ML20249B503
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| Site: | 07001113 |
| Issue date: | 05/21/1998 |
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GROUNDWATER MONITORING GUIDELINE VALUE FOR URANIUM FORMER NORTHWEST CALCIUM FLUORIDE STORAGE AREA GENERAL ELECTRIC WILMINGTON, NC FACILITY
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General Electric Company
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Wilmington, North Carolina l
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by Thomas E. Potter Radiation Protection Consultant Washington, D.C.
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May 21,1998
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9006230233 900610 PDR ADOCK 07001113 C
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TABLE OF CONTENTS
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1.0 INTRODUCTION
AND
SUMMARY
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2.0 BACKGROUND
2 2.1 SETTING AND HISTORY 2
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2.2 AREA GEOLOGY AND HYDROLOGY 4
2.3 KEY GEOCHEMICAL FEATURES 4
2.4 POTENTIAL AFFECTED AREA AND LAND USE 5
3.0 TECHNICAL DEVELOPMENT 5
3.1 POTENTIAL HEALTH EFFECTS OF URANIUM 6
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3.2 MONITORING GUIDELINE VALUE DERIVATION 7
4.0 CONCLUSION
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5.0 REFERENCES
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I ABBREVIATIONS
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BEIR Biological Effects of Ionizing Radiation (committee of the National Research Council) l Bq becquerel (unit of radioactivity)
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CaF calcium fluoride 2
CEDE committed effective dose equivalent CFR United States Code of Federal Regulations FOR Federal Guidance Report ft feet (distance) 2 ft square feet (arca)
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ft/ day feet per day (velocity)
. EPA Emironmental Protection Agency fi fractional uptake from the gut to the bloodstream ICRP International Commission on Radiological Protection L/ day liter per day (volume intake rate)
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LE U low enriched uranium l
MCL maximum contaminant level l
MCLG maximum contaminant level goal -
1 mg/L milligrams per liter (mass concentration by volume)
NRC Nuclear Regulatory Commission pCi picocurie (unit of radioactivity)
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pCi/ day picocurie per day (radioactivity intake rate)
. pCi/g picoeurie per gram (radioactivity concentration by mass) pCi/L picoeurie per liter (radioactivity concentration by volume) pCi/ g picoeurie per microgram (radioactivity concentration by mass)
RfD reference dose (daily inteke that is likely to be without an appreciable risk
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of deleterious health effects during lifespan j
RSC relative source contribution Sv sievert (unit of committed effective radiation dose) pCi/g microcurie per gram (activity concentration) pg/ day
. microgram per day (mass intake rate)
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GROUNDWATER MONITORING GUIDELINE VALUE FOR URANIUM
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FORMER NORTHWEST CALCIUM FLUORIDE STOllAGE AREA
' GENERAL ELECTRIC WILMINGTON, NC FACILITY
1.0 INTRODUCTION
AND
SUMMARY
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In 1996, General Electric (GE) excavated and removed approximately 70,000 cubic feet of calcium fluoride (CaF ) and a larger volume of associsted soils from a storage area located in the northwest 2
quadrant ofits 1,664-acre site about 6 miles north of Wilmington, North Carolina. The CaF was j
2 a by-product of uranium fuel fabrication operatiens at the facility and contained low concentrations oflow-enriched uranium. Soils remaining in the storage area after excavation retain only very low
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concentrations of uranium-less than the U.S. Nuclear Regulatory Commission (NRC) limit of 30 pCi/g for release oflands for unrestricted use (USNRC,1981; FR,1981). GE is proposing a continuing program of groundwater monitoring, although area characteristics indicate that no biologically significant concentrations of uranium in groundwater would be expected from the very low concentrations of uranium remaining in soils at the former storage area. The purpose of this
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report is to derive a technically grounded risk-based guideline value for the concentration of uranium in groundwater for evaluation of the results from the monitoring program, i.e., a monitoririg guideline value.
This report first discusses relevant information about the area. Among other things, this information establishes the following:
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The area potentially affected is relatively small.
There is no present or likely future use of groundwater for human consumption.
Virtually the entire uranium source that has been present in soil for nearly three decades has been removed.
e' Continued general declines in uranium concentrations in groundwater are expected as a result
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of natural attenuation processes.
This report then develops a risk-based monitoring guideline value for low-enriched uranium to i
apply in the continuing groundwater monitoring program. The development of the monitoring l
guideline value generally follows the procedures used by the U.S. Environmental Protection i
y Agency (EPA) in its development of proposed National Primary Drinking Water Regulations for i
certain radionuclides, including uranium (FR,1991). Potential radiobiological effects and potential chemical effects are both considered in the development of the risk-based monitoring guideline value.
l A risk-based monitoring guideline value of 0.045 mg/L or 68 pCi/L is derived for low-enriched uranium in groundwater in or near the Former Northwest CaF Storage Area. The derived 2
monitoring guideline value corresponds to a conservatively derived lifetime radiobiological mortality risk of 1 x 10t This risk level is consistent with EPA's proposed drinking water standards for radionuclides, and incorporates a substantial margin of conservatism, given the
- conditions of the area outlined above.
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The calculated radiation dose (CEDE) from consumption of water at the monitoring guideline value is 7.6 millirem per year. This is far below the NRC limit on radiation dose to members of the public from regulated radioactive material,100 millirem per year (10 CFR Part 20). It is also
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far below the average annual radiation dose to a person in the United States from naturally occurring sources,300 millirem per year. The derived monitoring guideline value also prosides a
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large margin of protection against any potential chemical effects of uranium. Application of this limit in the evaluation of data collected from the continuing groundwater monitoring program would assure that the monitoring program would identify the need for any further evaluation or
- action to protect groundwater adequately.
