AIR-BEAM ROLLER STOCKPILE COVER (ARSC)

ARSC covers materials you can't walk on - if you want to cover materials that are not load-bearing (such as biosolids, sewage sludge, grain, industrial organic wastes) an Air-beam Roller Stockpile Cover is the answer - you simply roll it out across the stockpile. You can walk on the ARSC even when it would be impossible to walk on the stockpile it is covering.

ARSC stockpiles do not re-wet, which means they do not slump or spread. In the case of soil improvers for land application, they are as good (or better) when they come out of an ARSC stockpile as when they went in. The geotextile lets water vapour out, which means the surface dries.

ARSC stockpiles do not smell - the geotextile contains all odours. There might still be odour when a stockpile is spread, but at least that is transient and can be managed by rapid incorporation.

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Awaiting Image 2

When the ARSC was rolled back this stockpile was dry and odour-free and the underside of the ARSC was clean.
     

ARSC improves legal compliance - UK law requires that a stockpile is "secure in relation to waste kept in it" and this is achieved "if all reasonable precautions are taken to ensure that the waste cannot escape from it and members of the public are unable to gain access to the waste". Other countries have similar requirements: some even stipulate covering. If a person or animal got into a stockpile, or if it were to move or cause pollution by runoff, it would be difficult to argue in defence that the stockpile had been secure.

ARSC reduces haulage costs - if the risk of movement or odour currently restricts the siting of stockpiles to shallow gradients, remote from neighbours, ARSC will give you greater freedom of choosing sites and hence access to more land.

ARSC - The Issues

Wet weather degrades stockpiles of biomaterials (dewatered biosolids, composted materials, industrial organic wastes, etc.). They are liable to slump and/or to release run-off. This can be a water pollution risk, and a risk to property. Whatever the site where the biomaterial is going to be used there will be a limited time window for application, but invariably the production facility is producing all the time. Farmers etc. appreciate seeing the biomaterial on site (safely contained in an ARSC) so that they know that application is guaranteed.

Wet slumping stockpiles encroach on the surrounding land. They are diffficult to contain and, when the time comes to spread, application is slow, less precise, more difficult and more costly. If you know your stockpiles might slump you should site them where the gradient is shallow; but this is a restriction on the land that can be treated and therefore increases costs.

Can you contain a stockpile that starts to move? It is difficult because the side pressures are immense. Building a wall with large straw bales might be successful, but it is expensive in labour and materials and there is the problem of what to do with the rotting bales at the end of the job. If rain continues the stockpile can move the bales and then you need to secure them by driving stakes into the ground; that too can fail and release the contents. If you push up earth walls you make a lagoon, with consequent risk of drowning, etc. unless you put up expensive fencing.

Will improving dewatering prevent slumping? No - even digested biosolids that had been dewatered to 25%DS have slumped during wet winters.

Lime stabilised dewatered biosolids do not slump. That's true but because stockpiles drain they lose leachate which is a water pollution risk. An ARSC can also get over the pH>12 issue associated with this otherwise very useful treatment process.

Does compost need ARSC? Yes it does; when stockpiles of composted materials become saturated with water oxygen is excluded; this sets up anaerobic conditions which produce compounds that are malodorous and/or phytotoxic.

Legal issues related to stockpiles. In many countries it is an offence to make stockpiles that are not secure and contained. In the EU there is added obligation if the pH is 12 or greater. Odour nuisance can be a legal offence. ARSC avoids all these issues.

What about adding structure and strength with bulking agent? This can be done but it is more expensive than ARSC and it does not satisfy the legal obligation for safe containment. Also there is the question of finding bulking agent free from contaminants (including weed seeds).

ARSC - The Answers

The answer is to keep the rain out - then there are none of these problems of stockpile movement and leachate etc. Keeping rain out has been difficult until now but "

Air-beam Roller Stockpile Cover" (ARSC) answers all the issues. ARSC can be made in sizes to suit your requirements. ARSCs are made from high performance HDPE/LDPE laminate geotextile using specialist HF welding technology. The geotextile is rated for at least 5 years' external use. It is olive green and "sympathetic" in the landscape. An ARSC for a 25 m x 25 m stockpile only weighs about a quarter of a tonne. When the airbeam is inflated it is a rigid cylinder. The beam has low rolling resistance because of its large diameter, which means that it can be rolled across the stockpile easily. It only takes 2 people about 15 minutes to roll out the cover and the same time to roll it up. Rolling means that the cover is not smeared with the material in the stockpile and that it is not ripped if the stockpile contains sharps

ARSC covered stockpiles are contained and secure; they look professional, eliminate odour and maintain quality so they are easy to spread. ARSCs are quick to deploy and recover; they are reusable and inexpensive.

