URANIUM MILL TAILINGS 

RADON FLUX CALCULATIONS

PIÑON RIDGE PROJECT

MONTROSE COUNTY, COLORADO

Submitted To: Energy Fuels Resources Corporation

44 Union Boulevard, Suite 600

Lakewood, Colorado 80228

Submitted By: Golder Associates Inc.

44 Union Boulevard, Suite 300

Lakewood, Colorado 80228

August 2010 Project No. 073-81694.23

REPORT
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EXECUTIVE SUMMARY

Energy Fuels Resources Corporation (EFRC) proposes to license, construct, and operate a conventional 

acid leach uranium and vanadium mill at the Piñon Ridge Property in western Montrose County, 

Colorado. The Piñon Ridge Mill includes an administration building, a 17-acre mill, a 30.5-acre tailings 

cell with phased expansion capacity to 91.5 acres, a 40-acre evaporation pond area with an expansion 

capacity to 80 acres, an approximately 6-acre ore storage pad, and access roads. The mill is designed to 

process ore containing uranium and vanadium produced from mines located within a reasonable haul 

distance on the Colorado Plateau. 

Golder Associates Inc. (Golder) was commissioned by EFRC to evaluate the operations of the uranium 

mill tailings storage facility at the Piñon Ridge Mill in terms of the 20 pCi/m2s radon (Rn-222) flux standard 

that applies to uranium tailings facilities constructed prior to 1989. Although this flux standard does not 

apply to new facilities such as the Piñon Ridge Mill, it did play an inherent role in establishing the tailings 

disposal practices and maximum areas specified for new facilities under the U.S. Environmental 

Protection Agency (EPA) regulations found in 40 CFR 61 Subpart W, “National Emission Standards for 

Radon Emissions from Operating Mill Tailings” (EPA, 1998). EFRC had expressed a desire to maintain 

radon flux levels from the tailings to “As Low As Reasonably Achievable” (ALARA) levels, as required by 

State of Colorado and U.S. Nuclear Regulatory Commission (NRC) regulations. To achieve this goal, 

EFRC requested that Golder evaluate radon flux levels under a range of potential operating conditions. 

The radon flux calculations presented in this report were conducted using the WISE Uranium Mill Tailings 

Radon Flux Calculator, as updated on November 23, 2009 (WISE, 2009). The results of these 

calculations show that the radon flux levels of the proposed uranium mill tailings facility at the Piñon Ridge 

Mill site will be less than 20 pCi/m2s under normal operating procedures whereby the tailings are 

maintained in a saturated state. Golder also assessed various unsaturated scenarios that could occur in 

the event of temporary equipment failure or during pre-closure operations when the water cover will be 

eliminated, and found that the radon flux remained less than 20 pCi/m2s under drying conditions with up 

to 20 percent of the tailings surface being unsaturated.
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Table of Contents

EXECUTIVE SUMMARY ........................................................................................................................ ES-1

1.0 INTRODUCTION.....................................................................................................................................1

2.0 SITE DESCRIPTION...............................................................................................................................2

3.0 MILL TAILINGS RADON FLUX EVALUATION.......................................................................................3

3.1 Description of the Uranium Mill Tailings Radon Flux Calculator......................................................... 3

3.2 Input Data............................................................................................................................................ 3

3.2.1 General Tailings Properties ......................................................................................................... 4

3.2.1.1 Ra-226 Activity Concentration in the Uranium Tailings [pCi/g]............................................. 4

3.2.1.2 Ra-226 Activity Ratio in Slimes vs. Sand.............................................................................. 4

3.2.1.3 Rn-222 Emanation Fraction in Slimes .................................................................................. 4

3.2.1.4 Rn-222 Emanation Fraction in Sand..................................................................................... 4

3.2.1.5 Fraction Passing #200 Mesh (75 μm)................................................................................... 5

3.2.1.6 Fraction of Pond Area with less than 1 m depth ................................................................... 5

3.2.1.7 Average Pond Depth for Areas greater than 1 m deep ........................................................ 5

3.2.1.8 Ra-226 Activity Concentration in Impounded Water [pCi/L] ................................................. 5

3.2.1.9 Effective Stagnant Water Transport Coefficient [m2/s] ........................................................ 5

3.2.2 Zone-Specific Tailings Properties ................................................................................................ 6

3.2.2.1 Surface Area [m2].................................................................................................................. 6

3.2.2.2 Bulk Density [g/cm3] .............................................................................................................. 6

3.2.2.3 Porosity ................................................................................................................................. 6

3.2.2.4 Moisture Content [dry wt %].................................................................................................. 7

3.2.2.5 Fraction Passing No. 200 Mesh (75 μm) .............................................................................. 7

3.2.2.6 Rn-222 Effective Diffusion Coefficient [m2/s] ........................................................................ 8

4.0 RADON FLUX MODELING RESULTS.................................................................................................10

4.1 Mill Tailings Operational Scenarios................................................................................................... 10

4.2 Radon Flux Model Calculation Results ............................................................................................. 11

4.3 Atmospheric Radon Concentrations ................................................................................................. 12

5.0 CONCLUSIONS....................................................................................................................................13

6.0 USE OF THIS REPORT........................................................................................................................14

7.0 REFERENCES......................................................................................................................................15
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List of Tables

Table 1 Results of Radon Flux Model

Table 2 Radon Flux with Unsaturated Tailings Exposure

List of Figures

Figure 1 Site Location Map

Figure 2 Site Facilities Map Full Build-Out

Figure 3 Proposed Piñon Ridge Tailings Cell Zones

Figure 4 Radon Flux vs. Percent Water Cover

List of Appendices

Appendix A Details of Radon Flux Calculations for Saturated and Submerged Tailings

Appendix B Details of Radon Flux Calculations for Allowable Unsaturated Tailings Exposure
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1.0 INTRODUCTION

This report was prepared by Golder Associates Inc. (Golder) to assist Energy Fuels Resources 

Corporation (EFRC) in developing its operating plan for the Piñon Ridge tailings cells and evaporation 

ponds (EFRC, 2010). The average radon (Rn-222) flux levels for its proposed tailings cells were 

evaluated under normal operating conditions and under drying conditions where a portion of the tailings 

may lose saturation. The resulting flux levels were compared to the 20 pCi/m2s flux limit adopted for the 

much larger pre-1989 tailings facilities in 40 CFR 61 Subpart W, “National Emission Standards for Radon 

Emissions from Operating Mill Tailings” (EPA, 1998). This standard does not apply to the Piñon Ridge 

Mill per se, as the mill tailings facility meets the standard found in 40 CFR Subpart W 61.252 (b) (1) for 

facilities constructed after December 15, 1989 for phased disposal. This standard limits phased disposal 

to no more than two tailings impoundments in operation at any one time and limits the maximum size of 

the impoundments to 40 acres. However, EFRC plans to reduce radon flux levels to “As Low As 

Reasonably Achievable” (ALARA) levels, as defined in the Colorado Department of Public Health and 

Environment (CDPHE) and U.S. Nuclear Regulatory Commission (NRC) regulations by implementing 

tailings operating practices designed to limit radon flux. The 20 pCi/m2s flux level represents a convenient 

yardstick for evaluating tailings operating practices, as this flux rate was used by the U.S. Environmental 

Protection Agency (EPA) in its previous Subpart W rulemaking in assessing the associated health risks of 

both pre- and post-1989 tailings facilities. 

