Final Report



### REPORT ON THE REVIEW OF METHOD 115

TO MONITOR RADON EMISSIONS

FROM URANIUM TAILINGS

Prepared by

S. Cohen & Associates 1608 Spring Hill Road, Suite 400 Vienna, VA 22182

Under

Contract Number EP-D-05-002 Work Assignment No. 4-11, Task 6

Prepared for

U.S. Environmental Protection Agency

Office of Radiation and Indoor Air 1200 Pennsylvania Avenue, N.W. Washington, DC 20460

Reid J. Rosnick Work Assignment Manager

September 25, 2008In accordance with the Quality Assurance Project Plan: Technical and Regulatory Support to Develop a Rulemaking to Modify the NESHAP Subpart W Standard for Radon Emissions from Operating Uranium Mills (40 CFR 61.25) , this document has been reviewed and approved by the following individuals:

Work Assignment Task Manager: ________________________ Date: __ 09/25/2008

__ Harry Pettengill

Project Manager: ________________________ Date: __ 09/25/2008

__ Abe Zeitoun

Corporate Quality Assurance Mgr: ________________________ Date: __ 09/25/2008

__ Gregory Beronja

Work Assignment QA Ma nager: ________________________ Date: __ 09/25/2008

__ Stephen Ostrow

WA 4-11, Task 4 – NESHAPs History i SC&A – September 25, 2008TABLE OF CONTENTS

1.0 Introduction ......................................................................................................................... 1

2.0 Objectives ........................................................................................................................... 1

3.0 Measurement Frequency ..................................................................................................... 2

4.0 Conclusion .......................................................................................................................... 6

5.0 References ........................................................................................................................... 7

WA 4-11, Task 6 – Method 115 Compliance ii SC&A – September 25, 20081.0 INTRODUCTION

EPA promulgated its NESHAP for emissions from uranium tailings in 1989. Section 112(q) of the Clean Air Act (CAA), as amended, requires the EPA to review, and if appropriate, revise or update the Subpart W standard on a timely basis (10- year interval). EPA has determined that it is reasonable and appropriate to re visit this standard at this time , especially in view of renewed interest in uranium exploration and recovery.

Currently, compliance with the existing emission standards for uranium tailings is achieved through the use of Method 115, as prescr ibed in Appendix B of 40 CFR 61.253.

2.0 OBJECTIVES

The purpose of this report is to evaluate whet her Method 115 is still curr ent and applicable to monitor radon emissions from uranium tailings. Secondarily, it evaluates what other methods using current technology may be employed to meet the emissions st andard in lieu of dependence upon Method 115.

Furthermore, this report reviews Method 115 as it was first designed and includes consideration

of those variations in detecti on methodologies that could be empl oyed to meet the requirements of Subpart W.

The review also considers various aspects of Subpa rt W in the context of what is known, or has been learned since its promulgation, regardi ng radon diffusion through uranium tailings or improvements in radon detection capability.

Subpart W of 40 CFR 61, National Emission Standards for Radon Emissions from Operating Mill Tailings , is basically a three-part standard (EPA 1991), summarized as follows:

(1) Radon-222 emissions from an existing uranium mill tailings pile must not exceed 20 pCi/m 2 -sec (implicitly this includes background)

(2) Tailings piles after December 15, 1989, have to be designed, constructed, and operated to meet one of two work practices:

- Phased disposal in lined ta ilings impoundments that have an area of no more than 40 acres with no more than two impoundme nts in operation (open) at any one time

- Continuous disposal of tailings requires that they are dewatered and immediately disposed of with no more than 10 acres being uncovered at any time

(3) All mill owners and operators must comply with 40 CFR 192.32(a) in the operation of tailing piles (design of impoundments)

The above performance standards depend in part on certain definitions, such as dewatering, which is defined as removing moisture until th e water content is less than 30% by weight. This definition can invoke other parameters, which can further influence radon flux from the tailings. For example, the radon flux from ta ilings with 6% moisture is actually 3.5 times

WA 4-11, Task 6 – Method 115 Compliance 1 SC&A – September 25, 2008that from tailings with 0.2% moisture (typical of the southw est) and slowly increases to saturation (NRC 1983). Thus, no ma tter whether the moisture c ontent is 6%, 30%, or even 60%, the radon flux will be about the same (NRC 1983). The 30% moisture definition appears somewhat arbitrary and does not really affect radon flux reduction considerations.