2.0 BACKGROUND
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. Detailed descriptions of the history and characteristics of the Former Northwest CaF Storage Area 2
are provided in other reports (GE,1989; GE,1996; RTI,1995; RTI,1997; NFS,1996a; NFS, 1996b; CSMRI,1984). The information presented here includes briefdescriptions of the:
setting and history of the former storage area, e
area geology and hydrology,
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e key geochemical features, and the e
potentially affected area and land use.
e 2.1 SETTING AND HISTORY
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As shown in Figure 1, the Former Northwest CaF Storage Area is situated on a small, sandy 2
peninsula bounded on three sides by swampy area. The CaF material had been placed in seven 2
soil-covered storage trenches over a period of time from 1968 through 1972, in accordance with U.S. Atomic Energy Commission Special Nuclear Materials license SNM-1097. The average uranium concentration in the CaF was approximately 2,500 ppm (CSMRI,1984). %c average 2
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and maximum depths of the storage trenches were approximately 5 ft and 9 ft, respectively. The
- NRC concentration limit for unrestricted release is 30 pCi/g. The GE excavation plan was designed to remove materials exceeding 75% of that limit. The intent was to provide sufficient assurance that the required final status survey would demonstrate that the site is suitable for unrestricted release. Consequently, excavation entailed removing not only the CaF material, but 2
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substantial quantities of soils near the trenches. The excavation has resulted in an open pit of 2
appror'mately 43,000 ft (about I acre) in area and 5-7 ft in average depth.
A description of the groundwater quality over time is provided in a technical update report (RTI,1997). As noted in that report, transient elevated concentrations of uranium in groundwater were observed in some shallow 3vells near Former Northwest CaF Storage Area early in 1996, but 2
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concentrations declined rapidly after removal of the CaF. It is expected that uranium 2
concentrations in groundwater will continue to trend generally downward due to natural attenuation processes.
The radionuclides ofinterest-uranium-234, uranium-235, and uranium-238-are all naturally p
occurring radionuclides. The uranium processed to produce commercial nuclear fuel at GE and at other uranium fuel fabrication facilities is natural uranium that has undergone chemical and physical processing prior to arrival at the fuel fabrication facility. Consequently, although undisturbed naturally occurring uranium typically has long-lived progeny radionuclides (radium-226 and others) associated with it, uranium processed at GE an i aber uranium fuel fabrication facilities does not. He prior chemical processing includes semi-refinement of the ore
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and chemical conversion of the semi-refined ore to a purified uranium hexafluoride gas. The prior l
physical processing, enrichment, is a uranium hexafluoride gaseous diffusion process. Although it 1
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is designed to increase the proportion of uranium-235, it also removes chemical contaminants.
His chemical and physical processing cfTectively separates out all uranium progeny radionuclides.
7 The characteristics of the uranium decay chains are such that long-lived progeny will not reach equilibrium for thousands of years. Herefore, no long-lived uranium progeny radionuclides are of current or potential importance in this analysis. (Although the enrichment process modifies slightly the proportions of uranium-234, uranium-235, and uranium-238 in the uranium used at fabrication facilities in comparison to natural uranium, this modification has no radiological consequence. On a per-unit-activity basis, the three isotopes are practically equivalent from the radiobiological
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standpoint, so the mix ofisotopes is not consequential. This is demonstrated more completely in Section 3.3 below.) The enriched uranium used to produce commercial nuclear fuel is called low-enriched uranium, and that term is used in this report to distinguish uranium processed at GE from uranium occurring naturally in the environment.
Hus, three uranium radionuclides-uranium-234, uranium-235, end uranium-238-are the primag species ofinterest in this analysis. Two short-lived beta-emitting progeny from uranium-238, thorium-234 and protactinium-234 come to equilibrium with uranium-238 quickly and contribute slightly to dose. Heir contribution can be included with the uranium-238 contribution. Because their half-lives are short,24 days and 6.7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br />, respectively, they do not warrant independent assessment. Thorium-231, a beta-emitting product of uranium-235 with a half-life of 25.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br />, has been omitted from this analysis because its contribution to dose or risk would be negligible compared to that from its uranium-235 parent, which, in turn, is small relative to contributions from uranium-234 and uranium 238.
2.2 AREA GEOLOGY AND HYDROLOGY The geology and hydrology of the Former Northwest CaF Storage Area are described in a 2
geologic assessment report (RTI,1995), which, except as noted, is the source of the following information. Soils in the Former Northwest CaF Storage Area are undifferentiated sands of 2
varying size and color. No continuous clay layer was found to be present in this area of the site within the investigated depths (approximately 90 feet below grade). Groundwater in the area is under unconfined (water table) conditions and is directly influenced by rainfall. Groundwater near the Former Northwest CaF Storage Area generally occurs at a depth of 5-10 feet below grade.
2 Groundwater flow direction is somewhat variable, but generally flows from the upland regions of the peninsula toward the surrounding swampy area (see Figure 1). During periods oflow rainfall, groundwater flows from the former storage area to the north-northeast (referenced to plant north),
but shifts more to the northwest during periods of high rainfall. Based on elevations and gradients, shallow groundwater from the Former Northwest CaF Storage Area is believed to discharge to the 2
lower elevation swampy area generally to the north of the GE property (RTI,1995). The hydraulic gradient, based on site characterization measurements, is approximately 0.005. The average linear groundwater velocity is approximately 0.31 fl/ day (NFS,1996a).
2.3 KEY GEOCHEMICAL FEATURES Natural organic matter such as that found in the soils of the swampy area near the Former Northwest CaF Storage Area would tend to reduce any uranium in groundwater to the +4 valence 2
state in which it forms only extremely insoluble compounds (Bodek,1985). The environmental mobility of uranium in such reducing conditions would be extremely low. Therefore, the swampy area soils would be expected to form a geochemical boundary for potential uranium transport from the Former Northwest CaF Storage Area. Because groundwater flows from the former storage 2
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area toward the swampy area, the swampy area boundaries are expected to confine the zone that may have potential for increasing concentrations of uranium in groundwater.
'2.4 POTENTIAL AFFECTED AREA AND LAND USE The Former Northwest CaF Storage Area encompassed approximately 43,000 ft (about I acre).
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Based on the size of the storage area, groundwater flow direction, and distance to the swampy area, the potentially affected area north of the former storage area encompasses approximately 260,000 i
square feet (approximately 6 acres). None of the potentially affected area is currently inhabited,
. and no groundwater is currently drawn from the area for any purpose (i.e. no human groundwater receptors are present downgradient of the former storage area). A portion of the potentially affected area is located on GE property, and the remainder of the area that is off-site is used as part of a hunt club.
