Regulatory Guide 4.14

Measuring, Evaluating, and Reporting Radioactivity in Releases of Radioactive Materials in Liquid and Airborne Effluents from Uranium Mills

ML13350A202
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Issue date:	06/30/1977
From:	Office of Nuclear Regulatory Research
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RG-4.014
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U.S. NUCLEAR REGULATORY COMMISSIONJune 1977'REGULATORY GUIDE41 OFFICE OF STANDARDS DEVELOPMENTREGULATORY GUIDE 4.14MEASURING, EVALUATING, AND REPORTING RADIOACTIVITY IN RELEASES OFRADIOACTIVE MATERIALS IN LIQUID AND AIRBORNE EFFLUENTS FROMURANIUM MILLS

A. INTRODUCTION

Section 20.106, "Radioactivity in effluents to un-restricted areas," of 10 CFR Part 20, "Standards forProtection Against Radiation," provides that alicensee shall not release to an unrestricted arearadioactive materials in concentrations that exceedlimits specified in 10 CFR Part 20 or as otherwiseauthorized in a license issued by the NuclearRegulatory Commission. Section 20.201, "Surveys."of 10 CFR Part 20 further requires that a licenseeconduct surveys of concentrations of radioactivecases, modifications of the described programs maybe accepted or required by the NRC staT'f dependingon individual site characteristics, plant designfeatures, unique operations, or other factors. Theneed for modilied programs will he determined by theNRC staff on a case-by-case basis.

B. DISCUSSION

Information on the radionuclides in liquid and air-borne effluents from .uranium-mills, ore piles, andtailinps is neededmaterials as necessary to demonstrate compliance .with Commission regulations. I. For evaluation :by the" NRC staff of the en-vironment~al impact of1radioactive materials in cl-Section 20.401, "Records of surveys, radiation fluents,'1includinfg estimates of the potential annualmonitoring, and disposal," requires that records of radiaitionvdlose'to the public.surveys be maintained.. : ?urese aitnd 2;+To&ascertain whether regulatory requirementsSection 40.65, "Effluent monitoring reporting re- '; ve. been met and whether concentrations ofquirements," of 10 CFR Part 40, "Licensing, -:f 'radioa'ctive materials in liquid and airborne effluentsSource Material," requires the submission ofsimiian" hShve been kept as low as is reasonably achievable.nual reports to the Commission specifying the quan-tity of each of the principal radionuclides ieleased to 3. For evaluation by the licensee and NRC staff ofunrestricted areas and such other informatiori':as the (I) the adequacy and performance of effluent con-Commission may require to estimate,- maximum trots and (2) the ore and tailings retention systems.potential annual radiation doses to "tle publicresulting from effluenJ.00buses. It is essential to have I degree of uniformity in theParagraph (c).,f "Purposee" of 10CFR Part 2,.I Wi'j ti~,t every reasonable effortshould bq e by einses to maintain radiation ex-posur d ,ase~f radioactive materials in ef-fluen id areas as far below the limitsspecifie Part 20 as is reasonably achievable.This guide describes programs acceptable to theNRC staff for measuring, evaluating, and reportingreleases of radioactive materials in liquid and air-borne effluents from typical uranium mills. In someprograms or measuring, evaluating, recording, andreporting data on radioactive material in effluents.'rhis guide provides a uniform basis for comparingdata from different sources and permitting thepreparation of consistent summaries of data for useby the NRC staffas bases for assessing a liccnsee's ef-fluent controls and the potential environmental im-pact of radioactive material in effluents.This guide outlines general guidelines for accep-table effluent monitoring programs. However, theseguidelines are not requirements. The licensing re-USNRC REGUL.ATORY GUIDES Co'tes~~~~ i -i~ ,~. .~ i t,, (: .........*.Regulatory Guides aie ,51.ue,1 lo dql~,th and mjr,,,, avaitlable to the public m'ethods 0.4.C'ttos~,.sJ int n .:'01A6. A ii. liacce~latbl,, to the NRfC staff of trntieeni.nt;n 54m-ctlir. PJ'till$ Of V Comms,rngstn% t'it~'regulations to llrlinelore W.ieclnttits .Is- Il~it' 1h, i Itaf in lo,agitt.rig uwec,fl,' i'nlterns q-,ita.'.Otie ti Ii,.- tiltAt.lI ills,.l i ,iof ~OtisuI,'i-d jcrj'Jenii. or to :ioto-Ir qutdnc.- Il appicants. Re'gulatory Guidesare nol stohsintules fci ieguilations. and coinliti'nce with Irwi is n'ot retisi,,i't. I. o av, t,',,c~ 6 P1.'i.0,tiMethod% InlndOI t~ltain% iJit terent fro inhoi. tel noti ill I he qid-tl' wtill bt' .cCtli 2.Rs. Is, atid I. 4,i, .ti.ahle. d they arntm ,lhs's lo, the fitndtngi 'tilaistle its it,. nttumn-i 0r conltinuancs 3 Fz,¶., ~,i~.i Ft" It,'.iof a IsermsO at ibns tntot Conii,,tvnn. .1En .te-"istl 1)lSi' 'i~tit.n~.Commients f i ,qteltn itl ,i,¶tilttitfi it, Ilhwitt- , i -irowtiiled ItM

