ML072000420

E-Mail Dated April 17, 2007, from Robert Jones, Smud, to John Hickman, NRC, Regarding Groundwater Sampling Procedure for Rancho Seco

ML072000420
Person / Time
Site:	Rancho Seco
Issue date:	04/17/2007
From:	Rosalyn Jones Sacramento Municipal Utility District (SMUD)
To:	John Hickman NRC/FSME/DWMEP/DURLD
References
Download: ML072000420 (21)

Text

Rancho Seco Groundwater Sampling Page I of I John Hickman - Rancho Seco Groundwater Sampling From: "Robert E. Jones" <RJones2@smud.org>

To: <jbh@nrc.gov>

Date: 04/17/2007 12:50 PM

Subject:

Rancho Seco Groundwater Sampling

John, Attached is the sampling procedure used for the groundwater monitoring at Rancho Seco in support of the LTP development. I've also am sending some information regarding the laboratory qualifications. I tried to find a copy of a NUPIC audit on the NUPIC site. There was an audit completed in August 2006, but I couldn't find the report on their website. There was some information regarding the audit that discussed a finding that was closed in Sept. 2006, but not the entire report.

Let me know if this is adequate for your needs and if you want me to submit something on the docket.

Thanks, Bob Jones

<<Rancho Seco Groundwater Sampling SOP.DOC>> <<SamplingFigures.pdf>>

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Subject:

Rancho Seco Groundwater Sampling Creation Date 04/17/2007 12:48:40 PM From: "Robert E. Jones" <RJones2(@smud.org>

Created By: RJones2@~smud.org Recipients nrc.gov OWGWPOO4.HQGWDOO1 JBH (John Hickman)

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Sampling Groundwater from Monitoring and Extraction Wells 1.0 PURPOSE This standard operating procedure (SOP) establishes procedures for collecting groundwater samples from monitoring and extraction wells at Rancho Seco Nuclear Facility (Rancho Seco). The site location and the installed' well locations are detailed in Figures 1 and 2 respectively. The type of monitoring well sample collection system discussed is the portable bailer/pump. Extraction well systems are sampled using procedures different than those used for monitoring well systems. The extraction well sampling procedures are discussed in Section 4.3.

This SOP will help ensure quality and consistency in sample collection procedures. These procedures may be used in conjunction with other documentation and recordkeeping procedures.

2.0 APPLICABILITY This SOP is intended for personnel who participate in groundwater sampling, data review, and reporting activities at Rancho Seco.

3.0 TERMS AND DEFINITIONS DO - Dissolved oxygen DPM - Disintegrations per minute GWMP - Groundwater Monitoring Program NRC -_ Nuclear Regulatory Commission OVM - Organic vapor meter PPE - Personal protective equipment psi - Pounds per square inch redox - Reduction-oxidation SOP - Standard operating procedure VOC - Volatile organic compound QA/QC - Quality assurance/quality control U.S. EPA - U.S. Environmental Protection Agency 4.0 EQUIPMENT AND PROCEDURE DESCRIPTIONS Groundwater sampling is performed to obtain samples representative of the groundwater surrounding the well screen. Use of consistent procedures and sample collection equipment ensures that

C, Figure 1.

Location of Rancho Seco Nuclear Generating Station

0 MW3 SW Legend OW-3 $i- Existing Well MW-10 New Well Construction Area WW Z Existing Well SS - Seasonal Swale SW O Seasonal Wetland 0 400 VP 4 Vernal Pool Approx.

Scale in Feet SM 40% Seasonal Marsh Figure 2. Locations of Wells' .etted'at Rancho Seco Nuclear Generating Station

the analytical results reflect the quality of the groundwater at a geographic location and a monitoring zone as accurately as possible.

4.1 Equipment Rancho Seco wells are typically sampled using the system described below:

Bailer and Submersible Pump - An electric submersible pump and/or a Teflon bailer are used to purge water and collect samples at wells not equipped with dedicated systems. The pump is typically used to purge the well while the bailer is used for sample collection. A flow control valve attachment on the bailer transfers the sample to the sample bottles; this minimizes sample agitation that could release volatile organic compounds (VOCs). Shallow wells with small water columns, or wells that produce insufficient volume to allow the use of a pump, are both purged and sampled with a bailer.

4.2 Procedures General pre- and post-sampling procedures (e.g., planning, equipment decontamination) are discussed in Section 4.2.1. Quality assurance/quality control (QA/QC) sampling procedures are described in Section 4.2.2. The bailer/submersible pump sampling procedures are described in Section 4.2.3.

