Notice of Issuance of Branch Technical Position on Screening Methodology for Assessing Prior Land Burials of Radioactive Waste Authorized Under Former 10 CFR 20.304 and 20.302 for Interim Use and Comment

NUCLEAR REGULATORY COMMISSION

Notice of Issuance of Branch Technical Position on Screening

Methodology for Assessing Prior Land Burials of Radioactive Waste

Authorized Under Former 10 CFR 20.304 and 20.302 for Interim Use and

Comment

SUMMARY: This notice is to advise the public of the U.S. Nuclear

Regulatory Commission's issuance of a Branch Technical Position (BTP)

which provides a screening methodology that the staff finds acceptable

to determine the need for further characterization and/or remediation

of prior low-level radioactive waste disposal conducted under the

provisions of former 10 CFR 20.304 and 20.302.

Burial of certain quantities of radioactive waste in soil, by

licensees, without prior NRC approval, was authorized on January 29,

1959 (22 FR 548). This authorization was codified in former 10 CFR

20.304. On January 28, 1981, the NRC concluded that it was

inappropriate to continue generic authorizations of burials pursuant to

10 CFR 20.304 without regard to factors such as location of burial,

concentrations of radioactive material, form of packaging, and

notification of NRC. Therefore, NRC rescinded 10 CFR

[[Page 56717]]

20.304 (45 FR 71761). As of January 28, 1981, licensees wishing to

perform on-site disposal of the type previously authorized under 10 CFR

20.304 were required to obtain prior NRC approval in accordance with 10

CFR 20.302.

Disposals made pursuant to former 10 CFR 20.304 and 20.302 at

facilities licensed under 10 CFR Parts 30, 40, and 70, and that have

been unused for NRC licensed operations for a period of 24 months, are

subject to the requirements of the ``Final Rule on Timeliness in

Decommissioning Nuclear Facilities'' (59 FR 36026, effective August 15,

1994) (hereinafter called the ``Timeliness Rule''). Licensees who have

unused outside areas (e.g., burial areas) containing elevated levels of

licensed radioactive materials, are required to notify NRC, that they

are in possession of these areas and must begin following a schedule

for decommissioning these areas. For timing provisions related to

decommissioning, see 10 CFR 30.36(d), 40.42(d), 70.38(d), and 72.54(d).

On August 19, 1996, NRC published Information Notice 96-47

``Recordkeeping, Decommissioning Notifications for Disposal of

Radioactive Waste by Land Burial Authorized under Former 10 CFR 20.304,

20.302, and Current 20.2002.'' This notice re-emphasized NRC's position

that former burials are covered under the Timeliness Rule, outlined the

decommissioning schedule required by the rule, and stated that NRC

would develop a screening methodology for assessing former burials.

This screening methodology is being issued as a draft BTP and is

attached to this notice.

Because of the deadlines associated with the Timeliness Rule, this

BTP is being issued for public use and comment for 90 days. At the end

of the 90 day period, the comments received will be evaluated to

determine if the BTP should be revised. Since there is a possibility

that the comments could result in a substantial change to the BTP, NRC

will not make any decisions regarding the assessment of prior burials

until after the comments can be evaluated.

All comments should be addressed to Heather Astwood, Mail Stop T-

7F-27, U.S. Nuclear Regulatory Commission, Washington, DC 20555. A copy

of the BTP is also located in the NRC's Public Document Room, 2120 L

Street NW., Washington, DC 20555. A copy is also on the NRC homepage

which can be accessed at www.nrc.com.

FOR FURTHER INFORMATION CONTACT: Heather Astwood, Division of Waste

Management, Office of Nuclear Material Safety and Safeguards, U.S.

Nuclear Regulatory Commission, Mail Stop T-7F-27, Washington, DC 20555,

telephone (301) 415-5819.

Dated at Rockville, MD this 25th day of October 1996.

For the U.S. Nuclear Regulatory Commission.

Michael F. Weber,

Chief, Low-Level Waste and Decommissioning Projects Branch, Division of

Waste Management, Office of Nuclear Material Safety and Safeguards.

Draft--Branch Technical Position

Screening Methodology for Assessing Prior Land Burials of Radioactive

Waste Authorized Under Former 10 CFR 20.304 and 20.302

October 1996

Low-Level Waste and Decommissioning Projects Branch, Division of Waste

Management, Office of Nuclear Material Safety and Safeguards

Table of Contents

1.0 Purpose

2.0 Introduction

3.0 Discussion

4.0 Regulatory Position

4.1 Scope

4.2 Screening Methodology

4.2.1 General Approach

4.2.2 Step 1--Records Review

4.2.3 Step 2--Ingestion

4.2.4 Step 3--Exhumation Concentration

4.2.5 Results

4.3 Dose Screening Level and Basis

Appendix A Analysis of Other Pathways

Appendix B Metric Conversion Table

Appendix C Sample Calculations

Draft--Screening Methodology for Assessing Prior Land Burials of

Radioactive Waste Authorized Under Former 10 CFR 20.304 and 20.302

1.0 Purpose

This Branch Technical Position (BTP) provides a screening

methodology that the staff finds acceptable to determine the need for

further characterization and/or remediation of prior low-level

radioactive waste disposals conducted under the provisions of former 10

CFR 20.304 and 20.302. This BTP is intended to be a final evaluation

for former burials. Decisions made based on this BTP are not expected

to change because of the issuance of future rules or standards.

