Derivation of Dose-Based Detection Limits for Drinking Water and Effluent Compliance Ken Sejkora Entergy Nuclear Northeast – Pilgrim Station Presented at the 17 th Annual RETS-REMP Workshop Philadelphia, PA / June 2007

Reason for Concern NRC vs. EPA … different limits due to: Age-specific differences Ingestion rates Dose models and dose factors – ICRP-2 vs. ICRP-30 Total body vs. Critical Organ Various limits exist governing effluent compliance, safe drinking water standards, and dose/risk assessment

Basis for Detection Limit Based on equal dose consequence?? Approach used by EPA for drinking water standard Based on argument of “reasonable survey”?? Loose basis of current ODCM LLD requirements What’s reasonable… 1 hour analysis? 8 hour analysis? Radiochemical separation? Dose is a common denominator representative of risk, and should be used as basis, but reasonableness should be considered in cases of extremely low LLDs.

NRC Effluent Concentration Limits Specified in Appendix B to Part 20-- Annual Limits on Intake (ALIs) and Derived Air Concentrations (DACs) of Radionuclides for Occupational Exposure; Effluent Concentrations; Concentrations for Release to Sewerage Derived from ICRP-30 dose models, adult age class Committed dose of 100 mrem/yr for public Preamble to Effluent Concentration Limit Tables “Consideration of non-stochastic limits has not been included in deriving the air and water effluent concentration limits because non-stochastic effects are presumed not to occur at the dose levels established for individual members of the public.”

EPA Drinking Water Standard Specified in 40 CFR Refer to: Committed dose of 4 mrem/yr Based on drinking water consumption of 2 liters/day = 730 liters/yr H-3 = 20,000 pCi/L Sr-90 = 8 pCi/L

EPA Drinking Water Standard … where did it come from? Roots in ICRP-2, circa late 1950s Based on NRC maximum permissible concentration (MPC) value, where 1 MPC = 500 mrem/yr total body… “second generation derivative” Step 1: Dose Conversion Factor = mrem/pCi Step 2: Max perm. Intake = pCi to yield 4 mrem/yr Step 3: Max perm. Conc. = pCi/L to yield intake of MPI, assuming ingestion rate of 730 L/yr

EPA Drinking Water Standard …why it’s important Standard limit adopted by state regulatory agencies… often takes precedence over ODCM limits if groundwater is involved Used as basis for tables in standard ODCM guidance – NUREG-1301/1302 Table , “Reporting Levels”… 20,000 pCi/L for drinking water; 30,000 pCi/L for non-DW Table , “Lower Limit of Detection”… set at 1/10 of Reporting Level = 2,000 pCi/L for DW; 3,000 pCi/L for non-DW.

Other ICRP-2 based Factors Regulatory Guide 1.109, age-specific DCFs LADTAP Factors… refinement of RG factors RG and LADTAP dose conversion factors are the de facto values used in most plants’ ODCMs, effluent control programs, and effluent dose calculation software

ICRP-30 based Factors Based on ICRP-26 “standard man” approach, occupational exposure… circa early 1970s Single age class = adult male Basis for current values in 10CFR20 Appendix B, and EPA Federal Guidance Report 11

ICRP-60/72 Factors Based on ICRP-60 metabolic models… most modern, circa late 1990s Non-occupational exposure, latest risk quality factors, multiple age classes Standard among international community, but not widely adopted in USA, nor endorsed by NRC; however, adopted in EPA FGR-13

Deriving dose-based LLD: Body Step 1: Dose Factors Age-specific factors from LADTAP Total Body Dose Factors = mrem/pCi Ingested NuclideAdultTeenChildInfantICRP-30 H-35.99E E E E E-08 Mn E E E E E-06 Co E E E E E-05 Sr E E E E E-04 Cs E E E E E-05

Deriving dose-based LLD: Body Step 2: Maximum Permissible Intake pCi/yr intake to yield on 1 mrem/yr Total Body Dose 25% of EPA “dose limit” of 4 mrem/yr; easy to scale NuclideAdultTeenChildInfantICRP-30 H-31.7E E+065.7E+061.6E+07 Mn-541.1E+068.5E+053.5E+052.2E+053.6E+05 Co-602.1E+051.6E+056.4E+043.9E+043.7E+04 Sr-905.7E+034.9E+031.9E+031.7E+037.0E+03 Cs E+041.9E+042.2E+042.3E+042.0E+04