Procedures generally adhere to the Compendium of Superfund Field Operations(U.S. Environmental Protection Agency [U.S. EPA], 1987).

Sample Planning The following sections contain procedures that should be followed for groundwater collection using any type of system (dedicated delivery or portable bailer) and any type of analyte collected (VOC, inorganic species, or radionuclides).

Health and Safety Proj ect-specific health and safety plans will be followed during all field activities. During standard groundwater sampling activities, field personnel will wear personal protective equipment (PPE) at a minimum of level D (safety glasses, steel-toed boots, and nitrile/latex gloves). PPE requirements will be upgraded as necessary, in accordance with the project health and safety plan.

Staging Area All necessary equipment and supplies will be gathered in the staging area and put onto sampling vehicles before sampling occurs. Non-consumable items include bailers, generators, water level meters,

hoses, buckets, pH meters, conductivity meters, thermometers, multi-meters, and control boxes.

Consumable items should be checked and restocked each day before sampling. Consumable items include sample containers (VOA bottles, plastic 250 mL, 500 mL, or 1-liter bottles, 1 L glass bottles, and others), labels, filters, gloves, monofilament line, calibration solutions, Ziploc bags, ice, fuel for generators/air compressors, and black ball point pens. (For a complete list of equipment, refer to project-specific SOPs or project instructions.) Ensure that trip blanks are included in the sample cooler when VOCs are collected.

Initial Sampling Procedures After arriving at the sampling site, the following steps should be performed.

1. Don appropriate PPE.

2. Validate ID of well, using a current monitoring well location map.

3. Calibrate meters, unless the meters do not require calibration at each well, i.e. many multi-parameter meters only require weekly or monthly calibration. Follow procedures in the respective meter's operating manuals.

4. Open well, allow it to "off-gas,".

5. Decontaminate equipment, purge well, and collect samples following procedures in Sections 4.2.1 through 4.3.

6. Collect QC samples (blanks, duplicates, or additional volume for laboratory spikes) as designated in the field sampling plan (FSP) or task instructions.

4.2.1 Equipment Decontamination Procedures To decontaminate bailers (when disposable bailers are not used), submersible pumps, water level meters, and any other equipment that comes into direct contact with samples:

1. Rinse with ASTM II (deionized) water.

2. Rinse with hexane, then with reagent-grade methanol.

3. Rinse again with ASTM II water after solvents have dried.

submitting "blind" samples. The actual time of sample collection will be used during data validation to determine holding time compliance. Follow standard sampling procedures in Sections 4.2.3 through 4.3.

4.2.2.5 Matrix Spike/Matrix Spike (MS/MSD) Duplicates A matrix spike/matrix spike duplicate (MS/MSD) sample is an exact duplicate of a normal sample taken. Sample ID labeling is identical to the original samples. Additional sample volume is collected for laboratory analysis QA/QC purposes. In the laboratory, the MS/MSD is prepared by spiking known concentrations of target analytes into the additional sample volume prior to sample preparation and analysis.

4.2.3 Sampling Procedures for the Bailer/Submersible Pump Systems Well purging is an integral step in recovering samples representative of the quality of groundwater flowing through the monitoring zone. Each monitoring well sampled using dedicated (not low-flow) or bailer/submersible pump systems is purged immediately prior to sample collection, ensuring the sample is fresh monitoring zone groundwater rather than stagnant water that has been standing in the well casing.

Purging steps are as follows:

1. Prior to purging, calculate the minimum purge volume that must be collected (i.e., three wetted casing volumes) as follows:

Minimum Purge Volume (gallons) = 3x V where:

3 V = 3.14 r2 L x 7.48 gallons/ft V = One wetted casing volume (gallons);

r = Inside radius of casing (feet); and' L = Height of water column in well (feet).

The height of the water column in the well is determined by reading the depth to the top of water level (using a decontaminated water level meter) and subtracting this value from the total depth of the well.

A 5-gallon bucket (or similar container of known capacity) is used to measure the amount of water remoyed from the well during purging. Elapsed time is noted as the container is filled,

4. Store and transport small pieces of equipment used for organic samples on decontaminated aluminum trays or wrap them in aluminum foil.

Clean, disposable gloves are worn during decontamination.