2.0 Introduction

Burial of certain quantities of radioactive waste in soil, by

licensees, without prior NRC approval, was authorized on January 29,

1959 (22 FR 548). This authorization was codified in former 10 CFR

20.304. On January 28, 1981, NRC concluded that it was inappropriate to

continue generic authorizations of burials pursuant to 10 CFR 20.304

without regard to factors such as location of burial, concentrations of

radioactive material, form of packaging, and notification of the

Nuclear Regulatory Commission. Therefore, NRC rescinded 10 CFR 20.304

(45 FR 71761). As of January 28, 1981, licensees wishing to perform on-

site disposals of the type previously authorized under 10 CFR 20.304

were required to obtain prior NRC approval in accordance with 10 CFR

20.302.

On May 21, 1991, 10 CFR Part 20 was revised (56 FR 23360) and 10

CFR 20.302 was replaced by 20.2002. According to 10 CFR 20.1008(b),

licensees were required to comply with the new 10 CFR 20.2002

exclusively on January 1, 1994. The requirements of 10 CFR 20.2002 are

similar to the original requirements in former 10 CFR 20.302, with the

addition of requirements for submitting analyses and procedures for

maintaining doses within established dose limits and as low as

reasonably achievable (ALARA).

Disposals made pursuant to former 10 CFR 20.304 and 20.302 at

facilities licensed under 10 CFR Parts 30, 40, and 70, and that have

been unused for NRC licensed operations for a period of 24 months, are

subject to the requirements of the ``Final Rule on Timeliness in

Decommissioning Nuclear Facilities'' (59 FR 36026, effective August 15,

1994) (hereinafter called the ``Timeliness Rule''). Licensees who have

unused outside areas (e.g., burial areas) containing elevated levels of

licensed radioactive materials, are required to notify NRC, that they

are in possession of these areas and must begin following a schedule

for decommissioning these areas. For timing provisions related to

decommissioning, see 10 CFR 30.36(d), 40.42(d), 70.38(d), and 72.54(d).

The evaluations required before the Commission terminates a license

or releases a former burial area from a license related to disposed

material were discussed in the supplemental information to the final

rule on the ``General Requirements for Decommissioning Nuclear

Facilities'' (53 FR 24021), published June 27, 1988. In the statement

of considerations for the final rule, NRC stated that it ``. . . will

take a hard look at the extent to which the site has been previously

used to dispose of low-level radioactive waste by land burial and

decide what remedial measures, including removal of such soil off-site,

are appropriate before the site can be released for unrestricted use

and the license terminated.''

On August 19, 1996, NRC published Information Notice 96-47

``Recordkeeping, Decommissioning

[[Page 56718]]

Notifications for Disposals of Radioactive Waste by Land Burial

Authorized under Former 10 CFR 20.304, 20.302, and Current 20.2002.''

This notice re-emphasized NRC's position that former burials are

covered under the Timeliness Rule, outlined the decommissioning

schedule required by the rule, and stated that NRC would develop a

screening methodology for assessing former burials.

3.0 Discussion

During decommissioning, NRC will evaluate disposals authorized

under former 10 CFR 20.304 and 20.302, to determine whether they are

acceptable for release for unrestricted use, based on their potential

impact on the health and safety of the public. The acceptability of a

disposal will depend on the potential for significant exposure to

members of the public who may, at some time in the future, develop and

use the disposal site for a private residence, farm, business, or other

purpose.

This methodology is intended to be used by the licensee as a

screening tool to determine which burial sites, in general, are

acceptable for release for unrestricted use, recognizing that

exceptions may be identified by NRC and/or the licensee. This screening

tool will be based on the total activity disposed of in the burial

ground and the potential for that activity to produce a significant

dose to a member of the public. Although this methodology estimates

doses, they are very conservative estimates. Actual doses produced by a

site would be a fraction of the doses estimated using this screening.

For those sites which pass this screening, in general, the staff

will require no further characterization or remediation effort. Those

sites that do not pass the screening would require more detailed

analysis. This may consist of site characterization and dose

assessments by the licensee and NRC. Remediation may also be necessary.

This is not to say that sites that do not pass the screening will be

required to remediate. This process is intended to screen out simple

sites with small inventories. More detailed evaluations can then be

performed for the more complex sites, or sites with unique

circumstances (i.e., no records, or burial located under a building).

It is recognized that spot concentrations in the waste may exceed NRC's

radiological criteria for decommissioning (57 FR 13389, ``Action Plan

to Ensure Timely Cleanup of Site Decommissioning Management Plan

Sites''), but the overall risk to the public is limited by the total

inventory, site characteristics, or other factors. It is also

recognized that these burials may not be the only residual activity

contained at a site. This screening is intended to evaluate the risks

posed by an on-site burial independent of any other evaluations of dose

contributions from other areas of the site. A facility which contains

larger quantities of contamination would be required to complete a site

and facility characterization program and a detailed dose assessment

that accounts for doses from all sources. Because such a site/facility

could conceivably have residual contamination levels that result in

doses that are just below the unrestricted release criterion, it is not

justified to exclude a former burial site or sites. Therefore, this

screening cannot be used for sites that have surface soil or building

contamination outside of what is contained in the burial site and sites

where members of the public would be exposed concurrently to both the

burial and other residual radioactivity. It is restricted for use at

those sites where a former burial is expected to be the only source of

residual contamination at time of decommissioning.

