Water quality affected by interactions with filter media in raingardens

Abstract

The objective of this thesis is to investigate how the filter media in raingardens can affect the water quality. This will be done by comparing water quality of the water entering the raingarden with the quality of the water exiting the raingarden. Water sampling and flow measurements will be done in the research raingarden and a mesocosm experiment at NMBU Campus As and the Bolstadhagen raingarden and along Bjørnstjerne Bjørnsonsgate in Drammen. The water will be tested for nutrients, metals, and salts as well as PCBs, PAHs and oil in the raingardens in Drammen. Due to the composition of the raingardens with both an organic rich mixed soil layer and a sand layer it should be able to both adsorb dissolved components and remove particulate bound contaminants. To study these effects, soil samples will be tested for cation exchange capacity and organic matter and compared with samples from before the raingarden was planted.

The analysis in the research rain garden showed low levels of pollutants but an increase in colour. The mesocosm experiment showed leaking of nutrients as well as an increase in colour. The increase in colour can also be seen in increased turbidity and total carbon measurements. The analysis conducted in the Bolstadhagen raingardens showed no PCBs, PAHs or oil in the water entering, but some PAHs in the water in the outlet. There was a decrease in chloride and sulphide between the inlet and the outlet. Infiltration tests conducted in Bolstadhagen showed an increased infiltration compared with previous infiltration test.