quirements are determined by the NRC staff on acase-by-case basis during individual licensing review.Individual applicants or licensees may propose alter-natives for new or existing effluent monitoringprograms that need not necessarily he consistent withthis guide. The justification for such alternatives willbe reviewed by the NRC staff, and the acceptabilityof proposed alternatives will be determined on a case-by-case basis during individual licensing reviews.

C. REGULATORY POSITION

!. METHODS OF SAMPLING AND ANALYSISEffluent monitoring is required to (I) demonstratecompliance with I0CFR Part 20 and any special con-ditions of the license. (2) allow evaluation of the per-of retention systems and effluent controls,and (3) permit evaluation by the NRC staff of en-vironmental impact and estimation of the potentialannual radiation doses to the public. Because radia-tion dose is dependent on the radionuclides to whichthe individual is exposed, monitoring programsshould provide accurate information on the specificradionuclides in airborne effluents and any liquid ef-fluents from the plant. ore piles. and tailings reten-tion system.Methods of sampling and analysis of theradionuclides associated with uranium milling arediscussed in sources listed in the bibliography. Thelisting of these documents does not constitute an en-dorsement by the NRC staff of all of the methods inall of the listings. Rather, these listings are provided.as sources of information to aid the licensee indevelcping a program.2. SAMPLING PROGRAM2.1 Airborne Effluents2.1.1 Stack SamplingEffluents from each stack should be sampled atleast semiannually during normal operations. Thesampling should be adequate for determination of therelease rates and concentrations of natural uraniumfor all stacks. The sampling of the yellow cake drierand packaging stack should also be adequate for thedetermination of rejease rates and concentrations ofthorium-230 and radium-226.2.1.2 Sampling at Site BoundaryAir particulate samples should be collected con-tinuously at a minimum of three site boundary loca-tions. The sampling should be adequate for the dcter-mination of concentrations of natural uranium.thorium-230, radium-226, and lead-210. Normally,filters for continuous, ambient air samples arechanged at least weekly.The sampling locations should be determined ac-cording to the specific site and milling operation. Thefollowing factors should be considered in determin-ing the sampling locations: (I) averagemeteorological conditions (windspeed. wind direc-tion, atmospheric stability), (2) prevailing wind direc-tion, (3) site boundaries nearest to mill, ore piles, andtailings piles, (4) direction of nearest residence, and(5) location of estimated maximum concentrations ofradioactive materials.Samples should be "ollected continuously for atleast one week per mcnth, for the determination ofthe concentration of radon-222. The sampling loca-tions should be the same as those for the continuousair particulate samples. Normally, sampling time forradon is 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> or less: therefore several samplesnor week will need to be analyzed for each samplinglocation.2.2 Liquid EffluentsA;.ll liquid discharges to unrestricted areas shouldbe sampled continuously. The samples should be ade-quate to determine concentrations and release ratesof natural uranium. t, )riumn-230, and radium-226.Samples of groundwater should be collected atleast quarterly from sampling wells locatedhydrologically downslope from the tailings retentionsystem.Samples should be collected at least quarterly fromany surftace seepage that reaches an unrestricted areaand anro natural body of water, such as a lake orcreek, that crosses from the restricted area into an un-restricted area. (Surface seepage is defined as seepagefrom the tailings area that come," to the surface beforeit reaches th,: unrestricted area.)Samples coll-cted from groundwater, surfaceseepage, or natural bodies of water should be ade-quate for the determination of concentrations ofnatural uranium, thorium-230, and radium-226.Any unusual releases that are not part of normaloperations should be sampled. The sampling shouldbe adequate to determine release rates and concentra-tions of natural uranium, thorium-230, and radium-226.2.3 Quality of SamplesProvisions should be made to ensure that represen-tative samples are obtained by use of proper samplingequipment, proper locations of sampling points, andproper sampling procedures (see