Community Wastewater Infiltration at 69o Northern Latitude – 25 Years of Experience.

When Bardu municipality located at 690 northern latitude in Norway were to renew their wastewater treatment facility in the early 80«s they chose to pump the sewage effluent from the 5000 inhabitants of Setermoen into a nearby glaciofluvial sand and gravel deposit. Initially the system consisted of two open sedimentation basins succeeded by three 2m deep open v-shaped alternating infiltration basins. The deep basins were chosen so that the surface could freeze while the water would still infiltrate below the ice. In year 2000 the municipality decided to install garbage grinders in all homes. This increased the organic load to the system and a new sedimentation basin succeeded by a simple surface trickling system was constructed up front of the existing system. The unsaturated zone below the basins is 7m. Since the startup in 1987 groundwater has been pumped regularly from a well between the infiltration basins. A large groundwater survey (1995 -1998) showed that this well gave representative values of the treated water. The overall treatment performance has been 85-90% for COD, 60-70% for total nitrogen (N) and 99% for phosphorus (P). The water meets European standards for swimming water with respect to indicator bacteria. Despite an average annual temperature of +0.7oC nitrification with subsequent denitrification can explain the high N-removal. Under each basin the capacity for P-removal is estimated to last 14 years. The system has saved the municipality an estimated 45 million NOK over 25 years compared to investment and operation of a conventional mechanical/chemical treatment system.