Experimental Investigation of Strontium Mass Transfer in a Dynamic Vadose Zone - Aquifer - River System
EMSL Project ID
25703
Abstract
At a number of DOE sites, groundwater flowing through contaminated sediments before discharging to a river is being relied on to meet regulatory standards. This natural flushing (i.e., monitored natural attenuation) solution has generally proven to be significantly less effective than predicted (e.g., Hanford 300 Area, Old Rifle UMTRA). Missing from these model predictions was the impact of river stage fluctuations on the contaminant flux between the vadose zone and aquifer, and the aquifer and river. At the 100-N Area on the Hanford Site, Sr-90 concentrations in the groundwater are up to three orders of magnitude higher than EPA drinking water standards. Seasonally and episodically elevated aquifer water levels due to river stage fluctuations are associated with higher Sr-90 concentrations in the groundwater. Mobilizing sorbed Sr-90 from contaminated sediments in the lower vadose zone during these hydrologic transients appears to provide a long-term source as well as a dispersal mechanism. Strontium sorption is governed by competitive ion exchange and is thus sensitive to solution chemistry. Near the river the concentration of the principal exchangeable cations, calcium and magnesium, dynamically range between the river and groundwater end members. In this case, the concentration of all the major ions in the river water are several times lower than the groundwater, which should result in significantly higher Sr-90 sorption. Intermediate-scale column and flow cell experiments are proposed to come to an improved understanding of the dynamic behavior in fluctuating water table systems.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2007-08-01
End Date
2009-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members