The Timeliness Rule, published August 15, 1994, outlines a schedule

for licensees to follow in performing decommissioning activities and

requires licensees to notify NRC of plans to meet this schedule. It

also requires licensees to decommission portions of their site,

including ``unused outdoor areas,'' which have not been used for a

period of 24 months. These outdoor areas include former 10 CFR 20.304

and 20.302 disposals, and are, therefore, subject to the Timeliness

Rule.

There are several issues associated with the assessment of prior

burials. Many licensees considered these burials to be permanent

disposals at the time of placement. Licensees did not budget the time

nor monetary resources to evaluate these sites at the time of

decommissioning. There is also a concern about the cost benefit of

evaluating these sites for decommissioning. Many universities and

hospitals disposed of small quantities of wastes associated with

research and medical applications. The cost to characterize and

remediate small burials of byproduct materials may outweigh the hazards

avoided. However, some burials may pose greater risks to the public,

such as those containing significant quantities of source and special

nuclear material wastes. At these sites, characterization and/or

remediation may be needed and costs of remediation will be considered

for sites that are below 100 mrem/yr and have an adequate ALARA

analysis. In addition, there are concerns about the quantity and

quality of available disposal records. At the time of decommissioning,

complete records of 10 CFR 20.304 and 20.302 disposals are necessary

for NRC to evaluate the acceptability of the disposals. Former 10 CFR

20.401(c)(3) stated that records of disposals made pursuant to 10 CFR

20.302 and 20.304 should be maintained until NRC authorizes their

disposition. However, for many of the older sites, these records are

scarce or unavailable. The sites that have no burial records, may be

required to evaluate and/or characterize the burials. Then, if NRC

determines that the site does not pose a risk to the public, the site

could be released for unrestricted use. If, however, it is determined

that the site could pose a significant risk, the licensee may be

required to remediate the burial. This analysis is based on the

radiological risks associated with the burial. If the burial areas

require characterization and/or remediation, other applicable local,

state, or federal radiological and non-radiological regulations should

be considered.

To help alleviate some of these concerns, the staff developed this

screening methodology to determine which former burials require

additional characterization and assessment and which burials are

acceptable for unrestricted use. To perform this screening, the

licensee will need a copy of Part 20, Appendix B, and NUREG-1500

``Working Draft Regulatory Guide on Release Criteria for

Decommissioning: NRC Staff's Draft for Comment.'' 1 The NRC will

defer decisions on releasing former burials based on this methodology

until this draft is finalized.

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\1\ NUREGs can be ordered by calling (202) 512-1800.

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4.0 Regulatory Position

4.1 Scope

The methodology of this BTP applies to prior burials of radioactive

material that were buried under 10 CFR 20.304 and 20.302. This

methodology is not intended to be applied to burial sites that are

currently in use or to evaluate former or proposed burials under 10 CFR

20.2002. The final rule on ``Decommissioning Recordkeeping and License

Termination: Documentation Additions,'' was issued on July 26, 1993 (58

FR 39628), and requires a single document listing: (1) All areas

outside restricted areas where current and previous wastes have been

buried, (as documented under 10 CFR 20.2108); and (2) other information

necessary to ensure that decommissioning is carried

[[Page 56719]]

out in accordance with the NRC's regulations. Therefore, for disposals

made pursuant to 10 CFR 20.2002, waste disposal records should be

sufficiently accurate and complete to demonstrate acceptability for

release in accordance with recordkeeping and decommissioning

requirements. In addition, recent approvals of 10 CFR 20.2002 disposal

requests have been based on the assumption that the site would be

released for unrestricted use. Guidance for evaluating these burials is

contained in NUREG-1101, ``Onsite Disposal of Radioactive Waste.'' As

stated previously, this screening is intended to be used for sites in

which the former burial is expected to be the only source of residual

contamination at the time of decommissioning. This screening is based

only on the radiological risks associated with the burial. If the

burial areas require characterization and/or remediation, or contain

hazardous and/or mixed wastes, other applicable local, state, or

Federal radiological and non-radiological regulations should be

considered.

This screening is intended to be used by both the licensee and NRC

to determine the ultimate disposition of the burial ground. Licensees

will perform the screening calculations, NRC staff will review the

calculations and make a final determination if the site passes the

screening. If the NRC's review indicates the site passes the screening,

no further evaluation or characterization of the site will generally be

required. The site can be removed from the license, if that is the wish

of the licensee, and the site will not need to be revisited during

license termination. Those sites that do not pass this screening will

require more detailed analysis to assess potential radiological risks.

The amount of analysis required beyond this screening depends on the

complexity of the site, the amount of available site characterization

information and site characteristics, and will be determined on a case-

by-case basis.