The radon flux calculations in this report were conducted using the WISE Uranium Mill Tailings Radon 

Flux Calculator, as updated on November 23, 2009 (WISE, 2009). The results of these calculations show 

that the proposed uranium mill tailings facilities at the Piñon Ridge Mill site will produce substantially less 

than 20 pCi/m2s radon flux under normal operating conditions and procedures whereby the tailings are 

maintained in a saturated state. This report also assessed various unsaturated scenarios that could 

occur in the event of temporary equipment failure or during standby or pre-closure periods when water 

cover would be reduced and found that the 20 pCi/m2s flux level was not exceeded under drying 

conditions with up to 20 percent of the tailings surface being unsaturated. 
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2.0 SITE DESCRIPTION

EFRC proposes to license, construct, and operate a conventional acid leach uranium and vanadium mill 

at the Piñon Ridge Property in western Montrose County, Colorado. The property covers approximately 

880 acres in the southeastern portion of Paradox Valley. The proposed Piñon Ridge Mill is located at 

16910 Highway 90, approximately 7 miles east of Bedrock, Colorado, and 12 miles west of Naturita, 

Colorado. Figure 1 shows the location of the proposed project site.

The Piñon Ridge Mill is designed to process ore containing uranium and vanadium produced from mines 

located within a reasonable haul distance on the Colorado Plateau. The facility includes an administration 

building, a 17-acre mill, a 30.5-acre tailings cell with phased expansion capacity to 91.5 acres, a 40-acre 

evaporation pond area with an expansion capacity to 80 acres, an approximately 6-acre ore storage pad, 

and access roads. The phased expansion plan is designed to meet the standard found in 40 CFR 

Subpart W 61.252 (b) (1), as only two 30.5-acre tailings cells would be in operation at any one time. This 

would only occur for a relatively short transition period when the first cell is reaching its full capacity and a 

second cell is being put into service. The proposed uranium mill and tailings facilities at full build-out are 

shown in Figure 2.

The mill will initially process 500 tons of ore per day (tpd), but is designed to accommodate future 

expansion of production capacity to 1,000 tpd. The projected operating life of the facility is 40 years, 

operating 24 hours per day, 350 days per year at 500 tpd.

The ore to be processed at the mill contains elevated concentrations of natural uranium and its decay 

products. The average uranium content in the blended ore is 0.23 percent U3O8.
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3.0 MILL TAILINGS RADON FLUX EVALUATION

3.1 Description of the Uranium Mill Tailings Radon Flux Calculator

The Uranium Mill Tailings Radon Flux Calculator evaluates the radon flux from a bare and/or watercovered uranium mill tailings storage area. The calculator is based on the modeling work of Nielson 

(Nielson and Rogers, 1986). 

The model performs one-dimensional, steady-state radon diffusion calculations for various areas of the 

tailings deposit. For the submerged area, the model calculates the radon transport from the tailings 

through the impounded water to the top of the surface, and radon released from radium dissolved in the 

impounded water that covers the submerged tailings. It assumes that all radon reaching the top 1-meter

(3.28 foot) layer of the water is released into the air, as well as all radon produced from dissolved radium 

in this top layer. The following areas are calculated in the model:

 Submerged Tailings Under Impounded Water. This area is primarily comprised of the 

smaller particle size material in the tailings (“slimes”) which are preferentially 

accumulated in the center of the tailings storage facility as tailings are deposited. The 

submerged tailings consider two separate areas in the calculation:

 Submerged area at a depth of 1 meter or less; and

 Submerged area at greater than 1 meter.

 Saturated Beach. This area is located on the perimeter of the tailings storage facility and 

represents a mixture of particle size material (“slimes and sands”) which deposits on the 

perimeter beaches. This area, while not covered with tailings water, will be wetted with 

recycled raffinate solution or tailings water to keep the tailings fully saturated. Keeping 

the tailings saturated in this manner minimizes the radon flux from the beach areas of the 

tailings cell.

 Unsaturated Zone. While it is the intent of EFRC to keep all beaches fully saturated, 

there may be some interim period where small areas of the tailings surface may become 

temporarily unsaturated due to mechanical failure of the water recycle system, or due to 

reduction in water cover during standby or pre-closure periods. Hence, calculations were 

performed to evaluate the maximum percentage of unsaturated tailings exposure that 

would still result in a radon flux level below 20 pCi/m2s. 

The various areas used for the radon flux calculations are shown in Figure 3.

3.2 Input Data

The physical and radiological properties of the uranium mill tailings that were input into the model are 

defined below. While the model allows for default parameters to be used, the most meaningful results for 

actual site conditions are obtained if site-specific data is used. Since the tailings facility has not been built 

and no actual tailings have been processed, data from other representative uranium mill sites has been 

used wherever possible together with sampling data for typical Salt Wash ores that will comprise the 

proposed feed to the Piñon Mill. The effective radon diffusion coefficients were obtained using methods 

developed by Nielson and Rogers (1986) and Rogers and Nielson (1991). 
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3.2.1 General Tailings Properties

This section provides discussion of the general tailings properties used in the radon flux modeling and the 

specific values used for the Piñon Ridge project.

3.2.1.1 Ra-226 Activity Concentration in the Uranium Tailings [pCi/g]

This input parameter is the overall activity concentration of radium-226 in the bulk tailings material. The 

value for the equilibrium concentration of radium-226 was calculated based on the average grade of the 

ore that will be processed. The average uranium content in the blended ore is expected to be 0.23 

percent U3O8. 

The activity of U-238 in the Piñon Ridge uranium tailings was evaluated as follows:

EQUATION 1

( )

( ) 647

( )

330,000( )

( )

0.85( )

( )

0.0023( ) 238

238

238 238

3 8

3 8

ore

U

U

U

U O

U

ore

U O

g

pCi

g

pCi

g

g

g

g Activity −

−

− −

 =



 





⋅

















⋅ 



 



 =

Assuming secular equilibrium in the ore between uranium-238 and radium-226, and that all radium goes 

into the tailings, the activity of radium-226 will be 647pCi/g. 

