Category Archives: Guest Posts

Research Update on Geomembranes at Tailings Storage Facilities

This is a guest post by Sahar Pakzad, Marketing and Communications Coordinator at Klohn Crippen Berger Ltd.

Professor Kerry Rowe and Klohn Crippen Berger (KCB) alumnus Alan Chou of the GeoEngineering Centre at Queen’s University recently presented an update to KCB staff on the use of geomembranes at tailings storage facilities (TSFs). This update is a result of a multi-year research program, partly funded by KCB, involving fellow researcher Professor Richard Brachman, and KCB’s Dr. Prabeen Joshi and Harvey McLeod, P.Eng, P.Geo. The aim of the research is to quantify the amount of leakage through geomembranes at TSFs and the potential for the migration of tailings through holes in geomembranes into the surrounding environment.

Geomembranes are thin plastic sheets (usually less than 0.3 cm thick) installed as an impermeable barrier to limit the leakage of liquids or gases from containment facilities, such as municipal landfills, coal ash impoundments at power plants, heap leach pads and TSFs at mine sites. While installing geomembranes is standard practice for municipal and some industrial settings, only a small percentage of TSFs globally are lined by geomembranes, in part, because until now, there has been little research on their performance.

This research collaboration between Queen’s University and KCB is part of a longer-term research program at the university on how physical and chemical factors, including installation techniques, affect the performance and service life of geomembranes.

Geomembranes 101

Since the introduction of geomembranes in the mid-20th century, their properties and performance have significantly improved through advancements in polymer chemistry and installation techniques. Geomembranes are designed to resist degradation from exposure to UV rays, extreme temperatures and chemical reactions (including oxidation), and they must be strong and flexible to prevent stress cracking if they are folded or strained under significant loads.

Geomembranes are manufactured by combining a polymer resin with additives such as antioxidants, stabilizers, plasticizers, fillers, carbon-black, and lubricants (as a processing aid). These additives enhance the long-term performance of geomembranes by protecting the polyethylene from degradation (Ewais and Rowe 2014). There are several geomembrane types, including the most commonly-used high-density polyethylene (HDPE) and linear low-density polyethylene (LLDPE) geomembranes.

Not all geomembranes are the same, even from the same manufacturer; they differ in polymer additives and antioxidants, in colour, and in their physical properties such as stress crack resistance and service life. Geomembranes may also be custom blended to prevent reaction with containment materials.

Geomembranes are produced in long sheets, which are a few metres wide, and may be laid down and welded into panels on site (Figure 1a) or welded together in a factory before installation at site (i.e. fabricated geomembranes) (Figure 1b).

Figure 1a: Workers laying down a geomembrane
Figure 1b: Rolled fabricated geomembrane ready for installation
Figure 1b: Rolled fabricated geomembrane
ready for installation

Today, many jurisdictions mandate the use of geomembranes as part of a barrier system for specific applications. For example, in British Columbia, Canada, a landfill barrier system “shall be comprised of a primary High Density Polyethylene (HDPE) geomembrane liner and a secondary compacted clay liner or Geosynthetic Clay Liner (GCL)” (BC MOE 2016). Likewise, in Ontario, Canada, landfills must be lined by a “clayey liner with organic carbon content, in addition to an HDPE geomembrane liner, together with a leachate collection system” (Government of Ontario 2011). In the U.S., the Environmental Protection Agency requires that the bottom and sides of landfills be lined by “two feet of compacted clay soil” overlain by a geomembrane layer to “protect groundwater and the underlying soil from leachate releases” (USEPA 2017).

Leakage through Geomembranes

Geomembranes are not leak-proof as they degrade over time and may be punctured during installation, or by stones in the foundation material. They can also develop stress cracks at wrinkles or folds in the geomembrane following placement of the cover soil or tailings.

The team at the GeoEngineering Centre studied the performance of geomembranes under simulated field conditions typical for TSFs to quantify potential leakage. They found that leakage through holes up to 2 cm in diameter is less than 5 mL/s/km2, which is several orders of magnitude lower than leakage from unlined containment facilities (Joshi, P., pers. comm.). They also found “evidence of an increase in fines in the tailings and underliner in and around the hole” (Rowe et al. 2017).

Professor Rowe and his team performed puncture tests on geomembranes and found that a fine-grained foundation containing isolated stones may cause more geomembrane defects than a packed gravel foundation. They also found that stress cracks occur when there are wrinkles or folds in the geomembrane, when there is differential settlement of the foundation, and when the weight of cover soil or tailings drags the geomembrane down slope.