bibliography).Samples collected at the same location may becomposited for analysis if they represent a samplingperiod of one calendar quarter or less. Samples4.14-2 should not be composited (I) if they represent asampling period of more than one calendar quarter,(2) if they are from different sampling locations, or(3) if the samples are to be analyzed for radon-222.Samples collected for analysis of radon-222 shouldbe analyzed quickly enough to minimize decay lossesand allow for adequate precision and accuracy ofresults.2.4 Alternative Sampling ProgramsApplicants or licensees may propose alternatives tothe sampling programs outlined in this regulatoryguide. It is anticipated that programs that do not in-clude continuous air samples at the site boundary willinclude more extensive stack sampling and moresampling locations than are described in this guide, aswell as meteorological data and additional en-vironmental monitoring requirements.3. ANALYSIS OF SAMPLES3.1 Air SamplesStack effluent samples should be analyzed fornatural uranium. Samples from the yellow cake drierand packaging stack should also be analyzed forthorium-230 and radium-226. The volume dischargerate of the stack effluents should be measured to theextent that it is necessary to estimate radionucliderelease rates.Air particulate samples collected at the site boun-dary should be analyzed for natural uranium,thorium-230, radium-226, and lead-210.Air samples collected at the site boundary shouldbe analyzed for radon-222. (Note: NRC regulationsallow the analysis of radon daughters instead ofradon-222. However, the NRC staff does not recom-mend this option because (I) techniques for long-term measurements of radon daughters at low levelsare more difficult and (2) measurement of radondaughter concentrations near the site boundary in-stead of radon-222 would make estimates of dose tothe public more difficult.)These results should be used to determine theradionuclide release rates for the stacks and theradionuclide concentrations for the stacks and thesite boundary.3.2 Liquid SamplesLiquid samples should be analyzed for naturaluranium, thorium-230, and radium-226.The volumes of liquid discharges should bemeasured to the extent necessary to determine theradionuclide release rate.These results should be used to determine theradionuclide release rate for liquid discharges and theradionuclide concentrations for liquid discharges.groundwater, surface seepage, and natural bodies ofwater.3.3 Solubility of Radioacuise MaterialTable II of Appendix B to 10 CFR Part 20 listsseparate values forsoluble and insoluble radioactivematerials. Therefore, both the soluble and insolubleportions of radionuclides in an effluent should alwvavsbe analyzed. In order to determine compliance with10 CFR Part 20, the licensee has two options: (I) thelicensee may analyze all of a particular radionuclidein a sample and assume that it has the solubilitv cor-responding to the lesser value in Table II of AppendixB to 10 CFR Part 20, or (2) the licensee may separatethe soluble and insoluble portions in a sample.analyze each portion separately, and report eachresult separately, referring to the respective max-imum permissible concentrations for soluble and in-soluble materials.3.4 Lower Limit of DetectionThe lower limits of detection for analysis of air par-ticulate samples collected at the site boundary shouldbe 0.1% of the concentration limits listed in Table IIof Appendix B to 10 CFR Part 20. For example. thelower limits of detection should be 5 x 10-'microcuries per milliliter for natural uranium. 8 x10"' microcuries per milliliter ror soluble thorium-230, 2 x 10'" microcuries per milliEter for insolubleradium-226, and 4 x I0"I microcuries per milliliter forsoluble lead-210.The lower limit of detection for analysis of radon-222 samples should be 3 x 10"t' microcuries per mil-liliter.The lower limits of detection for stack effluentsamples should be 10% of the 10 CFR Part 20. Ap-pendix B, Table 11 concentration limits.The lower limits of detection for liquid samplesshould be 1% of the concentration limits listed inTabie II ofAppendix B to 10CFR Part 20 for naturaluranium. thorium-230. and radium-226.Obviously, if the actual concentrations of radio-nuclides being sampled are higher than the lowerlimits of detection indicated above, the sampling andanalysis procedures need -only be adequate tomeasure the actual concentrations.An acceptable method for calculation of lowerlimitsof detection is described in the appendix of thisguide.04.14-3

