L

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                                   EPA-520/5-76-005
RADIONUCLIDE  ACCUMULATION


 IN A REACTOR COOLING  LAKE
             R.  L. Shearin



               R. J.  Lyon





  Eastern Environmental  Radiation Facility



            P. 0. Box  3009



       Montgomery, Alabama  36109
              July 1976
              ** v *. j. .» j  
              — "- THmMnf* --
   U. S. ENVIRONMENTAL PROTECTION AGENCY



       Office of Radiation Programs



          Waterside Mall East



          401 M Street, S.W.



         Washington, DC  20460

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                        FOREWORD
     The Office  of  Radiation  Programs  carries  out  a
national program designed to evaluate the exposure of man
to ionizing and nonionizing radiation, and to promote the
development  of  controls necessary to protect the public
health and safety and assure environmental quality.

     Technical  reports  allow  comprehensive  and  rapid
publishing   of   the  results  of  Office  of  Radiation
Programs' intramural and contract projects.  The  reports
are  distributed  to  State and local radiological health
offices. Office of Radiation Programs' technical and  ad-
visory  committees,  universities, laboratories, schools,
the press, and other interested groups  and  individuals.
These reports are also included in the collections of the
Library   of   Congress   and   the   National  Technical
Information Service.

     I encourage readers of these reports to  inform  the
Office  of Radiation Programs of any omissions or errors.
Your additional comments or requests for  further  infor-
mation are also solicited.
                                 W. D. Rows, Ph.b.
                          Deputy Assistant Administrator
                              for Radiation Programs
                           iii

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                         PREFACE
     The Eastern Environmental Radiation Facility  (EERF)
participates  in the identification of solutions to prob-
blem  areas  as  defined  by  the  Office  of   Radiation
Programs.   The  Facility  provides analytical capability
for  evaluation  and  assessment  of  radiation   sources
through  environmental studies and surveillance and anal-
ysis.  The EERF  provides  technical  assistance  to  the
State  and local health departments, in their radiological
health programs and provides special  analytical  support
for  Environmental Protection Agency Regional Offices and
other federal government agencies as requested.

     This study is one of several current projects  which
the  EERF is conducting to assess environmental radiation
contributions from fixed nuclear facilities
                            Charles' R. Porter
                                 Director
                 Eastern Environmental Radiation Facilitv

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                     ACKNOWLEDGMENT
     The authors acknowledge  the  invaluable  assistance
and  notable  cooperation  provided by the South Carolina
Department of Health and Environmental Control, Bureau of
Radiological Health.  The Bureau provided relative infor-
mation, consultation, and liaison services  and,  contrib-
uted  a  significant  amount of manpower and field equip-
ment .

     The cooperation and assistance of the Carolina Power
and Light Company  employees,  especially  those  at  the
H. B. Robinson Plant, is also acknowledged.  Their supply
of data resources, pertinent information and friendly co-
operative spirit helped to accomplish this work.   .  ••

     The  authors also recognize this report as a product
of  the  entire  staff  of  the   Eastern   Environmental
Radiation  Facility  (EERP).   Significant individual co-
operation and team'efforts contributed directly  to  make
this work possible.  .

     The  EERP acknowledges the capable consultative sup-
port and field assistance provided  by  the•  headquarters
staff  of  the Environmental Protection Agency, Office of
Radiation Programs,  Washington, DC.
                            v

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                          CONTENTS
                                                         Page
FOREWORD.,	................................ ,iii

PREFACE.	,	 iv

ACKNOWLEDGMENT	  v

ABSTRACT	 ix

SECTION I.    INTRODUCTION AND OBJECTIVES.................  1

SECTION II.   STUDY SITE.....,..,....,......,...,...»..,..  4

              Power Plant	  4
              Sources of Radioactivity Releases.......«.,,  6
              Lake Robinson	  7

SECTION III.  STUDY METHODOLOGY.	 . U

              Study Design................................ 11
              Lake Survey	 12
              Sampling	 12

SECTION IV.   WATER.	 17

              Lake Model	 17

                   Evaluation of the Model for Tritium.... 19
                   Downstream Dilution of Tritium,........ 26
                   Tritium in Well Water.,	 28

              Gamma Emitting Radionuclides	29

                   Cobalt.	29
                   Cesium................................. 32
                   Chromium.	,».	 35
                   Manganese.............................. 35
                  • Iodine	 35

              Observations and Summary.................... 37

              Additional Radionuclide Measurements,.».,,,. 37

                   Strontium~9 0	 3J
                   Gross Alpha and Beta Counting,,	 38

              Physical Measurements in Water	 41

                              vi

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                                                          Page

 SECTION V.    AQUATIC VEGETATION.	 44

 SECTION VI.   1ENTHIC          ........................... 51

 SECTION VII,   FISH	56

 SECTION VIII.  SUMMARY AND CONCLUSION...................... 58

               Behavior of Lake Components................. 58
               Surveillance Techniques*..*.....*......*.*.* 62
               Conclusion.	 64

               REFERENCES.	..........................65

               APPENDIX I	 A-l


                            TABLES

 1.  The distribution of tritium concentration within
     Lake Robinson.	..........	21
 2.  Paired *t" test of tritium concentrations in surface
     and bottom lake water	............................23
 3.  Observed  concentrations of tritium downstream......... 26
 4.  Tritium concentrations in wells,...................... 29
 5.  Statistical comparison of observed and predicted
     concentrations of cobalt-58 in Lake Robinson water.,., 31
 6.  Statistical comparison of observed and predicted
     concentrations of cobalt-60 in Lake Robinson water,,.. 33
 7.  Observed  and predicted concentrations of radioisotopes
     of cesium in Lake Robinson.	 34
 8.  Average chromium-Si, manganese-54, and iodine-131
     concentrations observed in Lake Robinson water........ 36
 9.  Gross alpha and beta activity concentrations in Lake
     Robinson  water.«.«.,...,*	,	,	......39
10.  Correlation of gross beta determinations with total
     specific  analyses	.,.40
11.  Average pH and solids content of Lake Robinson water.. 42
12.  Average stable element concentration in Lake Robinson
     water	...,.,.43
13.  Aquatic weeds observed in Lake Robinson	 45
14.  Environmental confirmation of radionuclides released
     in liquid wastes,	.,....,,...«,,,».»..,,,.,, 46.
15.  Radioactive cobalt in Lake Robinson aquatic vegetation 47
16.  Radioactive cesium in Lake Robinson aquatic vegetation 48
17.  Radioactive iodine and strontium in Lake Robinson
     aquatic vegetation.	••	.49
                                via.

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                                                           Page

 18»  Radioactive chromium and manganese in Lake Robinson
      aquatic vegetation...,«...»...»,,...».,.,	 50
 19.  Radioactivity in Lake Robinson sediments,»......«..,.» 52
 20.  Radioactivity in Lake Robinson fish	 57
 21.  Projected range of equilibrium concentrations at
      various lake flows.«.»*..»*.*.....»..»,*,**...*.*..... 60
 22.  Projected range of doses to an adult swimming 50 hours
      in expected concentrations.,...........»........*....» 61
                                FIGURES

  1»  Schematic of H, B, Robinson Unit 2 Power Plant,	  5
  2.  H. B. Robinson Unit 2 liquid waste disposal system..,.  ?
  3,  Geographical location of Lake Robinson	  9
  4.  H. B, Robinson site,..»»,,.........,....»....«,..	 10
  5.  Important radionuciide pathways to man via surface
      water.	 11
  6,  Components of reactor-lake system.........,.,.......,, 11
  7.  Environmental sampling sites in Lake Robinson	 14
  8.  Principle dynamic factors reacting within the Lake
      System	 17
  9.  Predicted and observed tritium concentrations in
      Lake Robinson.	........,,,....,.. 20
 10.  Observed and predicted concentrations of cobalt-58 in
      Lake Robinson.»,..,..	 30
 11,  Dredge sampling locations in Lake Robinson,.....,,.,.. 53
 12.  Radioactive cobalt in sediment  (position a),.,..,....» 54
 13.  Radioactive cobalt in sediment  (position b)........... 54
 14,  Radioactive cobalt in sediment  (position c)........... 54
 15.  Radioactive cobalt in sediment  (position d)........,., 55
 16.  Radioactive cobalt in sediment  (position e).»...*,...* 55
 17.  Radioactive cobalt in sediment  (position f)........... 55

A-l.  Gross power generated (7)	 A-2
A-2.  Liquid radioactive waste releases of tritium (7).,.,,.A-2
A-3.  Liquid radioactive waste releases - non-tritium  (7),.,Ji-3
A-4.  Lake Robinson discharge rates (6)...	.A-3
                                 vxn

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                        ABSTRACT
     In the utilization of a cooling lake for  a  commer-
cial  power reactor, low-level quantities of liquid waste
are released to the lake water.  Due to the retention and
recycling  of  water  for  condenser  cooling   purposes,
concentrations  of  radionuclides  can increase to levels
which are directly measurable in the water.  Such a  site
design  is  represented  by  the  H.  B.  Robinson Unit 2
operated by the  Carolina  Power  and  Light  Company  at
Hartsville, SC.