The colour of a geomembrane can be an important factor in its tendency to wrinkle. Even at moderate temperatures, a black geomembrane can become very hot, making it prone to wrinkling or folding, and in the process losing contact with its foundation. Researchers at the GeoEngineering Centre found that at the same air temperature, white reflective geomembranes can be 21–23°C cooler than black geomembranes, and that white geomembranes are less prone to wrinkling and developing stress cracks (Rentz et al. 2017).

The researchers concluded that damage to geomembranes can be minimized and the potential for leakage reduced by the appropriate selection of geomembranes, proper construction techniques (including adequate construction quality assurance), and by laying the geomembrane over a well-graded smooth foundation, preferably with a protective layer of sand or geotextile (Joshi et al. 2017). Geotextiles are permeable fabrics used for reinforcing slopes and filtering fine-grained material, while allowing water to drain.

Service Life of Geomembranes

The service life of a geomembrane is reached when it no longer adequately contains the material in the containment facility as designed. Its service life depends on its polymer type and additives, its exposure to UV rays, extreme temperatures and chemical reactions, and the potential for puncturing (predominantly by stress cracking).

The key to an effective barrier system is a protective layer between a drainage layer and the geomembrane. The protective layer not only reduces the risk of puncture in the short-term during installation and the initial placement of tailings, but helps to ensure an adequate geomembrane service life (Rowe 2016).

At TSFs, in addition to designing specialized geomembranes for resisting degradation, their degradation may also be reduced by a protective thick layer of tailings with consistently low ground temperatures (McLeod, H., pers. comm.).

A Critical Component of TSF Barrier Systems

By installing geomembranes at TSFs as part of a designed barrier system, mine operators can comply with local environmental regulations by significantly reducing the risk of leakage from TSFs into the environment and improving the recovery and recycling of water from tailings to other mine processing streams.

Ask us how we can help you with your tailings management needs.

For more readings on this topic, refer to the references below:


BC Ministry of Environment (BC MOE). 2016. “Landfill Criteria for Municipal Solid Waste.” Accessed June 26, 2017.

Ewais, A.M.R., and R.K. Rowe. 2014. “Degradation of 2.4 mm-HDPE geomembrane with high residual HP-OIT,” in 10th International Conference on Geosynthetics (10th ICG), Sept. 21-25, 2014. Berlin, Germany: International Geosynthetics Society.

Government of Ontario. 2011. “O. Reg. 232/98: Landfilling Sites.” Accessed July 24, 2017.

Joshi, P., R. K. Rowe and R. W. I. Brachman. 2017. “Physical and Hydraulic Response of Geomembrane Wrinkles Underlying Saturated Fine Tailings”. Geosynthetics International. 24(1): 82-94.

Rentz, A.K., R.W.I. Brachman, W.A. Take and R.K. Rowe. 2017. “Comparison of Wrinkles in White and Black HDPE Geomembranes.” Journal of Geotechnical and Geoenvironmental Engineering. 143(8)

Rowe, R.K., P. Joshi, R.W.I. Brachman and H. McLeod. 2017. “Leakage through Holes in Geomembranes below Saturated Tailings.” Journal of Geotechnical and Geoenvironmental Engineering. 143(2)

Rowe, R.K. 2016. “Recent Insights regarding the Design and Construction of Modern MSW Landfills,” in EurAsia 2016 Waste Management Symposium, May 2-4, 2016. Istanbul, Turkey.

United States Environmental Protection Agency (USEPA). 2017. “Municipal Solid Waste Landfills.” Accessed June 21, 2017.

Guest Author: Ms. Sahar Pakzad, Marketing and Communications Coordinator at Klohn Crippen Berger Ltd.

Acknowledgement: Geotechpedia team would like to thank Ms. Sahar Pakzad, Marketing and Communications Coordinator at KCB Ltd, for sharing this post through Geotechpedia.

Disclaimer: Any views or opinions represented in this post are personal and belong solely to the author and all content provided is for informational purposes only. Geotechpedia makes no representations as to the accuracy or completeness of any information on this post or found by following any link on this post.



Measuring Permeability and Fluid Storage in the Ground

This is a guest post by Mr. Ian Gray, Managing Director of Sigra Pty Ltd.