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Development of the area in a way that would make use of the groundwater resource for human consumption appears to be impractical and, therefore, highly unlikely. Groundwater typically encountered by shallow domestic wells in this area of the county is of poor quality with respect to the natural presence ofiron, sulfur, and other constituents. As a result, domestic water supplies from wells that tap the surficial aquifer in this area are typically pre-treated or augmented with L
bottled water for potable purposes.
- According to the available Wilmington area local water supply plans, groundwater in this area is not expected to be used as a future public water source (North Carolina State Water Supply Plan, updated April 7,1997). The nearest existing groundwater well is a hand pump located over 2,000 feet east of the area. This well is not in use. The location of this well is cross-gradient and,
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therefore, would not intercept groundwater from the former storage area. The minimum distance from the Former Northwest CaF Storage Area to the nearest well in use, conservatively assumed 2
to be the westernmost residence currently existing in the Wooden Shoe subdivision, is approximately 7,100 feet and would not intercept groundwater from the former storage area.
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3.0 TECHNICAL DEVELOPMENT
. This section describes the basis for selecting a risk-based monitoring guideline value for uranium in groundwater associated with the Fonner Northwest CaF Storage Area, discusses considerations 2
important in deriving the value, and presents the derivation of the value.
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The monitoring guideline value for uranium in groundwater associated with the Former Northwest CaF Storage Area was developed using a technically grounded approach based on risk analysis.
2 In this approach, risk analysis is used to derive a guideline value that is low enough to assure that risk is controlled to an acceptably low level. Such an approach is consistent with current regulatory practice at both EPA and NRC, where use of risk-based regulation has steadily
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increased in recent years. A risk-based approach is the most appropriate for this situation, and is conservative, given following considerations:
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There is no present use and, most likely, there will be no future use for drinking water of groundwater from the potential affected area.
. The potential affected area is small and well bounded by geochemical barriers (chemically T
reducing zones).
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Virtually the entire uranium source that has been present in soil for nearly three decades has
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been removed.
Continued general declines in uranium concentrations in groundwater are expected as a result of natural attenuation processes.
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'There are two other potential candidates that could possibly serve as a basis for a monitoring guideline value for uranium in groundwater associated with the Former Northwest CaF Storage 2
Arca. For purposes of discussion, these are identified as the "non-zero," and " greater than-3 background" approaches. For reasons discussed below, neither of these approaches is appropriate for the Former Northwest CaF Storage Area. In the "non-zero" approach, any non-zero value, or 2
any value above the measurement limit, is considered indicative of a concentration that warrants further evaluation, and, perhaps, remedial action. This approach is not feasible because the
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radionuclides ofinterest are ubiquitous in the environment, usually at concentrations above measurement limits (Reid,1993a; Reid,1993b; Hess,1985; Cothern,1983).
In the " greater-than-background" approach, any greater-than-background value is considered
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indicative of a concentration that warrants further evaluation, and, perhaps, remedial action. The l
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difficulty with a greater-than-background approach is that residual icw uranium concentrations in
. groundwater from past elevated levels preclude its use. While a background concentration for uranium in ground water may not be very precisely determinable, the uranium concentration in groundwater at the excavation area likely exceeds what is likely to represent background levels in the area. However, because uranium concentrations in groundwater at the excavation area are expected to decrease generally with time due to natural attenuation processes, remedial action 1
would not be warranted simply because concentrations may exceed background. Thus, a risk-based monitoring guideline value would be the most appropriate for this situation.
3.1
' POTENTIAL HEALTH EFFECTS OF URANIUM y
The first step in the development of a risk-based monitoring value for uranium in groundwater is to identify the potential adverse health effects for which risk is to be controlled. The U.S.
Environmental Protection Agency (EPA) has identified these in the course of developing proposed National Primary Drinking Water Regulations for certain radionuclides, including uranium (FR,1991). The two potential adverse health effects identified by the EPA as warranting risk control in water supplies are a radiobiological effect and a chemical effect, each of which is
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discussed briefly below. The only exposure pathway ofinterest for these potential effects is ingestion of water. Dermal exposure, an important exposure pathway for some chemicals and radionuclides, is insignificant for uranium. This is because there is negligible dermal uptake of uranium into the body through the skin and because the low-penetrating alpha radiation frun any uranium on the skin surface would be entirely absorbed within the thin layer of dead surface tissue y
. where no biological effect is possible.
Tests ofingestion of natural uranium have failed to show any radiobiological effects. For reasons
' discussed below, the results of these test's should apply to low-enriched uranium, as well.
Nevertheless, for purposes of cautious regulation, all uranium radionuclides are assumed to be potentially radiobiologically toxic because they emit alpha radiation, a form ofionizing radiation.
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lonizing radiation in general is known to be carcinogenic in animals and humans at high doses received over a short per'xl of time. Furthermore, uranium radionuclides ofinterest here share f
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certain properties with radium radionuclides, which also emit alpha radiation and are known to be carcinogenic in animals and humans at high doses and high dose rates. In addition, although no
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radiobiological effects were observed in mice following injection of natural uranium, carcinogenicity was observed following injection of high specific activity (high pCi/g) uranium radionuclides uranium-232 and uranium-233. The probable explanation of these conflicting results is that the relatively high specific auivity of radium isotopes, uranium-232 and uranium-233 resulted in far higher radiation doses and dose rates than did natural uranium, which has a relatively low specific activity. The specific activity of the low-enriched uranium used by GE is
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far Icwer than the specific activities of the radium isotopes, uranium-232, and uranium-233 that were shown to be carcinogenic, and ia only slightly greater than the specific activity of natural uranium. For this reason, the results of testing natural uranium would be expected to apply to low-enriched uranium, as well. That is, t: sting oflow-enriched urarium would also be expected to fail to demonstrate a radic. ' logical effect. Nonetheless, for purposes of conservatism in regulation i
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and risk assessment, a potential radiobiological effect is assumed for natural uranium and low-enriched uranium with a risk magnitude that is scaled downward in proportion to dose from risks observed at high radiation doses and dose rates. As explained in Section 3.3 below, this approach to risk estimation may be highly conservative.