     For  a  4-year period lake water and other lake com-
ponents such as fish,  aquatic  vegetation,  and  benthic
sediments  were  sampled and analyzed to determine if any
long-terra buildup occurred.  Results indicated  that  the
lake   water   concentrations   followed  general  mixing
equations and that turnover rates in the individual  com-
ponents  of  the  lake  were too short to quantitate with
this study design.  This indicates that concentrations of
radionuclides in the lake would be primarily  a  function
of  parameters  such  as  radioactivity released and lake
flow for the previous year and essentially independent of
earlier parameters.  An estimate of annual external doses
to an individual utilizing the lake for recreation (i.e.,
swimming,  boating,  and  fishing)  would  be   about   5
microrem.

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                        SECTION I

               INTRODUCTION AND OBJECTIVES
     Nuclear power plants generate  large  quantities  of
radioactive  wastes.   These wastes are primarily fission
products of the fuel ands secondarily activation products.
The majority of the fission products are retained  within
the fuel elements until removed during fuel reprocessing,
A relatively small quantity of fission products and acti-
vation  products accumulate in the primary coolant.  Most
of this radioactive waste is concentrated and removed for
off-site shipment and controlled disposal.   Small  quan-
tities  of  low-level  radioactive wastes which cannot be
efficiently processed or contained are  released  to  the
environment, in liquid and gaseous forms.

     Quantities  of  radioactive  wastes  released to the
environment have generally been much  below  the  10CPR20
limits established by the U. S. Atomic Energy Commission,
currently  the Nuclear Regulatory Commission (NEC).  More
recently, stricter dose  and  release  design  objectives
have  been  imposed  in the form of Appendix I to 10CFR50
(1),  In general, these design  objectives  are  about  a
factor of 100 below 10CFR20 (2) limitations and represent
a  greater  compatibility  with  actual reactor operating
experience.  With the proliferation of nuclear  power,  a
point  of  major  concern is the long-term buildup in the
environment  of  long-lived  radioactive  wastes.    This
buildup  will occur when the rate of accumulation exceeds
rate of  disappearance  for  a  particular  radionuclide.
Such  action  increases the concentrations of radioactive
waste in one or more compartments  or  locations  of  the
environment.

     Many  nuclear  power plants- utilize large volumes of
water to disperse low quality waste heat from their power
system.  These volumes of  water  are  also  conveniently
available  for  dilution  of small amounts of radioactive
wastes which are considered of such low hazard  potential
as  to  be  impractical  for holding in radioactive waste
storage.   Dilution  further  reduces  the  environmental
hazard.   A  common reactor site design has been to use a
river or estuary for water source and disposal.   Such  a
system  releases radioactive materials to the environs in
such dilute concentrations  that  positive  environmental

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measurements   are   extremely   difficult  with  current
analytical techniques.

     A second type of siting design is the impoundment of
a stream to create a large reservoir.  The reservoir acts
as "both the cooling water source and the receiving  water
body  for the'liquid radioactive waste discharges,  water
is circulated through the power  plant's  main  condenser
and  the  lake  several  times  before it continues down-
stream.   For  this  design,  concentrations   begin   to
approach  the  detectable  limits  of the best analytical
methods available.  This siting design was chosen in this
study to provide data yielding a more  definitive  deter-
mination of radionuclide behavior. - The determination can
produce  a  reasonable basis for projecting environmental
cost in terms of radiological contamination of the  envi-
ronment .

     The  particular  site  chosen  for  the study is the
H. B. Robinson Plant near Hartsville, SC» operated by the
Carolina Power and Light Company,  The plant consists  of
a-   185  MWe  coal-fired-  unit  and  a  739  Mw"e  (gross)
pressurized light-water reactor  unit.   The  plant  uses
cooling  water  from a reservoir formed by a dam on Black
Creek.   The  resultant  reservoir  interfaces  with  the
larger  aquatic  system  of Black creek through the creek
inflows and the dam overflows.  Such limited  connections
facilitate  a  demarkation  of  the  system  under inves-
tigation.

     The specific objectives of this study were:

     1.   To  identify  and  quantitate  any   long-lived
          radionuclides  released  to  the environment by
          the nuclear plant;

     2.   To determine the concentration of  such  radio-
          nuclides    in   representative   environmental
          samples of the lake system;

     3.   To determine the rate of  radionuclide  buildup
          within  the  various  components  of  the  lake
          system;

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     4.   To extend any observed  buildup  rates  through
          the  expected  life  of the reactor in order to
          evaluate the impact of the power plant  on  the
          general public and the environment.

     The study design was based on the approach which was
applied  to man by the International Commission on Radia-
tion Protection   (ICRP)  (3),   The  ICRP  described  the
existing  quantity  of  radioactivity  in man as his body
burden and then expressed the content  within  particular
organs  in  terms  of fractions of the total body burden.
These fractions were then accepted  as  equilibrium  con-
stants  and constituted a simple mathematical model which
became the  basis  for  various  Radiation  Concentration
Guides.   In  a  lake  system it is recognized that these
fractions are not constants but dynamic  variables  which
change with time due to external forcing functions.  This
study was designed to identify and describe the principle
forces  that  govern  the  transfer and storage of radio-
nuclides in the lake compartments of water, flora, fauna,
and benthos.  Their actions are formulated  in  a  mathe-
matical expression such that transfer coefficients can be
determined for a given set of forcing function parameters
such  as  waste  release  data and lake flow data.  Using
time increments of at least a month,  erratic  day-to-day
variations were smoothed to a general trend curve.  Thus,
a macroscopic analysis rather than a microscopic analysis
was  chosen  which would then supply information directly
applicable to a dose-to-man model.

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                       SECTION II

                       STUDY SITE
•jjower JPlant

     The  H=  B.  Robinson  electric   power   generation
facility  at  Hartsville,  South  Carolina,  is owned and
operated by the Carolina Power and  Light  Company.   The
facility  is  composed  of  two units:  Onit 1, a  185 MWe
fossil fuel plant and Unit 2r a 739 MWe pressurized water
reactor.  Unit 2 constitutes the entire source  term  for
radioactive  materials  released  in  this  study.  A low
power operating license  (<5MWt) was issued July 31 , 1970.
Initial criticality was achieved September 20, 1970,  and
authorization  to  operate  the unit at full power  (2,200
MWt} was obtained from the AEC on September 23, 1970.  H.
B. Robinson Unit 2 was declared to be in commercial oper-
ation on March lf 1971  (See figure A-1, appendix I)
     Westinghouse Electric Corporation provided both  the
Nuclear  Steam  Supply  System   (NSSS)  and  the turbine-
generator system.  The NSSS includes a pressurized  water
reactor, the reactor coolant system  (RCS) , and associated
auxiliary fluid systems (figure  1}".  Although designed to
initially  produce  2r200  MWt  (739 MWe gross), the power
train for H. B. Robinson Unit 2  is expected to  be  ulti-
mately capable of producing 2,300 MWt.

     The  reactor  core  features  a typical three-region
cycled core.  Fuel rods are cold-worked  zircalloy  tubes
containing   slightly   enriched   (1,85  to  3.10  weight
percent)  uranium  dioxide  fuel.   A  total  of   79,561
kilograms  of uranium dioxide fuel is loaded into the 157
fuel assemblies contained in the core  (4) .

     Three  closed  but  interconnected  reactor  coolant
loops , each containing a reactor coolant pump and a steam
generator,  comprise  the  bulk  of  the  reactor coolant
system,  A pressurizer, a pressurizer relief  tank,  con-
nective piping, and instrumentation are also provided.

     Auxiliary  coolant systems include the Residual Heat
Removal System (RHRS) , the spent fuel pit cooling system,
and the component cooling system.   The  RHRS  cools  the
reactor  coolant  system during shutdown procedures while
the component cooling system cools  the  reactor  coolant

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system  when  shutdown is accomplished.  During the power
operation the component cooling system cools the  reactor
coolant  system  letdown  flow to the Chemical and Volume
Control System (CVCS)  as well as other primary plant com-
ponents.  Other auxiliary fluid systems exist to  provide
a safety function and plant performance information (sam-
pling systems) .

     The  turbine-generator system is the secondary cool-
ant system and is composed  of  the  shell  side  of  the
vertical  0-tube  steam generators, the turbine generator
equipment, two condensers, feedwater apparatus, and asso-
ciated piping.  Steam produced in the steam generators is
sent to the  turbine-generator  to  produce  electricity.
Steam  from the turbine is condensed and deaerated at the
condenser,  heated, and pressurized  by  'the   feedwater
system, and routed back to the steam generators.

