RISK-BASED MINIMUM DETECTABLE CONCENTRATIONS

FOR RADIOLOGICAL ANALYSES OF ENVIRONMENTAL MEDIA

AT THE SAVANNAH RIVER SITE

 

 

G. Timothy Jannik,1 B.S. Crandall,2 and P.D. Fledderman1

 

1Westinghouse Savannah River Company

Savannah River Site

Aiken, SC  29808

 

2Severn Trent Laboratories St. Louis

13715 Rider Trail North

Earth City, MO  63045

 

 

 

EXTENDED ABSTRACT

 

 

Other than for drinking water, there is no definitive guidance in existing federal or state regulations concerning the appropriate minimum detectable concentrations (MDCs) that should be achieved for radiological analysis of environmental media.

 

At the Savannah River Site (SRS), it has been proposed that, where realistically achievable, MDCs for environmental samples should be risk based. It also has been proposed that MDCs for various environmental media be no more than the concentration that equates to a potential lifetime risk of 1E-06.

 

Calculations have been performed to determine radionuclide concentrations in environmental media that equated to this lifetime risk by using

 

1)      applicable and reasonable pathways to man

2)      maximally exposed individual usage rates appropriate for the SRS area

3)      U.S. Department of Energy (DOE) approved dose factors (DOE, 1988)

4)      dose-to-risk factors from the International Commission on Radiological Protection

5)      a 30-year exposure time

 

This technical presentation describes the process used to determine appropriate MDCs for selected environmental media. Also, a comparison of the risk-based MDCs to the SRS Environmental Monitoring Section’s (EMS’s) existing environmental media MDCs is discussed.

 

Exposure Pathways and Usage Parameters

 

At SRS, the principal pathways (Jannik, 1996) by which offsite people may be exposed to released radionuclides are

•     inhalation

•     ingestion of water and food

 

The maximally exposed individual usage parameters applicable to the SRS area are provided in Table 1.

 

Table 1

 

Maximally Exposed Individual Usage Parameters for the SRS Area

 

Parameter

Value

Inhalation*

8,000 (m3/y)

 

 

Ingestion**

 

Cow milk

230 (L/y)

Meat

81 (kg/y)

Leafy vegetables

43 (kg/y)

Drinking Water

730 (L/y)

Fish

19 (kg/y)

 

*              From Regulatory Guide 1.109 (NRC, 1977)

**           From Hamby, 1991

 

 

Risk to Dose to Concentration Calculations

 

Radionuclide concentrations that equate to a total, lifetime, stochastic risk of 1E-06 have been estimated using the total risk coefficient developed by the ICRP in its Publication 60 (ICRP, 1990).

 

The ICRP-60 total-risk coefficient, which is 7.3E-07 per mrem, includes factors for 

 

•   fatal cancers (5.0E-07 per mrem)

 

•   nonfatal cancers (1.0E-07 per mrem)

 

•   hereditary effects (1.3E-07 per mrem)

 

According to risk assessment guidance provided by the U.S. Environmental Protection Agency (EPA) (EPA, 1991), the upper bound value of 30 years has been used to determine lifetime risks. 


 

By using these parameters, the annual dose that equates to a lifetime risk of 1E-06 has been determined as follows:

 

 

 

The annual average radionuclide concentrations in various environmental media, which equate to a dose of 0.05 mrem per year, have been determined using the applicable DOE dose factors and the maximally exposed individual usage parameters shown in Table 1.

 

The following equation shows a sample calculation for cesium-137 in fish;

 

 

 

 

Comparison to Existing MDCs

 

For each environmental medium sampled by EMS, risk-based radionuclide MDCs have been determined and compared to the existing EMS MDCs. Using the previous example, the risk-based MDC for cesium-137 in fish is 0.05 pCi/g. The existing EMS MDC for cesium-137 in fish is 0.04 pCi/g, which compares favorably (Arnett, 2000).

 

However, several risk-based MDCs were determined to be less than the existing EMS MDCs, which indicates that improvements in analytical methods may be required. In some cases, for the standard analytical methods employed by EMS, the risk-based MDCs were determined to be less than technically and/or reasonably achievable MDCs. In these cases, the reasonably achievable MDC will be left as is.   

 

 

References:

 

Arnett, M.W, and A.R. Mamatey, eds., Savannah River Site Environmental Data for 1999, WSRC-TR-99-00301, Savannah River Site, Aiken, SC, 2000.

 

Hamby, D.M., Land and Water Use Characteristics in the Vicinity of the Savannah River Site, WSRC-MS-91-17, Savannah River Technology Center, Aiken, SC, 1991.

 

International Commission on Radiological Protection, Recommendations of the ICRP, Publication 60, Elmsford, NY, 1990.

 

Jannik, G.T., Critical Radionuclide/Critical Pathway Analysis for the U.S. Department of Energy’s Savannah River Site, Risk Analysis, Volume 19, No 3, p. 417, McLean, VA, 1999.

 

U.S. Department of Energy,  External and Internal Dose Conversion Factors for Calculation of Dose to the Public, DOE/EH-0070 & 71, Washington, DC, 1988.

 

U.S. Environmental Protection Agency,  Risk Assessment Guidance for Superfund, Volume I, Human Health Evaluation Manual Supplemental Guidance “Standard Default Exposure Factors,” OSWER Directive: 9285.6-03, Washington, DC, 1991.

 

U.S. Nuclear Regulatory Commission, Calculation of Annual Doses to Man from Routine Releases of Reactor Effluents for the Purpose of Evaluating Compliance with 10 CFR 50, Appendix I, Regulatory Guide 1.109, Washington, DC, 1977.

 

 

 

Prepared for the U.S. Department of Energy in connection with work under contract #DE-AC09-96SR18500