3.2.1.2 Ra-226 Activity Ratio in Slimes vs. Sand

This input parameter estimates the ratio of radium-226 activity concentrations in the slimes fraction vs. the 

sand fraction of the tailings material. The radium-226 activity concentrations typically increase with 

decreasing particle size and the slimes will contain a higher concentration of radium-226. A ratio of 4 has 

been used in the calculations, which corresponds to the value used by Nielson and Rogers (1986) in the 

development of the model.

3.2.1.3 Rn-222 Emanation Fraction in Slimes

This input parameter is the fraction of the total amount of radon-222 produced by radium decay that 

escapes from the solid fraction of the slimes tailings particles and gets into the pores of the material. The 

value depends on the tailings material and the moisture content. It varies over a range of 0.1 to 0.4 with 

typical values in the range of 0.2 to 0.3. Nielson and Rogers (1986) uses a value of 0.22 for the tailings 

slimes, and this value was used in the calculation for the Piñon Ridge project.

3.2.1.4 Rn-222 Emanation Fraction in Sand

This input parameter is the fraction of the total amount of radon-222 produced by radium decay that 

escapes from the solid fraction of the sand tailings particles and gets into the pores of the material. The 

value depends on the tailings material and the moisture content. This parameter typically varies over a 

range of 0.1 to 0.4. Nielson and Rogers (1986) uses a value of 0.15 for the tailings sands, and this value 

was used in the calculation for the Piñon Ridge project.
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3.2.1.5 Fraction Passing #200 Mesh (75 μm)

This input parameter is the fraction by weight of the overall bulk tailings material passing a No. 200 mesh, 

corresponding to a particle diameter of 75 μm or less. Since a 75-μm particle diameter typically marks the 

sand/silt dividing line, this figure denominates the fraction that is not sand, or the fraction of combined silt

and clay contents ("slimes").

The value used for this parameter is taken from data as reported in Golder (2008a). The fraction for the 

bulk tailings material passing the #200 mesh is 0.379 (i.e., 37.9 percent). This gradation is based on data 

obtained from processing of Salt Wash ores at the White Mesa Mill in Blanding, Utah.

3.2.1.6 Fraction of Pond Area with less than 1 m depth

This input parameter is the fraction of the pond area that has less than 1 meter of water cover. This 

fraction was determined graphically for various percentages of total water cover based on the projected 

slope of the underlying coarse and fine tailings. The tailings with less than 1 meter of water cover 

contribute to the radon flux of the facility.

3.2.1.7 Average Pond Depth for Areas greater than 1 m deep

This input parameter is the depth of the pond area that has greater than 1 meter of water cover. This 

depth was determined graphically for various percentages of total water cover based on the projected 

slope of the underlying coarse and fine tailings. The tailings with greater than 1 meter of water cover do 

not contribute to the radon flux of the facility.

3.2.1.8 Ra-226 Activity Concentration in Impounded Water [pCi/L]

This input parameter is the activity concentration of dissolved radium-226 in the impounded water 

covering the deposited tailings material. As previously discussed, the uranium content of the projected 

ore to be processed at the Piñon Ridge Mill has been determined to be 0.23 percent U3O8 , which leads to 

a radium activity of 647 pCi/g (refer to Section 3.2.1.1). The specific Ra-226 content of the impounded 

water in equilibrium with the tailings material was estimated using the values previously established for a 

model mill in the U.S. Nuclear Regulatory Commission (NRC) NUREG-0706 “Final Generic EIS on 

Uranium Milling” (NRC, 1980; Table 5.3). This document lists an activity level of 250 pCi/L Ra-226 for 

tailings solution at the model mill based on an activity level of 280 pCi/g Ra-226 in the ore. Scaling up to 

the expected higher uranium and radium activity levels in the Piñon Ridge ore of 647 pCi/g, the calculated 

radium activity level of the tailings solution in equilibrium with the tailings is 581 pCi/L.

3.2.1.9 Effective Stagnant Water Transport Coefficient [m2/s] 

This parameter describes radon transport in water. The established value for this parameter is 3x10-7

m2/s, as determined by Nielson and Rogers (1986).
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3.2.2 Zone-Specific Tailings Properties

The following parameters describe the specific properties of each tailings area: (i) the area submerged 

under impounded water; (ii) the saturated beach area; and (iii) the unsaturated area.

3.2.2.1 Surface Area [m2]

This parameter is the surface area for a given type of tailings. A calculation was made for each of the 

three areas in the tailings cell: the submerged area, the saturated area, and the unsaturated area. If no 

tailings exist in any particular area, then a value of zero (0) is entered and the area is discarded. The 

calculations were based on a tailings cell area of approximately 30.5 acres (120,365 m2).

3.2.2.2 Bulk Density [g/cm3]

Each area of the tailing cell will have specific bulk density properties due to the nature of the deposition of 

tailings in the tailings cell. As reported in the tailings settlement report (Golder, 2010), the average dry 

density of tailings after initial settlement with release of water to the tailings pool is expected to be 79.2 

pounds per cubic foot (pcf), or 1.27 grams per cubic centimeters (g/cm3

). The submerged, saturated, and 

unsaturated areas in the tailings cell will each have different dry densities depending on the amount of 

slimes and sands in these areas.

For the submerged area, which is mostly comprised of finer particle material (“slimes”), a bulk density 

value of 70 pcf was used. This corresponds to the expected average density for the material that will 

collect in the central part of the tailings cell, which will be submerged for most of the time while the tailings 

cell is being filled. This corresponds to a dry bulk density of 1.12 g/cm3

. For the saturated transition area, 

which is comprised mostly of sandy material with some amount of slimes, an average bulk density value 

of 80 pcf was used. This corresponded to a dry bulk density of 1.28 g/cm3

. For the sandy beach 

material, a bulk density of 90 pcf was used, which corresponds to a dry bulk density of 1.44 g/cm3

. 

These dry density determinations were made after reviewing the available physical parameter information 

for the Atlas Moab tailings area (Golder, 2005), which indicated that the tailings density ranged from 50.2 

pcf to 88.6 pcf for the slimes to a range of 81 to 106 pcf for the sand materials. The Piñon Ridge Mill 

tailings facility is expected to achieve higher densities because dewatering will be facilitated by the bargemounted pump-back system and the tailings cell underdrain system. It is important to note that the dry 

density of 70 to 90 pcf for the Piñon Ridge tailings applies only to the near-surface tailings that are

contributing to the radon flux. Tailings at depth will have substantially higher densities due to 

consolidation. The tailings density will also increase further after placement of the soil cover during cell 

closure. 

