This engineer manual transmits a document which describes CQA inspection requirements for hazardous waste landfill covers and liners. The appendix of this document is a template for landfill CQA plans to assist designers in incorporating the important aspects of CQA. The document may also be used in reviewing CQA plans developed by others.

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There are a lot of elements in the argument for and against phased restoration of a landfill. Well before making your decision, it’s going to be important and vital to make sure you know and fully grasp these pros and cons. This article explains some of the important plusses and minuses associated with the development, operation and restoration of landfills in a series of phases of sufficient size for efficient landfill operation.

The method of landfilling is known as phased restoration. It has many advantages, and in many national waste regulation regimes is considered to be a central requirement of sanitary landfill practice, and to show a well planned Restoration Phasing Plan is a pre-requesite of obtaining any site licence. In a number of the industrializing nations this does not apply which appears surprising when there are such huge benefits in:

• increase landfill gas yield
• reduced leachate production.

However, the requirements of pregressive restoration interact with other site aspects, and it is unlikely that all angles can be obtained perfectly at any given site. To be able to make the decision which is correct for you, you will need to know the following:

Benefits: Points In Favor Of phased restoration of a landfill

1. Landfill development should be based on the progressive use of the landfill area, such that at any given time parts of the site may be in the process of being:

- capped and restored
- capped
- actively filled
- prepared to receive waste, or as yet undisturbed,

and the aim of the restoration program is always designed to minimize incident rainfall soaking into the waste, and maximize early completion of discrete areas (Phases) to the final restoration profiles to allow maximum landfill gas extraction from full depth vertical landfill gas wells.

2. It allows progressive restoration. Progressive excavation of on-site materials, allows for efficient nearby storage of restoration materials, and minimisation of double handling of development and restoration soils.

One other good reason for the advance planning, development, operation and restoration of landfills in a series of phases, of sufficient size for efficient landfill operation, is minimisation of double handling of development and restoration soils.

This has the additional advantage of avoidance of unnecessary earthworks soils materials handling, that is certain to protect against making the mistake of large quantities of restoration materials being found to be needed toward the end of the landfill period, when otherwise useable material is then covered with waste and cannot be excavated and used.

3. It minimises the area required for active landfill operations and concentrates activities within a sequence of defined areas, reducing nuisance and polluting emissions.

And then there’s less visual intrusion caused by the landfill, and also site restoration funding requirements are more progressve and less peaky.

All these are advantages for the site that is continuously restored and each restoration work construction period is carried out by the site owner every year to 18months. It’s also very important as it could otherwise mean that without progressing restoration very large areas of only temporarily covered unsightly waste would be left for longer, for the alternative non-phased restoration of a landfill.

Also, perhaps all of us will agree that it must surely be best to plan full height restoration, and avoid large areas of waste left open and uncapped for long periods. Once you take that under consideration, then it makes sense to plan, and implement a plan, for phased landfill restoration using progressive restoration techniques.

The points above show the positive aspects of phased restoration of a landfill. There exists a down side also. Here’s a discussion of some of the drawbacks, but never overestimate the drawbacks!

Drawbacks: Arguments Against phased restoration of a landfill.

1. Physically excessively placing a limit on operational space

If you consider the phased restoration of a landfill, some parts may be too steep for the restoration works plant, within the phasing plan – especially for very deep landfills may limit operational space. That’s clearly a bad thingbut should be avoidable with good planning in most cases and all but the narrowest and deepest “quarry filling” landfills.

2. The direction of phasing usually needs to be resolved between screening for visual, wind and noise and allowing adequate flexibility for the passage of vehicles across the site.

Other factors to consider which will be present for the designers of many phased landfills will be

- potential instability in part-filled void, where support from future waste is absent
- need for protection of temporary edge of lining/capping
- need to protect against leachate overflow into unlined areas
- achievement of agreed final landscape plan after settlement.

