Radon Geochemistry
in Evaluation of NAPL Contamination

Radon geochemistry of groundwater and soil gas is useful for detecting, quantifying and monitoring contamination by Non Aqueous Phase Liquids (NAPL).
  • Radon is present in readily detectable concentrations in nearly all subsurface environments.
  • Radon has an affinity for organic liquids, and in the presence of NAPL the radon concentration in groundwater or soil gas is reduced due to partitioning into the organic NAPL phase.
  • Thus, by measuring radon it is often possible to identify those locations where NAPL is likely present, and to limit the use of more costly procedures when searching for hydrocarbon contamination.
  • The reduction in radon concentration in groundwater can sometimes be quantitatively correlated with the amount of NAPL present, and it is sometimes possible to obtain quantitative estimates for NAPL saturation.
  • Semprini et al. (see below) propose the use of radon in groundwater "for monitoring changes in NAPL quantities resulting from remediation activities".
  • In the case of soil gas, radon:thoron ratios are more sensitive still. These ratios have proven successful in uranium exploration Link and should prove useful in NAPL searches as well. We have a formula to resolve radon from thoron giving on-the-spot results with our field instruments.
  • We measure: radon - radium - thoron - radon daughters - alpha radiation.
  • The Lucas cell is recognized as the most sensitive and reliable method for these elements.
  • Intrinsically safe functions.
  • Sensitive to geochemical trace levels necessary for radon in lake water and for radon-thoron isotope ratios.
  • immune to beta and gamma radiation.
  • one monitor works with a number of (less expensive) detectors.
  • Our instruments are used around the world in exploration for uranium, oil & gas, groundwater and hydrothermal, and in environmental protection, health physics, earthquake prediction, and evaluation of hydrocarbon and NAPL contamination etc.
  • Same instruments used for radon and radium in soil, sediment, plant parts, rocks, water, soil gas, air, snow, food, and for radon and thoron daughters in air.
  • Winter and summer, from the Sahara Desert to the Canadian Shield, our instruments have faced up to severe field conditions.
  • In the radon business since 1968, our instruments are updated regularly with the most recent major re-design in 2015. Modern, low-power, field-rugged electronics. Some earlier versions still working after 40 years.
  • Continuous real-time monitoring and data recording.
  • RS232 port/pc software.
  • User programmable measurement intervals, sample and count periods and alarm level settings.
  • Can work in a tent without electricity or be carried from point to point in the field.
  • 50 readings per day. Results available immediately.
  • Portable. Rechargeable battery pack good for a long day in the field and recharges in a few hours.
  • Can be operated by junior personnel if carefully supervised.
  • EPA and CE Mark compliant.
  • Click here (www.finderschoice.com/rn) for more details of our radon instruments, and for other instruments, components and accessories we provide.
  • Technical specification sheets and pictures of our instruments provided on request.
  • Multilingual consulting and training (if required).
For instruments contact

Robert H. Morse, Ph.D., P.Eng.
July 20, 2010
Click here for studies of radon in uranium and hydrocarbon exploration
Dyck, W. and J.R.Jonason, 2000. Geochemical Remote Sensing of the Sub-Surface. Edited by: Hale, M. © 2000 Elsevier, Chapter 11 on radon. An extensive scientific discussion of the geochemistry of radon
K. Fan, T. Kuo, Y. Han, C. Chen, C. Lin and C. Lee, 2007
Radon distribution in a gasoline-contaminated aquifer.
Radiation Measurements Volume 42, Issue 3, Pages 479-485 Link
Abstract: "Naturally occurring radon-222 gas in groundwater was investigated as a partitioning tracer to detect non-aqueous phase liquid (NAPL) in a gasoline-contaminated aquifer. The radon-222 activity of groundwater decreased significantly from an average of 7.38 +/- 1.68 Bq/L measured in monitoring wells located upgradient in the uncontaminated zone to an average of 2.30 +/- 0.60 Bq/L measured in monitoring wells inside the NAPL source zone. Meanwhile, the radium-226 concentrations measured in aquifer matrix were virtually homogeneous at several locations both upgradient of and inside the NAPL source zone. Furthermore, the NAPL concentration obtained from the Radon Deficit Factor agrees reasonably with the results derived from direct sampling and chemical analysis of soil samples taken from the residual NAPL source zone. The field results of this study confirmed the general applicability of groundwater radon to detect residual NAPL source zone."
J.E. Garcia-Gonzalez, M.F. Ortega, E. Chacon, LF. Mazadiego, E. De Miguel, 2008
Crupo de Ceoquimica Ambiental, Universidad Politecnica de Madrid, E.T.S. Ingenieros de Minas, Alenza 4, 28003 Madrid, Spain
Field validation of radon monitoring as a screening methodology for NAPL-contaminated sites.
Applied Geochemistry, Volume 23, Issue 9, September 2008, Pages 2753-2758 Link
Measured radon-222 in soil gas.
If a non aqueous phase liquid (NAPL) is present, radon is enriched in the NAPL and depleted in the gas phase. There is less radon free to enter our sampling tool and we should find low radon values over hydrocarbon enrichments.
Based on a field study of 67 station, the authors conclude:
"...as was theoretically predicted, reductions of Rn concentration in soil air above subsurface accumulations of hydrocarbons can be deterministically differentiated from background values (the former being between 5 and 10 times lower than the latter) under real field conditions."
"Emanometry has the advantage that it can locate and determine the boundaries of free-phase plumes of contaminants even when the amount of organic vapors reaching the surface is very low or non-existent."
The paper cites a number of studies which gave similar results.