Chemical health effects of uranium have been reported in a number of studies (Benticy,1985;
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Dy';ert,1949; Goodman,1985; Maynard,1949, Maynard,1953; Pozzani,1949; Rothermel,1949; Rothstein,1949; Spiegl,1949; Stokinger,1953). Uranium has been identified as a nephrotoxin metal (toxic to the kidney). In this respect it is similar to, but less potent than more commonly known nephrotoxin metals (cadmium, lead, mercuy). Here is no available evidence of nephrotoxicity in humans from ingestion of uranium. Animal studies indicate that the
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nephrotoxicity of uranium is low relative to other elements. Many of the nonradioactive heavy metals such as lead, arsMc, and mercury would produce very severe, perhaps fatal, injury at the levels of exposure comparable to those at which uranium causes relatively minor effects. Animal studies also indicate that kidney damage tends to reverse after cessation of uranium exposure.
3.2 MONrlORING GUIDELINE VALUE DERIVATION
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In its development of proposed National Primary Drinking Water Regulations for radionuclides, the EPA derived proposed Maximum Contaminant Level Goals (MCLGs) and Maximum Contaminant Levels (MCLs) for uranium and established relationships between uranium concentration in water and health risk (FR,1991). The EPA has not published et final rule, but is
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revising its proposed rule based on nmv data and methodology. The complete results of that work vill not be available in time to be reflected in a derived monitoring guidehnc value. The approach adopted here is to use the 1991 EPA work as a point of departure, updating as possible and appropriate for the Former Northwest CaF: Storage Area. This approach is followed below, first for the potential radiobiological effect, and then for the potential chemical effect. At the end of this 3
section, the monitoring guideline values derived for the t vo separate potentia!"nealth effects are integrated to establiA a single monitoring guideline valm Potential Radiobiolocical Effect In its 1991 work, EPA derived a risk / concentration value of 5.9 x 10 per pCi/L for the lifetime
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radiobiological mortality risk from ingestion of uranium in water (FR,1991). This is based, in part, on the work of the International Commission on Radiological Protection (ICRP) and the National Academy of Sciences, National Research Council, Commi5 tee on the Biological Effects of
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lonizing Radiation (BEIR). Specifically, the EPA estimate is based on ICR P 30 biokinet;c models (ICRP,1979; 1980; 1981; 1988), ICRP 38 radionuclides pysical data (radiation properties, etc.)
(ICRP,1983), and EPA dose / risk estimates based on radiobiological data collected up through
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BEIR III and BElR IV (NAS, 1980; 1988). This estimate was also based on an assumed life expectancy of 70 $ years, a consumption rate of 2 L/ day, and an f factor (fractional uptake froni i
i the gut to the bloodstream) of 0.05. The risk / concentration derived above results in concentrations of 170,17, and 1.7 pCi/L for lifetime mortality risks of I x 10",1 x 10, and I x 10,
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respectively.
Since completion of EPA's work leading to its 1991 proposed rule, the ICRP has extensively updated its biokinetic models (ICRP, 1989; 1993; 1994; 1995a; 1995b; 1995c; 1996) and the 1
National Research Council has published an v7 ated review of ndiobiological data, BEIR V d
(NAS,1990), which the EPA has used to produce revised dose / risk estimates (USEPA,1994).
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The EPA has integrated all of this information to produce tables that contain, among other quantities, risk cc:fficients for ingesdon of radionuclides in tap water, expressed as the probability of radiobiological mortality per unit activity intake, where the intake is averaged over all ages and both genders. This information is presented in interim Federal Guidance Report (FGR) 13 I
(USEPA,1998). The ri k estimates tabulated in FOR 13 are intended mainly for prospective assessments of estimated radiobiological risks from long-term exposure to radionuclides in
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envisnmental media for purposes such as preparation of environmental impact statements and development of assessments in support of generic rule making for control of radiation exposure.
It has been argued that the approach used to derive risk coefficients in FGR 13 leads to values that may be far too high. In its position paper on risk assessment (HPS,1995), the Health Physics
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Society, a non-protit i,cientific organization dedicated exclusively to the protection of people and the environment from radiation, recommends that assessments of radiogenic health risks be limited to dose estimates near and above 10 rem (far higher than the range ofinterest in this analysis).
The position paper notes that cancer and other health effects have not been observed consistently at low doses (<10 rem) because the magnitude of risk is so low that it is not detectable by current l
epidemiological data and methods. The paper notes further that in order to estimate radiation risk l
in the low-dose region (typical of most occupational and environmental expsures) risk of health effects in the high dose region (>100 rem) is extrapolated to the low-dose region using a variety of mathematical models including the linear, no-threshold model in which the risk is considered directly proportional to dose. In warning about the possibly excessive conservatism in such an approach, the position paper quotes the National Acc.demy of Sciences in its discussion of potential
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limitations in extrapolation of radiological risk to the millirem range. The Academy noted (NAS,1990) "..the possibility that there may be no risks from exposures comparable to external natural background radiation cannot be ruled out. At such low doses and dose rates, it must be acknowledged that the lower limit of the range of uncertainty in the risk es.imates extends to zero."
Application of FOR 13 in this analysis is not intended as an endorsement of the FGR 13 risk estimates. However, the FGR 13 approach doc, constitute a conservative basis for development of
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a monitoring guideline value.
In the new EPA approach, age-specific biokinetic models are used to calculate the time-dependent inventories of activity in various regions of the body fo; lowing acute intake of a unit activity of the radionuclides. For a given radionuclides and intake mode, this calculation is performed for each of
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six " basic ages at intake: infancy (100 days); 1,5,10, and 15 years; and maturity (usually 20 years, but 25 years in the biokinetic models for some elements). With a few exceptions, tir systemic biokinc:ic models ar.d gastrointestinal uptake fractions are taken from the ICRP's recent
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I series of documents on age-specific doses to members of the public from intake of radionuclides (ICRP,1989; 1993; 1995a; 1995b; 1996). The respiratory tract model is taken from ICRP
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Publication 66 (ICRP,1994), and the model for transit of materit through the gastrointestinal tract is taken from ICRP Publication 30, Part 1 (ICRP,1979). Age-specific dosimetric models are used to convert the calculated time-dependent regional activities in the body to absorbed dose rates (per unit intake) to radiosensitive tissues as a function of age at intake and time after intake.