4.2 Screening Methodology

4.2.1 General Approach

This methodology consists of three steps. The first step involves

collecting information on the materials which were buried at the site.

The other two involve conservative dose assessments using this

historical information to determine the possible consequences from

human exposure to the buried material. The Step 2 calculations are

performed first because they require a minimal amount of information

about the site, and are easy to perform. If a site passes Step 2, there

is no need to collect additional information required to perform Step 3

calculations because Step 2 is more conservative. If the site does not

pass Step 2, then Step 3 calculations should be performed. If a site

fails both Steps 2 and 3, this site requires more detailed analysis to

determine whether it poses an unacceptable risk to the public.

4.2.2 Step 1--Records Review

The first step for the licensee should be a review of the burial

records. These records should indicate the activity and types of

isotopes that were disposed of at the site and the time period for

those disposals. All available and relevant records should be used to

develop a complete inventory for the burial area. The total activity of

each isotope in the entire burial site should be determined and

converted into microcuries (Ci). This total inventory should

be adjusted to account for radioactive decay which has occurred since

the time of burial.

It may be difficult to find records for some of the older burials.

Many of these sites may have had several changes in management or

location of record storage, and the records may have been misplaced or

lost. If no records are available, this methodology can be performed

using the original possession limits contained in the license for the

site for the actual or reasonable estimate of time in which the trench

was in operation and estimating the throughput resulting from the

licensed activity during that time. This approach would most likely

overestimate the quantities in the burial site because the activity

disposed of in a burial is typically only a fraction of the activity

allowed to be possessed under the license based on NRC staff

experience. This will only be allowed for estimating the total

inventory for use in Step 2. If there are no records, the trench size

could not be determined, and, therefore, Step 3 could not be

implemented. If using the original possession limits results in not

passing this screening criteria, the licensee should consult with NRC

for case-by-case guidance for evaluating the site. The maximum quantity

that was allowed to be buried in the trenches under rescinded 10 CFR

20.304, Appendix C cannot be used as an estimate for the quantity of

isotopes in the trenches because NRC has identified instances in

decommissioning burial sites where disposal limits were exceeded.

Without some evidence (i.e., disposal records) that these guidelines

were followed, the licensee and NRC can have little confidence in the

trench inventory.

If no records are available and the use of license limits result in

a failure at Step 2, the licensee can take some intrusive samples of

the burial ground to determine the general type and concentration of

isotopes at the site and then perform this screening. The level of

characterization necessary (i.e., number of samples) will be determined

on a case-by-case basis in consultation with NRC staff. NRC draft

``Branch Technical Position on Site Characterization for

Decommissioning Sites,'' dated November 1994, contains a description of

the type of site characterization information that could be required.

After Step 1 is complete and the total activity for each isotope in the

burial site is estimated, the licensee should continue with Step 2.

4.2.3 Step 2--Groundwater Pathway

Following the general screening model approach described in NCRPM

Report No. 123, this step assumes that the total activity for each

isotope is leached into the minimum quantity of water needed to meet a

family of four's average use in one-year (91 m\3\). Therefore, the

activity of each isotope (after decay) should be divided by 9.1E7

milliliters (ml) to obtain a concentration (C) for each isotope as

follows:

[GRAPHIC] [TIFF OMITTED] TN04NO96.011

The concentration of each isotope can be compared to the effluent

release criteria contained in Part 20, Appendix B, Table 2, Column 2

for water. The concentrations contained in this table are estimated to

produce a dose of approximately 50 mrem/yr assuming an individual

consumes 2 liters/day. Because Appendix B lists concentrations in

Ci/ml for isotopes which result in a dose of 50 mrem, this

concentration/dose ratio can be used to estimate the dose produced from

a different concentration of that isotope. The potential dose from the

estimated concentration for the isotopes in the burial can be estimated

as follows:

[GRAPHIC] [TIFF OMITTED] TN04NO96.012

where:

C=the concentration of a burial site isotope in groundwater

Ci/ml;

B=the Appendix B, Table 2, Col. 2 concentration for the same isotope;

and

D=the dose from exposure to this isotope.

This calculation should be performed for all isotopes in the burial

site. After the doses are estimated for each isotope,

[[Page 56720]]

the doses should be totaled. If the total dose is less than the 100

mrem/yr screening level, the site passes Step 2 and, in general, the

site will require no additional evaluations. If the dose is greater

than the 100 mrem/yr screening level, then the analyses of Step 3

should be performed.

Note: Step 3 CANNOT be used for isotopes with atomic numbers of

88 or higher. Step 3 uses draft NUREG-1500, which is currently

undergoing revisions for these isotopes. If a site contains these

isotopes, licensees should consult with NRC staff for case-by-case

guidance for evaluating these sites. If a site passes Step 2, then

it passes the screening. If a site contains isotopes with atomic

weight greater than 88, and it fails Step 2, then the site fails the

screening and must be evaluated on a case-by-case basis.

