynthetics has been increasing very rapidly.  In particular, exposed geo-membranes, geo-membranes with soil cover and GCL’s with soil cover are currently being used.  In addition, geo-textiles and geo-net composites are utilized for protection / gas transmission.

Animal Waste Odor Control Covers

A growing number of scientists and public health officials have traced a variety of health problems to vast amounts of concentrated animal waste which emit toxic gases such as hydrogen sulfide and ammonia.  Odor control covers can be a low cost geomembrane or coated fabric or they can be a more expensive engineered floating geo-composite cover system dependent on the design and criticality of the containment.

Shown here: Irrigation canal

Water Conveyance
Geosynthetics and most notably geomembranes have been used for decades in preserving and transporting clean water for on farm use.  The conveyance of water in ditches, laterals and main canals for delivery to crops is as common as on farm water storage tanks and ponds.  However, water is becoming more and more scarce and more costly especially with the drought conditions in many parts of the World.  Seepage loss in canals and ditches can approach 30 to 50% but loss of valuable water can be eliminated with the use of geosynthetics as lining systems.  Both soil covered and exposed geomembranes are used extensively in the lining of both new and old canals that require rehabilitation.

In addition, old cracked concrete lined canals have lost their effectiveness over the years and are being replaced or repaired with geomembranes.  Water conveyance systems utilize other geosynthetics in conjunction with geomembranes such as protection geo-textiles, geocomposites and geo-grids.

Water Containment
Water containment in ponds and concrete tanks for on farm use is just as important as water conveyance in that seepage and loss of valuable water should be minimized, especially for remote ponds and tanks.  Soil covered geomembranes and GCL’s are used for the construction of new or the rehabilitation of old ponds.  Exposed geomembranes are used to re-line old stock water concrete tanks or to line

Anaerobic Digesters
Anaerobic digesters are used to rapidly decompose animal waste in a controlled environment thus allowing the recovery and use of methane-rich low Btu biogas.  Biogas is used to fuel combined heat and power (CHP) generators that produce on farm electricity, process heat and domestic hot water.  They are also a viable method of waste management due to the fact that both bottom lining systems as described above and flexible cover systems are used.  With every digester constructed, geosynthetics are used to either line the anaerobic lagoon or cover the lagoon for collection of biogas. The number of operating digesters is rapidly increasing worldwide as government funding is becoming available for farm installations.

Data provided with compliments http://www.geosyntheticssociety.org and R. Frobel.