     The  excess  heat of condensation from the secondary
coolant loop is transferred to lake water'  using  a  heat
exchanger  as  a steam condenser in the coolant loop fol-
lowing the last generating turfcine stage.  This is accom-
plished by removing lake water from near  the  dam,  cir~.
culating  it through a heat exchanger at rates up to 29.7
m3/sec and returning it to the upstream  portion  of  the
lake through a 6,7 kilometer cooling canal.
       Nuclear Steam Supply
Station (NSSS) Turbine
Steam Generator
Reactor ^S^^~*N
Vey^ Iff
•
Core jta

\ ******
'„..
\ 1 Typical , i
^- — •/ Coolant i "*"b
Loop | /
(total = 3 loops) (F
|
Steam
1
Generator System
.. Turbine
r>CL^
" L
" ~ — | Generator

•J^ 1
J To Lake
I r 	
(
}! F i : 1
f Condenser
-r-r-z-^ L
7 1-3^
"eed'A'ater i
Pumps &, 1
Stater/
'——Primary 	 Secondary
Coolcnt Coolant
! t
ler i :
f'
Lake Cooling1-? \V: ,
V¥ater . / Cooling \ i
I Water J i
\Pumps /
", ,
Wat
Cooiing
tr
Figure 1.  Schematic of H. B. Robinson Unit 2 power plant

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 Sources  of Radioactivity  Releases

      As   fuel   burnup occurs  fission products  increase  in
 the uranium oxide matrix  which serves as  an initial  con-
 tainment barrier.   The zircalloy cladding of the rod pro-
 vides the  next  barrier to  fission product waste trans-
 port. A third barrier to its  release is  the  enclosed
 primary   coolant loop which also provides neutron modera-
 tion and heat  transfer capability  to the  power generation
 loop. The primary coolant loop scavenges  much  of the
 fission   product  leakage  and  much  of   the  radioactive
;neutron  activation products  that   become  transferrable.
 The  water  in  this   loop also contains  a chemical shim,
 boric acid, to provide for  control  of   the   additional
 reactivity  within the core.   The primary coolant circu-
 lates through  the core in three   parallel distribution
 systems,  each  driving  its  own steam generator.   Decon-
 tamination and chemical adjustment controls on  the  pri-
 mary  coolant  are provided by the  Chemical Volume Control
 System (CVCS)  which utilizes  ion exchange  techniques  to
 control  and reuse the water as well as to provide-make-up
 water for the primary coolant loops.   A  single CVCS sup-
 plies and maintains the three primary loops.   The primary
 loops operate  at about 154.1  bars  and  are  driven  by   a
 pump in  each loop.

      Sources  of  liquid   waste occur as minor and major
 leaks develop  in seals, flanges, and other necessary and
'inadvertent openings.    Shutdown, opening, and repair  of
 the system and its supportive equipment,  also/  provide   a
 mechanism   for  release   of   liquid  radioactive  waste.
 Equipment leakage is  collected  in  the  reactor  coolant
^drain tank and  is  usually  routed to the 'boron recovery
 subsystem of the CVCS.    Liquids  from the CVCS  holdup
 tanks are  pumped through •  ion exchangers (for lithium,
 cesium,  molybdenum, and yttrium removal),  a filter,  and
 the  gas stripper.  Degassed  liquid,from  the gas stripper
 is  then  evaporated in the boric acid  evaporator  conden-
 sate  demineralizer  and   filter,   and accumulated in the
 CVCS monitor tanks.   This liquid may then be sent to the
 primary   water  storage tank  for reuse, to the  evaporator
 condensate demineralizers for the  CVCS holdup   tanks for
 further   treatment, or it may be discharged.   Miscellane-
 ous leakages are collected in the   containment   sump and
 usually   routed-  to  the   waste holdup tank in  the liquid
 waste disposal system (figure 2).   These  leakages   amount
 to  only  a few  liters  per  minute

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                                  to dfvmmlng facility
Figure 2.  H, B. Robinson Unit 2 liquid waste disposal system
     The secondary coolant loop which is a water-to-steam
loop contains lesser quantities of radioactivity than-the
primary  loop.   This  radioactivity  is  the  result  of
inadvertent leakage across the barrier between  the  pri-
mary  and secondary systems.  The secondary loop contains
323,300 liters of water at 2200 MWt operation.  Since the
water chemistry in the secondary  loop  is  closely  con-
trolled  in a manner similar to that of the primary loop,
a continual amount is removed.  Although  the  concentra-
tion of these radioactive wastes may be"less than that of
liquids  from the primary coolant, the larger volumes may
make this release significant.  There are  other  miscel-
laneous liquid radioactive waste sources.  These are col-
lectively  summarized  in figure 2 and include additional
locations such as  radioactive  laboratory  drains,  fuel
handling  building  drains,  and  laundry  and hot shower
drains,  all of these sources can be fed into the  liquid
waste .disposal system.

Lake Robinson

     Lake  Robinson is an impoundment of Black Creek com-
pleted fcy Carolina Power and Light  Company  in  1957  to
provide  a source of cooling water for the H. B. Robinson
power production facilities.  The impoundment is  located
in  the  southern  sand  hills  region  of northern South
Carolina and detains water from a watershed of 443 square
kilometers,

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     The lake has a north-south orientation with the  dam
located' at the southern end of the impoundment.  The 911
hectare lake contains about 3.8 x 107 m3 of water.   This
volume  is  considered  constant since its variations are
generally less  than  20  percent,  or  well  within  the
experimental error of this study.  Forced evaporation due
to  the thermal loading on the lake effects loss of water
at rates of ,4 to .6  m3  per  second.   Water  discharge
varies  seasonally  relative  to  rainfall.   The average
discharge rate is 4.8 m*  per  second,  but  this  varies
daily from low rates of .74 m3 per second to higher rates
of  31 m3 per second (ft).  This varying discharge rate is
a major parameter in the racliomiclide budget of the  lake
(See figure ft-4 of appendix I)»  The discharge flows into
a smaller impoundment,  Prestwood Lake, about 8 kilometers
downstream.   Prestwood  Lake  supplies  water to several
industrial users for  manufacturing  processes.   Neither
Prestwood  lake  nor  downstream Black Creek is used as a
supply of drinking water.

     Lake  Robinson  was  constructed   on   land   which
contained  primarily  second  growth pines, bottom lands,
swamp, and some hardwoods.   The  shoreline  consists  of
grasses, pine seedlings and granite fill used for erosion
control.   The  lake  is approximately 12 kilometers long
from north to south with a mean width of .8 kilometers.

     The lake has a basin 12 to 18  meters  deep  at  the
southern  end  near  the  dam.  The old creek 'bed forms a
twisting channel 6 to 8 meters deep near  the  basin  but
only  3 to 4 meters deep near the bridge at the upper end
of the -lake.  On either side of the channel lie extensive
"shallow" flats which cover significant areas with depths
of 1 to 2 meters.   North  of  the  bridge  the  area  is
flooded  hardwood land  with a treacherous bottom littered
with'decaying debris such as stumps and dead trees.   The
feedwater  of  Black Creek passes through several bogs or
marshland areas acquiring the  "brown  water"  coloration
from the humic acids of these areas.

     Lake  Robinson, therefore, has attained the charac-
teristics of a "bog lake" or "trown water"  lake  as  de-
scribed by Ruttner (5),  Such characteristics include low
nutrients,  low pH, and high discoloration.  The biologi-
cal productivity of the lake could,  therefore,  be  pre-
dicted as being relatively low.