Towards a technology for shallow testing in civil projects

Permeability chart

We have found that the equipment and methodology being employed for permeability testing in shallow wells to be, if not inadequate, at the very least misapplied.

We propose a cross-disciplinary approach — involving new technology and the application thereof — to meet the requirements of shallow permeability testing.

Permeability measurement is important because it is part of the prediction of the rate of fluid inflows, fluid loss, or how fluid pressures vary in the ground. For instance, a civil engineer will want to know whether ground water will pose a problem for whatever structure they are designing and building.

Apart from the rare instance of a steady state situation, all formation pressures change with time, and therefore the ability of the ground to store fluid matters.

To sensibly conduct any measurement one must first understand the geology.

While it’s acceptable to gain such an understanding from either borehole samples, borehole geophysics, or broad area methods like seismic or resistivity, we feel it’s much more useful to employ all these methods together.

Each engineering discipline has developed its own way of measuring permeability and storage behaviour, and we do feel that these practices have often proved inadequate, specifically in reference to civil projects, and could be improved with some understanding of the process and the use of suitable technology.

Let us examine these practices.

Methods and issues encountered by hydrogeologists and petroleum engineers.


The hydrogeologist who requires groundwater will choose to drill a well or wells into a suitable aquifer, and will pump from this to determine the production rate versus pressure (head) depletion in the well.

They will then observe pressure (head) changes in adjacent wells, so that the storage behaviour of the aquifer may be deduced.

These other wells are of course an extra cost to any project. However, they are the only way in which the storage behaviour in the ground may be properly determined.

Long term pumping tests of wells and the response in adjacent wells is a very good way to determine aquifer characteristics. Hydrogeologists will interpret their measurements in terms of hydraulic conductivity, which is a combination of absolute permeability of the ground and the viscosity of water.

They will describe the storage behaviour in terms of yield of fluid per unit area per unit fluid head change. The storage term used for a confined aquifer is storativity, and for the unconfined case, specific yield.

Petroleum Engineer

The petroleum engineer will drill a well which is usually deep and expensive. They wish to test the formation (ground) as quickly as possible because drill rig time is real money.

They seldom use pressure measurements in adjacent wells to determine storage parameters, due to the prohibitive costs of such wells for pressure sensing.

Because of the variation in fluids with location and time, the petroleum engineer focuses on absolute permeability and in determining the fluid parameters, such as viscosity and density, separately. The determination of storage behaviour is as much as possible determined by laboratory studies of core.

The key words regarding storage here are porosity and compressibility (change in porosity) of the rock, and compressibility of the fluids. They are a function of fluid pressure.

The hydrogeologist and the petroleum reservoir engineer both want to know permeability and storage. In addition, the hydrogeologist will probably want to know something about the recharge mechanism of groundwater. Any field testing undertaken by either of these disciplines will focus on examining transient behaviour.

The hydrogeologist will usually want to pump at a constant rate until the transient behaviour of the well can be defined, while the petroleum engineer will frequently use a drill stem test (DST) to produce fluid for a short period, then shut in the production zone and wait until the transient recovery behaviour is well established.

Both disciplines will want to obtain information on their reservoir or aquifer away from the test well. This is accomplished by the use of pressure measurement in surrounding wells, or by suitably designed test methods and analysis.

Permeability testing methods used in Civil Engineering and the issues they encounter.

The civil engineer, and to some degree the mining engineer, want to know whether water will be a problem for whatever structure they are designing and building. Their concern then is likely to be water make into an excavation, tunnel or mine, water loss from a dam or through an embankment.

Very frequently they wish to know what the pressure distribution is within the ground, as it directly affects the effective stress, and therefore the potential for failure.

Sometimes the civil or mining engineer will employ a full pumping test with associated pressure observation by piezometers. These cases are however unusual. Time and cost pressures have tended to lead to a series of short term tests that have been historically used.

In soils, these are typically falling head or slug tests, in which a hole is filled with water and the rate of change of head and hence volume change within the hole, is monitored for a period.

In rock, the test method is typically the packer test, in which a section of hole is sealed, and water is pumped in at a fixed pressure of one atmosphere as measured at surface, and the rate of inflow is monitored.

The final supposedly steady state (10 minute) flow rate is measured in Lugeons (litres/metre/minute), a value that was developed originally to simply determine whether the ground would take cement grout.

However, neither of these tests can be analysed to produce real values of permeability, and by definition single hole tests cannot provide any information on the storage behaviour of the ground.

