40CFRPart61                                         EPA 402-R-98-009
National Emission Standards
for Hazardous Pollutants
                        Background Information Document
            ADDENDUM: Risk Assessment for Research and Development
                             Uses of Phosphogypsum
                                November 1998
                      U.S. Environmental Protection Agency
                        Office of Radiation and Indoor Air
                            Washington, D.C. 20460


       The Environmental Protection Agency (EPA) is promulgating revisions to 40 CFR Part
61, Subpart R, National Emission Standards for Radon Emissions from Phosphogypsum Stacks.
This Background Information Document (BID) has been prepared in support of the final
rulemaking.  This BID contains an introduction, background of phosphogypsum, a general
description of phosphogypsum, scope of the reassessment of risks to laboratory researchers,
reassessment of the risks from 700 pounds of phosphogypsum, the assessment of risks from
multiple activities in the same laboratories, and the  summary of the  reassessment

       Copies of this BID, in whole or in part, are available to all interested persons. For
additional information, contact Eleanor Thornton-Jones at (202) 564-9773 or write to:
                    Director, Radiation Protection Division
                    Office of Radiation and Indoor Air (6602J)
                    U.S. Environmental Protection Agency
                    401 M Street, SW
                    Washington, D.C.  20460



                                  ^tefypna wtm wen eaofiiMd to stacks or
                 of aiaM. d» Apoey proonlpttd » NESHAP te ptmobocywa f 40

             wooldiaeecpoctt rifDifieittqD^^
A|ncyioiMQQtidirttepnbftitkmor«taafl^    It I99ath«A|«cyrin»d i limited
fflfi&btn of ft* pobik tan te m* of pbotpbocypnm In ^ricata«,kro*ia»«nxtioc,tDdin
                          ~h» mote of thiM risk nwHDRtti (EPA92) sbow tfatt
exponn to ttM pnsM ndbtfoa ad to ate ttd its teqr pradocts demiBato te risks fbr ail
                                   dag 10 pCU| or ton nfiom-226 to b« usad in
                                                      nqoir^Dntt, asd

 Gting unnecessary restrictions in the Agency's final rule, the Fertilizer Institute (TFI), on behalf of
 industry, again petitioned for reconsideration, and the Agency has Vfrminnl thai mother partial
 reconsideration is warranted. This reconsideration is limited to a reassessment of the risks for
 research and development activities *^TIAU^*^ in laboratories and certain details of the monitoring

In the 1990-1992 reconsidfrsrioB ruiemakmg. the Agency's risk iiinimrm of research and
development activities considered the ptKential risks that wouW be incuntd by research
with pboaphogypsum in a laboratory environment Bajed on a scenario where pbosphogypsum is
radiation from the poosphogypeum and inhalation of radon and itt decay products dominate the
potential risk. It also determined that limiting the cool Quantity of phosphogypson used fort
single research and development activity to 700 pounds (a single 55-gaUon dram) would assure the
lafrty tf tfaf irtftfftrn  TheWetiiiierUtatD«raeejci»orito
laboratory, given 700 pounds of nboepoogypsum wtth aRa-226 concentration of 26 pCi/g. were
estimaatd to be 9.1E-07 from exposure to the direct gsmrnm radiation and XIB^ from exposure
to radon and its decay products.

la inpetition for reconsideration, TH cooBsnds that the sceriario assumed by the EPA maasessing
the rista from laboxiiory e^oauM to phoapb^^
     tocy with poor ventilation (50 •» tree air votan» and 2 air dungee per hc«)f and ignores
basic labontory safety pcoc«inm. Inwviewiiigittriikaa«ttsinstrtmUgr«ofthe^
the Agency diicovwd that the risks from ea^o«»iondflnsnditidBC»yprakictidie4inEPA92
       cooeously b«ed on five 33-galloo drums of phogphogypsum (^pco«iniaiely 3,300
       I rather than a single drum being present in me taboninfy and the teeearcher being piesent
pounds) rather than a single drum being present
for more then 4.000 houa per year, ft atodetraMdthit white me aiiuinntk» that aU emanated
rvi^ is rdeaaed to the laboratory is overryujum^atr^
non-conservative as it does not address te po«lleJfoenMm|aeeapoaareif^
riitgte resesrrh tnri fJe^hT^^ *^l"t7t*'*g «•*»«*•*
 la light of to review, the Ajncy astod SCAA win