4.2.2 Quality Assurance/Quality Control (QA/QC) Sampling Procedures Field QA/QC samples are used to assess the influence of sampling procedures, equipment, and handling on the reported analytical results.

4.2.2.1 Trip Blank Trip blanks are taken by placing two 40-ml VOA bottles containing highly purified organic-free water into each cooler shipped to the laboratory (or in the number of coolers required to meet the frequency designated for the sampling effort) at the beginning of the sampling day. Handle trip blanks in the same manner as VOA bottles used for VOC sampling (Section 4.2.5.2).

4.2.2.2 Ambient Blank Ambient blank samples are taken at the monitoring well site just prior to actual groundwater sampling. Fill 40-ml VOA bottles directly from a glass bottle containing ASTM II deionized water.

4.2.2.3 Equipment Blank Equipment blank samples are obtained from a decontaminated bailer just prior to actual groundwater sampling.

I. Decontaminate bailer following procedures in Section 4.2.1, Equipment Decontamination Procedures.

2. Fill bailer with ASTM II water or radionuclide-free water.

3: Fill sample containers following directions in Sections 4.2.3 through 4.3.

4.2.2.4 Field Duplicates A field duplicate is the second sample collected at the same timeas the original sample. For some projects, field duplicate samples may be submitted to the laboratory as "double blind" samples. To maintain the anonymity of the field duplicate sample, a coded sample ID and a sampling time of 12:00 will be assigned. If the field duplicate sample is given the same sampling time as the original sample, the laboratory could easily determine the location of the duplicate sample, thus defeating the purpose of

thereby allowing calculation of the discharge rate. The total amount of water purged from each well is recorded on the field sheets (Attachment A);

2. Position the bailer or pump near the middle of the screened interval (if feasible) to ensure that standing water is removed and fresh formation water is drawn into the well. Purged groundwater will be disposed of on the ground surface..

3. Purging is considered complete when the minimum purge volume has been collected and the pH, temperature,' and conductivity have stabilized. The pH, temperature, and conductivity are considered stable when the variation in two successive readings does not exceed:

pH: < +/-0. pIH unit Temperature: < I.00 C Conductivity: < +/-5% change in microsiemens If parameter stabilization has not occurred after three well volumes have been purged, continue purging and taking readings. Samples may be collected after a total of six wetted casing volumes have been removed from the well, even.if readings have not stabilized.

Turbidity and oxidation-reduction (redox) potential will be measured and recorded during purging and sample collection, if specified in the FSP.

4. In low-yield wells that may be purged dry before three wetted casing volumes have been removed, the sample shall be collected when enough water has re-entered the well to obtain the volume of water needed for all sample containers. The time when the well is purged dry is recorded on the groundwater field sheets (Attachment A), as well as the volume of water removed prior to sampling.

4.2.4 Sample Collection and Handling Procedures This section describes guidelines and procedures for the collection and handling of groundwater samples for radionuclides.

Sample Planning Groundwater samples are collected in a prearranged priority so that collection and handling of samples occurs as efficiently as possible. Although the actual sample collection protocol will depend on the analytes of interest, general sample collection procedures must be consistent. Prior to using the bailer or collecting a sample from the discharge line, don new, clean disposable gloves to avoid cross-contamination. Samples for volatile constituents are collected first, to avoid loss of volatiles to the air, followed by inorganics and radionuclides.

During all sampling activities, position the support equipment so that any potential volatile organic sources, such as vehicles, gasoline-driven generators, or air compressors and fuel tanks, are downwind. Contamination caused by entrapment of volatile contaminants in the sample is thus avoided.

Any potential VOC sources that are unavoidable are noted on the well purging log.

Sample Container Labeling Label sample containers with sample I.D., location, date and time sample was taken, analyses to be performed, preservative, name of client, and the initials of the samplers. Use a black ball point pen when completing labels.

Sample Custody, Documentation, and Shipping All custody, documentation, and shipping procedures will adhere to the specifications described in Section 6.0 of the QAPP (Sample Custody and Documentation).

4.2.4.1 Radionuclides Groundwater is collected and analyzed for radionuclides in areas suspected of radioactive contamination. In order to prevent the spread of potential radioactive contamination, additional equipment, monitoring, and site control measures may be needed. The following screening equipment is used for groundwater collection for radionuclides analysis:

1. Zinc sulfide (ZnS) scintillation detector (alpha detector): An alpha particle detector attached to a survey meter OR

2. Geiger-Mueller counter with pancake probe (pancake probe): A Geiger-Mueller counter with a flat, round probe that is used to primarily detect beta radiation, and a portion of the gamma ray spectrum.