Absorbed dose rates for intake ages intermediate to the six basic ages at intake (infancy; 1,5,10, and 15 years; and maturity) are determined by interpolation. De derived radiobiological risk
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coefficients may be applied to either continuous, steady-state or short duration exposure to environmental radionuclides. Dat is, a risk coefficient may be interpreted either as average risk sr < Ut exposure for persors exposed throughout life to a constant activity concentration of a radivun lide in an environmental medium, or as average risk per unit exposure for persons acutely exposed to the radionuclides through the environmental medium, as long as the exposure involved is y
properly characterized as low acute dose or low dose rate.
In the new EPA approach, there are two significant departures from past practice that are of interest here. First, the assumed water consumption rate has been reduced from 2 Uday to 1.11 Uday lifetime average. (Age-and gender-specific relative consumption rates are inherently' incorporated into the derived risk coefficients.) The new estincte includes water consumed directly,
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water added to beverages, and water used in cooking, but not the water contained in food purchased. De second is that the f factor for uranium has been reduced from 0.05 to 0.02.
i Apart from other considerations, each of these two factors would tend to reduce the uranium radiobiological mortality risk factor expressed in tams of risk per pCi/L from the value derived b; EPA in its 1991 proposal. The first modification also has implications for derivation of a
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monitoring guideline value for the potential chemical effect, as discussed further below.
The FGR 13 risk coefficients for ingestion of uranium-234 (U-234), uranium-235 (U-235), and uranium-238 (U-238) in tap water are similar, as shown in the table below. Inclusion of contributions from thorium-234 (Th-234) and protactinium-234 (Pa-234), shon-lived, beta-emitting progeny of uranium-238, increases the uranium-238 risk coefficient only slightly.
Nuclide FGR 13 FGR 13 Lifetime Mortality Risk Lifetime Mortality Risk per Bq ingested per pCiingested U-234 1.24 x 10*
4.59 x 10-"
)
U-235 1.21 x 10*
4.48 x 10-"
I U-238 1.13 x 19*
4.18 x 10-"
j (1.52 x 10* with Th-234 and Pa-234 (5.62 x 10-" with Th-234 and Pa-234 l
progeny included) progeny included)
' Total 1.30 x 10*
4.81 x 10-"
. LE U
)
ne becqueres FBq) umt ir a special unit of radioactivity in the international system of uniid5i). One Bq is equal to j
one nuclear transformation per second. He Curie is an older special unit equal to 3.7 x 10" nuclear transformations i
per second One picoeurie (pCi)is equal to 10'" curie, or 0.037 Bq.
The entries in the table for " Total LE U"(total low enriched uranium) are isotope-weighted risk
)
coefficients based on an alpha activity distribution by isotope in low-enriched uranium of 75%
uranium-234,3% uranium-235, and 22% uranium-238 (NFS,1996a). The corresponding risk / concentration ratio for a lifetime average consumption rate of 1.1 Uday and a lifespan of 75.3 9
).
1
)
4 years (FGR 13 values)is 1.47 x 10 per pCi Total U/L This is about a factor of 2.5 higher than the ratio derived by EPA in its 1991 work, discussed above. He newly derived risk / concentration
)'
results in uranium concentrations in water of 68,6.8, and 0.68 pCi/L for lifetime monality risks of 1 x 10",1 x 10, and 1 x 10, respectively.
4 4
In deriving risk-based concentration limits, EPA generally uses risk levels in the range of I x 10 4 to 1 x 10"(FR,1991). In its 1991 proposed National Primary Drinking Water Regulations (FR, 1991), intended to apply to public water supplies, EPA proposed concentration limits (MCLs)
F 4
corresponding to a lifetime mortality risk of I x 10 for most radionuclides. (A lower salue proposed for uranium was controlled by the potential chemical effect, discussed in the next section.) Selection of a lower mortality risk to determine a radiobiological risk-based monitoring guideline value for the Former Northwest CaF Storage Area would be highly inconsistent with I
2 levels of protection proposed by EPA for public water supplies and inappropriate for that reason
)
alone. Beyond that, the extra conservatism that might be afforded by selection of a risk level in the lower part of the EPA range is unnecessary in this case. Site-specific characteristics of the Former Northwest CaF Storage Area provide such conservatism:
2 There is no present use and, n:ect likely, there will be no future use for drinking water of
. groundwater from the potential arTected area.
t The potentist affected area is small and well bounded by geochemical barriers (chemically
)
reducing zones).
Virtually the entire uranium source that has been present in soil for near,; threc decades has been removed.
. - Continued general declines in uranium concentrations in groundwater are expected as a result ofnatural attenuation processes.
l
)
These considerations argue for application of a risk level of I x 10" for determining the appropriate monitoring guideline level for the potential radiobiological effect. The monitoring guideline value corresponding to a lifetime radiobiological mortality risk of 1 x 10"is, as noted above,6% pCi/L This corresponds to a uranium mass concentration of 0.045 mg/L for low-enriched uranium. (He comspondence between mass and activity for enriched uranium is derived below.)
)
The significance of the monitoring guideline value derived above,68 pCi/L, can be placed in context by comparing the potential annual radiation dose to an individual consuming 1.1 L/ day contain:.ng that concentration to various points of reference. Suitable points of reference would be the NRC limit on radiation dose to members of the public from regulated radioactive material,100
)
millirem per year (10 CFR Part 20), and the average annual r'adiation dose to s person in the United States from naturally occurring sources, 300 millirem per year, of which approximately 200 l
millirem per year is du, to inhalation of radon progeny sNCRP,1987), The doses stated above are j
expressed in terms of effective dose equivalent from sources of exposure both internal and external to the body.
) '
Radiation doses from internal exposure (inhalation or ingestion) are computed using dose factors l
developed using current methodology, specifically those in Federal Guidance Report i 1 (USEPA, 1988). In conformance with this guidance, the term " dose," as it applies to the values calculated in this report, means " committed effective dose equivalent" (CEDE). The maximum dose factor values from FGR 11 for ingestion of uranium-234 (U-234), uranium-235 (U-235), and uranium-
)-
238 (U 238) are similar, as shon in the table below, Values in the table below include i
contributions from short-Iked progeny.
