Ochre and Subsurface Drainage in Finland

The risks of ochre deposition in subsurface drains are common on the sandy and peaty soils of Central and Northern Finland. The iron concentrations of ground water and sandy soils, and the mean for 14 fields with subsurface drainage being 23.2 ppm, were found to be high compared with the threshold values for risk of ochre deposition in Central Europe. The problems have, however, been small, which can be assumed to be due to the climatic conditions and method of underwater drainage, which has been applied systematically.