All instruments will be used and checked for performance following the guidelines in the Radiation Detection Instrument General Operation and Performance Check SOP, McAFB-038.

Sampling Procedures As during any sampling activity, personnel must take the necessary health and safety precautions outlined in the applicable site-specific health and safety plan. Equipment which has come into contact with groundwater will be screened for radionuclides and decontaminated as necessary. The sampling procedures are as follows:

1. Collect groundwater in a non-preserved 1-liter plastic bottle.

2. If necessary to the analysis, within one hour after collecting the sample, filter through a cellulose nitrate 0.45-micron filter into a 1-liter plastic bottle preserved with 2 ml nitric acid (70%), using a peristaltic pump.

A. Decontaminate the in-line filter holder by rinsing with a 10% nitric acid solution. When using a Geopump system, attach the in-line filter holder to the Tygontubing and rinse both the tubing and filter holder.

B. Follow with an ASTM II water rinse.

C. Open the in-line filter holder and insert a 0.45-micron cellulose nitrate filter. Filter the 1 liter of non-preserved water from Step 1 into a preserved 1-liter plastic bottle. If collecting a water sample for tritium analysis (Method E906), glass bottles without chemical preservatives should be used in Step 1 and Step 2.

D. After all water has been filtered, dry the filter by pumping air through the filter until it has sufficiently dried.

E. Place filter in a labeled Ziploc bag. The filter ID should correlate it to the water sample. Each 1-liter sample of water should have, one corresponding filter. If more than one filter is needed to filter a liter of sample, submit additional filters in their own Ziploc bag. Additional filter IDs should correlate to the water sample, but distinguish it from other filters. The purpose of the filter residue is to quantify the total radioactivity (if any) of the raw groundwater.

3. Place groundwater sample and filter in a cooler at 4'C.

Post-Collection Radiological Screening and Decontamination of Equipment

1. Screening of sampling equipment and radiological survey instruments may be conducted after use in radiologically contaminated areas. If possible, disposable sampling equipment and encapsulated instruments should be used at radiological sites.

Screening levels for clearance of radioactive materials are presented in industry standard ANSLHPS N13.12-1999, Surface and Volume Radioactivity Standardsfor Clearance.Values in Table 1 of ANSIHPS N13.12, and presented in Attachment B, are total radioactivity levels without regard to the loose or removable radioactivity components.

2. Wipe with a cleanmoistened cloth all equipment that has come into contact with the ground-water. Dry bailers, pumps, pH meters, conductivity meters, thermometers, water level meters, and personal protective equipment.

3. Using appropriate radiation detection and measurement instrument(s), survey/screen all decontaminated equipment that has come into contact with the groundwater.

4. Radiological sampling equipment and field monitoring instruments will only be cleared for reuse if it is decontaminated to pre-use alpha/beta/gamma background radiation levels.

Other equipment not used for radiological sampling or field measurement Will be released for reuse if residual radioactivity is less than 50% of the surface screening decontamination levels presented in Table 1 of ANSIiHPS N13.12-1999 (Attachment B). Proceed to decontaminate according to standard chemical decontamination procedures in Section 4.2.1. Instrument readings can be converted to units of dpm/100 cm2 following the equation in SOPs McAFB-046, Section 4.2.7, or McAFB-047, Section 4.2.2.

5. Equipment is considered contaminated if readings are above 50% of the surface screening levels.

cited in Table 1 of ANSI/HPS N13.12-1999 (Attachment B). The equipment must be decontami-nated before leaving the site. An effort should be made to limit the amount of wastewater generated while decontaminating radioactive equipment. Where possible, equipment should be wiped with a cloth and re-screened. If readings are below 50% of the decontamination action levels, the equipment is considered no longer contaminated and can then be decontaminated for other potential contaminants following standard chemical decontamination procedures in Section 4.2.1.

Equipment destined for unconditional release or disposal and found to have residual radioactivity between 50% and 100% of the values in Attachment B, may be released by the Project Health Physicist without further decontamination on a case-by-case basis.

6. Screen wipe cloths for residualradioactivity and dispose as clean waste. If readings are less than 50% of the decontamination action levels of ANSI/HPS N13.12-1999 Table 1 (Attachment B). If readings are greater than 50% of these action levels, the wipe cloths are considered low-level radioactive waste.