3. Achieving the normal preference for leachate drainage to start at lowest point, may conflict with topographical requirements

The last pssible justification put forward to avoid phased restoration of a landfill is achieving the normal preference for leachate drainage to start at lowest point admittedly, this may conflict with topographical requirements. Everyone ought to consider this point very carefully, considering the fact that it can cause difficulties later with leachate wells in difficult to access or excessively deep locations if you decide to go for the phased restoration of a landfill. However, despite the complexities of phased landfill design, the fact is that it is genuinely the best option for probably about 90% of MSW landfills.

And so that’s that. There are the positives and negatives of phased restoration of a landfill. It may not be the right thing for some rare landfills, but it is most certainly beneficial to nearly all MSW landfill operations. So, you should carefully look at the above information and comparisons. Hopefully your final decision process will be aided in detail because of the pro and con info offered here.

Realize methods to understand local waste facilities by visiting my Waste Facilities web site at wastefacilities.org.

There is very little information available about the motivations and origins of the design principles behind the work of a landfill CQA engineer, so we decided to write this (based on a 1994 paper by Harris, Knox and Walker).

CQA principles must logically be applied to all landfills where the wastes accepted potentially pose a risk of water pollution, mainly those accepting household, commercial and industrial wastes. These wastes account for a relatively small proportion of total waste arisings (approximately 20% of the UK’s total of 516 Mt (3), the rest being demolition waste, mining and smelting wastes, fly ash from power stations, sewage sludge and agricultural wastes). Nonetheless, this fraction presents the most intractable difficulties of the total.

Whilst the nature of the wastes deposited in landfills may have evolved through man’s history, the operational methods until recently, remained largely unchanged and unsophisticated.

Over the last forty years or so, a much wider understanding of processes involved in waste stabilization has been developed. This has coincided with a worldwide increasing environmental awareness leading to demands for environmental improvements.

These demands are well founded, in fact although clean unpolluted UK water supplies are, as everywhere, vital for the survival of the population some experts have suggested that as much as one third of all UK groundwater supplies are now contaminated to some extent by pollutants. If the rate of damage to our water resources was sustained for another century the situation would have become extremely serious for public health, even without the further pressures on water supply anticipated from climate change.

Legislation in the UK has matched public demands for change, by the implementation of Directives issued by the Council of the European Communities. Most importantly in the 1980s, the introduction of the Groundwater Directive has caused an evolution in the standards of site preparation works and operational practice being demanded for all new landfill projects in order to prevent pollution of the water environment.

This evolution was accelerated by the inception of the National Rivers Authority in 1989 and the introduction of their Groundwater Protection Policy in December 1992.

The changed requirements have led largely to the discontinuation of the “attenuate and disperse” concept of landfill with the emphasis now on “engineered containment and operational safeguards”.

This is generally achieved by the installation of either an engineered clay liner or a composite liner, so called because it combines the use of natural materials (e.g. compacted clay) with polymeric membranes, otherwise known as flexible membrane liners (FMLs). Using these materials, emphasis is placed on preventing the release of leachate into the geologic environment.

In addition, there are concomitant operational requirements considered necessary to limit further the potential for leachate release from the site. There are two broad components.

The first is concerned with the limitation of leachate production.

This can be effected by infilling in a series of cells sized on the basis of water balance calculations to (in theory at least) avoid the generation of leachate during the operational phase by utilising the absorptive capacity of the waste.

Rainwater accumulating in other parts of the site can be kept separate and discharged in an uncontaminated condition.

Leachate production is further reduced by progressive capping and restoration of each cell as it is infilled to final levels and by ensuring that these restoration layers are laid to a high standard to prevent rainfall infiltration.

The second component is designed to ensure that any leachate produced can be removed easily from the site.

The composite lining system for engineered containment is protected by a blanket of free draining material incorporating a perforated drainage pipework system. Not only will this prevent mechanical damage to the liner, it will also facilitate the easy removal of leachate, limiting the potential for building up a head of leachate in contact with the liner.