Note: It is likely that if the authors had used our formula to distinguish between radon and thoron,
and plotted both the radon and radon/thoron ratios, results would have been better.
Michael Schubert , Klaus Freyer, Hans-Christian Treutler and Holger Weiß, 2001
UFZ Centre for Environmental Research, Permoserstrasse 15, 04318 Leipzig, Germany.
Using the soil gas radon as an indicator for ground contamination by non-aqueous phase-liquids. Journal of Soils and Sediments, Volume 1, Number 4 / December, 2001 .
Quote from abstract:
"Both the results of the lab experiments and the on-site findings demonstrate that the soil-gas radon concentration can be used as an indicator for subsurface NAPL contamination. The investigation showed that NAPL-contaminated soil volumes give rise to anomalous low soil-gas radon concentrations in the close vicinity of the contamination. The reason for this decrease in the soil-gas radon concentration is the good solubility of radon in NAPLs, which enables the NAPLs to accumulate and ‘trap’ part of the radon available in the soil pores."

Note: It is likely that if the authors had used our formula to distinguish between radon and thoron,
and plotted both the radon and radon/thoron ratios, results would have been better.
Michael Schubert, Albrecht Paschke, Steffen Lau, Wolfgang Geyer and Kay Knöller, 2006.
UFZ Centre for Environmental Research, Permoserstrasse 15, 04318 Leipzig, Germany.
Radon as a naturally occurring tracer for the assessment of residual NAPL contamination of aquifers. Environmental Pollution, February 2007, Pages 920-927.
Abstract: "The noble gas radon has a strong affinity to non-aqueous phase-liquids (NAPLs). That property makes it applicable as naturally occurring partitioning tracer for assessing residual NAPL contamination of aquifers. In a NAPL contaminated aquifer, radon dissolved in the groundwater partitions preferably into the NAPL. The magnitude of the resulting radon deficit in the groundwater depends on the NAPL-specific radon partition coefficient and on the NAPL saturation of the pore space. Hence, if the partition coefficient is known, the NAPL saturation is attainable by determination of the radon deficit. After a concise discussion of theoretical aspects regarding radon partitioning into NAPL, related experimental data and results of a field investigation are presented. Aim of the laboratory experiments was the determination of radon partition coefficients of multi-component NAPLs of environmental concern. The on-site activities were carried out in order to confirm the applicability of the “radon method” under field conditions. The paper presents the theoretical concept and experimental results which confirm the applicability of naturally occurring radon for assessing residual NAPL contamination of aquifers."
M. Schubert, P. Peña, M. Balcázar, R. Meissner, A. Lopez and J.H. Flores, 2005
UFZ Centre for Environmental Research, Permoserstrasse 15, 04318 Leipzig, Germany.
Determination of radon distribution patterns in the upper soil as a tool for the localization of subsurface NAPL contamination Radiation Measurements, Volume 40, Issues 2-6 , November 2005, Pages 633-637
Abstract: "A radon survey was carried out at an abandoned military airfield, heavily contaminated with non-aqueous phase-liquids (NAPLs). Geo-statistical analysis of the data was used to confirm the validity of the chosen soil gas sampling pattern. The survey revealed a non-uniform distribution of the soil gas radon concentration in the upper soil in spite of a virtually homogenous geological situation. The radon distribution pattern showed minimum zones with radon concentrations decreased by up to 90% with regard to the local background level. The determined radon minimum anomalies could be explicitly associated with the NAPL subsurface contamination. The observed effect is due to the strong partitioning of radon into NAPLs from soil gas or groundwater. Corresponding partitioning coefficients were determined in the laboratory for some NAPL. As result of the study, it was shown that naturally occurring soil gas radon has the potential to be used as an indicator for the localization of subsurface NAPL contamination."

Note: It is likely that if the authors had used our formula to distinguish between radon and thoron,
and plotted both the radon and radon/thoron ratios, results would have been better.
Semprini, 1992.
Stanford University (Partially Supported by the U. S. Department of Energy)
Radon-222 Method for Locating and Quantifying Contamination by Residual Non- Aqueous Phase Liquids in the Subsurface:
Link (page 30)
Measured radon-222 in solution in groundwater.
Refers to some work commenced in 1989 at CFB Borden in Ontario, in cooperation with University of Waterloo.
Semprini, Lewis ; Istok, Jack, 2008.
Radon-222 as Natural Tracer for Monitoring the Remediation of NAPL Contamination in the Subsurface.
Technology Certification Program, U.S. Department of Defense Link
Measured radon-222 in solution in groundwater.
"This Cost and Performance Report describes the use of naturally occurring radon-222 (Rn) as a partitioning tracer for locating and quantifying NAPL contamination in the subsurface and for monitoring changes in NAPL quantities resulting from remediation activities."
"...it is an easy method to implement and apply with other methods, such as monitoring the chlorinated solvents concentration in groundwater samples. The best use of the method would be as a monitoring method where changes in radon concentration in groundwater samples could be tracked over time as a means of monitoring the progress of remediation."

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