4.2.4 Step 3--Exhumation Concentration

In this step, it is assumed that the total inventory of the site is

evenly distributed throughout the burial trenches. Most burial sites

consist of several burial trenches located at the same site. The

activity of each isotope should be divided by the total grams of

material in the trenches. This will produce a trench concentration

(Ci/gram of waste) for each isotope. This calculation should

only consider the specific burial area containing the waste and

contaminated soils. It should not include the soil cap, if one is

present, or the 6 feet of clean soil which was required to be placed

between burials conducted under the provisions of 10 CFR 20.304. For

example, if a 100 m\3\ site contained 6 burial trenches with each one

having a volume of 10 m\3\, the total inventory would be assumed to be

evenly distributed over the volume of the trenches (60 m\3\), not the

volume of the site (100 m\3\). For sites where the volume of the

trenches cannot be reasonably determined, licensees should consult with

NRC staff for case-by-case guidance for evaluating these sites.

This step of the methodology assumes that a member of the public

builds a house directly on the burial site. The Draft Environmental

Impact Statement developed for 10 CFR Part 61, ``Licensing Requirements

for Land Disposal of Radioactive Waste,'' dated September 1981 (NUREG-

0782), contains information concerning the dilution of waste caused by

exhumation of a building foundation. Appendix G of NUREG-0782 contains

the inadvertent intruder scenario and states that the waste

concentration should be reduced by a factor of 4 to account for

dilution during excavation (the contaminated material would be mixed

with the clean cover material as well as the clean soil surrounding the

burial). This concentration should be converted into picocuries per

gram (pCi/g) for comparison with NUREG-1500 values. NUREG-1500,

Appendix A, Table A-1, ``Total Dose'' column contains the total dose

calculated using a residential scenario, with default assumptions, and

is based on 1 Pci/g of an isotope. To calculate a screening dose for

the burial site, the above calculated exhumed concentration can be

multiplied by the Appendix A values.

[GRAPHIC] [TIFF OMITTED] TN04NO96.013

where

C=the concentration of a single isotope in the burial ground;

A=the NUREG-1500 Appendix A, Table A-1 dose for the same isotope; and

D=the dose from exposure to this isotope.

This calculation should be performed for all isotopes in the burial

site. After the doses are estimated for each isotope, the doses should

be totaled. If the total estimated dose is less than the 100 mrem/yr

screening level, the site passes the screening and no further analysis

is generally necessary for the site; however, extenuating circumstances

may warrant further review. If the estimated dose is greater than 100

mrem/yr screening level, the site fails this screening analysis and the

licensee will be required to perform additional site-specific analyses

(Section 4.3.5). Example calculations are provided in Appendix C.

4.2.5 Results

If the site passes one of the steps above, the site would generally

not require any further characterization or remediation. The licensee

should submit the results of this screening, including a description of

the site, as known, and copies of the calculations performed for this

screening. This should be submitted to NRC, along with a statement

concerning the licensee's intention to take no further actions at the

site. In accordance with recordkeeping requirements, the licensee will

be required to maintain these records until the NRC authorizes their

disposal. Assuming that the licensee submitted the notification and

analysis in a timely manner (as described in IN 96-47), NRC would then

issue a letter stating that the licensee has complied with the

Timeliness Rule and that the former burial is suitable for unrestricted

release. It will then be determined by NRC and the licensee when the

burial site would be released. This BTP is intended to be a final

evaluation for former burials. Decisions made based on this BTP are not

expected to change because of the issuance of future rules such as

NRC's radiological criteria for license termination.

There may be instances where the licensee's calculations indicate

the site passes the screening, but NRC determines the site requires

more evaluation to consider additional hazards that may be associated

with the waste. This would include sites which contain both radioactive

and hazardous wastes. This methodology may determine the site is

suitable for release based on the radioactive materials alone. However,

the presence of hazardous chemical wastes may warrant additional

evaluation to ensure protection of the public and the environment. This

could also include sites where it is known the burial will be excavated

in the future (i.e., the burial is in the path for a future road),

sites with very limited burial records, and sites where there is other

residual contamination outside of the burial area.

If the site fails Step 3 above, the licensee will be required to

perform more specific characterization of the site. The details of the

characterization process and the level of detail required will be

determined on a case-by-case basis. NRC draft ``Branch Technical

Position on Site Characterization for Decommissioning Sites,'' dated

November 1994, contains a description of the type of site

characterization information that could be required. In some cases, if

the characterization information indicates that total activity in the

burial site is less than the activity originally used in the screening

method, this more realistic total activity can be used in the screening

methodology. If the site then passes the screening using this new

activity, the site would not require further evaluation. If the site

fails again, then the licensee will have to work with NRC staff to

develop a plan for additional actions to be taken at the site.

Evaluations beyond this methodology may require site characterization

information and a dose assessment. More detailed assessment of the

environmental transport and potential doses should be conducted in

accordance with Policy and Guidance Directive PG-8-08, ``Scenarios for

Assessing Potential Doses Associated with Residual Radioactivity.'' In

such cases, sites will be acceptable for unrestricted release, if

projected doses are a small fraction of 100 mrem/yr and ALARA,

considering corrective actions. The staff will consider the magnitude

of the projected dose, and existing radiological criteria for

decommissioning, in conjunction with

[[Page 56721]]

the objectives of keeping residual contamination levels ALARA, to

determine if the waste may pose a significant risk to the public and

the burial requires remediation.

