Experimental Investigation of Sr-90 Subsurface Contamination Sequestration in Hanford 100N Area Sediments by Surface Infiltration of an Apatite Solution
EMSL Project ID
25640
Abstract
Strontium-90 (Sr-90) discharge from past-practice liquid waste disposal sites in the Hanford 100N area have resulted in Sr-90 release to groundwater, Columbia River, and biota on the Columbia River bank. Although liquid discharges were terminated in 1993, Sr-90 adsorbed on aquifer solids remains as a continuing source to the Columbia River. The current implementation plan is to inject a low concentration (10 mM citrate) apatite-forming solution, which should result in sufficient removal capacity of Sr-90 for ~10 years followed by higher concentration injections to develop further capacity. Because most (50 - 70%) of the Sr-90 contamination is in the shallow, variably saturated Hanford Formation, the most efficient means of treating this zone may be surface infiltration of the apatite-forming solution, but there has been no development of this technology for vadose zone application.We propose to develop an infiltration strategy that defines the precipitation rate of an apatite-forming solution and Sr sequestration processes (Fig. 1a) under variably saturated (low water content) conditions. We will develop this understanding through small-scale column studies, intermediate-scale 2-D experiments, and numerical modeling, to quantify individual and coupled processes associated with apatite formation and Sr-90 transport during and after infiltration of the Ca-citrate-PO4 solution. Development of capabilities to simulate these coupled biogeochemical processes during both injection and infiltration will be used to determine the most cost effective means to emplace an in situ apatite barrier with a longevity of 300 years to permanently sequester Sr-90 until it decays. After peer review, this project was funded by U.S. DOE/EM-22 for late FY06 through FY08. To date, unsaturated batch studies have demonstrated that citrate biodegradation and apatite precipitation occurs (Figure 1b) and a sat./unsat. reactive transport code (42 reactions, 51 species) has simulated 1-D transport experiments well.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2007-05-25
End Date
2010-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members
Related Publications
J. Szecsody, J. Fruchter, C. Burns, M. Rockhold, M. Oostrom, M. Williams, V. Vermeul, and R. Moore, Sr-90 Immobilization by Infiltration of a Ca-Citrate-PO4 Solution into the Hanford 100N Area Vadose Zone. Waste Management 2008 Conference, Phoenix, AZ, Feb 24-28, 2008. (paper and presentation)
Szecsody JE, ML Rockhold, M Oostrom, RC Moore, CA Burns, MD Williams, L Zhong, JS Fruchter, JP McKinley, VR Vermeul, MA Covert, TW Wietsma, AT Breshears, and BJ Garcia. 2009. Sequestration of Sr-90 Subsurface Contamination in the Hanford 100N Area by Surface Infiltration of a Ca-Citrate-PO4 Solution . PNNL-18303, Pacific Northwest National Laboratory, Richland, WA.
Szecsody, J., Rockhold, M., Oostrom, M., Moore, R., Burns, C., Williams, M., Zhong, L., Fruchter, J., McKinley, J., Vermeul, V., Covert, M., Wietsma, T., Breshears, A., and Garcia, B., 2009, Sequestration of Sr-90 Subsurface Contamination in the Hanford 100-N Area by Surface Infiltration of a Ca-Citrate-Phosphate Solution, Pacific Northwest National Laboratories, PNNL-18303.
Thompson, K.M., R.J. Fabre, J. Szecsody, V. Vermeul, R. Fellows, M. Williams, J. Fruchter, An innovative approach for constructing an insitu barrier for strontium-90 at the Hanford site, Washington, Waste Management 2009.