Issues associated with the Falling Head Test

The falling head test produces a varying rate inflow.

The problem with this is the difficulty in separating pressure loss around the well bore, usually associated with drilling, from the response of the soil outside the zone of influence of the well.

This problem is made much worse because the process of injection almost invariably carries soil particles into the zone around the well bore, thus changing the near well bore behaviour. This means that it is not generally possible to separate near well bore pressure (head) loss from the transient response in the ground.

The results of such tests are therefore misleading—if the test is left for long enough to come to stabilisation it can yield information on the groundwater fluid level.

Issues associated with the Packer Test

The methodology of the packer test is that it should reach a steady state of fluid injection. If in fact it does so, it is an indication that the pressure drop between the rock and the fluid pressure within the hole are dominated by near well bore losses, typically by the size of the joint openings to and adjacent to the borehole.

The real information from such tests on the rock mass being tested is lost, because no attempt is made to determine the transient response of the ground.

Neither does the test provide information on the fluid pressure (head) within the ground, nor take this into account in how it affects the inflow rate.

Literature abounds on how to interpret such tests, and spurious correlations are published between the value of Lugeons and units of hydraulic conductivity, and by consequence, permeability.

We therefore have two tests that are widely used by the civil engineering industry which cannot provide the information that is required. Indeed, the results obtained are misleading, and their adoption could lead to serious errors in design. What can be done to remedy this?

The short answer is to change test methods.

Adopting the oilfield Drill Stem Test (DST) for civil and mining applications.

The most effective way to do this is to adopt the analogue of the oilfield DST for civil and mining applications. We have used these extensively for the coal seam gas and deep coal mining clients. We developed equipment and analysis to suit these applications.

The test needs a period of flow followed by zero flow from the test zone, during which pressure stabilisation is achieved. This is followed by an inflow period and then a period of no flow from the test zone, during which the pressure buildup is monitored.

This buildup time must be long enough to get a meaningful answer.

Low permeability ground tends to take a lot of time for the pressure recovery to deliver results with a useful measure of permeability. If there is no need to measure permeability down to low levels, then the test may be terminated early without providing precise value.

While flow from the test zone is the best choice, as it avoids contamination of the well bore with foreign fluids and clay particles, it is sometimes more practical to inject for a period at a constant rate, or by falling head, in the drill string. Changing the flow direction does not change the basis of analysis.

In Soil

These test techniques may be applied to soils, where the test may be conducted through a casing or standpipe, with the use of a downhole packer and pressure transducer to control flow. In rock, the equipment required to conduct a test comprises a single or straddle packer system, which incorporates a valve to control flow from the test zone.

Flow from the test zone is facilitated by purging the drill string of fluid prior to the test, or by running the tool into the hole with an empty drill string so that flow may occur into the drill string.

Pressures in the test zone need to be accurately logged, something that is relatively easy with the range of transducers and logging devices available.

Such tests can yield accurate information on permeability, and such features as barriers to flow or recharge boundaries within the ground. What they cannot do is provide information on the storage characteristics or the anisotropic nature of permeability.

To achieve this, other pressure sensing points (piezometers) must be installed.

This brings the testing process full circle, to one where a full pumping test might be used with at least three correctly placed piezometers to enable the determination of anisotropy in permeability and the storage behaviour.

The problem with this approach is that it is not possible to differentiate between anisotropy and inhomogeneity.

There is an alternative that enables the measurement of both inhomogeneity and anisotropy: Pulsed DST.

This involves sequentially testing individual boreholes and placing piezometers in these as each borehole test is finished. The next borehole to be tested sends a pressure transient to those boreholes drilled before and fitted with piezometers. The most convenient way to test each well is by conducting a DST in the test zones. Hence the name “pulsed DST”.

This method enables multiple measurements of mean permeability and directional permeability, so that both inhomogeneity and anisotropy may be assessed.

Guest Author: Mr. Ian Gray – BE, MAppSc, PhD, RPEQ, MAusIMM, SPE, Managing Director, Sigra Pty Ltd, Brisbane.

Acknowledgement: Geotechpedia team would like to thank Mr. Ian Gray, Sigra Pty Ltd, Managing Director for sharing this post through Geotechpedia.

Disclaimer: Any views or opinions represented in this post are personal and belong solely to the author and all content provided is for informational purposes only. Geotechpedia makes no representations as to the accuracy or completeness of any information on this post or found by following any link on this post.