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     Lake Bobinson is available to the general public  and
is  used for recreational purposes such as boating, water
skiing, sport fishing, and  swimming.   Numerous  private
residences  have  been  built on the eastern shore of  the
lake.  Figure 3 and figure 4 present the location and  the
arrangement of lake* creek flow, and reactor.
                                              Atlantic Ocean
  Figure 3.  Geographical location of Lake Robinson

                           9

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             H, B, Robinson
                Units:
site  boundary
                                 Lake  Robinson
                                 dam

                                Black Creek
    Figure 4,  H« B.  Robinson site

                     10

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                       SECTION III

                    STUDY METHODOLOGY
St.ud% Design

     The approach to this study began with a  generalized
model  or  grouping  of the components of the lake system
and the dominant environmental factors  interacting  with
the   system.    Figure   5   represents   the  important
radionuclide pathways to man selected as  the  bases  for
the  design  of  this  study.  The model is applicable to
liquid releases to most,  aquatic  ecosystems.   Figure  6
depicts  the salient relations of this particular system.
From such a grouping the study design  was  developed  to
either  measure or infer through simulation, the signifi-
cance of each particular interaction or  component  stor-
age.   The  stepwise approach was to use observed data to
guide subsequent alterations in the study design so  that
system  characteristics would emerge as the research pro-
gressed.  An example  of  this  was  the  utilization  of
tritium  data  to  verify physical attributes of the lake
such as lake volume and mixing properties.

radioactive
material
i

surface
water




<•»!•*
sediment

aquatic
plants
U« 	 , 1 1
~* 1
t 	 9,
•»• ihaestfon 	 	


aquatic
animals

\
j




Figure 5.
Important radionuclide pathways to man via surface
water
plant I
I plant
discharge
creek
water
1
lake
water
!
lake
efecharge
lake
flora
2

L
r
Iteke
benthos

lake I
fauna I

    Figure 6.  Components of reactor-lake system
                          11

-------
     Lake-flow data  from  the  United  States  Department  of
 Interior   (6) ,   physical  ' parameters used in  the  environ-
 mental  evaluations  .by   the   Carolina  Power  and   Light
 Company   (4) ,   effluent release data,  and other operating
 data as reported by  the Company |7)  were vised to  develop
 a   dynamic   picture  of the system.   This dynamic picture
 was evaluated  by a series of  10 surveys  spaced over  a  4-
-•year  period.    Thus,  the effort was similar to  taking a
 series of  10 in-depth, still  photographs over a 4-year
 period  to   represent a complex, dynamic system in motion
 on  a macroscopic scale.   The  intent  was  to  determine con-
 tent of  radioactive pollutants  within the  components
 represented  in  figure 6 and observe the effect  of  flows
 or  transport between the  components,

 L_ake Survey

     Lake Robinson represents the  focal point  of   this
 study.   In  order   to  acquire an  adequate  radiological
 "portrait" of  the lake, an in-depth  field survey  protocol
 was developed.   Each element  of the  survey  was chosen  to
 provide  data  on the radionuclide content of  an ecosystem
 component and  associated  parameters  which  might  monitor
 physical  and   biological actions within the  system.  The
 sampling strategy was to  collect  numerous  small volume
 samples  for  radionuclide analysis  of readily detectable
 nuclides and fewer but larger volume samples   for radio-
 nuclides  which  occurred  in  smaller concentrations and
 were more difficult  to detect.  The  analytical data was
 correlated   with analyses of  reactor  waste streams and
 lake flows.  The surveys  were spaced from 3 to 6 months
 apart  to provide adequate time increments  such that mea-
 surable changes could occur.
     The sampling protocol was  directed towards determin-
ing the radionuclide content of the water,  benthic   soil
and  sediments,  aquatic  flora,  and aquatic fauna.  The
primary effort was to sample for positive indications of
radioactivity.   To  implement  the protocol, a team of at
least four EPA field survey members was  required,  along
with  the  assistance of Carolina Power and Light Company
personnel and two technicians   from  the • South  Carolina
Department of Health and Environmental Control, Bureau of
Radiological  Health,   The  surveys  were conducted  on  3
successive days and  required   the  use  of  a  specially
equipped 4.3 meter outboard motor boat and a varied quari-
                           12

-------
tity  of sampling equipment arid operational gear.  In the
course of each sampling trip, approximately 100  environ-
mental  and  in-plant  samples  were taken.  The sampling
program  required  that  not  only  the  lake  itself  be
accurately  represented, but also that effects downstream
be identified, transport to  the  underlying  aquifer  be
evaluated,  and background radioactivity data be obtained
either from points upstream and unaffected by the reactor
or from a nearby lake of similar nature, also  unaffected
by the reactor.

     The  major emphasis in the survey was the evaluation
of the lake water itself.  To accomplish this, three sam-
pling systems were established to provide for varying re-
quired sensitivities for the different radionuclides  and
for  better  determination of physical distribution about
the lake.

     The first system was established for analyzing  tri-
tium  in the lake water.  Since it was expected that tri-
tium concentrations would exceed the  minimum  detectable
limits of .2 nCi/liter after the reactor had operated for
about  9  months (8)  a simplified analytical method could
be used.  This permitted the analyses of a  large  number
of  samples.  The system for tritium samples consisted of
23 lake sampling locations.  Nineteen of these  locations
were  on the center line of the lake beginning at the dam
and extending  uplake  with  a  separation  of  about  ,5
kilometer.   Four  sites  were located on a cross section
line of the lake at the sixth site north of  the  dam  or
about  2.7  kilometers.   This  provided  five  locations
evenly spaced across the lake from shore  to  shore.   At
each  location  two  1-liter samples were drawn, one near
the surface and one just above the bottom  (approximately
.5 meter).  In addition to determining tritium concentra-
tions,  this  system  was designed to provide information
relative to lake mixing and  lake  volume.    The  1-liter
sample  size  was  chosen to provide adequate quantity of
samples for replicate analyses.    The  normal  analytical
procedure required 100 milliliters of water per analysis.

     The  second water sampling system consisted of eight
sampling sites up the center of  the  lake.   The  sample
size  for this set was 19 liters.   The samples were drawn
from 1 to 2 meters deep.  The sites began at the darn with
three in the lower lake area at  .8  kilometer  intervals
and  five  in  the upper lake area at .8 kilometer inter-
vals, one centerlake opposite the mouth of the  discharge
                          13

-------
canal,  two  north   of   that point, and two south of that
point.  This   sample set  provided  measurements  at  an
intermediate   level  of  sensitivity for all gamma emitting
radionuclides  as well as strontium-89, strontium-90,  pB,
stable elements, and dissolved and undissolved solids.

     A  third  sampling system was established to provide
maximum feasible  sensitivity  of  measurement  of  gamma
emitting  radionuelides  in  the  water by using a sample
volume of 200  liters.   These sampling sites were:  two in
the lake center .8 kilometers above and below  the  mouth
of  the  discharge   canal,  two in the lower lake ,8 kilo-
meters and 2.^ kilometers north of the dam  at  the  lake
center, one at the cooling  water intake, one at the cool-
ing  water discharge to the canal and one at the mouth of
the discharge  canal.  A background sample  of  this  size
                     This was  initially drawn from Black
                     1   highway  bridge.   Later  it  was
                     the background  sampling  point  to
                     This small lake had  chemical  char-
                      to Lake  Robinson, but received no
was  also   taken.
Creek at the  U.   S.
decided .   to   move
Beaverdam  Millpond.
acteristics  similar
surface drainage front the  H.   B.
figure 7 on sampling locations).
                                   Robinson  Unit   2   (See
  scale
  1 km,
 I	;——«
                                                          D
                                                   visitors center
                              discharge canal

          "bridge

                         legend

           a = 200 liters of water for resin cartridge

           0=1  liter  of water for tritium analysis

           A = 19 liters of water, sediment,

                 vegetation is collected where  available in Sake


Figure 7.  Environmental sampling sites in Lake Robinson

                            14

-------
     Benthie  soils or silt samples were collected with a
Peterson dredge at the eight locations selected  for  the
19-liter  water  sample system.  The dredge "bite" repre-
sents .078 m*.  A single sample represented two bites  or
.156  m2.  The sample was dried, weighed, and analyzed by
gamma spectroscopy (gamma scanned),

     Aquatic vegetation was  collected  in  the  littoral
areas as near as possible to the eight locations selected
for 19-liter water samples 'and benthic soil samples.  The
priority  of  choice  of  -vegetation was submerged weeds,
floating weeds, and emergent  weeds,   of  the  submerged
weeds,  Myriophylum  was one of the available species and
Najas flexilis  was  another.   Of  the  floating  weeds,
Braesnia was most commonly selected.  Assistance in plant
identifications  was  provided by the Biological Services
Branch of  the  EPA  Environmental  Research  laboratory,
Athens,   Georgia,    These   were  washed,  drain-dried,
weighed, gamma scanned, ashed, weighed, and gamma scanned
for the second time."

     Fish samples were supplied  by  the  South  Carolina
State  wildlife  Department and South Carolina Department
of Health and Environmental Control  personnel  who  used
electrical  shocking  to  collect  fish.   Because of'the
techniques employed and because of a  low  population  of
fish,  significant  sample  sizes  were  not available to
correspond  with  each  field  trip.   When   fish   were
available, they were separated into sets of species, each
set  being counted separately.  Large individual fish and
large numbers  of  single  species  were  separated  into
viscera, bone, and flesh;  then, analyzed,'

     At  the  inception  of  the  study,  the power plant
reported liquid releases in curies of tritium  and  "non-
tritium"  on  a  monthly  basis.   This hampered isotopic
evaluation; therefore, with the  assistance"  of  Carolina
Power  and  Light, liquid wastes samples, proportioned to
the quantity released, were  collected  and  analyzed  to
estimate isotopic releases.  By July 1972,  Carolina Power
and  Light  Company began reporting specific radionuclide
releases.  After an overlap  of  procedures  demonstrated
close  agreement  between composite release estimates and
the power plant's reported releases, the composite system
was dropped in January 1973.

