Cost savings of up to £1 Million per development have been identified as being possible across the sector if secondary containment options are investigated at an early stage in plant development.

All too frequently a common misconception is raised, being that concrete must be used for secondary containment systems. While there is no issue with using concrete for secondary containment, it should be the final of 3 options when selecting which containment system to install around your plant from both an environmental and cost perspective.

When undertaking a cost benefit analysis, the 3 options which should be investigated at a site selection stage are:

1 Mineral (engineered clay) containment system

2 Geosynthetic (with of without mineral liner) containment system

3 Concrete containment system

The best way of thinking about containment for your AD Plant is comparing it to how we go about containing waste across the world.

We do not construct landfills from reinforced concrete for very good reason. Firstly it is not impermeable and secondly the cost and environmental impact from doing so would be inordinate!

Household and commercial waste poses a much greater threat to groundwater from leachate than an AD plant presents from digestate and more commonly that not the point raised here is that the digestate poses little risk as it is spread on the land as fertiliser. While being very true, the risk from digestate is that gross discharge to a watercourse of vulnerable aquifer can have disastrous effects, hence its importance and requirement.

While not every site is suitable for a mineral (engineered clay) lining system, more often than not the local drift geology is perfectly suited to inclusion of a mineral liner, or a local source can be used for importing materials. With clay costs potentially being irrelevant if available on site the cost savings start to mount up very quickly.

Benefits

Cost: The main benefit from a commercial perspective of using a mineral lining system is cost. If available on site these costs are negligible, if imported from a local source then costs can be as little as £2 m3. Add in engineering costs and construction of a mineral liner could be as little as £3-5 m2.

Speed: Mineral lining systems are fast to install. Engineering of up to 1,000 m2 per day is easily achievable.

Durability: Concrete isn't durable. In fact its not impermeable over such a large area as penetrations, joints and cracks all afford weakness to the system.

Indirect Cost Saving: Using a concrete secondary containment system limits the amount of buried pipework so gantries and insulation must be factored into the cost. A mineral liner allows the use of buried pipework systems as the mineral liner can be easily designed to allow fill to be placed above and increase levels where necessary.

Aesthetics: Lets face it the aesthetic appeal of concrete in a rural setting isn't great. A mineral liner should be covered with topsoil and vegetated which provides a great opportunity to both appease planners and the local community. Additionally, if vegetated in non trafficked areas the secondary containment area can even provide additional feed stock for the plant.

Piling: You cant pile through a mineral or geosynthetic clay liner (GCL) is something which frequently gets raised. Piles rely on friction provided by drift geology. Enhancing this medium could even reduce the number and depth of piles required. Even GCL can be piled through with tolerances of less than 6 mm between the pile and the GCL.

Self Healing Properties: Concrete doesn't take well to bangs and knocks. Once damaged repairs can be costly and difficult to undertake. One main advantage of a mineral or GCL liner is that they are self healing. Any small damage will self heal under normal conditions.

To Summarise

With tariffs reducing the need to cut CAPEX has never been greater. If you haven't yet looked at the possibilities of using a mineral or geosynthetic containment system there has never been a better time to do so.

CQA International Ltd are able to advise on all aspects of your containment needs from planning, site investigation, design, Quality Assurance and more. Feel free to contact us on 01782 338979 or email enquiries@cqainternational.co.uk to discuss in further detail.