3.2.2.3 Porosity

The porosity (n) of the tailings material is the ratio of the pore volume (air- and water-filled) to the total 

volume of the tailings. This value was calculated using the following relationship:
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EQUATION 2

e

e

n

+ = 1

where e is the void ratio. Limited data on void ratio is available for existing tailings facilities. The data 

from the Moab tailings area showed that the void ratio for the finer particle material (“slimes”) was 1.35 

using the same criteria for densification modifications that were used for the determination of the dry bulk 

densities. This corresponds to a porosity of 0.57 for the slimes. This value, which was input into the 

model, is higher than the default value used in the model and is considerably more conservative (i.e., a 

higher porosity results in a higher radon flux).

For the average tailings material in the saturated area and unsaturated area of the tailings cell, a void 

ratio of 0.65 was used based on data from the Moab tailings area, which resulted in a porosity of 0.39. 

The model uses a default value of porosity of 0.4 for all areas of the tailings cell. 

3.2.2.4 Moisture Content [dry wt %]

During the majority of operations, the tailings will either be submerged or fully saturated. The only area 

where percent moisture needs to be specified in the model is the unsaturated area. The moisture content 

of unsaturated tailings was assumed to be 15 percent, which is a relatively conservative estimate. By 

comparison, the moisture content in the unsaturated Atlas tailings ranged from approximately 21 percent 

to 28 percent when measured in the early 1980s (Golder, 2005).

3.2.2.5 Fraction Passing No. 200 Mesh (75 μm)

The fraction of material passing the No. 200 mesh provides an indication of the particle size of the 

material. Since 75 μm (the opening size of the No. 200 mesh) typically marks the dividing line between 

silts/clays (“slimes”) and sands, each of the zones in the tailings cell will have different characteristics for 

this parameter. The average amount of fines passing a No. 200 mesh in the tailings discharge has been 

estimated to be 0.379 (Golder, 2008a). An estimate of the distribution of these fines through the various 

areas of the tailings cell was made based on a material balance calculation. Assuming that the tailings 

cell consists of 33.3% submerged fines, 33.3% transitional sands/fines and 33.3% sandy material, the 

fraction passing through the No. 200 mesh would be 0.72, 0.36 and 0.05 respectively. These proportions 

are roughly based on the percentages of fines observed in the Atlas Tailings Impoundment of 0.95, 0.45, 

and 0.21 for slimes, sand/slimes, and sands, respectively (Golder, 2005). However, the Atlas Mill 

processed ores from several different formations (using both acid and alkaline leach processes) and the 

resultant tailings contained more fines than the proposed Salt Wash ores. 

The model uses a default distribution for minus No. 200 mesh tailings of 0.5, 0.3 and 0.0 for the three 

areas. Because the model has a higher default value for fines passing a No. 200 mesh in all of the 

tailings (i.e., 0.40) than the Salt Wash ores (0.379), it is apparent that the model assumes a 
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proportionately larger area of slimes. This large slime area was common at historic tailings 

impoundments, which were typically 100 acres or more in size and the tailings were discharged from only 

a few points. This resulted in greater segregation between finer and coarser particles and a larger slime 

area. The smaller Piñon Ridge tailings cells will have multiple discharge points around the perimeter of 

each cell that is expected to result in the concentration of finer tailings within the center of each cell and in 

the development of a larger and more uniform transitional area between the slimes and sands.

3.2.2.6 Rn-222 Effective Diffusion Coefficient [m2/s]

The effective diffusion coefficient (De) for radon-222 is defined from Fick's equation as the ratio of the 

diffusive flux density of radon activity across the pore area to the gradient of the radon activity 

concentration in the pore or interstitial space. The diffusion coefficient in porous media is a property of the 

diffusing species, the pore structure, the type of fluids present in the pores, the adsorption properties of the 

solid matrix, the fluid saturations, and temperature. The Radon Flux Calculator Model calculates this 

value from the correlations from Nielson and Rogers (1986) using porosity and moisture content. The 

model also allows the input of experimental radon diffusion coefficients or coefficients obtained from more 

reliable sources.

The effective radon diffusivity values in porous media can vary over a wide range of values depending on 

the porosity of the material and particularly on its degree of water saturation. In a fully saturated soil 

material, the radon diffusion coefficient may be as low as 10-10 m2/s and, at the upper limit, the diffusion 

coefficient for air of 1.1x10-5 m2/s. Typically, the effective diffusion coefficient of radon in unconsolidated 

soil material with varying moisture content ranges from 10-6 m2/s to 10-10 m2/s. While the radon flux model 

uses an existing correlation to determine the effective radon diffusion coefficient, the user is encouraged to 

input experimentally determined effective diffusion coefficients or other more reliable diffusion coefficient 

information to increase the accuracy of the calculation. 

Subsequent to the correlations that were used in developing the radon flux model, Rogers and Nielson 

(1991) have conducted additional correlations and proposed an updated correlation for the effective 

diffusion coefficient, De, as follows:

EQUATION 3

exp( 6 6 ) 14 t p

e o t tRs Rs D = D p − p −

where Do (equal to 1.1×10-5 m2/s) is the radon diffusivity in open air, pt is the total soil porosity, and Rs is 

the water saturation in the soil (or the fraction of the pore space filled with water, also called the saturation 

ratio).

This correlation has also been used in the latest User’s Manual for RESRAD modeling (Yu et al., 2001) 

and in the support documentation for the modeling impacts on radioactive soils (Yu et al., 2003).
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Calculations to determine the effective radon diffusion coefficients were made using this updated 

correlation. For example, the calculation of De for the case of saturated tailings (i.e., Rs = 1) having a total 

porosity (pt) of 0.39 is as follows:

EQUATION 4

D x m s x m s e

5 2 (14 0.39) 9 2 (1.1 10 ) exp(( 6) (0.39) (1) (6) (1) ) 1.03 10 − ⋅ − = − ⋅ ⋅ − ⋅ =
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4.0 RADON FLUX MODELING RESULTS

4.1 Mill Tailings Operational Scenarios

Details of the design and operation of the proposed 30.5-acre tailings facility are given in Golder (2008b). 

The evaluation of radon flux from various operational scenarios from initial filling of the tailings cell to full 

capacity has been calculated for the following cases:

 Case 1: Initial Fill - 100% water cover;

 Case 2: Partial Fill - 80% water cover;

 Case 3: Partial Fill - 50% water cover;

 Case 4: Partial Fill - 20% water cover; and

 Case 5: Final Fill - 0% water cover.

Typically, the tailings cell will operate with 20 to 80 percent water cover with the smaller water cover 

occurring during the summer evaporation season and the larger water cover occurring in the winter. One 

hundred percent water cover would normally occur only during the initial filling of the cell when the area of 

tailings deposition is much smaller, or after a very large precipitation event. Zero percent water cover 

would normally occur only during the pre-closure period when the tailings solution is removed to achieve 

final deposition grades and allow for the start of closure activities (EFRC, 2010). 