     Other in-plant systems were sampled in order to pro-
vide a potential insight as  to  the  sources  of  liquid
                          15

-------
wastes  within  the  plant.   This  included samples from
available sampling points in the primary  coolant,  CVCS,
secondary system, and other miscellaneous systems such as
the component cooling water system.  Information at these
points  gave  a  more  complete picture of the extent and
significance of these systems in total  liquid  releases.
All  in-plant  samples  were  taken by plant personnel in
accordance with their established procedures, with sample
size determined by expected concentrations and  available
sample quantity.

     In  addition  to  these  major  sampling procedures,
several peripheral programs were implemented  to  provide
information  connecting the lake system, the reactor, and
the surrounding environment.  One  such  effort  was  the
sampling of 10 private drinking water wells at residences
bordering  the  lake.   One-liter  samples were taken for
tritium analyses to detect any significant transport from
the lake to the water supplying aquifer. 'Additional sam-
pling was initiated downstream on Black Creek  to  deter-
mine  the  dilution  and  dispersion  as the flow travels
downstream'.  Midway through the study, Carolina Power-and
Light Company suggested that  a  drainage  ditch  leading
from the reactor directly to a point below the dam should
be monitored.  Subsequently, water and vegetation in this
ditch  were  sampled when available.  The effects of flow
down the cooling canal and through two side pools on  the
cooling canal were also monitored.  Water, sediments, and
littoral vegetation were sampled at this location.
                          16

-------
                       SECTION IV

                          WATER
Lake Model

     The  simplest  description of the turnover of radio-
activity in the  lake  is  one  derived  from  the  major
physical  aspects  of  the  lake  system.   The  model is
similar to a continued insertion of a radionuclide into a
tank with an inflow  and  a  discharge  rate.   Figure  8
represents this in block diagram form.
                     evaporation
            creek flow
                            lake discharge
                    reactor wastes


Figure 8.   Principle dynamic factors reacting within the
           Lake System

     The mathematical expression for the change in radio-
activity in this lake would be as follows:
da
dt

Where:

dA
dt

A

P


Qflow

^evap
            =  P -
                     V
            ~  Fate of change of radioactivity in the lake


            =  Radioactivity in the lake

            =  Rate radioactivity is added to the lake

            =  Rate of water discharged from lake

            =  Bate of evaporation from the lake

            =  The radionuclide decay constant

            =  take volume
                            17

-------
     In  order to reduce the expression to a more manage-
able form the effective removal rate is defined as:

     xeff = Qflow  +  Qevap  +  xi
            ~~~VV

     Thus the differential equation is expressed as:

                                               (Equation 1)

     |f  -  -*.ff.tA


     This equation integrated becomes:
     &0  =  Radioactivity in the lake at the beginning of
            time period "t"

     h±  =  Badioactivity of radiomielide "i" in the lake
            at the end of the period

     Expressing this in terms of concentration of an  "i"
radiomielide, the equation becomes:

                                             (Equation 2)

     C±  =  Pj       (l-e"xeff,it) + C0e~Aeff,it

                  i
     It  should  be  observed  that  the equation and its
application implies several assumptions:

     1.   The lake  volume  is  assumed  constant.   This
assumption  seems reasonably valid based on lake data (9)
which shows the lake level has a limited variation.   The
value used was 3.8 x 107 m3.

     2.   The  radionuclide  release  rate  is   constant
throughout  the  period of concern.  This was a necessary
assumption due to the lack of records  on  times,  dates,
and  quantities  of  releases.  The official records show
total releases for the  month  and  do  not  detail  when
specific  releases  occurred.   In general these releases
were of sufficient number and quantity to  be  reasonably
approximated by the constant rate assumption.
                          18

-------
     3,   Rapid mixing occurs in the - lake  to  establish
uniform  concentrations.   This  is  not  an unreasonable
assumption since the cooling water pumps  move  the  lake
water at 29,7 m3/see through the main condensers and down
the  discharge  canal as compared to an average lake dis-
charge of ^.8 m3/sec.

     tt.   The loss or removal from  the  lake  by  evapo-
rative  transport  was  applicable  to tritium only.  For
other radionuclides this did not constitute a significant
radionuclide   transport   mode   and   was,   therefore,
neglected,

     5,   There is no other significant storage or escape
route from the lake water.  This assumption is apparently-
valid for tritiums however, possible departures for other
radionuclides will be discussed later.

     Evaluation of the Model for Tritium

          Tritium appeared to be a natural tracer for the
     evaluation of the water turnover  model  represented
     by  equation 2.  The primary form of the tritium was
     HTO and, therefore, the  tracer  behaved  chemically
     and  physically  like  water.   Additionally, liquid
     releases would be expected to be in sufficient quan-
     tities that the resultant concentration in the  lake
     could be easily measured by sufficiently simple ana-
     lytical procedures so that numerous samples could be
     processed  to  provide  a  solid broad data base and
     increase power of the statistical tests.

          The model is  compared  to  the  observed  lake
     values  over the 4-year period to observe the corre-
     lation between the predicted  and  observed  values.
     Figure  9  shows a comparison of observed and calcu-
     lated values for the duration of the study.

          The calculated values were determined using the
     release rates  reported  by  the  company  in  their
     operating  reports  (7)  for the respective month and
     an initial concentration as calculated for  the  end
     of  the previous month.   The flow data was that pro-
     vided  by  the  United  States  Department  of   the
     Interior,  Geological  Survey,  in Columbia, SC, for
     the gaging  station  102130910  located  305  meters
     below  the  Lake Robinson dam (6)«  The mean monthly
     flow observed for the specific month in question was

-------
   used.   The concentration  was   determined  from  the
   selected  month's  data  and   plotted, as the concen-
   tration in the lake existing on the first day of the
   next month.
U  2
                                                     legend

                                                    predicted

                                                  * observed
       1971
1972
1973
1974
   Figure 9.  Predicted and  observed tritium concentrations
              in Lake Robinson
                        20

-------
                                  Table 1

      The distribution of tritium concentration within Lake Robinson

                                  nCi/1
   Trip    No. of
   Date	Samples  Mean
Max     Min
S.D.
            Percent
            Observations .
Analytical  in Analytical
Range
I
12/01/70
II
03/09/71
III
09/21/71
IV
03/14/72
V
07/10/72
VI
10/31/72
VII
02/06/73
VIII
06/05/73
IX
11/05/73
<
46
46
46
43
41
50
41
43
43
43
<.2 <.2 <,2 ± .2
•28 .4 <.2 .11 ± .2
•47 .6 .3 .08 ± ,2
1-69 1.9 1.1 .14 ± .2
2-18 2.5 1.1 .22 ± .2
3-05 3.4 1.6 .33 ± .2
1.15 1.4 .4 .28 ± .2
•61 -9 -4 .10 ± .2
3-70 4.8 2.9 .27 ± .3
2.65 2.9 2.2 .14 + .7
100
100
100
91
93
72
78
95
88
as
05/14/74
                                    21

-------
     Two sections of  the  figure  show  significant
disagreement  between  the  observed  and  predicted
values.  The  period  of  May-to-September  of  1971
shows   observed   concentrations   from  .5  -to  .7
nCi/liter as compared "to predicted values  of  about
.2   nCi/liter.   These  observed  values  represent
duplicate analytical runs on separate dates.  Unless
contamination of the sample occurred in  the  field,
there  is  strong  indication that they are correct.
During the time period from May  29  to  August  20,
1971, the reactor was shut down for extensive gener-
ator  repairs  as well as for other numerous mainte-
nance operations.  It might be-reasonable to suspect
that recorded releases were in error.  Another plau-
sible explanation is that  extensive  stratification
was  occurring  due  to the reduced operation of the
circulating cooling water pumps during the shutdown,
Such reduction undoubtedly  would  affect  the  lake
mixing  action and consequently reduce the effective
mixing  volume  of  the  lake.   Consequently,   the
observed  concentration  would  appear  higher  than
expected.  This effect, however, would show a faster
turnover rate which was not apparent.

     A second significant  discrepancy  occurred  in
February 1972 where predicted concentrations reached
3.4  nCi/liter  and  observed concentrations reached
about 1.8 nCi/liter.  It is believed that this is  a
question  of  timing  of  releases  and  the  month-
grouping method of handling  the  data.   Thus,  the
peaking  described  by the model could have occurred
between or prior to the two 1.8 nanocurie samples.

     Aside from the aforementioned sections  of  the
study,  the  predicted  and  observed  concentration
values demonstrate excellent agreement.  Such agree-
ment seems to recommend the acceptance of the  model
and its parameters as a valid simulator of the water
behavior  of  the lake.  This infers that the stated
assumptions are likely valid.