Deriving dose-based LLD: Body Step 3: Drinking Water Concentration Adult=730 L/yr; Teen/Child=510 L/yr; Infant=330 L/yr pCi/L to yield 1 mrem/yr Total Body Dose NuclideAdultTeenChildInfantICRP-30 H-32.3E+043.2E+041.7E E+04 Mn-541.6E+031.7E+036.9E+026.7E+024.9E+02 Co-602.9E+023.1E+021.3E+021.2E+025.1E+01 Sr-907.8E+009.6E+003.8E+005.3E+009.6E+00 Cs E+013.8E+014.2E+017.0E+012.7E+01

Deriving dose-based LLD: Organ Step 1: Dose Factors Age-specific factors from LADTAP Maximum Organ Dose Factors = mrem/pCi Ingested NuclideAdultTeenChildInfantICRP-30 H-35.99E E E E E-08 Mn E E E E E-06 Co E E E E E-05 Sr E E E E E-03 Cs E E E E E-05

Deriving dose-based LLD: Organ Step 2: Maximum Permissible Intake pCi/yr intake to yield 1 mrem/yr Maximum Organ Dose 25% of EPA “dose limit” of 4 mrem/yr; easy to scale NuclideAdultTeenChildInfantICRP-30 H-31.7E E+065.7E+061.6E+07 Mn-547.1E+048.3E+049.3E+045.0E+041.2E+05 Co-602.5E+042.7E+043.4E+043.9E+042.0E+04 Sr-901.1E+029.8E+013.9E+013.5E+016.5E+02 Cs E+036.7E+033.1E+031.6E+031.8E+04

Deriving dose-based LLD: Organ Step 3: Drinking Water Concentration Adult=730 L/yr; Teen/Child=510 L/yr; Infant=330 L/yr pCi/L to yield 1 mrem/yr Maximum Organ Dose NuclideAdultTeenChildInfantICRP-30 H-32.3E+043.2E+041.7E E+04 Mn-549.8E+011.6E+021.8E+021.5E+021.7E+02 Co-603.4E+015.4E+016.7E+011.2E+022.7E+01 Sr-901.6E-011.9E-017.7E-021.1E-018.8E-01 Cs E E+005.0E+002.5E+01

Comparison of Derived Concentrations Total Body vs. Maximum Organ pCi/L to yield 1 mrem/yr Dose Consequence Most-limiting concentration based on LADTAP DCFs NuclideTotal BodyMaximum OrganRatio H-31.7E E+00 Mn-546.7E+029.8E+016.9E+00 Co-601.2E+023.4E+013.5E+00 Sr-903.8E+007.7E-025.0E+01 Cs E+015.0E+003.9E+00

Comparison of Derived Concentrations Total Body vs. Maximum Organ pCi/L to yield 1 mrem/yr Dose Consequence Most-limiting concentration based on ICRP-30 DCFs NuclideTotal BodyMaximum OrganRatio H-32.1E E+00 Mn-544.9E+021.7E+022.9E+00 Co-605.1E+012.7E+011.9E+00 Sr-909.6E+008.8E-011.1E+01 Cs E+012.5E+011.1E+00

EPA vs. NRC Approach EPA drinking water approach only addresses intake and dose from drinking water ingestion NRC RG approach assumes multiple pathways: Drinking water ingestion Fish and shellfish ingestion Shoreline sediment Food crop ingestion from irrigated plants Animal product ingestion… milk, meat Far-field dilution… dose consequence based on concentrations at location of exposed receptor, instead of concentrations at point of discharge How much dose are we missing?

Deriving Total Pathway Dose Factors Use Reg Guide approach and pathways, assuming freshwater lake Assume irrigation 50% of year Assume concentration of 1 pCi/L in water, derive corresponding concentration in each pathway media type Apply age-specific usage factors to each pathway media type Determine age-specific dose from each pathway media type

Combined Pathway Dose Adult Total Body Adult Dose Factor - mrem/yr/pCi/L PathwayH-3Mn-54Co-60Sr-90Cs-137 Sediment0.00E E E E E-03 Water4.37E E E E E-02 Aquatic Food1.40E E E E E+00 Crops3.50E E E E E-01 Milk1.86E E E E E-01 Meat6.59E E E E E-02 Total1.05E E E E E+00 Total/Water

Combined Pathway Dose Teen Total Body Teen Dose Factor - mrem/yr/pCi/L PathwayH-3Mn-54Co-60Sr-90Cs-137 Sediment0.00E E E E E-02 Water3.08E E E E E-02 Aquatic Food1.08E E E E E+00 Crops4.06E E E E E-01 Milk2.42E E E E E-01 Meat3.93E E E E E-02 Total1.01E E E E E+00 Total/Water