4. PRECISION AND ACCURACY OF RESULTS4.1 Random ErrorThe random error associated with the analysis ofsamples representing concentrations above the lowerlimit of detection should be calculated. The calcula-tion should take into account all significant randomuncertainties, not merely counting error.For samples representing concentrations below thelower limit of detection (see appendix), the licenseehas two options: (1) the licensee may calculate thestardard deviation associated with the analysis, or (2)the licensee may merely report the result as less thanthe lower limit of detection with no statement of un-certainty.For effluents with concentrations at or below theconcentrations listed in 10 CFR Part 20, Appendix B.Table II, the standard deviation estimated for ran-dom error should be less than both of the following:(I) 50% of the count and (2) 10% of the appropriateconcentration listed in Appendix B. Table 11. For ef-fluents with concentrations greater than the con-centrations listed in Appendix B, Table 1I, the stan-dard deviation estimated for single counts should beless than 10% of the count.4.2 Systematic ErrorIf the analyst estimates that systematic errors as-sociated with the analysis are significant relative tothe random error, the magnitude of the systematic er-ror should be estimated.4.3 CalibrationIndividual written procedures should be preparedand used for specific methods of calibrating allsampling and measuring equipment, including ancil-lary equipment. The procedures should ensure thatthe equipment will operate with adequate accuracyand stability over the range of its intended use.Calibration procedures may be compilations ofpublished standard practices, manufacturers' instruc-tions that accompany purchased equipment, orprocedures written in house. Calibration proceduresshould identify the specific equipment or group of in-struments to which the procedures apply.To the extent possible, calibrations of measuringequipment should be performed by using radioactivesources that have been calibrated by a measurementsystem traceable to the National Bureau of Stan-dards' radiation measLurements system.*Calibrations should generally be performed atregular intervals. Frequency of calibration should be*L. M. Cavallo ct al.. "'Neds for Radioactivity Standards andMeasuremcnis in Different Fields,~ Nuclear Instruments andMehl.ds., Vol. 112. pp. 5-18, 1973.based on the stability of the system. If appropriate,equipment may be calibrated before and after use in-stead of at arbitrarily scheduled intervals. Equipmentshould be recalibrated or replaced whenever it issuspected of being out of adjustment, excessivelyworn. or otherwise damaged and not operatingproperly. Functional tests, i.e.. routine checks per-formed to demonstrate that a given instrument is inworking condition, may be performed using sourcesthat are not calibrated by a system traceable to theNational Bureau of Standards.4.4 Quality of ResultsA continuous program should be prepared andimplemented for ensuring the quality of results andfor keeping random and systematic uncertainties to aminimum. The procedures should ensure that thesamples are not changed prior to analysis because ofhandling or because of their storage environment.Tests should be applied to analytical processes, in-cluding duplicate analysis of selected effluent samplesand periodic cross-check analyses with independentlaboratories.5. REPORTING OF RESULTS5.1 Sampling and Analysis Re.,sults5.1.1 Air SamplesFor each air sample, the following should bereported:1. Location of sample.2. Dates during which sample was collected.3. For analyses indicating results above thelower limit of detection:a. The concentrations of natural uranium,thorium-230, radium-226, and radon-222for site boundary samples.b. The concentration of natural uranium forstack effluent samples, plus the concentra-tions of thorium-230 and