10
)
)
l Nuclide h FGR 11 FGR 11
).
CEDE per Unit Intake CEDE per Unit Intake Sv per Bq ingested millirem per pCi ingested 4
U-234 7.66 x 10 2.83 x 10" U-235 7.19 x 10'8 2.66 x 10" 4
U-238 6.88 x 10 2.55 x 10" Total 7.47 x 10'8 2.77 x 10" I
LE U The sievert (Sv)and millirem are units of radiation dose equivalent. One Sv is equal to 100 rem. The becquerel (Bq) unit is a special unit of radioactivity in the intemational system of units (SI). One Bq is equal to one nuclear transfonnation per second. 'Ihe Curie is an older special unit equal to 3.7 x 10" nuclear transfonnations per second.
One picoeurie (pCi) is equal to 10'" curie, or 0.037 Bq.
).
The entries in the table for " Total LE U" are isotope-weighted dose factors based on an alpha activity distribution by isotope in low-enriched uranium of 75% uranium-234,3% uranium-235, and 22% uranium-238 (NFS,1996a).
The corresponding radiation does (CEDE) for a consumption of water containing 68 pCi/L
)
Total LE U for 365 days / year at a rate of 1.1 L/ day is the product of those factors and the CEDE per Unit intake for Total LE U,2.77 x 10" millirem per pCi ingested. The calculated radiation dose (CEDE) from consumption of water at the monitoring guideline value is 7.6 millirem per year.
This is far below the NRC limit or radiation dose to members of the public from regulated radioactive material,100 millirem per year (10 CFR Part 20). It is also far below the average annual radiation dose to a person in the United States from naturally occurring sources,300
)
millirem per ycar.
Potential Chemica! Effg_c1 in its 1991 work, EPA proposed a value of 0.02 mg/L for uranium in drinking water that, in its
)
judgment, could serve as the Maximum Contaminant Level Goal (MCLG), neglecting consideration of any potential radiobiological health effect (FR,1991). The estimate is based on chemical effect data available at the time-in particular the study of the chemical effect in rabbits, application of an uncertainty safety factor of 1,000 (standard EPA practice when only animal data are available), an assumed consumption rate of 2 Ilday, and an assumed relative source contribution factor (the fraction of uranium intake assumed to derive from drinking water) of 0.2.
In developing its new proposed rule, EPA is considering new, more limiting animal chemical effect data and a more reasonable relative source contribution. The reduced consumption rate applicable to EPA's new work in developing radiation risk coefficients, should apply to revised chemical effect considerations, as svell. Taken together, these factors would tend to be somewhat off-setting.
Y The outcome of EPA's evaluations cannot be foreseen at this time. However, it should be noted that in its 1991 work, EPA estimated that 1,500 public water supply systems (serving 875,000 people) that would require treatment to reduce uranium concentrations to 0.02 mg/L. The EPA i-also estimated that the number of public water supply systems requiring treatment to reach a lower limit of 0.005 mg/L wo.ild increase to 7,200 (FR,1991). Given that there has been no manifestation of chemical effect in humr.ns that could be related to uranium in those public water supplies, it is reasonable to conclude that the value of 0.02 mg/L derived by EPA in its 1991 work i1
provides some margin of conservatism for protection of public water supplies. Furthermore, it is apparent that a higher value would be more than adequately conservative for use as a monitoring guideline value for uranium in groundwater at the Former Northwest CaF Storage Area, where the 2
water ofinterest is not likely to be ingested in any case.
As noted above, the EPA; in deriving its 1991 proposed limit of 0.02 mg/L, applied multiple safety factors. The first was the factor of 1,000 for the sole reliance on animal data. The second was the factor of 1.8 in the assumed water con:umption rate. As noted above, this factor has been climinated in the recent EPA work on potential radiobiological effects from radionuclides.
The third safety factor applied was a factor of approximately 5 inherent in EPA's selection of a value of 0.2 for the relative source contribution (RSC)-the fraction of uranium intake assumed to derive from water. As EPA noted in its 1991 rulemaking proposal (FR,1991), the default lower value of 0.2 was selected for the RSC because of particular limitations in the available data en uranium intake from food. The EPA noted that available data was focused on the east and west coasts, and that there wa: an absence of data from the midwest and west regions of the country.
The EPA reasoned that, because uranium concentrations in soils in the midwest and west might be expected to be higher than in soils along the coasts, the proposed rule may need to maintain lower contributions of uranium from water in the midwest and west regions to maintain a sufficiently low
)
intake of uranium in the total diet in those regions. The EP A acknowledged that its approach was conservative, even for the universally applicable proposed regulation. In any event, the Wilmington, North Carolina site ofinterest in this case is on the east coast, where the available data are directly applicable. Therefore, the reluctance of EPA to use the available data to calculate an RSC for drinking water standards to be applied nation-wide is not warranted in this case.
The EPA notes that the data show that uranium intake from food is generally low-approximately 1.3 pCi/ day as an average, with a 96* percentile value of about 5 pCi/ day. Based on the 1.3 pCi/pg activity to mass ratio used t>y EPA for natural uranium in water, accounting for the slightly increased ratio of uranium-234 to uranium-238 from alpha recoil, the corresponding mass concentrations are 1.0 and 3.8 g/ day, respectively. The EPA-derived reference dose (RfD, the
)
daily intake that is likely to be without an appreciable risk of deleterious health effects during the lifespan) is 200 g/ day. The uranium intake from food represents only 0.5 to 1.9 percent of this reference dose. From this, one may conclude that the RSC appropriate for application as a monitoring guideline value for the Former Northwest CaF Storage Area is greater than the EPA 2
default ceiling value of 0.8, and is very nearly 1.0,
)
Based on an RfD of 200 pg/ day, a water consumption rate of 1.1 IJday, and an RSC of 0.98, a value of 0.18 mg/L is proposed as the monitoring guideline value for potential chemical effects from uranium in groundwater et the Former Northwest CaF Storage Area. (As explained in the 2
section below, this corresponds to a uranium activity concentration of 270 pCi/L for low-enriched
)
uranium.) This value is the 1991 MCLG derived by EPA, corrected for a reduced consumption rate and a higher relative source contribution than those used in EPA's derivation. The safety factor of 1,000 for reliance solely on animal studies is retained, and should provide a large margin to accommexlate any reasonably anticipated changes in the estimated potential chemical effect of uranium, particularly when limited to the context of this application.