7. Materials and equipment showing residual radioactivity greater than the Values set forth in Table 1 of ANSI/HPS N 13.12 (Attachment B), even after three successive decontamination attempts, can be disposed of as low-level radioactive waste. Equipment that would not cause cross-contamination .ofsamples may be released for reuse within a radiologically controlled area with the approval of the Project Health Physicist on a case-by-case basis. Such material/equipment will be clearly marked to indicate that the items possess residual radioactivity greater than the screening levels in Table 1 of ANSI/HPS N13.12 (Attachment B) and are to be disposed of as low-level radioactive waste upon completion of use. All items classified as being radiologically contaminated or disposed of as low-level radioactive waste will be handled in accordance with

.applicable radioactive materials license conditions, issued by the State or NRC.

Sample Control Although it is anticipated that all samples will be analyzed on-site at the Rancho Seco Nuclear Facility, the following protocols will be used when shipping samples off-site. In addition to all standard shipping procedures (Section 6.0 of this QAPP, Sample Custody and Documentation), the following procedures will be added when shipping samples for radiochemistry analyses. All samples for radiochemistry analyses should be shipped promptly. Additional sample shipping procedures will be in accordance with 49 CFR 173. Before a package containing samples for radiochemistry analyses is shipped, a swipe of the exterior of the shipping container will be performed. The purpose of the swipe sample is to assure that the package surface does not exceed Department of Transportation (DOT) radiation limits. A swipe sample is collected by rubbing filter paper with moderate pressure over a 300 cm2 area on the package's lid or sides. This filter paper is then submitted to the lab for analysis, or screened using a fixed location instrument with an internal proportional counter. Maximum permissible limits shall be 2,200 dpm/100 cm' for'beta-gamma emitting radionuclides, and 220 dpm/l100 cm2 for alpha emitting radionuclides (49 CFR 173.443 Table 11). Shipping restrictions for individual carriers, should be checked to ensure compliance.

Analytical The radiochemistry analyses performed on soil or water will be specified in individual field sampling plans. Samples collected for radiochemistry analyses will be sent to either the laboratory at the Rancho Seco Nuclear Facility or a laboratory either with a radioactive materials license issued by the Nuclear Regulatory Commission (NRC) or regulated under the jurisdiction of an NRC agreement state.

Each laboratory will have sample screening guidelines and notification requirements that must be followed.

4.3 Water Supply Well System A water supply well consists of a dedicated pump and piping for removing water from the ground and sending it to wherever needed. The water supply well system does not require standard sampling equipment such as portable pumps or bailers. Water supply wells are sampled by opening the flow control valve; only 3 gallons need to be purged from the well before sampling provided the well has been running continuously for five minutes prior to beginning the purge. When sampling fromextraction wells, the following steps should be performed:

1. Don appropriate PPE, in accordance with the field sampling plan or task instructions.

2. Validate well ID, using a current map of base monitoring and extraction wells.

3. Calibrate pH meter and conductivity meters, if necessary, by following the procedures in the operating manual.

4. Open the flow control valve on the sampling port. Purge 3 gallons of water from the well, take water parameter readings each gallon (four readings total, including initial reading), and continue purging and readings until readings stabilize, if necessary.

5. Fill sample containers directly from the flow control valve. Follow procedures in Section 4.2.4.1 (for radionuclides).

6. Store samples in a cooler at 4'C.

7. Follow sample labeling, documentation, and handling procedures described in Section 4.2.4 (Sample Collection and Handling Procedures).

5.0 REFERENCES

0

American National Standard Institute, Inc., Health Physics Society (ANSI/HPS), 1999. Surface and Volume Radioactivity Standardsfor Clearance.

Interstate Technology and Regulatory Council (ITRC), 2002. Recommendationsfor the Use of Polyethylene Diffusion Bag Samplersfor the Long-Term Monitoringof Volatile Organic Compounds in Groundwater.

Puls and Barcelona, 1995. Low-Flow (MinimalDrawdown) GroundwaterSampling Procedures.

Title 49, Code of Federal Regulations (CFR), Part 173 U.S. Environmental Protection Agency (U.S. EPA), 1987. Compendium of Superfund Field Operations.,

U.S. Geologic Survey (USGS), 2001. User's Guide for Polyethylene-BasedPassiveDiffusion Bag Samplers to Obtain Volatile Organic Compound Concentrationsin Wells.