Historically, compliance with the radon flux standard was met through the use of Method 115 of Appendix B, “Test Methods:”

§ 61.253 Determining compliance Compliance with the emission standard in this subpart shall be determined annually through the use of Method 115 of A ppendix B. When measurements are to be made over a one year period, EPA sha ll be provided with a schedule of the measurement frequency to be used.

Method 115 in Appendix B, entitled “Monitori ng for Radon-222 Emissions,” consists of

numerous sections that discu ss the frequency, distribution, number of measurements, and quality assurance from three types of uran ium mining or rec overy operations:

(1) Radon-222 Emissions from Underground Uranium Mine Vents (2) Radon-222 Emissions from Uranium Mill Tailings Piles (3) Radon-222 Emissions from Phosphogypsum Stacks.

The most important elements are measurem ent frequency and measurement methodologies employed to demonstrate compliance.

3.0 MEASUREMENT FREQUENCY

These were assumed based on reviews of historic ta ilings piles constructed prior to the standard. In other words, peripheral discharges of ta ilings from one or more spigots would have eventually resulted in sands depositing close to the spigot (the dam or beach area) and slimes (material less than 200 mesh) depositing furthe r downgrade forming a “pond.” According to Sears et al , the slimes typical ly contained up to 80% of the ra dioactivity (ORNL 1975) and were often allowed to dry naturally befo re being covered or mixed with the sands. The size of these piles varied considerably, but 100 acres was common [NRC used 124 acres (50 hectares) in Regulatory Guide 3.59 (NRC 1985)]. On the ot her hand, the ORNL (1975) report used 100 acres in the adopted model mills.

Section 2.1.3 of Method 115 require s the following measurements:

(1) Water covered area – no measurements require d, as radon flux is assumed to be zero

(2) Water saturated beaches – 100 radon flux measurements

(3) Loose and dry top surface – 100 radon flux measurements

(4) Sides – 100 radon flux measurements, except wh ere earthen material is used in dam

construction

WA 4-11, Task 6 – Method 115 Compliance 2 SC&A – September 25, 2008Thus a minimum of 300 radon fl ux measurements are required.

The question then becomes whether this require d frequency (300 measurements) is necessary under the new standard, which is requiring mu ch smaller ponds. For example, under the new standard, particularly continuous disposal with only 10 acres uncovered at one time, a possible configuration is a reclaimed ar ea and a 10-acre uncovered area with a water saturated beach, and dry top surface and sides. The 300 flux meas urements on a 10-acre area translate to one measurement every 1,500 square ft or one ev ery 40 ft. According to NUREG/CR-3166 (NRC 1983), the number of locations a parameter must be measured to determine its average value within a precision of 25% at the 95% confidence level is given by the following:

Number = 45 (coefficient of variation) 1

Measurements of the coefficient of variation on covered and uncovered taili ngs piles results in a range for the Number of 25 to 32 radon flux m easurements for older ponds (NRC 1983). The

recommended minimum number is 30 radon flux m easurements for these older and much larger tailings areas (typically 100 acres or more) (NRC 1983). This is an order of magnitude less than the strict interpretation of the current requi rements (requiring 300 measurements). It is

recommended that the basis for the number of measurements required in Method 115 be provided and perhaps revised. In addition, the de finition of water satura ted beach and dry top surface should be provided in terms of percen t (%) saturation.