For each of the scenarios, it is assumed that the tailings will be deposited uniformly on the tailings 

beaches around the tailings cell perimeter, and that all of the surface area of the tailings cell will contain 

tailings. This represents a point in the operation of the tailings facility when the cell is nearing full 

capacity.

The proposed operating procedures for the filling and maintenance of the tailings facility dictates that the 

tailings will be kept saturated by applying tailings or raffinate solutions on the deposited tailings material. 

The raffinate is the barren process solution that is pumped to the evaporation ponds for disposal. Since 

water saturation will aid in the retardation of radon release, the normal mode of operation will be to keep 

the tailings wet at all times. The tailings facility will be considered to be in an operational mode from initial 

filling through the pre-closure steps described in the “Operating Plan, Tailings Cells and Evaporation 

Ponds” (EFRC, 2010). Once full, the tailings cell will be considered in closure mode and a radon and 

evapotranspiration cover will be placed over the tailings to permanently suppress radon flux in 

accordance with plans approved by the Radiation Control Program of the Colorado Department of Public 

Health and Environment (CDPHE). 

Although EFRC plans to continuously keep the beach areas on the perimeter saturated during operations, 

there may be some interim period where a limited amount of the tailings surface may temporarily become 

unsaturated due to mechanical failure of the water recycle system, other unforeseen circumstances, or 

during the transition from operational to closure mode. While it is not the intent of EFRC to allow areas of 
August 2010 11 073-81694.23

i:\07\81694\0400\0406 fnlradonfluxcalcs 17aug10\07381694 fnlrpt radfluxcalcs 17aug10.doc

unsaturated tailings to be exposed for any significant length of time, a series of model runs were 

performed which evaluated how much unsaturated tailings material could be allowed on an interim basis 

while still staying below 20 pCi/m2s of radon flux. 

4.2 Radon Flux Model Calculation Results

The radon model was run for the various water cover scenarios outlined in Section 4.1. The results of 

these calculations are presented in Table 1 and Figure 4. The results indicate that the radon flux will be 

below 20 pCi/m2s for all scenarios. The radon flux generated for the case with 100 percent water cover is 

primarily attributable to the area with less than 1 meter of water cover. The model input parameters and 

data output are provided in Appendix A.

TABLE 1

RESULTS OF RADON FLUX MODEL

Case Water Cover

(%)

Radon Flux

(pCi/m2s)

1 100 2.62

2 80 3.27

3 50 5.05

4 20 6.79

5 0 7.44

Modeling of unsaturated tailings was also performed to determine how much unsaturated material could 

be exposed during operations should the solution application system be temporarily shut down for repairs 

or other reasons. These results are shown in Table 2 for the worst case of zero percent water cover. 

Other percentages of water cover of course would show allowable unsaturated tailings areas in excess of 

the values in Table 2. The percentages calculated were of the saturated material rather than the whole of 

the tailings area. As can be seen from this table, the radon flux for all cases shows that some degree of 

unsaturated tailings can be allowed while still remaining below 20 pCi/m2s of radon flux.

TABLE 2

RADON FLUX WITH UNSATURATED TAILINGS EXPOSURE

Case Water Cover

(%)

Unsaturated Tailings

(%)

Radon Flux

(pCi/m2s)

1 0 5 10.57

2 0 10 13.70

3 0 20 19.95

The details of these calculations are provided in Appendix B.
August 2010 12 073-81694.23

i:\07\81694\0400\0406 fnlradonfluxcalcs 17aug10\07381694 fnlrpt radfluxcalcs 17aug10.doc

4.3 Atmospheric Radon Concentrations

The results of radon flux values for the tailings facility cannot readily be converted to airborne radon 

concentrations due to the need for meteorological modeling and determination of where the airborne 

concentrations would be measured. EPA has estimated the maximum radon air concentration at the 

edge of a uranium tailings cell (WISE, 2009; EPA, 1983). Based on these estimates, and assuming a 

maximum radon flux at the surface of the tailings cell of 20 pCi/m2

sec, the maximum radon in the air 

would be approximately 0.28 pCi/l. Since the tailings cells will typically have a radon flux well below 

20 pCi/m2

sec, the air concentration of radon near the Piñon Ridge tailings cells is expected to be 

proportionately lower.

The report “Estimates of Radiation Doses to Members of the Public from the Piñon Ridge Mill” (Two 

Lines, 2009) also provides insight on the potential radon doses resulting from the ore stockpile, tailings 

cells, and mill emissions. This report is included in EFRC’s Radioactive Materials License Application to 

the Radiation Control Program of CDPHE. This study was conducted using the MILDOS Area model, 

which includes material properties, emission rates, and site-specific meteorological data as model inputs. 

The study projected that radon doses at the property’s fence line from all sources would range from 1.2 to 

9.0 millirems per year (mrem/yr), and the nearest residents to the mill would receive a dose of less than 

1 mrem/year. The study conservatively assumed that one tailings cell had reached capacity and a 

second tailings cell was in the initial stages of operation. 
August 2010 13 073-81694.23

i:\07\81694\0400\0406 fnlradonfluxcalcs 17aug10\07381694 fnlrpt radfluxcalcs 17aug10.doc

5.0 CONCLUSIONS

Golder was commissioned by EFRC to evaluate the operations of the uranium mill tailings storage facility 

at the Piñon Ridge Mill in terms of radon flux. The evaluation focused on identifying the flux levels 

produced during normal operations whereby tailings would be maintained in a saturated state with varying 

levels of water cover depending on the season and stage of operations. Operating flux levels were 

compared to the 20 pCi/m2s flux limit established by the U.S. Environmental Protection Agency (EPA) in 

40 CFR 61 Subpart W, “National Emission Standards for Radon Emissions from Operating Mill Tailings” 

(EPA, 1998) for pre-1989 tailings impoundments. The evaluation also looked at the flux levels that would 

occur as tailings lose some level of saturation due to drying conditions.

The radon flux calculations presented in this report were conducted using the WISE Uranium Mill Tailings 

Radon Flux Calculator, as updated on November 23, 2009 (WISE, 2009). The results of the radon flux 

modeling calculations demonstrate that the proposed normal mode of operation will maintain radon flux 

levels well below 20 pCi/m2s. The modeling has also shown that some fraction of the tailings deposition 

can be unsaturated while still maintaining flux levels below 20 pCi/m2s. This situation could occur as a 

result of equipment breakdown or during the transition from operational to closure mode. 
August 2010 14 073-81694.23

i:\07\81694\0400\0406 fnlradonfluxcalcs 17aug10\07381694 fnlrpt radfluxcalcs 17aug10.doc

6.0 USE OF THIS REPORT

This report has been prepared exclusively for the use of Energy Fuels Resources Corporation (EFRC) for 

specific application to the Piñon Ridge Project. The analyses reported herein were performed in 

accordance with accepted practices. No third-party engineer or consultant shall be entitled to rely on any 

of the information, conclusions, or opinions contained in this report without the written approval of Golder 

and EFRC.

