1. J. R. Giles, C. P. Oertel A Comprehensive Study of the Depth Profile of Cs-137 in Surface Soils at the Idaho National Laboratory Monitoring and Surveillance Committee Meeting November 17, 2011

2. Background Soil monitoring data required to meet Federal (DOE) Environmental monitoring regulations Soil monitoring data are an integral part of the radiological baseline for INL –Radiological baseline necessary for attracting new programs/projects –Radiological baseline data are used during emergency response for event mitigation Data must be defendable

3. Monitoring Goals and Methodology Goals: 1.Identify areas where Cs-137 > 0.23 pCi/g. Risk value of 1.0x10 -6, the risk based concentration for a 30 year residential scenario 2.Build multiyear database in order to closely monitor any trends and provide measurement efficiency Method: 1.Perform in situ measurements of Cs-137 2.Use measured data to generate predicted Cs-137 at unmeasured locations 3.Use advanced geostatistical methods to refine measurement locations

4. Equipment Description Standard Field Configuration: –n-type or p-type HPGe detector on tripod –20-m diameter uncollimated field of view @ 1-m height –Data analysis performed using Environmental Measurements Laboratory M-1 Protocol (HASL-300)

5. Equipment Calibration Calibration factor, N f /A m (cts/s)/(pCi/g), is given by: N f /A m = N 0 /φ ∙ N f /N 0 ∙ φ /A m N f /A m =peak count rate per unit concentration N 0 /φ=count rate per unit fluence rate at normal incidence –detector dependent N f /N 0 =angular correction factor at a given γ-ray energy –detector and source dependent φ /A m =fluence rate at detector per unit concentration –source dependent

6. Depth Distribution Depth distribution described as α/ρ (cm 2 /g), where α is defined as the inverse of the relaxation depth. The relaxation depth is the depth at which the concentration is 1/e of the surface value (~37% of the surface concentration; ρ is the soil density. Three common distributions: 1.Uniform – Typical of disturbed soil, α/ρ=0 2.Planar – Typical of recent fallout, α/ρ=∞ 3.Exponential – Typical of aged fallout, 0<α/ρ<10

7. Soil puck collection Soil puck samples collected at each sampling location. Samples are comprised of 10 subsamples, composited at 2.54 cm depth increments down to 30.5 cm, or refusal.

8. 3-D Depiction of Soil Sampling Plan for the Determination of the Cs-137 Depth Profile

9. Use of Puck Data to Measure α/ρ

11. Importance of α/ρ α/ρ (cm 2 /g)Cs-137 (pCi/g) 00.70 0.0630.49 0.100.38 0.50.15 1.190.11

12. Site-Wide α/ρ Values Facilityn Facility Average , cm 2 /g Facility Average Relaxation Depth, cm ARA120.183.7 ATRC80.183.7 CITRC60.164.2 INTEC140.213.1 Large Grid170.125.3 MFC60.213.1 NRF50.174.0 RWMC160.174.0 TAN80.144.8

13. Site-Wide α/ρ Statistical Summary , cm 2 /g Relaxation Depth, cm Minimum0.123.1 Maximum0.215.3 Average0.174.0 Standard Deviation0.030.72

14. Cs-137 Depth Distribution Across INL

15. INL in situ – 2006

16. Geostatistical Methods Applied to INL Soil Monitoring Network Basic Kriging with declustering applied to 2008 through 2010 data sets Kriging error surfaces used to optimally locate sample points 2011 data set large grid points were kriged and then error values analyzed using ESRI network densifier tool to produce new large grid locations for 2012 Some INTEC points from 2011 were eliminated for 2012 based on localized kriging error surface 2012 projected network is 248 points and is more spatially balanced

17. INL in situ Large Grid – 2011 and 2012

18. INL in situ – 2011 and 2012

19. Questions…?