It should be noted that the results of this screening are most

affected by the quantity and quality of the records available to

determine total inventory, and the assumptions used in determining the

trench concentration. Slight variations in the trench size could be the

difference between a site failing or passing the methodology.

4.3 Dose Screening Level and Basis

This methodology uses the public dose limit of 100 mrem/yr in Part

20 as a screening level for determining if a site poses a significant

risk to the public. Although this is higher than the dose levels

previously imposed for on-site burials (i.e., a few mrem/yr), the staff

believes this is appropriate for screening these sites because of the

high degree of conservatism built into the methodology and limitations

of existing information.

Following the general screening model approach described in the

National Council on Radiation Protection and Measurements (NCRPM)

Report No. 123, dated January 22, 1996, Step 2 of this methodology

assumes the total inventory in the burial ground is leached into the

minimum quantity of water needed to meet the average water use of a

family of four for 1 year (91 m\3\). The dose is then calculated

assuming an individual member of the family drank 2 liters/day of the

91 m\3\ for 1 year. The use of 91 m\3\ is also the screening default

value used in NUREG/CR-5512, ``Residual Radioactive Contamination From

Decommissioning'' (Table 6.22).

NRC staff analysis in NUREG-1500, Table A-1 contains estimated

annual total effective dose equivalent factors. These dose factors

indicate that there are cases, in which the inhalation of an isotope in

a residential scenario would produce a larger dose than the ingestion

of an equal amount of activity. It also indicates that the direct

exposure pathway for some isotopes may be more limiting than either the

ingestion or inhalation pathway. However, Appendix A, of this BTP,

contains an analysis which demonstrates that the ingestion scenario, as

used in this methodology, is so restrictive that inhalation and direct

exposure calculations are not necessary.

The staff considers the assumptions used in this ingestion scenario

to overestimate likely doses to potential members of the public, such

as: (1) There has been no migration from the burial so that the total

inventory originally placed in the burial remains; (2) the entire

inventory leaches into the groundwater in a one-year period; (3)

someone moves onto the site, and places a well near the burial ground

that would capture all of the contaminated water; (4) there is no

sorption of the radionuclide during transport and only limited dilution

and dispersion; (5) a single individual drinks only well water from the

site for that year. As shown in the example given later in this

section, more likely doses to a hypothetical individual would be a

small fraction of the doses estimated in this methodology and would

likely be in the range of a few millirem per year if the dose using

this methodology is less than 100 mrem/yr.

Step 3 of this methodology assumes that a farmer lives on top of

the burial ground at some point in the future. This scenario also

contains several conservative assumptions such as: (1) There has been

no migration from the burial so that the total inventory originally

placed in the burial remains; (2) that an intruder inadvertently digs

into the waste and brings the entire inventory to the surface; and (3)

the intruder fails to recognize the waste. These are assumptions used

in developing the exhumed concentrations. There are also several

conservative assumptions contained in the dose conversion factors

developed for soils in NUREG-1500, which are used in this step to

estimate screening doses.

NUREG-1500 uses a family farm scenario, in which an individual

lives on the site, drinks water from an on-site well, and ingests 25

percent of his/her food from a garden, on-site. The resident's house

and garden are assumed to be in the contaminated area, and the garden

alone is assumed to be 2500 m\2\ (NUREG/CR-5512, Table 6.23).

Therefore, to contain the house and garden, the contaminated area has

to be larger than 2500 m\2\. Many of the on-site disposals that have

been reviewed by NRC in the past have had areas less than 2500 m\2\.

These sites are generally too small to contain a house and a garden,

and, since they are smaller than those used in NUREG-1500, would likely

produce a smaller dose than predicted using NUREG-1500 values.

Therefore, based on the conservative assumptions used in both

estimating the soil concentration, and estimating the doses, the actual

doses produced from a site are expected to be a small fraction of the

screening doses predicted using this methodology.

The following example of a Cs-134 burial is used to illustrate the

level of conservatism in these scenarios. Assuming a burial contains

270 Ci 2 of Cs-134, the resulting dose for the ingestion

scenario in Step 2 equals approximately 160 mrem/yr. If this same

inventory is evenly distributed in a trench which is 5m x 2m x 1m, the

exhumation concentration is calculated to be 4.2 pCi/g Cs-134 based on

Step 3. Using NUREG-1500, this results in a dose of approximately 13

mrem/yr. As an independent check, a RESRAD analysis was also performed

using a concentration of 4.2 pCi/g Cs-134 and a contaminated zone area

of 5m x 2m, but no other site specific information. This analysis

produced a dose of 7 mrem/yr (assuming no soil cover and that the

groundwater was within 2 meters of the bottom of the burial).

Therefore, although the scenarios in this methodology can predict

elevated doses, they are only for screening purposes and do not

necessarily reflect actual doses which could be produced from the site.

The projected doses calculated using a more rigorous approach are a

small fraction of 100 mrem/yr screening level.