6.0 ATTACHMENTS Attachment A: Field Data Sheets Attachment B: Screening Levels for Clearance (ANSIWiPS N 13.12-1999, Table 1)

ATTACHMENT A FIELD DATA SHEETS

UBS Water Sampling Data Sheet Installation/Project: Site ID:

Location ID: Samplers:

Sample Date: Sample Time:

Sample Method:  !]Grab L3Spigot QHydropunch USimulprobe EBailer Static Water Level:

Weather: E]Sunny ECloudy LRainy U Foggy E Hazy Temp (OF): Wind Direction:

Comments:

Temp pH Codutiit SamplerlD

• I PIpH

°C I°nductivityl

..~(phmo~s) Comments.. . ,.

_Samples Collected METHOD:

Container Preserv.

Normal Sample Field Dup.

MS/MSD Eqpt. Blank Samples Calibration Log pH Readings Initial pH Readings Adjusted Time pH 7.0, pH 10.0 pH 7.0 pH 10.0 Post Check iiTime Conductivity Initial 700ps Conductivity Adjusted

.700ps Post Check "I

Rancho.Seco Location: Purge Method:

~1 Purge Rate (GPM): Required Purge Volume:

Sampler Initials: Water Level Meter #:

Volume T -0.

Tirfie Purged ýýt 2W Oriduct"', 16 rb idity, ORP, 'Comme rits 00)

Site Calibration Log Turbidity Meter #:

pH Meter #:

Time pNRaidg~s iiti6i i7.O pH pH.0*0.0

ýPN!ealnst jut~'

pHI-7.0 PiO 10.0f Initial J A-j.,ted:

Readin Post Check MeConductivrity

1. .. Initial

.nduc tvity Adjusted Meter #: I70,is 70Otps M4~PS1Op 6flps 14~~s I I 4 4 4 Post Check I- - I -

ATTACHMENT B SCREENING LEVELS FOR CLEARANCE (ANSI/HPS N13.12-1999, Table 1)

ATTACHMENT A Screening Levels for Clearance (ANSI/HPS N13.12-1999, Table 1)

Screening Levels Surface Screening Volume Screening Radionuclide Groupsa (S.I. Units)b (Conventional Units)b (Conventional Units)b (Bq/cm2 or Bq/g)c (dpm/100 cm 2) (pCi/g)

Group 1 Radium, Thorium, and 0.1 600 3 210 Transuranics:

228 P, 210 Pb 226Ra, Ra 228Th, 230Th' 2 32Th 2 37Np, Am, 244Cm, and 239PU pu, 240 4°Pu, 241,,24 associated decay chainsd, and othersa Group 2 Uranium and Selected 1 6,000 30 High Dose Beta-Gamma Emitters: 22 Na, 54Mn, 58 Co, 60 co, 65Zn, 90Sr, 94Nb, 106Ru, I1mAg, 134 Cs' 13 7Cs' 152Eu' 154Eu, 124 Sb' 34 192Ir, 2 U, 235 U, Natural Uraniume, and othersa Group 3 General Beta-Gamma 10 60,000 300 Emitters: 2 4Na, 36C1, 59 Fe, 109Cd, 1311, 1291, 144Ce' 198Au' 241pu, and othersa Group 4f Other Beta-Gamma 100 600,000 3,000 Emitters:. 3 H, 14 C, 32p, 35S, 45Ca, 51 Cr, "Fe, 63Ni, 9Sr, 99Tc, 1"1n, 125I, 147pm, and othersa a To determine the specific group for radionuclides not shown, a comparison of the effective dose factors, by exposure pathway, listed in Table A. I of NCRP Report No. 1231 (NCRP, 1996) for the radionuclides in question and the radionuclides in general groups above shall be performed and a determination of the proper group made, based on similarity of the factors.

b Rounded to one significant figure.

The screening levels shown are used for either surface activity concentration (in units of Bq/cm 2), or volume activity concentration (in units of Bq/g). These groupings were determined based on similarity of the scenario modeling results, as described in Annex B (ANSI/HPS N 13.12-1999).

d For decay chains, the screening levels represent the total activity (i.e., the activity of the parent plus the activity of all progeny) present.

Where the Natural Uranium activity equals 48.9% from 23 8U, plus 48.9% from 234 U, plus 2.25% from 235U.

f Radionuclides were assigned to groups that were protective of 10 gSv/y (1.0 mrem/y) and were limited to four groups for ease of application, as discussed in Annex B (ANSI/HPS N 12.13-1999).