                     gn have been ma^ to bccw                        T^e labontory
 K«irio ittelf hu b« gxptndgd to aisea to pott^
        nent tctivitkt m t sii«le labors

  2. Reassessment Of The Risks From 700 Pounds Of Phosphogypsum

  As the current NESHAP permits the use of 700 pounds of phosphogypsum, regardless of
  radmm-226 content, m a single research and development activity, the first stefoftoe
  reassessment is to correct the errors and overly conservative assumptions identified in the
  previous assessment and re-estimate the risks from exposure to the direct gamma radiation
  and to radon and ,ts decay products.  As exposure to radionuclides via inlLation of ai borne
  dust was shown  not to be a Significant contributor to the overall risk in the previous
  assessment, the dust inhalation pathway is eliminated from this reassessment.


  The computer code MICROSfflELD (version 3.13) was used to calculate the direct gamma
  exposure rate. The  magnitude of the exposure and me resulting risk from direct gamma   .
  radiauon depend on  the source strength, the source geometry, shielding, the distance from
  he researcher to the source, and the duration of the exposure.  As the  NESHAP does not
  limit the radmrn-226 content of phosphogypsum  used in research and development activities
 26 pC,/g (the highest average radium-226 content of phosphogypsum (EPA89))  is assumed '
  '    P;r'lg radlum-226- 7°0 Pounds of phosphogypsum would contain about 8  3E-6 Ci of
 radium-226^  As  700 hundred pounds of phosphogypsum is the quantity that can be contained
 in a single 55-gallon drum, the dimensions of a 55-gallon drum (-60 cm diameter and 74
 cm in  height) are used for the source geometry.  No shielding beyond that provided by the
 phosphogypsum (bulk density of 1.5 g/cm3), the 55-gallon drum (mild  steel with a wall
 thickness of 0 121 cm),  and the air gap between the source and the researcher is assumed
 I he distance between the researcher and the source is assumed to be  1  meter.

 Based  on these inputs, and using the Taylor method to calculate build-up, the
 MICROSHIELD code estimates the gamma exposure rate to be about 2 5 prem/hour
 Assuming that a researcher spends about half time in the laboratory (1,000 hours per'year)
 Oie resulting exposure would be 2.5 mrem/year.  This  estimate is the same as  reported in '
 EPA92, and the resulting lifetime fatal cancer risk from a single year of exposure would be
 y + L d™ /.


The EPA uses an indoor exposure risk factor of 4.4E-8 per pCi/m3 for radon (EPA92)   To
assess me risk to researchers from radon and its decay  products/it is necessary to define the
size and ventilation characteristics of the laboratory in  which the activity is conducted,  the
radon emanation coefficient, and the mechanism  by which the emanated radon in the '
phosphogypsum is released to the air, and the duration of the researcher's exposure.

 In EPA92, a small laboratory with relatively poor ventilation (50 m3 free volume and 2 air
 changes per hour) was assumed; assumptions that were challenged as overly conservative in
 TFI's petition for reconsideration. While recognizing that a typical laboratory would likely
 be larger and have a higher the ventilation rate, the Agency believes that it is not
 inappropriate when developing a generic exemption to select parameter values which reflect
 unfavorable rather than typical exposure conditions.  Therefore, for the reassessment, the
 laboratory size and ventilation rate are changed only marginally.  The laboratory is defined
 as 4 m wide by 6 m long by 3 m high with a free air volume of about 58 m3. The
 assumption of 2 air changes per hour is retained.

