90-100 million tons of aggregates are used annually in Finland, which is approx. 18 tons per inhabitant. Sand and gravel are extracted year from ca. 3000 gravel pits and rock aggregates from 300 extraction sites. Most extraction sites lack post-treatment or the post-treatment has been insufficient. Quarrying, especially gravel extraction often causes harmful changes to the landscape and to the characteristics of the groundwater. It is possible to reduce the harmful effects of aggregate extraction with regional planning and the post-treatment of extraction sites.
Over the last few years post-treatment research on gravel extraction sites has been conducted on a large scale as well as in small experimental areas and in laboratory. The suitability of several topsoil materials for the post-treatment of gravel extraction sites has been investigated using seep water monitoring in the lysimeter field, and by growth and soil analysis in experi-ment areas. The topsoil materials tested included peat, sludge from gravel washing, and the original topsoil from the gravel pit, soil surplus, decomposed bark, and mull.
The study presents the regional plans for areas suitable for aggregate extraction. This study also evaluates methods for integrating the sustainable use of groundwater and landscape pro-tection with aggregate production. This is done in order to ensure a good quality of groundwa-ter, the diversity of nature, and landscape values, as well as to secure the supply of good qual-ity aggregates near construction and civil engineering sites. In addition the study presents the principal goals for the rehabilitation and post-treatment of extraction sites and, in particular, the role of topsoil material.
Extraction sites lacking topsoil material including organic components are poor substrates for vegetation and are exposed to the seepage of harmful substances into the groundwater. The most suitable topsoil materials improved growth conditions because they increased the amount of organic matter, fertility and water retention capacity of the topsoil. Suitable materi-als did not allow leaching of significant concentrations of harmful substances into the groundwater, nor did they significantly decrease the total amount of aquifer groundwater. The best result was achieved when the original topsoil from the gravel pit was used as cover mate-rial. Unfortunately, the volume of this material is usually not enough to cover the area of the extraction sites. For this reason, other suitable materials have to be found elsewhere. In these cases the suitability of the topsoil material is confirmed with soil analysis before use. A mix-ture of decomposed peat and sand, for example, was the preferred topsoil material among those tested.