     The assumption of adequate lake  mixing  seemed
to  require  further evaluation.  Table 1 summarizes
the observed data for tritium showing -the number  of
observations, the mean, maximum, and minimum values,
the  standard  deviation,  and  the  percent  of the
observations contained within the range of the  mean
plus  and  minus  the stated analytical error.   From
                      22

-------
this table it should be noted that the  data  points
are  well  clustered about the mean within the range
of the analytical error.

     In an effort to test the effect of  stratifica-
tion  of  water,  a paired "t" test was used to test
the hypothesis that surface water samples had values
from the same sample  population  as  water  samples
taken  near  the  bottom  of the same lake location,
•The test was a two-tailed test  at ' the  95  percent
confidence level.  Multiple "t" tests are summarized
in table 2.  Nine trips had sufficient positive data
to analyze.


                        Table  2
        Paired  "t"  test  of  tritium concentrations

             in surface  and bottom lake  water


 n   =   179  pairs

 D   =     0.067  nCi/liter

 SD =     0.284

 a   =      .05            -

 Degrees of Freedom = 178

 Ho:  Surface Cone.  - Bottom Cone.  =  0

 Test  Statistic

                fc  =  0-067   (17S)%  =   3.15
                      0.284


 t        -   t (.025)  =   1.96 < 3.15   Ho:   rejected
  {a/2)

 Alt Ho;  Surface Cone.   >  Bottom Cone.

 Alt Ho; Accepted
                     23

-------
     The  test,  used 179 pairs of observations which
indicated  that  tritium  concentration  in  surface
water exceeded that of deep water an average of .067
nCi/liter,   The  sample  standard  deviation (SD) =
,284, degrees of freedom = 178, and  the  test  sta-
tistic "t" = 3.15.  Since 3.15 is greater than 1.96,
the  hypothesis  that  the  difference was zero, was
rejected and the alternate hypothesis that the  dif-
ference  was greater than zero was accepted.  Such a
hypothesis  indicates  that  some   physical   stra-
tification  does take place as the lake receives the
small amounts  of  radioactivity  mixed  with  water
which  is  at  a  temperature elevated above ambient
lake temperatures.  In general, it is  important  to
note  the magnitude of this stratification.  In this
particular test the average concentration  was  1.75
nCi/literr  and  the average observed difference was
.067 nCi/liter or less than 4 percent of the average
observed concentration.   The  difference  is  about
one-third  of  the  minimum detectable concentration
for tritium of ,2 nCi/liter,  The treatment  of  the
lake  by> the model as'a mixed lake should not intro-
duce an error greater than the errors introduced  by
sampling  and  analysis  and  thus  the  mixed  lake
assumption is realistic for the purposes  for  which
it was intended,

     This  comparison seems to verify the model as a
plausible description of dilution within  the  range
of  analytical  error.    It is, therefore, concluded
from these comparisons that  equation  2  adequately
describes  the  water  mixing properties of the lake
within the overall measurement error  of  the  study
and that the constant lake volume of 3.8 x 107 m3 is
a  valid  assumption.  It is also concluded that the
mixing of the water  is  sufficiently  effective  to
support  the  uniform  mixing  assumption  over time
periods of weeks or greater.  A subsequent inference
is that long-term buildup of the tti" radionuclide in
the water based on the model would  reach  an  equi-
librium or "steady state" value given by:

-------
                                         (Equation 3)
             equilibrium
     The  highest  release  rate of tritium reported
during this study was for  December  1973  at  79.2^
Ci/mo.   Such a release rate would result in concen-
trations from .8 nCi/liter to 4 .8 nCi/liter  depend-
ing on the lake discharge rate.  The highest concen-
tration  observed  from  a single sample in the lake
was 4.8 nCi/liter on-  November  6,  1973,   This  is
.16percent of 10CFR20 (2) , guideline for radioactive
"effluents   to  unrestricted  areas."  The  highest
tritium concentration representative of the lake was
3.7 nCi/liter or .1 percent of Appendix B  guideline
(2) ,    Thus  the  radioactive  waste  concentration
buildup is  controlled  by  lake  flow,  radioactive
decay  rate,  and  the  discharge rate of the radio-
active pollutant.  For long-lived radioisotopes with
half-lives of greater than a  year,  the  lake  flow
rate  is the dominating factor which affects buildup
for a given radioactive discharge rate.   Data  from
October  1966  to  September  1974  on  the  average
monthly lake flow shows that  this  parameter  might
vary  from  2.27  m3/sec to 13.65 m3/sec causing the
"half-life" time of a particle of water to vary from
23 days to 136 days.  Thus the maximum buildup of  a
long-lived radiontaclide could be determined by;
                                        (Equation 4)
               pi
               __

     Where:


     Pj_    =   Belease rate of nuclide "i"


     Q     =   Lake flow rate
                     25

-------
Downstream Dilution of Tritium

     Because  the  tritium   concentrations were well
above detectable levels,  it was   decided  that  an
evaluation  of  the  rate  of dilution downstream on
Black Creek was desirable.   On Trips  ¥111, IX,  and X
five points were sampled at  3,2r 6f  25,  32,7,  and «44
kilometers downstream.  These locations  were at  the
bridge  of  Highway 39  (3.2  kilometers),  pier  at the
end  of  Churchill  Street   in  Hartsville?  SC,  (6
kilometers),   the   bridge   of    Highway   52  (25
kilometers),  the  bridge  of  Highway   133   (32.7
kilometers),  and  the  bridge  of  Highway  35  (HH
kilometers).  The last point is about one  kilometer
above  the confluence of Black Creek  and the Pee Dee
River,  The tritium concentration values  are   given
in table 3.
                      Table 3

            Observed concentrations of tritium

                    downstream

                      nCi/1
Position
At
HW
the dan
39
Churchill St.
HW
HW
HW
52
133
35
Distance
{ km)
0
3.2
6
25
32,7
44
Trip
VIII
.6 ±
.6 ±
.5 ±
. .41
.5 i
.5 ±
.2
.2
.2
.2
.2
.2
3
4
2
1
1
1
Trip
IX
.7
.1
,9
,6
.8
.3
±
±
±
t
±
±
.2
.2
.2
.2
.2
.2
2.
2.
2.
1.
1,
1.
Trip
X
7 ±
7 ±
4 ±
7 ±
6 t
4 ±
,2
,2
.2
.2
.2
.2
                     26

-------
     Since  the  Trip  "VIII   data  seemed,  to  show no
trend due to its large fractional  error,  the   trip
data for IX an<3 X were used to determine an exponen-
tial curve of the form;
                  y  =  jjg.uji


This yielded the constant values of:


       Trip IX                       Trip X


     a  =  3.7                     a  =  2.7

     b  =  -.025                   b  =  -.016
     It is significant to note that the coefficients
of  determination for Trips IX and X are r =  .91  and
,98, respectively.  This indicates a relatively high
degree of correlation.  The resultant implied  model
for downstream dilution is;

                                        {Equation 5)
C  =  C
       L
C  =   concentration of nuclide downstream at «x"

       kilometers below the dam


CT -   average concentration of nuclide in the lake


x  =   kilometers downstream of dam  (not to exceed 45

       kilometers)
                     27

-------
     Tritium in well Water

          Tritium  concentrations were also determined in
     water samples from wells  surrounding  the  lake  to
     monitor  the significance of transport from the lake
     to the underlying aquifers.   The  results  of  this
     study  summarized  in  table  H are basically incon-
     clusive.  Even though an  enrichment  procedure  was
     used  to  increase the sensitivity of the analytical
     procedure on a selected group of these samples there
     seemed to be no significant correlation between  the
     average  of  the  well water samples and the average
     lake concentration; hence no  quantitative  estimate
     could  be made of any transport coefficient from the
     lake to'the aquifers.  Neither could one say conclu-
     sively that such transfer does not occur,

(gamma' Emitting Radionuclides

     Prom the liquid waste releases of the reactor  there
are  several  radionuclides  which  are gamma emitters, a
characteristic  which  simplifies  their  detection   and
analysis.   Many  of  these radionuclides are isotopes of
elements useful to biological systems and  are  therefore
reconcentrated  within  the  biological components of the
lake system.  Others have chemical forms which react with
components of the environment  so  as  to  effect  recon-
centration or dissolution through ion exchange, molecular
complexing, and other physical interactions.   Many radio-
isotopes  are  subject  to  both  physical and biological
forces.   In order to assess  the  significance  of  these
forces the lake water concentration must be determined or
inferred.   It  is  important in this study that not only
the  concentration  observed-  during  a  field  trip   be
accurate  but  some  estimate of concentrations with time
between trips be available.