The measurement of radon flux has been reviewed and discussed by many authors since the early 1960s (see, for example, Tanner 1964 and Tanner 1978). In the 1970s, the subject was further investigated as regulators began investigati ng uranium mining and milling (NRC 1983). In all these investigations, the basic technology remain ed the same. As the direct measurement of radon flux is extremely difficult and very likely c ould disturb the actual flux with the entry of measuring devices into the flux, an accumulati on (can) method was used. Cans, drums, etc., with one end opened are turned over and the open e nd sealed into the ground to prevent leakage. Radon is allowed to accumulate into the can when, after a period of time, an aliquot is sampled and measured. From knowledge of the can volume, area of the face, time and measured radon concentration, the average radon flux over that time period can be determined. The sampling device can be charcoal in a canister, loose charco al, a plastic chip (alpha track or track etch systems), or thermoluminescent dosimeters (TLDs) . Equivalently if the accumulator can has a valve, a sample can be bled off and measured in a scintillation cell (Lu cas cell), or directly measured by solid state devices or other “real time” detectors. The challenge is to determine the optimal measuring system.

The device described in Method 115 is a Large- Area Activated Charcoal Canister (LAACC) discussed in Appendix A of Radon Flux Measurements on Gardinier and Royster Phosphogypsum Piles near Tampa and Mulberry, Florida (EPA 1985). The method is basically a large charcoal caniste r composed of a 10-in diameter PV C end cap with open end, retainer spring, 1⁄2-in thick scrubber pad, 1⁄2-in thick charcoal support grid, 1⁄2-in thick scrubber pad, 1-in

1 The coefficient of variation (CV) or relative standard deviation (RSD) is a measure of precision calculated as the standard deviation value divided by the average of a set of values. For a population where σ is the standard deviation of a population and μ is the mean, the CV= σ /μ for a population.

WA 4-11, Task 6 – Method 115 Compliance 3 SC&A – September 25, 2008thick scrubber pad, 1⁄4-in hole (ven t) in the top. A close examina tion of the appendix indicates a number of potential problems with the design, including the following:

(1) The specifications of the scrubber materials ar e not defined. For example, is a scrubber pad made of steel wool?

(2) There are two scrubber pads adjacent to each other. Are they made of different

materials?

(3) What type of charcoal was used and how was the system calibrated?

The device is homemade and was developed and constructed by Pacific Northwest Laboratory [PNL, now known as Pacific National Northwes t Laboratory (PNNL)] whose machine shops, etc., constructed 50 of these LAACC devices. O bviously, the resources of other groups may be

much more limited than PNNL.

Variations of the LAACC have al so been used. One researcher used the basic technique of the LAACC, but instead of the loose charcoal, a comm ercial charcoal canister was secured inside the PVC holder (CoPhysics 2008).

A paper by Andreas C. George presented at th e Natural Radiation Environment Conference VIII in Buzios, Brazil (George 2007), and also publishe d in the November 2007 Radon Bulletin of the CRCPD, is particularly relevant in terms of radon measuring devices:

In the last 20 years, new instruments and methods were developed to measure radon by using grab, integrating, and continuous modes of sampling. The most
common are scintillation cell monitors, acti vated carbon collectors, electrets, ion chambers, alpha track detectors, pulse and current ionization chambers, and solid state alpha detectors.

The author breaks down radon det ection into two large groupings:

I. Passive integrating radon measurements

(1) Activated carbon collectors of the open f ace (OF) or diffusion barrier (DB) type. Charcoal canisters often employ a gamma spectrometer to count the radon daughters as surrogates (Bi-214, for example). Liquid sc intillation vials also use alpha and beta counting. About 70% of radon measurements in the United States are canister type.

(2) Electret ion chambers are being used for 2–7 days duration to measure the voltage reduction (drop). The voltage drop on th e electrets is propor tional to the radon concentration. About 10%–15% of radon measurements use this methodology.

(3) Alpha track detectors are used for long-term measurements. Alphas from radon penetrate a plastic lattice, which is etch ed with acid, and th e resulting tracks are

counted. There is some use in the United St ates, but this is more popular in Europe.