ARSC reduces haulage and spreading costs: stockpiles can be sited on more sloping ground or closer to housing than otherwise; this makes more land available.

ARSC improved quality - in a trial, when the ARSC was taken off a stockpile of digested dewatered biosolids after one month (May-June 2004) when the air temperature had peaked at 28.8°C (83.9°F) the surface had dried to 28.6%DS from 20%DS and the Escherichia coli content in the surface was only 1.85 log10 per gDS; deeper in the stockpile it was 3.69-4.07 log10. ARSC can usefully be part of a HACCP-designed treatment protocol.

ARSC - The Advantages

ARSC improves legal compliance - UK law requires that a stockpile is "secure in relation to waste kept in it" and this is achieved "if all reasonable precautions are taken to ensure that the waste cannot escape from it and members of the public are unable to gain access to the waste". Other countries have similar requirements: some even stipulate covering. If a person or animal got into a stockpile, or if it were to move or cause pollution by runoff, it would be difficult to argue in defence that the stockpile had been secure.

ARSC reduces haulage costs - if the risk of movement or odour currently restricts the siting of stockpiles to shallow gradients, remote from neighbours, ARSC will give you greater freedom of choosing sites and hence access to more land.

ARSC withstands strong winds - it has an integral system of ground anchoring that stops the wind getting underneath and moving it. This ground anchoring also stops rainwater running off the ARSC and back under the cover.

Awaiting Image 2 arsc_02 Gale force gusty wind peaking at force 8-9 (40 knots, 46 mph, 74 km/h) and rain had no effect on this ARSC and its stockpile.
     

ARSC - The Cost

ARSC is portable and reusable - it can be used in field situations or configured for a fixed facility. The materials themselves have a normal life of at least 5 years outdoors with exposure to sunlight.

ARSC is not expensive - the price of an ARSC depends on its size and the quantity ordered, e.g. 10 or more would enable less expensive fabrication. For example an ARSC to cover a stockpile 25 m x 25 m would add less than £1 / m3 for 5 uses of the cover. By 15 uses this comes down to about £0.50 / m3. This includes the initial cost and the labour and equipment for deploying and recovering the ARSC. On the same basis the cost for straw bale containment is approximately £1.75 / m3 . The cost of ARSC is easily offset, by savings in haulage and spreading, stockpile deterioration, alternative forms of containment and legal fees depending on circumstances.

What does ARSC cost? - the prices of ARSCs depend on the sizes and quantities ordered so please contact RCBWEL or TIM EVANS ENVIRONMENT to discuss your requirements and ask for a quotation. Even with conservative assumptions, ARSC only adds £1 / m3 to the total cost over 5 uses and that's before offsetting savings in haulage, etc. The breakeven compared with containment with straw bales (which are less effective) is less than 2 uses. Using an ARSC is always less expensive than straw incorporation.

ARSC DEPLOYMENT

  The ARSC is protected during transport and storage by its integral cruciform transport bag. arsc_03 With its carrying handles, the bag is easy to manoeuvre and position on the ground at the edge of the stockpile half way along one edge. If it is windy it is best to place the ARSC on the upwind side. arsc_04
  The transport bag is unfastened and the two sides of the ARSC are rolled out along the ground adjacent to the stockpile. It is best to fill the first water ballast tube when it has been rolled out because this secures the cover and prevents the possibility of wind movement. arsc_05 The air-beam roller is inflated using a portable air blower. A garden leaf blower does the job in less than 5 minutes. It is effective, inexpensive and readily replaceable. arsc_06
  The ARSC is rolled across the plateau; this is easy because of the large diameter of the roller. arsc_07    
  When the covering has been completed the roller is deflated and the remaining water ballast tubes are filled. It takes 2 people about 15 minutes to deploy an ARSC, and a similar time to roll it back again. The groundsealing water-ballast tubes have been filled. They exert about 17 kg per linear meter. A stockpile 25m x 25m needs about 1.75 m3 water. Rainwater cannot enter an ARSC stockpile and the cover will bear the weight of adults. arsc_08 Un-deploying is the reverse sequence. The ballast tubes are drained, the roller is inflated and rolled back across the stockpile using the grab-straps built into the cover. It is rolled onto the transport bag, the roller is deflated, and the two arms of the cover are rolled into the bag, which is closed with its ratchet straps. arsc_09