Combined Pathway Dose Child Total Body Child Dose Factor - mrem/yr/pCi/L PathwayH-3Mn-54Co-60Sr-90Cs-137 Sediment0.00E E E E E-03 Water5.92E E E E E-02 Aquatic Food8.98E E E E E-01 Crops6.33E E E E E-01 Milk3.83E E E E E-01 Meat4.76E E E E E-02 Total1.66E E E E E+00 Total/Water

Combined Pathway Dose Infant Total Body Infant Dose Factor - mrem/yr/pCi/L PathwayH-3Mn-54Co-60Sr-90Cs-137 Sediment0.00E+00 Water5.81E E E E E-02 Aquatic Food0.00E+00 Crops0.00E+00 Milk5.81E E E E E-01 Meat0.00E+00 Total1.16E E E E E-01 Total/Water

Combined Pathway Dose ICRP-30 Adult Total Body ICRP-30 Adult Dose Factor - mrem/yr/pCi/L PathwayH-3Mn-54Co-60Sr-90Cs-137 Sediment0.00E E E E E-03 Water4.67E E E E E-02 Aquatic Food1.50E E E E E+00 Crops3.74E E E E E-01 Milk1.98E E E E E-01 Meat7.04E E E E E-02 Total1.12E E E E E+00 Total/Water

Combined Pathway LLD: Body Step 1: Dose per Unit Concentration Combined Total Body pathway dose – mrem/yr/pCi/L NuclideAdultTeenChildInfantICRP-30 H-31.1E-041.0E-041.7E-041.2E-041.1E-04 Mn-544.1E-014.3E-014.7E-012.2E-031.3E+00 Co-608.9E-021.6E-012.1E-012.6E-024.6E-01 Sr-902.3E+003.0E+005.9E+005.1E-011.9E+00 Cs E+003.1E+001.6E+003.7E-013.4E+00

Combined Pathway LLD: Body Step 2: Pathway Water Concentration pCi/L to yield 1 mrem/yr Total Body Dose Consequence NuclideAdultTeenChildInfantICRP-30 H-39.5E+039.9E+036.0E+038.6E+038.9E+03 Mn-542.4E E+004.5E+027.7E-01 Co-601.1E+016.2E+004.8E+003.9E+012.2E+00 Sr-904.3E-013.4E-011.7E-012.0E+005.3E-01 Cs E-013.2E-016.3E-012.7E+003.0E-01

Comparison of Derived Concentrations Drinking Water vs. Combined Pathway pCi/L to yield 1 mrem/yr Total Body Dose Consequence Most-limiting concentration based on LADTAP DCFs NuclideDrinking WaterCombined PathwayRatio H-31.7E+046.0E+032.8E+00 Mn-546.7E+022.1E+003.2E+02 Co-601.2E+024.8E+002.5E+01 Sr-903.8E+001.7E-012.3E+01 Cs E+012.1E-019.2E+01

Comparison of Derived Concentrations Drinking Water vs. Combined Pathway pCi/L to yield 1 mrem/yr Total Body Dose Consequence Most-limiting concentration based on ICRP-30 DCFs NuclideDrinking WaterCombined PathwayRatio H-32.1E+048.9E+032.4E+00 Mn-544.9E+027.7E-016.4E+02 Co-605.1E+012.2E+002.3E+01 Sr-909.6E+005.3E-011.8E+01 Cs E+013.0E-019.2E+01

Which LLDs to Use? RG-1.109/LADTAP pathway approach includes exposure “missed” by drinking water standard Maximum organ values are not applicable… 10CFR20 Appendix B basis for discounting non-stochastic effects at low doses involved Age-specific dose factors and use factors Beyond scope of ICRP-30… ICRP-2 or ICRP-72? When dealing with deriving new concentration limits and LLDs, one could argue we should use the most up-to- date methodology and science available… ICRP-72

Summary Current EPA approach outlined in 40CFR141 only addresses dose from drinking water ingestion Overlooks dose from other pathways, which can contribute significantly more dose than water ingestion alone Considers single age class, overlooks age- specific variability in dose factors and consumption rates

Summary (continued) Use of organ-specific dose factors yields lower concentration limits Based on NRC approach in Appendix B to 10CFR20, non-stochastic dose effects are not applicable at the low dose levels assumed to occur from environmental exposure Concentration limits and LLDs should be derived from effective total body doses

Summary (continued) A consistent methodology should be used to derive water concentrations based on dose, but some LLDs may be difficult to achieve, and may necessitate a “reasonable survey” approach Consideration should be given to deriving stochastic dose-based concentrations using the most modern standard… ICRP-72