Golder sincerely appreciates the opportunity to support EFRC on the Piñon Ridge Project. Please

contact the undersigned with any questions or comments on the information contained in this report.

Respectfully submitted,

GOLDER ASSOCIATES INC.

Kimberly F. Morrison, P.E., R.G. Erich Tiepel, PhD., P.E.

Associate - Senior Project Manager Principal
August 2010 15 073-81694.23

i:\07\81694\0400\0406 fnlradonfluxcalcs 17aug10\07381694 fnlrpt radfluxcalcs 17aug10.doc

7.0 REFERENCES

Energy Fuels Resources Corporation (EFRC). 2010. “Operating Plan, Tailings Cells and Evaporation 

Ponds.”

Golder Associates Inc. (Golder). 2005. “Materials Handling Evaluation Study for the Moab Tailings 

Impoundment, Moab, Utah.” Submitted to S.M. Stoller. Reference No. 053-2269. 21 September 

2005.

Golder Associates Inc. (Golder). 2008a. “Project Design Criteria, Piñon Ridge Geotechnical Services.” 

Revision C. 5 May 2008. 

Golder Associates Inc. (Golder). 2008b. “Tailings Cell Design Report, Piñon Ridge Project, Montrose 

County, Colorado.” Prepared for Energy Fuels Resources Corporation. Reference No. 073-81694. 

October.

Golder Associates Inc. (Golder). 2010. “Tailings Cell Foundation and Closure Cover System Settlement 

Analyses Addendum, Piñon Ridge Project, Montrose County, Colorado,” Letter report to Mr. Frank 

Filas, Energy Fuels Resources Corporation, April. 

Nielson, K.K., and V.C. Rogers. 1986. “Surface Water Hydrology Considerations in Predicting Radon 

Releases from Water-Covered Areas of Uranium Tailings Ponds,” Geotechnical & Geohydrological 

Aspects of Waste Management, Fort Collins, Colorado, pp. 215-222.

Rogers, V.C., and K.K. Nielson. 1991. "Multiphase Radon Generation and Transport in Porous 

Materials," Health Physics, No. 60, pp. 807-815.

U.S. Environmental Protection Agency (EPA). 1983. “Final Environmental Impact Statement for 

Standards for the Control of Byproduct Materials from Uranium Ore Processing (40 CFR 1092),” 

Vol. 1, Report No. EPA/520/1-83-008-1, September.

U.S. Environmental Protection Agency (EPA). 1998. Regulations as found in 40 CFR 61 Subpart W, 

National Emission Standards for Radon Emissions from Operating Mill Tailings, April.

U.S. Nuclear Regulatory Commission (NRC). 1980. NUREG-0706, “Final Generic EIS on Uranium 

Milling.” Office of Nuclear Material, Safety and Safeguards, Washington, D.C., September. 850 pp.

WISE Uranium Project (WISE). 2009. Uranium Mill Tailings Radon Flux Calculator, November. 

http://www.wise-uranium.org/ctb.html?unit=c

Yu, C., C. Loureiro, J.J. Cheng, L.G. Jones, Y.Y. Wang, Y.P. Chia, and E. Faillace. 1993. Data 

Collection Handbook to Support Modeling Impacts of Radioactive Material in Soil. Environmental 

Assessment and Information Sciences Division, Argonne National Laboratory, Argonne, Illinois, April.

Yu, C., A.J. Zielen, J.J. Cheng, D.J. LePoire, E. Gnanapragasam, S. Kamboj, J. Arnish, A. Wallo III, W.A. 

Williams, and H. Peterson. 2001. Users’ Manual for RESRAD Version 6, Environmental Assessment 

Division, ANL/EAD-4, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois. EPA 

regulations as found in 40 CFR 61 Subpart W, National Emission Standards for Radon Emissions 

from Operating Mill Tailings, April 1998.
FIGURES
Piñon Ridge Project Area

Uncompahgre NF

Grand Mesa NF

Gunnison NF

Manti-Lasal NF

Gunnison NF

Uncompahgre NF

Colorado Natl Mon

Black Canyon 

of Gunnison CO

Curecanti Natl 

Rec Area

Mesa

Montrose

Delta

Ouray

Gunnison

San Miguel Hinsdale

Grand

COLORADO

UTAH

Delta

Paonia

Olathe

Ridgway Norwood

Crawford

Redlands

Palisade

Hotchkiss

Cedaredge

Fruitvale

Orchard City

Orchard Mesa

Loghill Village

Clifton

Montrose

Grand Junction

Nucla

Bedrock

Gateway

Naturita

70

50

550

6

141

65

92

90

25

133

62

145

348

347

97

141

141

90

Divide

D

Nucla Delta

Ff 70

265

133

Divide

107°30’0"W

107°30’0"W

107°45’0"W

107°45’0"W

108°0’0"W

108°0’0"W

108°15’0"W

108°15’0"W

108°30’0"W

108°30’0"W

108°45’0"W

108°45’0"W

109°0’0"W

109°0’0"W

39°0’0"N

39°0’0"N

38°45’0"N

38°45’0"N

38°30’0"N

38°30’0"N

38°15’0"N

38°15’0"N

10 0 10 5

MILES

1:500,000

Denver, Colorado

DESIGN

GIS

CHECK

REVIEW

PROJECT No. 073-81694

08/04/2010

FILE No. 11x17_SiteLoc.mxd

SCALE AS SHOWN REV 0

FIGURE 1

SITE LOCATION MAP

MONTROSE COUNTY, COLORADO

AJR

TITLE

PROJECT

SCALE

LEGEND

REFERENCES

Base Data: ESRI, 2009.

Imagery: ESRI API, Assorted Dates.

Projection: StatePlane, Colorado South, NAD83, Feet.

AJR 08/04/2010

WHEN PRODUCED AT SIZE 11X17IN

SS 08/04/2010

KFM 08/04/2010

ENERGY FUELS RESOURCES CORPORATION

PIÑON RIDGE PROJECT

Map Document: M:\Pinonridge\ArcMap\RadonFluxCalc\11x17_SiteLoc.mxd / Modified 8/4/2010 3:12:01 PM / Plotted 8/4/2010 3:12:01 PM by AReither

Property Boundary

Town

Interstate

Highway

Major Road

Local Road

National Park or Forest

State

County

Stream

Intermittent Stream

Dam

Reservoir

Submerged Saturated Unsaturated

d>1m d<1m

KFM Jul-10 

ET NTS ET TailingsZonationFigure.xls 

ENERGY FUELS RESOURCES CORP. 

