EXAMPLE Pathways of Liquid Effluents in Groundwater and Surface Water (Section 2.4.13 SAR)

1. EXAMPLEPathways of Liquid Effluents in Groundwater and Surface Water(Section 2.4.13 SAR) FRAMES-2.0 Workshop U.S. Nuclear Regulatory Commission Bethesda, Maryland November 15-16, 2007 Pacific Northwest National Laboratory Richland, Washington

2. Purpose • Demonstrate Hierarchical Modeling • SSAR assessment: instantaneous mixing, advection, retardation, decay • Modeling: mass balance, advection, dispersion, retardation, decay • Instantaneous release • Long-term release (20-yr leak) • Explore Conservative Assumptions • Full mixing over the Aquifer Depth • Largest Darcy Velocity • No Dispersion • Register and use an Excel Spreadsheet 2

3. Problem Description(direct quote from SAR) “Reactor Coolant Storage Tank is postulated to rupture, and 80% of its liquid volume (92 m3) is assumed to be released in accordance with Branch Technical Position 11-6…Flow from the rupture is postulated to flood the building and migrate past the building containment structure and sump collection system and enter the subsurface at the top of the building slab…(V)ertical downward flow ensues. A pathway is created that would allow the entire 92 m3 to enter the groundwater system instantaneously.” 3

4. Problem Definition • No vadose zone, aquifer only • Uses known tank concentrations • Instantaneously places 80% (not 100%) of the tank’s mass into only the aquifer’s effective pore space • Uses tank’s total liquid volume to estimate the plan view area of contamination • NOT an instantaneous release scenario, which requires mass balance checks on water and mass flux rates • Mixes contamination over the aquifer depth (conservative?) • Maximum Darcy velocity (noted as conservative) • Advection, Decay, and Retardation Only (noted as conservative) • No Dispersion (noted as conservative) 4

5. Source Upper Aquitard Fully Mixed River Upper Aquifer Unit Source Upper Aquitard Plume Plume River Upper Aquifer Unit Fully Mixed With Dispersion 5

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7. Modules Source, Vadose Zone, and Aquifer Transport • FRAMES Constituent Database Selection • Source (User-defined source term) – WFF Vadose Zone Module • MEPAS 5.0 Aquifer Module • MEPAS 5.0 River Module Exposure/Intake/Risk • MEPAS 5.0 Exposure Pathways Module • MEPAS 5.0 Receptor Intakes Module • MEPAS 5.0 Health Impacts Module 7

8. Model Input Registering an Excel Worksheet (separate presentation) 8

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12. Constituent Database 12

13. “Source-Term” Module 13

14. Aquifer Module 14

15. River Module 15

16. Chronic Exposure Module 16

17. Intake Module Impacts Module 17

18. Output Results 18

19. Constituent Concentrations in Aquifer at River’s Edge pCi/mL pCi/mL pCi/mL Years 19

20. Comments & Investigations • Modeling provides us with an opportunity to more fully understand the problem. SAR case ignores mass balance of water flux rate. • Maximum Darcy Velocity is conservative – Reduce SZ Darcy Velocity one order of magnitude • Fully mixed condition is conservative – Increase the aquifer depth 20

21. Check to see if a maximum saturated zone Darcy velocity is conservative: • Reduce the saturated zone Darcy velocity by an order of magnitude (i.e., 1/10th) 21

22. Reduced by 1/10th 22

23. Reduced by 1/10th 23

24. Reduced by 1/10th 24

25. Reduced by 1/10th 25

26. Constituent Concentrations in Aquifer at River’s Edge at 1/10th the Darcy Velocity pCi/mL pCi/mL pCi/mL Years 26

27. Hierarchical Modeling Results 27

28. Check to see if fully mixed conditions in the aquifer is conservative: • Increase the aquifer thickness. • This case was not run, but the modeling can provide insight on how aquifer depth can impact the conservative assumption. 28

29. Rule-of-Thumb Relationships 29

30. Rule-of-Thumb Relationship Definitions 30

31. Summary • Many important factors determine whether scenarios and assumptions are conservative • Interdependencies between parameters • Duration of release • Time of concentration • Water mass balance • Contaminant mass balance 31