     cobalt

          Radioisotopes of cobalt are of  particular  in-
     terest.   These  are  produced by neutron activation
     within the hardware of  the  reactor  core.   During
     Trip  I  the  concentration of cofoalt-58 was readily
     measurable in the lake water.  On  subsequent  trips
     cobalt-60  concentrations  were measurable using the
     large volume sample data.  Figure 10 shows  observed
     concentrations  of  cobalt-58 as compared to concen-
     trations predicted by equation 2 and  using  release
                          28

-------
                            Table 4


               Tritium concentrations in wells

                             nCi/1
Well
23-A
39-A
39-B
595-A
7 3 7- A
737-B
674
Trailer
House on
E. Shore
Avg.
SD
Lake Avg.
Trip IV
03/14/72
.15*
.4
,24
.10
,10
.41
- <.2
.3
.3

.24
.12
1.69
Trip ¥11
02/06/73
.13*
.3
.2
.01
,13
.4
.04 •'
NS
NS

.17
.14
' 1.15
Trip VIII Trip IX
06/05/73 11/05/73
<,2 < .2
,2 .3
.2 .4
<.2 < .2
«,2 < .2
.2 .3
<.2 ,2
.4 .4
NS NS

<.2 . .24
_
.61 3.7
•Trip X
05/14/74
.10*
.3
.2
.10
.2
.2
.10
NS
NS

.17
.08
2.65
NS - Mo sample.                                    - -     .
*    Data reported to the nearest hundredth was determined by a
     tritium enrichment procedure.
                                 29

-------
    data  as  available  from reactor operating records.
    The triangles enclosed in a square indicate that the
    value was less than detectable  and  is  plotted  at
    .025  pci/liter  or  one-fourth •  the  normal minimum
    detectable limits,   in order to  evaluate  the  com-
    parison  of observed versus expected values a paired
    "t" test was run to determine if  the  means  of  the
    two sample populations were significantly different,
    This  is  represented  in  table  5.  &s shown in the
    table the means were  not  statistically  different.
    Thus  the  model is a reasonable  estimate of the ob-
    served lake concentration of cobalt even though  its
    correlation  to observed data is  not as close as for
    tritium.
c_
0)
-  t
u
a
        O
       1971
      1972            1973
              date
1974
    Figure 10.
Observed and predicted concentrations of
cobalt-58 in Lake Robinson
                         30

-------
                            Table 5

Statistical comparison of observed and predicted concentrations of
               cobalt-58 ia Lake Robinson water
                            pCi/1
Trip
I
II
III
IV
V
VI
VII
VIII
IX
X
Ho: observed -
Date
12/01/70
03/09/71
09/21/71
03/14/72
07/10/72
10/31/72
02/06/73
06/05/73
11/05/73
05/14/74
estimated = 0
t.025 = +- 2'262
Confidence Level = 1-a = 95%
-2.262 < .095 < 2.262
Observed
1.78
1.10
ND
.12
1.07
.96
.02
.14
ND
ND
D =
SD =
df =
Predicted
1.0
.56
.66
.36
.79
.10
.11
.56
.1
.85
.0175
.5818
.095
9
          Ho:  accepted
    ND = Not•detected.
                               31

-------
      From toth the model  and the  observed   data  we
 see   that  measurable  concentrations were  likely in
 two periods;  November 1970 to July  1971   and  June
 1972  to  November 1972.  h third rise was  predicted
'by the model from May 197a to July   197£|r   but  this
 was not verified by the observations.

      A  similar  comparison  was made using observed
_and   predicted  values  of   cobalt-60,     This   is
 presented in table 6.  In this case  the poor fit be-
 comes more evident as the difference between the ob-
 served  and  predicted  is shown to  be statistically
 significant.  Furthermoref the test  indicates  that
 the   mean  of  the  estimated values is greater than
 that  of the observed values.  This would support use
 of the model as an upper  limit  estimator   of  lake
 concentration trends.

 Cesium

      toother  element having radioisotopes  which oc-
 curred in detectable concentrations  in the  water was
 cesium.  Cesium-137 and cesium-134 are generated  in
 the   fission  process  as opposed to the activation
 production of most of the other gamma  emitting  ra-
 dionuclides.  Thus, the appearance of these isotopes
 occurs  as  a  result  of leaking fuel elements and
 subsequent containment  leakages  unrelated  to  the
 activation product releases in the liquid wastes.

      Cesium-137  is a primary radionuelide  in world-
 wide  fallout and is present in small  quantities  in
 the   general  environment.   The  mean value for the
 concentration of cesium-137 in the  water   prior  to
 any reactor influence is  estimated as .11 pCi/liter,
 This  value  was determined, based on the average of
 all background water analyses performed from all the
 trips.  Table 7 summarizes the cesium data  for  both
 cesium-137  and cesium-13W,  The predicted  value for
 cesium-137 is calculated  by  adding  the  background
 value to  the  value calculated by  equation 2.  The
 standard deviation is not calculated when the number
 of values averaged is  less  than  four.    The  good
 agreement  between  observed and predicted  values is
 due mainly to the small   contribution  from  reactor
 releases  as  compared to background values,  Rs re-
 leases  became  more  significant,  the   divergence
 between   observed   and   predicted  concentrations
 occurs.  Table 7 summarizes  and  compares   observed
 arid predicted values for  cesium.

                     32

-------
                       Table 6

   Statistical comparison of observed and predicted
  concentrations of cobalt-60 in Lake Robinson water
                       pci/l
Trip              Date           Observed       Predicted
I
II
III
IV
V
VI
¥11
VIII
IX
I
12/01/70
• 03/09/71
09/21/71
03/14/72
07/10/72
10/31/72
02/06/73
06/05/73
11/05/73
05/14/74
Ho : observed - estimated = 0
t.025 = *
Confidence
-3.80 <
2.262
level - 1-cc =95%
-2.262
.1
.2
ND
.1
.1
.09
.05
.06
ND
ND
D = -.68
SD = .57
t = -3.80
df = 9
.025
.25
.74
1.4
1.3
.8
.22
.55
.56
1.65




       Ho;  rejected
ND - Not detected.
                          33

-------
                           Table 7
           Observed and predicted concentrations
        of radioisotopes of cesium in Lake Robinson
                           pCi/1
Trip
Date
I
12/01/70
II
03/09/71
III
09/21/71
IV
03/14/72
\
v
07/10/72
VI
10/31/72
VII
02/06/73
VIII
06/05/73
IX
11/05/73
X
05/14/74
Background
eesium-137
Observed Predicted
(Standard Deviation)
.2
(*)
.2
(*)
.22
(.11)
.13
(.03)
.18
(.06)
.16
(.03)
,15
(.06)
.24
(.04)
.19
(.04)
3.2
(.5)
,11
(.05)
.11
.11
,11
.11
.16
.16
.15
.75
.45
1.45

Cesium-134
Observed Predicted
(Standard Deviation)
ND
ND
ND
ND
ND
.02
(.05)
ND
.14
(.04)
.03
(.04)
2.4
(.7)
ND
ND
ND
ND
ND
.04
.04
.06
.24
.09
1.2

*Insufficient number of data points to estimate standard
 deviations,  (< 4)
ND - Not detected.
                             34

-------
Chromium

     Chromium-51,  an  activation  product:,  was ob-
served in  water  at  concentrations  from  1  to  2
pCi/liter during three of the sampling periods.  The
summary of this data is shown in table 8.  Predicted
values   using   equation   2   never  exceeded  .16
pCi/liter.

Manganese

     The  detection  of  the   activation   product,
manganese-54,    was    inconclusive    because   of
complications in interpreting  the  interference  of
manganese-54  with  a .83 Me¥ gamma with the .81 MeV
gamma energy of cobalt-58.  In most  cases  positive
analysis  of  these  two  could only be accomplished
following chemical separation prior to  gamma  spec-
tral  analysis  or  utilization of a Ge(Li) counting
system.  This factor reduced the sensitivity of  the
detection  and,  consequently  increased the minimum
detectable concentration to apparently .2 pCi/liter.
It is interesting that the  predictive  model  shows
the  concentration of manganese-54 to range consist-
ently between .1 and 1,0 pCi/liter.  The  concentra-
tions of manganese are summarized in table 8.