 A radon emanation coefficient of 0.2 is used in this reassessment,  which  is smaller than the
 coefficient of 0.3 used in EPA92.  The revision reflects the dependence of the emanation
 coefficient on the moisture content of the phosphogypsum and the  Agency's belief that
 phosphogypsum used in laboratory research and development activities will have a
 significantly lower moisture content than phosphogypsum exposed  to ambient outdoor
 conditions. Similarly,  the mechanism for the release of the emanated radon from the
 phosphogypsum has been revised.  In EPA92,  the simple assumption was made that all
 emanated radon was released to the laboratory  air.  This would be possible if the
 phosphogypsum was continuously stirred or aerated or if dry phosphogypsum was spread
 widely throughout the laboratory.  While such  mechanisms are plausible, the Agency believes
that release of the radon by diffusion from its storage container (a 55-gallon drum) is a much
more likely mechanism.

To  estimate the concentration of radon in the laboratory, we assumed that the 55-gallon drum
containing the phosphogypsum is  left uncovered and that, on average, the drum is half full.
Under these assumptions, the rate at  which radon enters the laboratory air can be estimated
using the following equation taken from NRC84:
J =
                                              tanh  X
       104    = cnr/m2
       R      - pCi Ra-226/g phosphogypsum
              = bulk density of phosphogypsum, g/cm3
       E      = emanation coefficient, dimensionless
              = Rn-222 decay constant, sec"1
       D      = radon diffusion coefficient, cnr/sec
       X      = diffusion distance, cm.

  The following values were used for these parameters:
        R  -26pCi/g
        p  * 1.5 g/cnV
        £  -0.2
        X  « 2.1x10* «c-i
        O  »0.08cmV*ec
        X  «37cm.

 "Hie steady state room air concentration is fives by:

       AD  • drum cross*cfictional area, m?
       Q  » volumetric flow rate from room («aV)
       ft » air chsfign per second. sec*i
       V  • free room volume, m>.

Based on the values presented previously far thesiae«idveaci2siiQ&rsttoftelfboratQcyttbe
estimated cottteotrBJioa of rsdtt                          In ten&s of risk, using the same
radon risk coefficient (4.4E4 per pQAnJ) aa WM uaad in tha 1M2
 UOOO hours per ytat exposuit, the lifetime risk to t nsearcher from CM ytar of exposure at S3
pCi/nP would be about X7E-7.


Summing (he risks from the direct gamma exposure aad the inhalation of radon and its decay
products yields a lifetime risk per year of exposure of 1.2B-6. Under the same assumption as was
used in the 1992 reconsideration nikmaking that s rwearchcr might be exposed to these levels for
10 yean, the total risk would be about 1E-5.

                3. Assesanee* Of The Risks rtaMuttpfel^
Since the Ufetimt ri»k from ft tingle RAD actrvityinvolvinf TOOpeiadsofphoepho^psumisan
the teaasesamot was to evalustt the potential for exposurea that cewld occur if muWptoWUS
         ^» ^^^v^yj ln
Uboratories within the same ftcility. The following subsections address the potential risks from
multiple txpofurt*.


 Tl* exposure that could result from tfae conduct of omltiple nMarch •etivitiu within t single
 laboratoiy wiU depend upoo the tool quantity of phoepbot^psum presetf u the Ubc*atory. the
 «on^confirff«iocoftheSS-|^^                                         Asa
 single 55- gallon drum is estimated to result in risks tbom an ord« of magnitude Iwer than the
 presumptively safe lifetime risk level of IB-4, the pointial riikc from 10 55-fiUoa drun» (7,000
 pounds) of pnospbofvpeum m •«t*t"*<
3.1.1 pOttniij] fbf HpPJUB tD
                     tha ^Jr^T fJUBIM P*titfHf> frnm Hlf r*^P^tyP*OTn ^fpTWlf 'T™ rh^
stonco |eo0Mtzy dint is assumed. rnrThapnrpn^»MiHf pfovided by each coDfifmttooi and ite dote ntei to a worim tofgttd at 1 TTY**** from
the doMat dram.
Tl» dote rates for the two confifuntioos an rwf^coo^anbta, 16mceoVytfertha«Jcked
confifuratioo of 10 dnum, and 17 mrenVyr (or the V