radium-226 foryellow cake drier and packaging stack ef-fluent samples.c. The percentage of the appropriate 10 CFRPart 20 Appendix B concentration limit.d. The estimated release rate of naturaluranium for stack effl ue'nt. samples,, plusthe release rates of thorium-230 andradium-226 for yellow cake drier andpackaging stack effluent samples.4. For analyses indicating results below thelower limit of detection:I4.14-4 a. The same information requested in (3)above orb. An indication that the results were belowthe lower limit of detection and the value ofthe lower limit of detection.5.1.2 Liquid SamplesFor each liquid sample, the following should bereported:I. Location of sample.2. Date of sample collection.3. For analyses kndicating results above thelower limit of detection:a. The concentrations of natural uranium,thorium-230. and radium-226.b. The percentage of the appropriate 10 CFRPart 20, Appendix B concentration limit.c. For discharges to unrestricted areas, therelease rates of natural uranium, thorium-230, and radium-226.4. For analyses indicating results below thelower limit of detection:a. The same information requested in 3 aboveorb. Ar, indication that the results were belowthe lower limit of detection and the value ofthe lower limit of detection.5.1.3 Error EstimatesResults that arc not reported as below the lowerlimit of detection should always include error es-timates. The standard deviation associated with therandom error of the analysis should be reported foreach result. If significant, an estimate of themagnitude of the systematic error should also bereported.Results reported as below the lower limit ofdetec-tion need not include error estimates. However, thevalue of the lower limit of detection should be in-cluded.I. Description of sampling equipment.2. Description of sampling procedures, includingsampling times, rates, and volumes.3. Description of analytical procedures.4. Description of calculational methods.5. Discuission of random and systematic error es-timates, including methods ofcalculation and sourcesof systematic error.6. Description of the calculation of 'he Itwer lim itof detection.7. DLiscussion of the program for ensuring thequalit% ot" results,8. Dscription of calibration procedures.9. Discussion of any unusual releases, includingthe circumstances of the release and any dataavailable on the quantities of radionuclidcs released.5.3 UnitsRadionuclide quantities should be reported incuries. Radionuclide concentrations should hereported in microcuries per milliliter. (In the Inter-national System of Units. a curie equals 3.7 x 10'becquerels. a microcurie equals 3.7 x 10' hecquerels,and a milliliter equals 10D cubic meters.)Standard deviations for random error should hereported in the same units as the result itself.Estimates of systematic error should be reported as apercentage of the result.Note: The Commission has discontinued the use in10 CFR Part 20 of the special curie definitions fornatural uranium and natural thorium (39 FR 23990.June 28. 1974). Reports to the Commission shoulduse units consistent with this change.5.4 Significant FiguresResults should not be reported with excessivesignificant figures. such that they appear more precisethan they actually are. The reported estimate of errorshould contain no more than two significant figures.The reported result itself should cont-,in the samenumber of decimal places as the reported error.5.5 FormatThe term '"not detected" or similar terms shouldnever be used. Each reported result should be (I) avalue and its associated standard deviation or (2) anindication that the result was below the Iower limit ofdetection and the value of the lower limit of detec-tion.5.2 Supplemental InformationThe following information should be included inthe first effluent monitoring report. Subsequentreports should include only changes in this informa-,ittion.4.14-5