WA 4-11, Task 6 – Method 115 Compliance 4 SC&A – September 25, 2008II. Passive or Active Continuous radon measurements

(1) Scintillation cell monitors mostly include the flow through type

(2) Current and pulse ionization chambers (mostly passive)

(3) Solid State devices are either passive or active if they use a pump to move air through the sensitive volume of the monitor like the RAD 7, which uses a solid state alpha detector (passive implanted planar silicon (PIPS) detector)

He further reviewed the groupings and compiled sens itivities of a number of monitors using data

from manufacturers or cited from published literature. He presents his results in three extensive tables, which were modified and summarized belo w in Table 1. Table 1 presets the sensitivity range for various types of commercially available OF or DB charcoal canisters, followed by the range of sensitivities of various types of continuous radon monitors (CRMs) utilizing solid state detectors or pulse ionization chambers. The la st group is the scintillation cells, which are typically cylinders coated with zi nc sulphide or other scintillati on materials that respond to the alpha decay of radon (also known as Lucas cells). In the first se ries, the exposed canisters are

counted and the radon is determined from the c oncentration of the Bi-214 or other daughter

surrogate.

For the second group, the first set of sensitivities range from 0.18 to 0.36 cpm/4.0 pCi/L). These detectors run continuously, which compensates for their lesser se nsitivity. Other solid state

monitors use PIPS as the detector or ionization chambers with somewhat higher sensitivities. The last group includes the scintillation cells , which vary in size and sensitivity.

Table 1. Sensitivity of Ra don Monitoring Instruments

Instrument Detection Principle Se nsitivity Range cpm/(4 pCi/L) DB canister (various types) gamma 0.80 to 4.2 (range)

OF canister gamma 250 Db (2g) canister alpha 54

Continuous radon monitor (CRM) Solid state 0.18–0.36

Other CRM (e.g., PIPS) Solid state 2.80

Pulse or continuous ionization Pulse ion 1.2–3.0

Pylon CRM others Scintillation Cell 5.7 to 24 (Lucas Cell or equivalent)

The paper also presents the results from various track etch detectors and electret ion chambers

with different units for the sensi tivity. The sensitivity of various track etch units ranges from 1.70 tracks per cm 2 /4 pCi/L-day to 23.4 tracks per cm 2 /4 pCi/L, while the sensitivity for the electrets are 8 volts per 4 pCi/L-d ay for short-term measurements to 0.7 volts per 4 pCi/L-day for long-term measurements.

WA 4-11, Task 6 – Method 115 Compliance 5 SC&A – September 25, 2008WA 4-11, Task 6 – Method 115 Compliance 6 SC&A – September 25, 2008 In summary, it appears that while no one type of detector is “better” than another type, it invariably depends more on the physical ci rcumstances and the time required for the measurement. For radon fluxes over a few days, a se ries of charcoal canisters can be used or a series of accumulator cans could be deployed, with samples taken periodically over a few days to get an average. It is important to note that ther e is no inherent advantage to fabricating and using an LAACC device, except for looki ng at a larger area. The devi ce was first designed to collect radon over a larger area, which, as mentioned, co uld be accomplished using a similar “shell” and

a canister. Note that the amount of charcoal in the LAACC was 400 ml or, assuming a density of 0.4 gm/cc, leads to a mass of 160 gm of activ ated charcoal. The EPA-recommended 4-in canister used in the home (the size of a tuna can) has a volume of about 66% of the LAACC and likely holds about half as much charcoal. The canisters, however, are easier to use and more standardized, and more importantl y, they are commercially available. While these “off the shelf” devices could be used instead of the LAACC, they would have to be evaluated against a specification to assure accuracy, prec ision, and importantly reproducibility.