           in the aane feUfey am also nlevmt to to detmnination of the quantity of
 thcint«narwtlUirecoo«ructodordad«bk^            In thfr in^wbeMe arm A
 reieaichei woridni in the caml lAonteyta to nlddli
 expooure from the ptoepbofypam In to 26 wrroundinj (8 a^acent. 9 above, and 9 below)
 labontoriee.  CNo» to aaaiffl$ik» of independent venting of to lAoratocieai^^
 additional riak from cxpoeura to r^on ickaaed in to other labonttciea would occur. Whikthia
 might loom noa* couervative, caounoo
conoenentka due to dilution with to air vote** in to cooidon.)
                         in tho pmma oqwuit, to thjck»a and materials audio
To evaluate the                                          	
coniauct tho floonaad walla in to facility would ham to be known. While btock walla and
poured concrete floon M typical of tfaeae typea of teilidoe, itmpk ibeet nek partition wi
wood finzned Soon cannot be locally diamiseed.  To avoid ti» uncertainty of the ihieldin|
provided by the building materials, a worn caae
expoiure hw bata made booed sinpiy oa to dtaocet becwen to recepcor ud tho vtrious
Given the dinwuiou cued above, and to fret that to pmmaexpoeure deoeeiet with the square
of the distance, the M«*»""m iacmee in the pmma exposure would be on the order of a fctor of
two. A two-fold iacreeie in the pmnariikrf
     would result in »UfWi»riik from a iifl$kye*r of w^^               Aasumin| 10
yean expocuit at thia level would yield a riak of 1.5E-4.

Figure 1:

H|ure 2: Qtaaary fat Muttpfc Drum Expoiun Scanario • V-Cccfi«nrttioa

Figure 3: Geometry tor Matt-Ubomofy Exposure Scenario

                          4. Summary Of The Rea«
                                    » condder tfa. iapm of multipta «ivi«iw within
 Bar a tinffe RAA ictivity uiiofTOO poundi of
          in the quantity ofphe»phofyp«in
                            .   _..           tobtpwaent in u» laboratory by a factor
of 10 (from 700 to 7,000 pounds) is uaed (o tvatoate the potential riaka from multiple RAD
activities being pursuedcoocumntiyintbeumelaboratory. Underthe least ftvocabkstorage
geometry (10 dnm» «ocued m a Vx»fl|i^^
single yen ctfupourt is ccunMcd to b, about 19E^ttonrofMveahiriwthMfortbe$iniic
jft«Bl^^ A^^^^^^J^          J                         "                            ™
^mT^l^^J ^^^^^^m^P^^m^J
      the potnfel for iDcmaed expnun dot to
                                                         conducted in mulUpk
laboratories ia the urafeility TO         UDdwtbeunltolyictoario that activitiet occur

from a sittgk 55-galloo dram of phoipbogypeum.


 EPA89  U.S. Environmental Protection Agency, Risk Aisesiments - Environmental Impact
         Statement NESHAPs fee HadfrrrnHHtt, Background Information Document * Volume
         2, EPA/33V149-006.1, Washington, D.C, September 1999.

EPA92  U.S. Environmental Protection  Agency, Potential Usea of Phosphogypsum tad
        Associated Riaka - Background Information Document, 402-R92-002, Washington,
        D.C, May 1992.
        Tailinp Cover Deaign. NUREQCR-3533, WaaUngmo, D.C, April 19M.