PIÑON RIDGE PROJECT

Tailings Zonation Model Assum

Submerged Saturated Unsaturated

d>1m d<1m
2

345678

Radon Flux (pCi/m

2s)

ET Aug-10 

KFM NTS 

ET 07381694 RadonFluxCalc Fig4.xls 

Radon Flux vs. Percent Water 

ENERGY FUELS RESOURCES CORP. 

PIÑON RIDGE PROJECT

012345678

0 10 20 30 40 50 60 70 80 90 

Radon Flux (pCi/m

2s)

% Water Cover
APPENDIX A

DETAILS OF RADON FLUX CALCULATIONS FOR 

SATURATED AND SUBMERGED TAILINGS
August 2010 Uranium Mill Tailings Radon Flux Calculations 

I:\07\81694\0400\0406 FNLRadonFluxCalcs 17AUG10\AppA\07381694 AppA EF RadFluxCalcs 0%Water 0%Unsatd ErichTiepel 06AUG10.xlsx

647 4 0.22 0.15 0.379 1 0 578 

Tailings Zone

Surface Area

 (m2)

Bulk Density

(g/cm3) Porosity Moisture Contents (dry wt_%) Fraction Passing #200 Mesh (75 μm) Rn - 222 Effective Diffusion Coefficient (m2/s)

Submerged 0 1.12 0.57 Saturated 0.72 5.08E-10

Saturated 120365 1.28 0.39 Saturated 0.36 1.03E-09

Unsaturated 0 1.44 0.39 15 0.05 3.53E-05

Ra - 226 A

Concentr

in Ponding 

(pCi/

Ra - 226 Activity 

Concentrations

 in Tailings

(pCi/g)

Input Data / 0% Water Cover / 0% Unsaturated 

Tailings Data

Radon Flux Results

pCi/m2s

7.44

Zone - Specific Tailings Properties

Fraction

Passing #200 Mesh 

(75 μm)

Fraction of Pond 

Area

with less than 

1 m deep

Average Pond Depth 

for Areas Greater than

 1 m deep

Ra - 226 Activity 

Ratio in 

slimes vs. sand

Ra - 222 Emanation 

Fraction

 in slimes

Ra - 222 Emanation 

Fraction

 in sand
August 2010 Uranium Mill Tailings Radon Flux Calculations 

I:\07\81694\0400\0406 FNLRadonFluxCalcs 17AUG10\AppA\07381694 AppA EF RadFluxCalcs 20%Water 0%Unsatd Erich Tiepel 06AUG10.xlsx

647 4 0.22 0.15 0.379 0.358 1.83 578 

Tailings Zone

Surface Area

 (m2)

Bulk Density

(g/cm3) Porosity Moisture Contents (dry wt_%) Fraction Passing #200 Mesh (75 μm) Rn - 222 Effective Diffusion Coefficient (m2/s)

Submerged 24073 1.12 0.57 Saturated 0.72 5.08E-10

Saturated 96292 1.28 0.39 Saturated 0.36 1.03E-09

Unsaturated 0 1.44 0.39 15 0.05 3.53E-05

Ra - 226 A

Concentr

in Ponding 

(pCi/

Ra - 226 Activity 

Concentrations

 in Tailings

(pCi/g)

Input Data / 20% Water Cover / 0% Unsaturated 

Tailings Data

Radon Flux Results

pCi/m2s

6.79

Zone - Specific Tailings Properties

Fraction

Passing #200 Mesh 

(75 μm)

Fraction of Pond 

Area

with less than 

1 m deep

Average Pond Depth 

for Areas Greater than

 1 m deep

Ra - 226 Activity 

Ratio in 

slimes vs. sand

Ra - 222 Emanation 

Fraction

 in slimes

Ra - 222 Emanation 

Fraction

 in sand
August 2010 Uranium Mill Tailings Radon Flux Calculations 

I:\07\81694\0400\0406 FNLRadonFluxCalcs 17AUG10\AppA\07381694 AppA EF RadFluxCalcs 50%Water 0%Unsatd Erich Tiepel 06AUG10.xlsx

647 4 0.22 0.15 0.379 0.19 2.43 578 

Tailings Zone

Surface Area

 (m2)

Bulk Density

(g/cm3) Porosity Moisture Contents (dry wt_%) Fraction Passing #200 Mesh (75 μm) Rn - 222 Effective Diffusion Coefficient (m2/s)

Submerged 60182 1.12 0.57 Saturated 0.72 5.08E-10

Saturated 60182 1.28 0.39 Saturated 0.36 1.03E-09

Unsaturated 0 1.44 0.39 15 0.05 3.53E-05

Ra - 226 A

Concentr

in Ponding 

(pCi/

Ra - 226 Activity 

Concentrations

 in Tailings

(pCi/g)

Input Data / 50% Water Cover / 0% Unsaturated 

Tailings Data

Radon Flux Results

pCi/m2s

5.05

Zone - Specific Tailings Properties

Fraction

Passing #200 Mesh 

(75 μm)

Fraction of Pond 

Area

with less than 

1 m deep

Average Pond Depth 

for Areas Greater than

 1 m deep

Ra - 226 Activity 

Ratio in 

slimes vs. sand

Ra - 222 Emanation 

Fraction

 in slimes

Ra - 222 Emanation 

Fraction

 in sand
August 2010 Uranium Mill Tailings Radon Flux Calculations 

I:\07\81694\0400\0406 FNLRadonFluxCalcs 17AUG10\AppA\07381694 AppA EF RadFluxCalcs 80%Water 0%Unsatd Erich Tiepel 06AUG10.xlsx

647 4 0.22 0.15 0.379 0.142 2.9 578 

Tailings Zone

Surface Area

 (m2)

Bulk Density

(g/cm3) Porosity Moisture Contents (dry wt_%) Fraction Passing #200 Mesh (75 μm) Rn - 222 Effective Diffusion Coefficient (m2/s)

Submerged 96292 1.12 0.57 Saturated 0.72 5.08E-10

Saturated 24073 1.28 0.39 Saturated 0.36 1.03E-09

Unsaturated 0 1.44 0.39 15 0.05 3.53E-05

Input Data / 80% Water Cover / 0% Unsaturated 

Tailings Data

Radon Flux Results

pCi/m2s

Ra - 226 Activity 

Ratio in 

slimes vs. sand

Ra - 222 Emanation 

Fraction

 in slimes

Ra - 222 Emanation 

Fraction

 in sand

Ra - 226 A

Concentr

in Ponding 

(pCi/

Ra - 226 Activity 

Concentrations

 in Tailings

(pCi/g)

