Abstract

There are various methods available for treating the runoff water from peat mining, and this research concentrates on measures applied within the peat production areas themselves. The work is divided into three sections: comparison of sod peat and milled peat production, development of a new subsurface drainage method and the use of barriers constructed of wood chips to equalize peak runoffs.

The research into peat mining methods was carried out by comparing similar production areas over a period of four years. The methods did not appear to have any effect on the mean runoff, but the peak runoffs from sod peat production were smaller than from milled peat production. The furrows made by the sod peat machine seemed to equalize the peak runoffs and at best reduced their value by 25 millimetres. The increase of mean phosphorus content resulting from milled peat production was statistically significant, and the peak solids content was higher, but the production method did not appear to affect other mean concentrations significantly.

A new subsurface drainage method that uses rock fibre boards as vertical water conductors was developed. These were used to lead rain water and meltwater from snow away from the production areas to the subsurface pipes so that no surface water entered the collector ditches serving the production area. The method was tested in two production areas over a period of six years. Subsurface drainage proved to be an efficient method, and the vertical water conductors eliminated problems arising from the poor water conductivity of peat and the presence of ground frost. Natural peatlands require pre-drying before subsurface drains can be constructed, however. Subsurface drainage is better able to equalize runoffs than open ditches, so that no high peak runoffs occur in properly planned production fields. Also, subsurface drainage reduces solids, COD and the colour by comparison with open ditches, but increases the iron content. The results regarding phosphorus and nitrogen vary a great deal and no clear difference could be detected. Concentrations in the areas where subsurface drainage was used varied very little and no peak concentrations similar to those in areas with open ditches were detected. This together with the uniform runoffs substantially reduces stress to the environment.

The feasibility of using barriers constructed of wood chips in bed ditches and in peat redistribution areas was also investigated. The barriers worked well in the peat redistribution areas and the research is being continued with attempts to improve the functioning of the structures. The use of these barriers in bed ditches proved too laborious.