It should be noted that the direct measurement of the radon flux from uranium tailings is not required by current guidance from the Nucl ear Regulatory Commi ssion (NRC). NRC requirements are presented in Re gulatory Guide 4.14, Revision 1, Radiological Effluent and Environmental Monitoring at Uranium Mills , April 25, 1980 (NRC 1980) and NUREG-1620 Standard Review Plan for the Review of a Reclamati on Plan for Mill Tailings Sites Under Title II of the Uranium Mill Taili ngs Radiation Control Act (NRC 2000). The regulatory guide calls for pre-operational radon flux measurements to establish background fl ux, but does not require operational flux measurements in this guide. This Regulatory Guide is expected to be updated by December 2009, as it is currently a phase 3 draft guide. The Standard Review Plan indirectly monitors radon emissions through calculations based on measurements or published values for the parameters governing radon diffusion, such as radium-226 concentration, soil type, diffusion coefficient moisture, and so on.

4.0 CONCLUSION

This review of Method 115 demonstr ates that its use can still be considered current for use to

monitor radon flux from uranium ta ilings. It is important to note, however, that the specific design protocols were developed with larger tailings impoundm ents in mind. Alternatively,

numerous commercial enhancements to that design are widely available and in use today. Other forms of passive detectors, as well active measur ement detectors, are also acceptable alternatives

to demonstrate conformance with the standard. In addition, the method as currently written has a number of elements and requirements that should be reviewed and possibl y revised, particularly the location and the frequency of measurement. These would be better based on statistical

considerations or some other technical basis.5.0 REFERENCES

CoPhysics 2008. Private communication between Ted Rahon (CoPhysics Corporation) and Les Skoski (SC&A, Inc.) www.cophysics.com , July 2008.

EPA 1985. “Radon flux Measurements on Gardin ier and Royster Phosphogypsum Piles near Tampa and Mulberry Florida,” EPA 520/5-85-029, Hartley, J.N, and H.D. Freeman. September

1985.

EPA 1991. “Guidance on Implementing the Ra dionuclide NESHAPS,” U.S. Environmental Protection Agency. July 1991.

George, A.C., 2007. “World History of Radon Re search and Measurement from the Early 1900s to Today,” Natural Radiation Environment C onference VIII (NRE VIII) in Buzios, Brazil, reprinted in November 2007 Radon Bulletin of the CRCPD.

NRC 1980. Regulatory Guide 4.14, Revision 1 “Rad iological Effluent and Environmental Monitoring at Uranium Mills,” April 25, 1980.

NRC 1983. “Recommended Procedures for Measur ing Radon Fluxes from Disposal Sites of Residual Radioactive Materials,” NUREG/C R-3166, Young, Y.A., V.W. Thomas, and P.O.

Jackson. March 1983.

NRC 1985. “Methods for Estimating Radioactiv e and Toxic Airborne Source Terms for Uranium Milling Operations,” Regulatory Guide 3.59. March 1987.

NRC 2000. “Standard Review Plan for the Review of a Reclamation Plan for Mill Tailings Sites

Under Title II of the Uraniu m Mill Tailings Radiation Control Act,” NUREG-1620, May 2000.

ORNL 1975. “Correlation of Radioactive Waste Treatment Costs and the Environmental Impact of Waste Effluents in the Nuclear Fuel Cycle for Use in Establishing ‘as Low as Practicable’ Guides-Milling of Uranium Ore,” ORNL-TM-4903 Vo lume 1, Sears, M.B., R.E. Blanco, R.C. Dahiman, G.S. Hill, A.D. Ryan, and J.P. Witherspoon. May 1975.

Tanner, A.B., 1978. “Radon Migration in the Ground: A Supplementary Review,” Natural Radiation Environment III (NRE III). U.S. Department of Energy 51 Symposium Series.

Tanner, A.B., 1964. “Radon Migration in the Ground: A Review” in The Natural Radiation

Environment , William Marsh Rice Universit y, Library Congress CCN 64-12256.

WA 4-11, Task 6 – Method 115 Compliance 7 SC&A – September 25, 2008