3.27

Zone - Specific Tailings Properties

Fraction

Passing #200 Mesh 

(75 μm)

Fraction of Pond 

Area

with less than 

1 m deep

Average Pond Depth 

for Areas Greater than

 1 m deep
August 2010 Uranium Mill Tailings Radon Flux Calculations 

I:\07\81694\0400\0406 FNLRadonFluxCalcs 17AUG10\AppA\07381694 AppA EF RadFluxCalcs 100%Water 0%Unsatd Erich Tiepel 06AUG10.xlsx

647 4 0.22 0.15 0.379 0.2 3.05 578 

Tailings Zone

Surface Area

 (m2)

Bulk Density

(g/cm3) Porosity Moisture Contents (dry wt_%) Fraction Passing #200 Mesh (75 μm) Rn - 222 Effective Diffusion Coefficient (m2/s)

Submerged 120365 1.12 0.57 Saturated 0.72 5.08E-10

Saturated 0 1.28 0.39 Saturated 0.36 1.03E-09

Unsaturated 0 1.44 0.39 15 0.05 3.53E-05

Radon Flux Results

pCi/m2s

2.62

Zone - Specific Tailings Properties

Fraction

Passing #200 Mesh 

(75 μm)

Fraction of Pond 

Area

with less than 

1 m deep

Average Pond Depth 

for Areas Greater than

 1 m deep

Ra - 226 Activity 

Ratio in 

slimes vs. sand

Ra - 222 Emanation 

Fraction

 in slimes

Ra - 222 Emanation 

Fraction

 in sand

Ra - 226 A

Concentr

in Ponding 

(pCi/

Ra - 226 Activity 

Concentrations

 in Tailings

(pCi/g)

Input Data / 100% Water Cover / 0% Unsaturated 

Tailings Data
APPENDIX B

DETAILS OF RADON FLUX CALCULATIONS FOR 

ALLOWABLE UNSATURATED TAILINGS EXPOSURE
August 2010 Uranium Mill Tailings Radon Flux Calculations 

I:\07\81694\0400\0406 FNLRadonFluxCalcs 17AUG10\AppB\07381694 AppB EF RadFluxCalcs 0%Water 5%Unsatd Erich Tiepel 06AUG10.xlsx

647 4 0.22 0.15 0.379 1 0 578 

Tailings Zone

Surface Area

 (m2)

Bulk Density

(g/cm3) Porosity Moisture Contents (dry wt_%) Fraction Passing #200 Mesh (75 μm) Rn - 222 Effective Diffusion Coefficient (m2/s)

Submerged 0 1.12 0.57 Saturated 0.72 5.08E-10

Saturated 114347 1.28 0.39 Saturated 0.36 1.03E-09

Unsaturated 6018 1.44 0.39 15 0.05 3.53E-05

Radon Flux Results

pCi/m2s

10.57

Zone - Specific Tailings Properties

Fraction

Passing #200 Mesh 

(75 μm)

Fraction of Pond 

Area

with less than 

1 m deep

Average Pond Depth 

for Areas Greater than

 1 m deep

Ra - 226 Activity 

Ratio in 

slimes vs. sand

Ra - 222 Emanation 

Fraction

 in slimes

Ra - 222 Emanation 

Fraction

 in sand

Ra - 226 A

Concentr

in Ponding 

(pCi/

Ra - 226 Activity 

Concentrations

 in Tailings

(pCi/g)

Input Data / 0% Water Cover / 5% Unsaturated 

Tailings Data
August 2010 Uranium Mill Tailings Radon Flux Calculations 

I:\07\81694\0400\0406 FNLRadonFluxCalcs 17AUG10\AppB\07381694 AppB EF RadFluxCalcs 0%Water 10%Unsatd Erich Tiepel 06AUG10.xlsx

647 4 0.22 0.15 0.379 1 0 578 

Tailings Zone

Surface Area

 (m2)

Bulk Density

(g/cm3) Porosity Moisture Contents (dry wt_%) Fraction Passing #200 Mesh (75 μm) Rn - 222 Effective Diffusion Coefficient (m2/s)

Submerged 0 1.12 0.57 Saturated 0.72 5.08E-10

Saturated 108329 1.28 0.39 Saturated 0.36 1.03E-09

Unsaturated 12036 1.44 0.39 15 0.05 3.53E-05

Radon Flux Results

pCi/m2s

13.7

Zone - Specific Tailings Properties

Fraction

Passing #200 Mesh 

(75 μm)

Fraction of Pond 

Area

with less than 

1 m deep

Average Pond Depth 

for Areas Greater than

 1 m deep

Ra - 226 Activity 

Ratio in 

slimes vs. sand

Ra - 222 Emanation 

Fraction

 in slimes

Ra - 222 Emanation 

Fraction

 in sand

Ra - 226 A

Concentr

in Ponding 

(pCi/

Ra - 226 Activity 

Concentrations

 in Tailings

(pCi/g)

Input Data / 0% Water Cover / 10% Unsaturated 

Tailings Data
August 2010 Uranium Mill Tailings Radon Flux Calculations 

I:\07\81694\0400\0406 FNLRadonFluxCalcs 17AUG10\AppB\07381694 AppB EF RadFluxCalcs 0%Water 20%Unsatd Erich Tiepel 06AUG10.xlsx

647 4 0.22 0.15 0.379 1 0 578 

Tailings Zone

Surface Area

 (m2)

Bulk Density

(g/cm3) Porosity Moisture Contents (dry wt_%) Fraction Passing #200 Mesh (75 μm) Rn - 222 Effective Diffusion Coefficient (m2/s)

Submerged 0 1.12 0.57 Saturated 0.72 5.08E-10

Saturated 96292 1.28 0.39 Saturated 0.36 1.03E-09

Unsaturated 24073 1.44 0.39 15 0.05 3.53E-05

Radon Flux Results

pCi/m2s

19.95

Zone - Specific Tailings Properties

Fraction

Passing #200 Mesh 

(75 μm)

Fraction of Pond 

Area

with less than 

1 m deep

Average Pond Depth 

for Areas Greater than

 1 m deep

Ra - 226 Activity 

Ratio in 

slimes vs. sand

Ra - 222 Emanation 

Fraction

 in slimes

Ra - 222 Emanation 

Fraction

 in sand

Ra - 226 A

Concentr

in Ponding 

(pCi/

Ra - 226 Activity 

Concentrations

 in Tailings

(pCi/g)

Input Data / 0% Water Cover / 20% Unsaturated 

Tailings Data