GPS based gamma survey for decommissioning NORM sitesE. Ruedig, PhD, CHP

T. Alecksen

M. Schierman, CHP

24 September 2019

ERG

True distribution of

soil contaminationInvestigation grid

+ =OR

ERG Note: figure after Lively, J. The Art and Power of Data Imaging. ICEM2013.

GPS gamma survey data➢ Method for gathering soil concentration data for gamma emitting NORM over large areas

Critical assumption: a stable correlation between soil concentrations and gamma count rate

➢ Cost effective compared to traditional soil sampling

➢Survey parameters can be optimized based upon study goals: obtain more quantitative survey data, with a commensurate response on survey cost, or perform a survey that is less quantitative in nature (scoping only – high uncertainties).

➢ Sensitive to all gamma-emitting radionuclides, including NORM, so the set of nuclides that contribute to ambient gamma must be understood at some phase of the project.

ERG

Overview –Ambrosia Lake West Facility

ERGAverage Ra-226 Concentration (Bq g-1)

Colorado

New Mexico

Me

an

Un

sh

ield

ed

Ga

mm

a C

ou

nt

Ra

te (

cts

s-1

)

p < 0.001

Adj R2 = 0.24

Grey bands represent the 95 prediction limits

Improving gamma survey data quality

Physical parameters:

• Scan more slowly

• Position the detector closer to the ground

• Survey tighter transects

• Use a shield

Detector parameters

• Use newer, digital electronics

• Avoid algorithmic processing of data

Environmental parameters

• Control for ambient radon

• To the detector, radon in the ground is the same as radon in the air!

Grey bands = 8am to 5pmERG

Date

Co

nc

en

trati

on

of

Rad

on

-22

2

(No

rma

liz

ed

)G

am

ma C

ou

nt

Rate

(N

orm

ali

ze

d)

Results: radium-226/gamma correlation

p < 1E-7

Adj R2 = 0.63

ERG

Mean Ra-226 Concentration (Bq g-1)Mean Ra-226 Concentration (Bq g-1)

p = 0.117

Adj R2 = 0.053

Me

an

Sh

ield

ed

Ga

mm

a C

ou

nt

Ra

te

(cts

s-1

)

Me

an

Un

sh

ield

ed

Ga

mm

a C

ou

nt

Ra

te (

cts

s-1

)

Grey bands represent the 95 prediction limitsGrey bands represent the 95 prediction limits2019 Survey2016 Survey

ERG

2019 Survey 2016 Survey

Note: histograms are log/log plots.Note: color bins in both figures generated using 10 geometric intervals with the same color ramp.

65m 65m

LOG - Normalized gamma count rate

LO

G -

No

rma

lize

d n

um

be

r o

f o

cc

urr

en

ce

s

(Grey) 2019 Survey

(Outlines) 2016 Survey

The authors wish to gratefully acknowledge:

BHP, for funding this work, and especially BHP’s site staff:Kent Applegate, Theresa Ballaine,

Michaella Gorospe, and Sandra Ross

Our field crew:Tom Bottomly, Jake Halstead,

Patrick Hendrickson, Sam Paterniti

Acknowledgements

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