More than 90 % of the Estonian basic power supply is covered by oil shale-fired thermal power plants. Every year about eleven million tonnes of oil shale is fired. The environmental impacts of the oil shale fired power plants start from the mining and pre-treatment of oil-shale followed by the energy production. Main negative impacts to environment caused by energy production are:

• emissions into air,
• use of natural resources,
• production of solid waste,
• land use. 

Handling of OSA is one of the most serious environmental problems in Estonia today.

Combustion of one tonne oil shale generates 0,43 – 0,44 tonnes of OSA. Estonian power plants based on oil shale are producing over 6 million tons of oil shale ash annually from which over 96% is deposited on ash fields. The ash fields are in contact with millions of cubic metres of rainwater each year; the water becomes polluted and is a risk to the quality of the groundwater sources. The possibilities to avoid ash deposits are valuable for the environment.  The best solution is to convert OSA into products for the construction markets. 

However, there exist factors which render OSA utilisation undesirable: the recovered material does in many cases not meet the quality standards for input materials in certain production processes; the contaminant content of materials containing OSA is considered to be a problem when the construction is (probably) later demolished; OSA products lack public acceptance and hence market value. Also the absence of product specification, usage information and a clear definition of potential product liability are obstacles to the utilisation. All these are challenges to this project.  

OSA has high content of lime (CaO) which is a valuable regarding the use of OSA for civil-engineering purposes. OSA also contains a number of critical, water soluble and environmentally harmful substances like heavy metals the interaction of which is highly pH-dependent. This has to be considered in the processing of civil engineering materials. Environmental testing for long-term leaching has to be conducted before full-scale OSA reuse is allowed, to protect human health and environment. 

Before disposal or reuse OSA or materials containing OSA may have to be treated in a way that all harmful components are immobilised. However, the project aims at demonstrating OSA as additive or binder for different stabilisation purposes.  In that case the total amount of OSA in the mass of soil or other aggregates is normally less than 15 %.  The experiences with ashes and commercial binders indicate that this will not be a risk to the environment. Anyway, this project is going to prove it.

There are also other environmental aspects to promote the use of OSA for stabilisation. Estonia like most certainly many other countries of Europe has to import high volumes of expensive and high-quality aggregates for the infrastructure projects. An efficient additive like OSA gives a low-cost alternative for the societies: Instead of the conventional use of high amounts of high-quality natural aggregates the projects can be implemented by combining stabilisation techniques and the use of existing lower-quality and on-site soil materials.  This may reduce the use of roughly 500 million tonnes of natural aggregates from non-renewable sources involving heavy long-distance transports in Europe. Also this is environmentally beneficial due to reduced atmospheric emissions and improved protection of landscape, natural gravel and rock resources, and groundwater sources.