The ability to remove leachate easily from the site must then be supported by a reliable system for its disposal.

This is usually the discharge to public sewer with varying degrees of pre-treatment though more rigorous on-site treatment with discharge to stream is increasingly being used as technical and management standards continue to improve.

The broad concepts behind this approach have been accepted and practised in the UK since the mid 1980s.

However, operational experience continued to highlight design and installation problems. Subsequently further design and landfill construction (base and capping) guidance and regulations were introduced through enactment of legislation on site licensing, and then permitting (under IPPC Regs – now known as Environmental Permits), driven by the Landfill Directive, and the amended Waste Directive.

The CQC and CQA engineering carried out as part of Landfill CQA is tasked with ensuring that the final link in the chain is achieved by verifying that the complaint design is fully implemented and achieved or exceeded during site construction.

This is a serious responsibility for the landfill CQC and CQA professionals when one considers the extremely high importance highlighted earlier to all future generations that we get this right, and the water environment does not become further damaged by pollution from landfills.

In theory, there are 2 main kinds of modern landfills, the quarry-type below ground and the land raising-type. In the quarry or pit type the seeping groundwater and/or leachate must be piped to vertical shafts which are placed in the waste to keep the landfill dry.

Bauku telescopic well schematic

Circular pre-cast concrete wells can be specified which are raised with the waste with each “cell lift” but they are stiff and unable to withstand the inevitable movement of the waste as it settles around it.

So, what very often happens is that the shaft “shears” and the rings are pushed off-centre. As soon as this happens the necessary occasional man access need to maintain such wells has to cease for safety reasons, sooner or later the a pump becomes stuck in the well or it becomes silted, and maybe due to concerns about landfill gas intrusion from damaged joints during maintenance – it cannot be cleaned.

The sad fact follows that damaging effects on the shafts, usually due to the settlement in the waste commonly of up to almost 40 percent by depth, destroy almost every other type of shaft construction.

Therefore the German company Bauku developed the supposed telescopic shaft about twenty years back. Here the individual shaft elements are stacked above each other flexibly and can move with the waste as it settles.

Generally the shafts have a diameter of 2000 mm or more as maintenance must be carried out in the shafts. This is done by lowering breathing apparatus equipped specialist access contractor’s operatives down the shafts on wire ropes.

At the base of the shaft there are pumps for the transport of the seeping water as well as the entrances to the leachate pipes laid on the landfill liner, which need to be cleaned at regular intervals.

The Bauku telescopic shafts permit construction heights of almost one hundred m in the waste mass.

The dump site Merchernich at Cologne is a reference case to exemplify a very tough installation project.

These days, as Bauku state in their web site, HDPE “PROFILEEN telescopic shafts are found in all pit-type disposals of the Federal Republic Germany and with the adoption of the European (EU) standards and Construction Quality Assurance guidances more neighbouring nations are also thinking about this cutting edge product when planning their waste disposal (landfill) sites.

Telescopic shafts may also be integrated into the existing landfills later so that the standard of the many old rubbish heap sites can be improved significantly. Bauku also inform us at their web site, that such projects were carried out by us on a large scale in Britain in the last few years.

The often proposed alternative landfill liner system to Low Permeability Clay Layer or HDPE Lining Membrane consists of replacing the default design of compacted clay liner (CCL) with a Geosynthetic Clay Liner (GCL).

There are currently two major types of commercially available GCLs. One type consists of bentonite encased between two geotextile fabrics and the second type consists of bentonite glued to a HDPE geomembrane.

The type of clay typically used in GCLs is sodium bentonite. Sodium bentonite is the name given to the highly plastic clay mineral montmorillonite, with sodium as the primary exchangeable cation.

Bentonites used to fabricate GCLs are processed in an unhydrated state such that they appear to have a granular consistency. However, upon hydration with water, the bentonite swells to form a continuous clay layer.