D. IMPLEMENTATION

The purpose of this section is to provide informa-tion to app!icants and licensees regarding the NRCstaff's plans for using this regulatory guide.Except in those cases in which the applicantproposes an acceptable alternative method for coin-plying with specified portions of the Commission'sregulations. the method described herein will be usedin the evaluation of license applications docketedafter February 15, 1978.If an applicant wishes to use this regulatory guidein developing submittals for applications docketed onor before February 15, 1978, the pertinent portions ofthe application will be evaluated on the basis of thisguide.4.14-6 AppendixLOWER LIMIT OF DETECTIONSFor the purposes of this guide, the Lower Limit ofDetection (LLD) is defined as the smallest concentra-tion of radioactive material sampled that has a 95%probability of being detected. (Radioactive materialis "detected" if it yields an instrument response thatleads the analyst to conclude that activity above thesystem background is present.)For a particular measurement system (which mayinclude radiochemical separation):4.66 sb3.7 x 101 EVY exp(-A,,t)VYis the sample volume (milliliters);is the fractional radiochemical yield(when applicable);whereLLDsbis the lower limit of detection(n~icrocuries per milliliter):is the standard deviation of the instru-ment background counting rate(counts per second);x is the, radioactive decay constant forthe particular radionuclide: anda t is the elapsed time between sample col-lection and counting.The value'of sb used in the calculation of the LLDfor a particular measurement system should be basedon the actual observed variance of the instrumentbackground counting rate rather than an unverifiedtheoretically predicted variance.Since the LLD is a function of sample volume.counting efficiency, radiochemical yield, etc., it mayvary for different sampling and analysis procedures.Whenever there is a significant change in theparameters of the measurement system, the LLDshould be recalculated.**For a more complete discussion or the LLD. see HASLProcedures Manual, John H. Harley. editor, USERDA, HASL-300(revised annually) and Currie, L. A.. "Limits for QualitativeDetection and Quantitative Determination-Application toRadiochemistry'" Anal. Chent. 40, 1968, pp. 586-93.3.7 x 10' is the number of disintegrations per se-cond per microcurie;E is the counting efficiency (counts perdisintegration);04.14-7 BIBLIOGRAPHYANSI N13.1-1969, "Guide to Sampling AirborneRadioactive Materials in Nuclear Facilities."American National Standards Institute. Inc., 1430Broadway, New York, N.Y. 10018.ANSI N13.8-1973. ' Radiation Protection inUranium Mines," Amer.cari National Standards In-stitute, Inc.. 1430 Broadway. New York. N.Y. 10018.ANSI N131L0-1974, "Specification and Performanceof Onsite Instrumentation for ContinuouslyMonitorine Radioactivity in Effluents." AmericanNational Standards Institute. Inc_. 1430 Broadway.New York. N.Y. Cavallo. L. 1M. et al.. "Needs for Radioactivity Stan-dards and Measurements in Different Fields,.',,V1olear Instruments and *I'thods. Vol. 112. 19- 3, pp.5-18.Gibson, W. M.. rhe Radiochentistrvjfir Lead. NAS-NS 3040, National Academy of Sciences-NationalResearch Council. 1961.Grindler. J. E.. 771-, Radiochemistrr' of UraniumwNAS-NS 3050, National Academy of Sciences-National Research Council, 1962.Ilaidbook of Raduichemical Analytical M¶hethods,EPA-680/4-75-001, USEPA. 1975.Harley, John H., editor, ItASL Procedur's A anual,HIASL-300, USERDA, revised annually.Flyde, E. K.. The Radiochemistrv of Thorium. NAS-NS 3004, National Academy of Sciences-NationalResearch Council. 1960.Instrumentation .1(r Environmental Mtfonitoring;Lawrence Berkeley Laboratory, LBL-1, Vol. 3, up-dated periodically.Kirby. H. W.. and Mi. L. Salutsky, TheRadiorhewmitr)v of Radium. NAS-NR 3057, NationalAcademy of Sciences-National Research Council.1964.,iMeihods of Air Sampling, and Anaysis, AmericanPublic Health Association, 1972.Percival, D. R., and D. B. Martin, "Sequential Deter-mination of Radium-226. Radium-228, Actinium-227. and Thorium Isotopes in Environmental andProcess Waste Samples," Analytical Chemistry. Vol.46, 1974, pp. 1742-1749,Radioassav Procedures jor liinvironen(mot Sampies,999-RH-27. USPHS, 1967.Shearer, S. D.. Jr. and C. W. Sill. "Evaluation of At-mospheric Radon in the Vicinity of Uranium MillT'ailinags.- iha/th Phy-sics. Vol. 17, 1969. pp. 77-88.Sill. C. W.. "An Integrating Air Sampler for Deter-nrination of Radon-222,'" Health Physics. Vol. 16,1969, pp. 371-377.Sill. C. W.. and C. P. Willis, "Radiochemical Deler-mination of Lead-21u in Uranium Ores and AirDusts.' .'Inal)vtical Chenistry, Vol. 49, 1977, l'p. 302-306.Sill. C. W., "Determination of Thorium andUranium Isotopes in Ores and Mill Tailings by AlphaSpectrometry," Analy-tical ChewnistrY, Vol. 49. 1977,pp. 618-621.Sill, C. W., et al., "Simultaneous Determination ofAlpha-Emitting Nuclides of Radium ThroughCalifornium in Soil," Analytical Chemistri', Vol. 46.1974. pp. 1725-1737.Sill, C. W., and R. L. Williams, "RadiochemicalDetermination of Uranium and the TrartsuraniumElements in Process Solutions and EnvironmentalSamples," Analytical Chemistry. Vol. 41, 1969, pp.1624-1632.Sill, C. W.. "Separation and Radiochemical Deter-mination of Uranium and the Transuranium Ele-ments Using Barium Sulfate," Health Physics. Vol.17, 1969, pp.89-107.Standard Mlethods for the Examination of Water andWastewater, 13th Edition, American Public HealthAssociation, 1971.S04.14-8