1 I Closure of the Oak Ridge National Laboratory Hydrofracture Facility: An Opportunity to Study the Fate of Radioactive Wastes Disposed of by Subsurface Injection1 C. Stephen Haase Karen L. Von Damm Stephen H. Stow CONF-8709170--1 DE88 001738 Environmental Sciences Division Oak Ridge National Laboratory Oak Ridge, Tennessee 37831-6317 ABSTRACT At Oak Ridge National Laboratory, subsurface injection has been used to dispose of liquid low-level nuclear waste for the past two decades. The process consists of mixing the liquid waste with cement and other additives to form a slurry that is injected under pressure through a cased well into a lowpermeability shale at a depth of approximately 300 m (1000 ft). The slurry spreads from the well along hydraulic fractures and sets to form irregularly shaped grout sheets of up to 200 m (650 ft) in radius. Over 2.6 x 106 gal (1.8 x 107 L) of slurry, containing more than 5.5 x 1016 Bq (1.5 x 106 Ci) of radionuclides (principally ^Sr and 13/ Cs), have been disposed of since this process was developed in Research sponsored by Office of Defense Waste and Transportation Management, U.S. Department of Energy, under contract DE-AC05-84OR21400 with Martin Marietta Energy Systems, Inc. 'The subminsd manuscript has heen " " " w a d by a contractor ol the U.S. Government under contract No. DEA C 0 5 - 8 4 O R 2 I 4 0 0 . Accordingly, the U S Government retains a noneadusivo. royalty-free license to publish or reproduce she pubished form of this contribution, or allow others to do to. for U.S. Government purposes.' MASTER ' the eaiiy 1960s. Under its underground injection control regulations, the state of Tennessee has tentatively assigned a Class V status to the well. In 1986, the U. S. Department of Energy, owner of the facility, decided to close the site. Closurerelated site characterization provides a unique opportunity to study the fate of the injected wastes. A series of monitoring wells are in place to measure groundwater chemistries within the injection strata and within overlying and underlying confining units. Initial results indicate that (1) contaminated groundwater surrounds the grout sheets in the injection zone, extending at least as far as 300 m (1000 ft) from the injection well; (2) contaminated groundwater is largely and perhaps exclusively confined to the host formation; and (3) of the two principal radionuclides disposed of (90Sr and 137 Cs), only ^Sr is present in the contaminated groundwater. The illite-rich mineralogy of the the injection formation strongly absorbs 137 Cs and greatly retards its; migration. Movement of 90 Sr, however, is not as greatly retarded by the injection formation. Geochemnv> Depth (m) Na+ K+ Mg +2 CV 2 Sr +2 Ba+2 Fe tot Mn tot ClBr SO 4 - 2 NCy 2 Alkalinity 9?Sr 3 1 2>>> 324 62,000 220 4,200 24,000 2,200 660 nm 3 nm 3 156,000 1,800 <100 400 15 i.2E5?2.5E4 nd 2 3C 320 57,000 230 4,400 26,000 2,600 610 130 100 150,000 2,100 <50 1,991 0 9.4E4?2E3 nd2 4<>> 266 12,000 77.0 260 2,800 210 1.5 23 3 24,000 210 522 <10 60 5e 182 27,000 nm 3 2,200 13,000 1.300 410 46 26 71,000 580 <50 20 <2 6f 213 30,000 740 2,700 13,000 1,300 89 5.3 3.4 98,000 840 <50 18 3 250?70 1.0+0.6 78 330 37,000 330 1,300 11,000 1,400 8.6 3.1 1.1 91,000 750 <50 66 20 2.0E4?2E <1 320 59,000 240 4,100 22,000 2,300 680 170 140 150,000 1,400 <50 442 0 3.5E4?2E3 nd 2 100?50 4.6?1.1 0.910.9 0.5410.1 Chemical data are are in jig/mL. Radionuclide data are in Bq/L. Uncertainties for chemical data are approximately 110%, and for radionclides as stated. 2 Not detected, ie. looked for but not found. 3 Not measured. a Well DM1-PV, sampled on January 31,1986 (Haase, Switek, and Stow 1987). b Well DM1-PV, sampled on November 19,1986 (Haase, Switek, Stow, King, and Pollard 1987). c Well DM2-PV, sampled on January 31,1986 (Haase, Switek, and Stow 1987). d Well DM3a-PV, sampled on January 30,1986 (Haase, Switek, and Stow 1987). << Well HF4-S200RC, sampled on May 22,1986 (Switek et al. 1987). f Well DM1-RT, sampled on January 30,1986 (Haase, Switek, and Stow 1987). g Well DM1-RM, sampled on January 30,1986 (Haase, Switek, and Stow 1987). DISCLAIMER This repor. was prepared as an account of work sponsored by an agency of the Uniled States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.