GCLs are shipped in rolls typically 3.7 to 5.3 meters wide and 25 to 60 meters long. They are installed by unrolling to form panels. Adjacent panels are overlapped, and for some products, powdered bentonite is placed between the panels at overlaps.

Large-scale laboratory testing has shown that, when installed in accordance with the manufacturer’s specifications, GCL overlaps are self-sealing and do not create a preferential pathway for liquid flow.

GCLs have been used in liner systems and cover systems for landfills, surface impoundments, and tank farms, as well as in other structures. When used in landfills, GCLs are often substituted for the compacted low-permeability soil component of a composite liner. The function of the GCL in the composite liner is identical to that of a compacted soil liner, which is to provide a low-permeability barrier to liquid flow through any defect in the overlying geomembrane.

The GCL material is manufactured under strict quality control (QC) guidelines. The QC requirements include conducting index and performance testing on both the supplied materials and finished product at specified frequencies. After the material is approved at the manufacturing plant, care is taken to keep the rolls dry, not stack them too high, and keep them from damage during handling.

Prior to acceptance in the field, information concerning the manufacturer’s name, product name, lot and roll number, and length, width, and weight must be submitted to the on-site CQA representative, who will verify all records.

To analyze the leakage through a composite liner utilizing a GCL instead of a CCL, D’Arcy’s equation is utilized based upon an assumed design hydraulic head over the liner.

The leakage through a membrane liner has been found to be closely correlated with the hole defects. In a recent paper a defect size per acre of 1 cm2 was assumed, however assessments of defects and their likely frequency and size vary widely.

The US Fabricated Geomembrane Institute (FGI) offers its popular short course, “Constructing with Fabricated Geomembranes“, on 23 October 2009 in Lakewood, Colorado at the Sheraton Denver West Hotel. This course will be presented by Timothy D. Stark, Stan Slifer, John Heap, Daren L. Laine, Bill Shehane, Stuart Lange, Andrew Mills, Gary Kolbasuk and other speakers. Course participants are eligible for 6 PDHs.

Those involved with the design, construction, operation and closure of potable water and irrigation ponds, floating covers, canals, landfills, waste water lagoons, secondary containment, golf course ponds, decorative applications, corrective action activities at closed sites, etc. are encouraged to attend this course. Participants will gain a broad knowledge of what is required to properly design, specify and construct with fabricated geomembranes and advantages of fabricated products over rolled geomembranes.

The fabricated geomembrane information will cover manufacturing, formulation, fabrication, shipping, installation, long-term performance, wedge welding, testing of field geomembrane seams, updated ASTM testing of geomembranes, and design and installation of various applications, such as floating covers, canals, decorative and irrigation ponds, and secondary containment.

AGENDA

The 23 October short course will unfold as follows:

7:30 – 8:00 am Registration / Continental Breakfast
8:00 – 8:20 am FGI Introduction, Activities, and Research
8:20 – 8:40 am Fabricated Geomembranes vs. “Rolled Goods”
8:40 – 9:30 am Manufacturing Fabricated Geomembranes
9:30 – 9:45 am Break
9:45 – 11:00 am Fabrication and Installation
11:00 – 11:30 am Leak Location with Fabricated Geomembranes
11:30 am – 12:30 pm Lunch on Your Own
12:30 – 1:30 pm Floating Covers and Potable Water
1:30 – 2:00 pm Canals, Decorative and Irrigation Ponds
2:00 – 2:30 pm Wastewater Ponds
2:30 – 3:00 pm Break
3:00 – 3:30 pm Secondary Containment
3:30 – 4:30 pm Case Histories
4:30 – 5:00 pm Summary and Questions
5:00 pm Geomembrane Welding Demonstration

REGISTRATION

The registration fee for industry professionals is $100 and the course is free for government employees and students. All receive one day of instruction, short course notes, refreshments and lunch. Industry professionals should register by 25 September 2009 to get the best rate. See the online event registration page to start the process: http://fgi.eventbrite.com/