---------------------------------------------------------------------------

\2\ NRC's standard metrification policy is to place metric units

first, followed by non-metric units in parentheses. However, the

supporting tables for this BTP (i.e., 10 CFR Part 20, Appendix B)

are presented in non-metric units, therefore, for comparison

purposes non-metric units are used in this BTP. A conversion table

is contained in Appendix B.

---------------------------------------------------------------------------

Appendix A--Analysis of Other Pathways

There are only a limited number of isotopes for which the

inhalation pathway is more limiting than the ingestion pathway for the

residential scenario in NUREG-1500, Appendix A, Table A-1. For all of

these, however, the direct exposure pathway is even more limiting than

either the inhalation or ingestion pathways. The staff created the

ingestion pathway scenario used in this methodology to be so

restrictive, that even for isotopes which are primarily an external

hazard (e.g., Co-60), the dose produced, based on ingestion, is higher

than one produced using an external scenario, as in NUREG-1500.

Based on calculations performed using Step 3 of this BTP and the

RESRAD, version 5.1, the dose modeling code, Step 2 of this methodology

produces a higher screening dose, and, therefore, is more restrictive

than the other two methods. Since both Step 3 and RESRAD consider all

pathways, including direct exposure, in the dose calculations, if Step

2 doses are high then the other pathways do not need to be considered

independently. To demonstrate this, it was assumed that there was a

burial trench which

[[Page 56722]]

contained a total activity of 270 Ci of Co-60. Co-60 was

chosen because NUREG-1500 indicates it produces the largest external

dose per pCi/g. It was assumed that the entire inventory of the burial

was contained in a relatively small trench, with an area of 10 m2

and depth of 1 meter. This area was used to be consistent with the

contaminated zone area used in the Step 3 screening of this BTP. It was

assumed that the groundwater was within 1 meter of the bottom of the

burial, and that there was no cover on the material. If the total

activity is used in Step 2, a screening dose of 48 mrem/yr is

estimated. Step 3 of the screening estimates a dose of approximately 40

mrem/yr, and a RESRAD analysis predicts 18 mrem/yr. A RESRAD analysis

using more site specific parameters (i.e., cover thickness, depth to

groundwater) would likely reduce this dose even further.

Appendix B--Metric Conversion Table

----------------------------------------------------------------------------------------------------------------

Quantity From To metric Multiply by

----------------------------------------------------------------------------------------------------------------

Activity............................ Ci (curie).................. MBq (becquerel)............. 37,000.0

Dose equivalent..................... rem......................... Sv (sievert)................ 0.01

Length.............................. ft (feet)................... m (meter)................... 0.3048

Volume.............................. ft3......................... m3.......................... 0.02831685

Volume.............................. gal (gallon)................ L (liter)................... 3.785412

----------------------------------------------------------------------------------------------------------------

Appendix C--Sample Calculations

1.0 Example Site No.1

This site contains 1-3 animal carcasses that were tagged with 41

millicuries (mCi) Cs-134, 10.5 Mci Fe-55, 60 Mci Zn-65, 2.7 Mci Co-60

and 25 Mci I-125. These animals were placed in a 5m x 2m x 1m burial

pit in 1980.

1.1 Step 1--Records Review

No burial records were available to determine how many of the

tagged animals were placed in the pits. There were records on the

number of animals tagged, and the maximum activity that was used to tag

these animals. Therefore, the maximum activity of each isotope was used

to estimate the total inventory. The burial has been in place for 15

years, which is sufficient time for Zn-65 and I-125 to decay to

insignificant activities. Therefore, they can be excluded from

consideration. The calculated activities for the remaining isotopes are

adjusted for decay.

------------------------------------------------------------------------

Isotope Ci

------------------------------------------------------------------------

Cs-134..................................................... 270

Fe-55...................................................... 233

Co-60...................................................... 376

------------------------------------------------------------------------

1.2 Step 2--Groundwater Pathway

The total inventory for each isotope was divided by 9.1E7 ml (91

m3) of groundwater. This represents the concentration in Ci/ml

of that isotope which could be ingested by a person in 1 year.

------------------------------------------------------------------------

Isotope Ci Ci/ml(water)

------------------------------------------------------------------------

Cs-134............................ 270 2.9E-6.

Fe-55............................. 233 2.5E-6.

Co-60............................. 376 4.1E-6.

------------------------------------------------------------------------

This concentration was then compared to Part 20, Appendix B, Column

2, limits. These limits represent concentrations in effluent releases

which could cause doses of approximately 50 mrem/yr assuming ingestion

of 2 liters per day. The Appendix B ratio of concentration to dose was

used to determine roughly the dose that could be produced from the

waste concentrations in groundwater. For example,

[GRAPHIC] [TIFF OMITTED] TN04NO96.014

161 mrem/yr from Cs-134

This calculation was preformed for the remaining two isotopes and

the results are included in the following table.

