As a first year Masters student in the Geosciences Department, my area of focus is groundwater hydrology. An understanding of the properties that influence subsurface flow is integral in making management decisions regarding groundwater resources. The project that I am working on is a groundwater-stream water interaction study in Riverton, Wyoming. The study site lies adjacent to a former uranium processing plant that was active in the 1950s and 60s. Used mill tailings were discarded on 72 acres of the floodplain between the Wind and Little Wind Rivers and remained there for 25 years. Years of weathering and exposure allowed for the leeching of uranium and other heavy metals into the surficial aquifer below, and there is currently a 2-km plume of contaminated groundwater migrating towards and discharging into the Little Wind River.
The aim is to determine the future duration of contaminant loading and a timeframe for natural attenuation. To asses this, we try to make some inferences on groundwater age. Groundwater age can be defined as the time from when the water parcel entered the subsurface to the point of sampling. An understanding of the timescales of groundwater can be used to deduce recharge rates, flow rates, and timescales of contaminant transport rates. We sample the groundwater for the environmental tracers CFCs and SF6 and compare these values to known atmospheric concentrations throughout time giving us the apparent age of groundwater. This age distribution throughout the site provides insight to subsurface flow rates and paths. By quantifying the flux of groundwater through the system we can generate a prediction about the future duration of contaminate loading. We will use new age tracer data along with historical records to calibrate a contaminant transport model. An estimate of the timeframe for the duration of this contamination will be useful in making future site management decisions.