U.S. Geological Survey scientists prepare a tracer solution

U.S. Geological Survey (USGS) scientists prepare a tracer solution to conduct a natural gradient tracer test to measure anammox activity in groundwater. The tracer solution is prepared by pumping groundwater into a gas impermeable bladder to maintain the in situ dissolved oxygen concentration and then mixing in the tracer chemicals. The bladder is contained in an ice-cooled water pool to maintain the groundwater temperature until the solution is pumped back into the aquifer.