Monitoring wells at the National Crude Oil Spill Fate and Natural Attenuation Research Site near Bemidji, Minnesota

Monitoring wells near the location of a 1979 oil spill at the National Crude Oil Spill Fate and Natural Attenuation Research Site near Bemidji, Minnesota, in October 2010. Some are for sampling groundwater, some are for sampling soil gas, some are for sampling oil. The green PVC collar in the foreground is for measuring soil carbon dioxide (CO2) efflux. The large boxes house data loggers that are connected to pressure transducers, rain gages, and and soil moisture sensors. This is one of the best-studies oil spill sites in the world and the wells make up an “underground observatory” to better understand what happens when petroleum is spilled in the subsurface. There are dramatic redox gradients and narrow reaction zones necessitating the dense well coverage.