+
t i
i 12
{
h
' Intearated Monitorina Guideline Value
)
Derivation of a single monitoring guideline value for uranium in groundwater at the Former Northwest CaF: Storage Area requires integration of the results of the derivations for the two differens potential health effects. This integration first requires derivation of the activity per unit mass oflow enriched uranium so that guideline values can be placed on equal bases. The activity per unit mass oflow-enriched uranium is derived directly from the isotope activity distribution, 75% uranium-234, 3% uranium-235, and 22% uranium-238 (NFS,1996a), and the isotepe half-
)'
lives. The activity per unit mass so derived is 1.5 pCi/ g.
On'this basis the monitoring guideline value for the potential chemical effect is 0.18 mg/L or 270 pCi/L. The monitoring guideline value based on the potential radiobiological effect is 68 pCi/L or 0.045 mg/L. The limiting guideline value is the lower value-68 pCi/L or 0.045 mg/L.
)
(based on the potential radiobiological effect).
4.0 CONCLUSION
S A risk-based monitoring guideline value of 0.045. mg/L or 68 pCi/L has been derived for low-enriched uranium in groundwater in or near the Former Northwest CaF Storage Area The
).
2
- derived monitoring guideline valuc corresponds to a conservatively derived lifetime radiobiological mortality risk of I x 10t The calculated radiation dose (CEDE) from consumption of water at the monitoring guideline value is 7.6 millirem per year. This is far below the NRC limit on radiation
- dose to members of the public from regulated radioactive material,100 millirem per year (10 CFR Part 20). It is also far below the average annual radiation dose to a person in the United States I
from naturally occurring sources,300 millircir per year. The derived monitoring guideline value also provides a large margin of protection against any potential che.nical eTects of uranium.
. Application of this limit in the evaluation 'of data collected from the continuing groundwater monitoring program would assure that the monitoring program wotid idemify the need for any further evaluation or action to protect groundwater adequately..
)-
.h; e
- 4 e
c l
r j
)
13 i
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Aminoaciduria in Rodents following Uranium intoxication," Bull Environ Contam Toxicol 34:407-416, 1985.
Bodek,1985. EnvironwantalInorganic Chemistry, Bodek, I., Lyman, W.J., Rechl, W.F.,
Rosenblatt, D.H., eds., Pergamon Press, New York,1985.
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Cothern,1983. " Occurrence of Uranium in Drinking Water in the U.S.," Cothem, C.R., and Lappenbusch, W.L., Health Physics, Volume 45, Number 1, pp. 89-99, July,1983.-
CSMRI,1984 " Uranium Reserve Estimates of Various Storage Sites at the Nucicar Fuel Facility, 3
7 Castle Hayne, North Carolina," Colorado School of Mines Research Institute, May 7,1984.
' Dycert,1949. Dygett, H.P., Pharmacology and Toxicology of Uranium Compounds.
McGraw-Hill flook Inc. pp. 666-672,1949.
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Federal Register,46, pp. 52061-3, October 23,1981.
FR,1991. " National Primary Drinking Water Regulations; Radionuclides; Proposed Rule,"
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GE,1996. "1996 Supplement to Environmental Report," General Electric Company, May,1996.
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Goodman,1985. Goodman, D.R.,"Nephrotoxicity. Toxic effects in the kidneys." In: Industrial 1
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4 HPS,' 1995. " Position Statement on Risk Assessment," Health Physics Society, McClean, VA, 1 April,1995.
Hess,1985. "The Occurrence of Radioactivity in Public Water Supplies in the United States," -
Hess, C.T., Michel, J., Horton, T.R., and Prichard, H.M., Health Physics, Volume 48, Number 5 pp. 553-586, May,1985.-
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ICRP,1980. International Commission on Radiological Protection. " Limits for latakes by l
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Workers."ICRP Publi::ation' 30, Part 3 (Pergamon Press, Oxford).
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.. ICRP,1983. International Commission on Radiological Protection. " Radionuclides Transformations
- i Energy and Intensity of Emissions."ICRP Publication 38 (Pergamon Press, Oxford).
Y ICRP,1988. International ( ymission on Radiological Protection. " Limits for Intakes by Workers: An Addendum."ICRP Publication 30, Pan 4 (Pergamon Press, Oxford).
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Press, Oxford).
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ICRP,1994. International Commission on Radiological Protection. " Human Respiratory Tract Model for Radiological Protection."ICRP Publication 66 (Pergamon Press, Oxford).
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. Members of the Public from Intake of Radionuclides, Part 4."ICRP Publication 71 (Pergamon Press, Oxford).
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ICRP,1995c. Intemational Commission on Radiological Protection. " Basic Anatomical and Physiological Data for Use in Radiological Prctection: The Skeleton."ICRP Publication 70 (Pergamon Press, Oxford.)
ICRP,1996. International Commission on Radiological Protection. " Age-Dependent Doses to
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Members of the Public from Intake of Radionuclides, Part 5. Compilation ofIngestion and Inhalation Dose Coefficients."ICRP Publication 72 (Pergamon Press, Oxford).
I Maynard,1949. Maynard, E.A., and Hodge, H.C., " Studies of the Toxicity of Veious Uranium
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Compounds when Fed to Experimental Animals, In: Pharmacology and Toxicology of Uranium Cornpounds, Voegtlin, l.C., and Hodge, H.C., eds., National Nuclear Energy Series (VI). New
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Maynard,1953. Maynard, E.A., Don, W.L., and Hodge, H.C., " Oral Toxicity of Uranium Compounds," In: Pharmacology and Toxicology of Uranium Compounds, Voegtlin, l.C., and Hodge, H.C., eds., New York, NY, McGraw-Hill,1953.