Appendix B

----------------------------------------------------------------------------------------------------------------

Ci/

Isotope Ci Ci/ ml/50 mrem/ mrem/yr

ml yr

----------------------------------------------------------------------------------------------------------------

Cs-134....................................................... 270 2.9E-6 9E-7 161

Fe-55........................................................ 233 2.5E-6 1E-4 1.25

Co-60........................................................ 376 4.1E-6 3E-6 68

----------------------------------------------------------------------------------------------------------------

The doses were summed and the result was a dose of over 230 mrem/

yr. This dose exceeds the 100 mrem/yr screening level, and, therefore,

this site fails Step 2 of the screening methodology. Since this burial

did not contain any isotopes greater than atomic number 88, Step 3 was

performed.

1.3 Step 3--Exhumation Concentration

In this step, the total inventory was averaged over the volume of

the burial ground, which is 5 m x 2 m and 1 meter deep or equivalent to

1.6E7 grams of waste and soil assuming a soil density of 1.6 g/cm3 to

determine an average concentration (activity per cm3). This

concentration is then converted into pCi/g for comparison with NUREG-

1500 values in Table A-1 and divided by 4 to represent expected

dilution from cover material and clean soil on the sides during

exhumation.

[[Page 56723]]

[GRAPHIC] [TIFF OMITTED] TN04NO96.015

Trench Concentration = 17 pCi/gram

[GRAPHIC] [TIFF OMITTED] TN04NO96.016

Exhumation Concentration = 4.2 pCi/g

------------------------------------------------------------------------

Isotope pCi pCi/gram

------------------------------------------------------------------------

Cs-134.............................. 2.7E8.................. 4.2

Fe-55............................... 2.3E8.................. 3.5

Co-60............................... 3.8E8.................. 5.7

------------------------------------------------------------------------

These concentrations were then compared to NUREG-1500 values in

Table A-1, Column 9, for the total dose in mrem/yr, as follows:

D mrem/yr = (4.2 pCi/g Cs-134)(3.06 mrem/yr), where NUREG-1500

relates 3.06 mrem/yr to 1 pCi/g Cs-134

D = 12.8 mrem/yr from Cs-134

This calculation was performed for the remaining two isotopes, and

the results are summarized in the following table.

NUREG-1500

----------------------------------------------------------------------------------------------------------------

mrem/yr/pCi/

Isotope pCi pCi/gram g mrem/yr

----------------------------------------------------------------------------------------------------------------

Cs-134.......................................................... 2.7E8 4.2 3.06 12.8

Fe-55........................................................... 2.3E8 3.5 1.65E-3 0.006

Co-60........................................................... 3.8E8 5.7 5.06 28.78

----------------------------------------------------------------------------------------------------------------

Based on the above calculations, the total dose is approximately 40

mrem/yr and is less than 100 mrem/yr. Therefore, this site passes

screening Step 3 and does not require any further characterization nor

remediation.

2.0 Example Site No. 2

This site contains process waste from the manufacture of uranium

fuel. The burial contains approximately 3 curies of uranium in several

trenches. The material was placed in trenches throughout the 1960s.

2.1 Step 1--Records Review

Burial records were available and reviewed to determine that

approximately 3 curies of uranium were disposed of in trenches. For

this example, it was assumed that there was 0.5 curies of U-234 and 2.5

curies U-238. Approximately 27 years have passed since the time of the

last burial, which is insufficient time for either uranium to have

decayed. Therefore, they cannot be excluded from consideration, and the

calculations will be performed with the quantities cited above.

------------------------------------------------------------------------

Isotope Ci

------------------------------------------------------------------------

U-234...................................................... 5E5

U-238...................................................... 2.5E6

------------------------------------------------------------------------

2.2 Step 2--Total Activity Ingested From Groundwater

The total inventory for each isotope was divided by 9.1E7 ml (91

m3) of groundwater. This represents the concentration in Ci/ml

of that isotope that could be ingested by a person in 1 year.

------------------------------------------------------------------------

Ci/

Isotope Ci ml

------------------------------------------------------------------------

U-234........................................ 5E5 0.005

U-238........................................ 2.5E6 0.027

------------------------------------------------------------------------

This concentration was then compared to Part 20, Appendix B, Column

2, limits. These limits represent concentrations in effluent releases

that could cause doses of approximately 50 mrem/yr. The Appendix B

ratio of concentration to dose was used to determine, roughly, the dose

that could be produced from the waste concentrations in groundwater.

For example,

[GRAPHIC] [TIFF OMITTED] TN04NO96.017

8E5 mrem/yr from U-234

This calculation was performed for the remaining two isotopes, and

the results are included in the following table.

----------------------------------------------------------------------------------------------------------------

App B Ci Ci/ m>Ci/ml mrem/yr

ml

----------------------------------------------------------------------------------------------------------------

U-234........................................................ 5E5 0.005 3E-7 8E5

U-238........................................................ 2.5E6 0.027 3E-7 4.5E6

----------------------------------------------------------------------------------------------------------------

[[Page 56724]]

The doses are well over the 100 mrem/yr screening level, and,

therefore, this site fails Step 2 of the screening methodology.

2.3 Step 3--Exhumation Concentration

This site contains isotopes that have atomic numbers greater than

88, and, therefore, cannot be used in Step 3. Since this site failed

Step 2 and cannot be used in Step 3, this site fails this screening

methodology.

[FR Doc. 96-28223 Filed 11-01-96; 8:45 am]

BILLING CODE 7590-01-P