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= NAS,1980. "The Effects on Populations of Exposure to low Levels of lonizing Radiation,"
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Academy of Sciences, National Research Council, BEIR IV,1988.
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r NAS,1990. " Health Effects of Exposure to Low levels of Ionizing Radiation," National
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).
' Nuclear Fuel Services, Inc., Erwin, Tennessee, Revision 2, February 28,19%.
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Pozzani,1949. Pozzani, U.C., In: Phormacolog and Toxicolog of Uranium Compounds, Voegtlin, I.C., and Hodge, H.C., eds., National Nuclear Energy Series (VI). New York, NY, McGraw-Hill,1949.
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Geological Survey, Raleigh. North Carolina, Bulletin 93, May,1991 (revised 1993).
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. Geological Survey, Raleigh, North Carolina, Bulletin 94, July,1993.
Rothermel,1949. Rothermel, J.J., " Uranium tetrachloride," In Pharmacology and Toxicolog of y
Uranium Compounds, Voegtlin, I.C., and Hodge, H.C., eds., National Nuclear Energy Series (VI). New York, NY. McGraw-Hill,1949.
Rothstein, l949. Rothstein, A., In: Pharmacology and Toxicolog of Uranium Compounds, Voegtiin, i.C., and Hodge, H.C., eds., National Nuclear Energy Series (VI). New York, NY, McGraw-Hill, pp. 635-648,1949.
RTI,1995. " Preliminary Geologic Assessment-Calcium Fluoride Storage Area-Northwest,"
- Research Triangle Institute, Research Triangle Park, North Carolina, Report Number 6103/007/01F, September 29,1995.
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RTI,1997. " Technical Update of Hydrogeological and Groundwater Quality Conditions in the Northwest Site Area," Research Triangie Institute, Research Triangle Park, North Carolina, Document Number 6448/018/01F, October 30,1997.
Spiegl, l 949.. Spiegl, C.J., In: Pharmacology and Toxicology of Uranium Compounds, Voegtlin, i
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l Stokinger,1953. Stokinger, H.E., Baxter, R.C., Dygent, H.P., " Toxicity following Inhalation for 1 and 2 Years," In: Pharmacology and Toxicolog of Uranium Compounds, Voegtlin, I.C., and L
- Hodge, H.C., eds., New York, NY,'McGraw-Hill,1953.
. USEPA,1988. " Limiting Values of Radionuclides intake and Air Concentration and Dose l Conversion Factors for Inhalation, Submersion, and Ingestion," Eckerman, K.F., Wolbarst, A.B.,
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and Richardson, A.C.B., United States Environmental Protection Agency, Washington, DC, EPA j
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520/1-88-020, Federal Guidance Report No. I1, September,1988.
USEPA,1994. " Estimating Radiogenic Cancer Risks," U.S. Environmental Protection Agency, Washington, DC, EPA 402-R-93-076,1994
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USEPA,1998. " Health Risks From Low-Level Emironmental Exposure To Radionuclides, Radionuclides-Specific Lifetime Radiogenic Cancer Risk Coefficients for the U.S. Population, Based on Age-Dependent Intake, Dosimetry, and Risk Models," Eckerman, K.F., Leggett, R.W.,
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USNRC,1981. " Disposal or Onsite Storage of Residual Thorium or Uranium (Either as Natural Orcs or without Daughters Present) from Past Operations," SECY-81-576, U.S. Nuclear Regulatory Commission, Washington D.C., October 5,1981.
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17
O Thomas E. Potter n"
Radiation Protection Consultant 4231 Jenifer St. NW Washington, D.C.
O 202-363-4727 Mr. Potter has worked in the nuclear field, primarily in radiation protection, for 33 years. His work as an independent consultant since 1991 has covered a wide variety of radiation protection matters, mostly for private U.S. Nuclear Regulatory Commission or Agreement State materials licensecs. Projects included enviromnental radiation dose assessments associated w;th operations and decommissioning, assistance in formulation oflicensee positions and comments on developing decommissioning regulations, radiation protection management reviews, radiation protection program audits, and assistance in planning implementation of revisions to 10 CFR 20.
From 1972 through 1990, Mr. Potter worked as a consultant in several firms. He was partner and O
consultant in the firm of Morton and Potter (1984-90), a consultant at Pickard, Lowe and Garrick, Inc. (PLG) (1973-84), and an assistant to Dr. G. Hoyt Whipple of the University of Michigan in his private radiation protection consulting practice (1972-73). During this period, Mr. Potter was responsible for a variety of projects on radiation protection matters related primarily to nuclear power and the nuclear fuel cycle. He managed and assisted in preparation of radiation protection g
programs and environmental radiological assessments for nuclear power plants and nuclear materials facilities. He also conducted radiation protection management reviews and radiation protection program audits. In 1986 he lectured and conducted cornputer workshops in Cairo as part of a course on environmental radiation dose assessment sponsored by the International Atomic Energy Agency for the Egyptian governraent. Projects at PLG included probabilistic analysts of off-site consequences of power reactor accidents as part of full-scope probabilistic risk O
assessments for nuclear power plants. He participated in the design and development of the CPJ. CIT code, a computer program for probabilistic assessment of power reactor accident consequences, and nr.naged development and integration of dose and health effect assessment modules. He also participated in a comprehensive assessment of off-site radiation from the Three Mile Island accident.
O From 1963 to 1970, Mr. Potter worked for the Nuclear Materials and Equipment Corporation (NUMEC) in several positions-Plutonium Process Chemist (1963-66), Plutonium Fuel Facility Hea'th and Safety Supervisor (1966-69), and License Administrator (1969-70). In 1967, he was responsible for institution at the Parks Township Site of NUMEC's personnel monitoring programs using thermoluminescent dosimetry and breathing-zone aerosol sampling. These were among the O
earliest implementations of progams that have since become standard industry practice.
Mr. Potter received a master of science degree in environmental science (emphasis in radiation protection) from the University of Michigan in 1972, where he was supported by a U.S. Atomic Energy Commission nuclear science and engineering graduate fellowship in radiation protection.
O He received a bachelor of science degree in chemistry from the University of Pittsburgh in 1963.
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