Iodine

     Iodine-131,  another  fission  product, was de-
tected in the final survey  at  an  average  concen-
tration  of 4.5 pCi/liter.  Prediction of iodine-131
concentrations were not attempted due to  the  short
half-life  of  8.1  days.  This would cause the lake
concentration  to  be  highly  responsive   to   tlie
specific  time of release and the quantity released.
Averaging the total monthly release would  introduce
an  unreasonable  error as compared to observed lake
concentrations.  The May 14, 1974, samples  averaged
4.5  pCi/liter  with  a  standard  deviation  of 1.9
pCi/liter,

-------
             Table 8





Average chromium-51, manganese-54



  and  iodine-131  concentrations



 observed in Lake Robinson water



             pCi/1
Trip
Date- 5 a Cr
I 2.2
12/01/70
II <.3
03/09/71
III <.3
09/21/71
IV 1.28
03/14/72
V 1.60
07/10/72
VI <.3
10/31/72
VII <.3
02/06/73
VIII <.3
06/05/73
IX <.3
11/05/73
X <.3
05/14/74
»Mn
<.05

<.05

<.05

<,05

.15

.03

<.05

.10

<.05

<.05

1 51 j
<,05

<.05

<,05

<.05

<.05

<.05

<.05

<.05

<.05

4.5

                 36

-------
Observations and summary

     The  non-tritium  data  demonstrates  an  increasing
divergence from the predictive model of equation 2.  This
is  likely  due to the origin and nature of this waste as
compared to tritium.  The tritium is not concentrated  in
the  waste  evaporators, and each release of liquid waste
will contain a quantity of tritium  consistent  with  the
tritium inventory which has leaked from the primary cool-
ant  loop.   Hence, the mathematical treatment of tritium
as a continuous rate release is usually quite valid.  The
non-tritium  radionuelides  originate  from  many  varied
points  within  the  reactor  core.  This is particularly
true of activation products.  The physical  and.  chemical
forms of these products regulate the effectiveness of the
waste  evaporator in removing these contaminants from the
system.  Iks a result, effective modeling  of  these  con-
taminants  should treat their releases as discreet events
as opposed to a continuous steady rate  occurrence.   The
same may be said for fission products which enter various
liquid  wastes The reactor operators who have a record of
liquid release data could easily maintain a running esti-
mate of radionuclide concentrations in the lake,

Additional Ra dionuc11de Me a surements

     Strontium-90

          Strontium-90 is a  fission  product  which  has
     been  released  to  the  earth's biosphere from past
     nuclear weapons tests and is found in many  environ-
     mental   samples.    Due  to  the  radiotoxicity  of
     strontium-90 and its  presence  in  reactor  wastes,
     water  samples  were analyzed for this radionuclide.
     Jk specific chemical  separation  for  strontium  was
     performed  on  1-liter  aliquots of lake water drawn
     from the 19-liter sample sets.  For survey Trips  I-
     IX no strontium-90 or strontium-89 was detected.  Of
     the eight water samples analyzed, for survey Trip X,
     four  indicated  less  than the detectable limits of
     .25 pCi/liter.  The other four indicated an  average
     of  «27  pCi/liter  of  strontium-90  and a standard
     deviation of  .017  pCi/liter.   Since  the%  minimum
     detectable limit was determined to be .25 pCi/liter,
     it  was  concluded  that  the lake concentration was
     likely less than the .25 pCi/liter  detection  limit
     for  strontium-90.   Ho strontium-89 was detected in
     any lake water samples.
                          3?

-------
Gross Alpha and Beta Counting

     Environmental radioactivity monitoring programs
have historically  reported  gross  alpha  and  beta
counts  to  serve  as  a  trend  indicator of radio-
activity in environmental samples.  In order to pro-
vide comparison data in this format,  table  9  sum-
marizes results of the current Lake Robinson survey.

     The gross beta data were tested for correlation
with  the  total  of the non-tritium activity in the
water.  This comparison is summarized in  table  10.
A  linear  regression  fit  was determined- using -the
dissolved solids gross beta  average  as  the  inde-
pendent  variable (x) and the sum of the non-tritium
average activity data as the dependent variable (y).
The resultant equation was:

               y = -1.43 + 1.8x

     Miere:

              y = Total non-tritium con-
                  centration (pci/liter)

              x = Observed gross beta in dis-
                  solved solids (pci/liter)

     The coefficient of determination   (.59)   demon-
strates  that.  the  gross  beta data were of limited
value for estimating concentrations  of  non-tritium
activity in the water.
                      38

-------
                             Table 9

           Gross alpha and beta activity concentrations
                       in  Lake  Robinson water
                             pCi/1
Trip
Date
I
12/01/70
II
03/09/71
III
09/21/71
IV
03/14/72
V
07/10/72
VI
10/31/72
VII
02/06/73
VIII
06/05/73
IX
11/05/73
X
Undissolved i

< 1 -

< 1 '

< 1

< 1

' 1.3 ± 1.9

< 1

< 1

< 1

< 1

1.5 ± 1.1
Solxds
Alpha
< 2

< 2

< 2

< 2

< 2

< 2

< 2

< 2

< 2

< 2
Dil
Beta
2.4 ±

3.4 ±

2.7 ±

1.1 ±-

1.75 ±

1.3 ±

1.44 ±

.9 ±

.89 ±

4.9 ±
3 solved

1.8*

.64

.39

.70

.53

.62

.69

1.1

.98

1.8
Solids
Alpha
< 2

< 2

< 2

< 2

< 2

< 2

< 2

< 2

< 2

< 2
05/14/74

*  Observed standard deviation.
                                39

-------
                        Table 10

     Correlation of gross beta determinations with
                  total specific analyses
                         pCi/1
Trip •
I
II
III
IV
V
VI
VII
VIII
IX
X
Equation Form:
Date
12/01/70
03/09/71
09/21/71
03/14/72
07/10/72
10/31/72
02/06/73
06/05/73
11/05/73
05/14/74
y = a0 +
Total
specific
activity
y
4.3
1.5
.2
1.6
.3.1
1.3
.2
.7
.2
10.1
1
Gross beta
(dissolved
solids)
X
2.4
3.4
2.7
1.1
1.75
1.3
1.44
.9
.89
4.9

                a0 = -1.43
                   = +1. 8
Coefficient of determination  =  .59
                          40

-------
Physical Measurements in Water

     In  order  to  characterize the lake water, numerous
physical measurements and analyses were  performed.   The
primary  intent was to scan these physical parameters for
any indications of unusual changes which  would  indicate
significant  shifts in the dynamic forces which distribu-
ted the radionuclides throughout the lake system.   Table
11  summarizes  the  pH  and  solids  found in the water.
Table 12 summarizes the dissolved stable element  concen-
trations.

     The  data  in  table  11 seem to indicate relatively
consistent values of dissolved  and  undissolved  solids.
No  unusual variations are apparent.  The pH was observed
to vary from a low of 4.7 to a high of 6.1.  The data did
suggest a seasonal dependency with low  pH  occurring  in
the  months of February and March and higher pH occurring
in July and August,  The seasonal variation, approximated
with a sine function, showed no difference  in  predicted
versus  observed values for nine trips using a paired "t"
test and a confidence level of 90 percent.  Such modeling
serves only to demonstrate the cyclic nature  of  the  pH
within a year.

     Table   12   demonstrates  relatively  constant  and
consistent stable element  concentrations.   Iron  varied
sufficiently  to  bear  some  comment.  Comparison of the
iron data to several parameters indicates that  the  most
significant  correlation  was  with  the  lake  discharge
rates.

The relationship is expressed as;
       concentration of Iron  * (Lake Discharge) -3
This may indicate that  the  iron  was  introduced  at  a
constant rate and was diluted fcy the rainfall.  The other
elements  were  more  likely  brought  into  the drainage
system of the watershed  with  similar  elemental  makeup
such  that  rainfall  or  flow  rates  did not affect the
concentration.
                          41

-------
                      Table 11

           Average pH and solids content
               of Lake Robinson water
Trip
Date
I
12/01/70
II
03/09/71
III
09/21/71
IV
03/14/72
V
07/10/72
VI
10/31/72
VII
02/06/73
VIII
06/05/73
IX
11/05/73
X
05/14/74
PH
5.
4.
5,
5.
6.
5.
4.
5.
5.
5.
2
7
6
8
1
7
9
5
8
2
Undissolved
Solids
mg/1
17
9
7
6
3
10
9
6
9
5
.3
.7
,9
.6
.7
.2
.8
.9
.1
.8
Dissolved
Solids
mg/1
22
18
29
13
7
19
17
19
29
22
,2
.3
.5
.3
.9
.8
.2
.0
,2
.5
Average
5.5
8.7
19.9
                          42

-------
                        Table 12


          Average stable element concentration

                 in Lake Robinson water

                          mg/1
                                 Standard
Element
Sodium
Magnesium
Potassium
Calcium
Manganese
Iron
Cobalt
Zinc
Strontium
Cadmium
Cesium
Concentration
1.54
.42
.46
.80
.0056
.56
.008
.020
<.005
.004
<1.0
Deviation
.15
.068
.077
.17
.0064
.22
.006
.009

.003

MDL
2
3
5
2
5
1
3
5
5
2
1
X
X
X
X
X
X
X
X
X
X

10" 3
10-"
io-»
10~a
<** 8
io-a
1Q-3
10- 3
10- a
10" 3

MDL ~ Minimum detectable level.
                           43

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                        SECTION ¥

                   AQUATIC VEGETATION

     In observing a lake ecosystem,  one  important  com-
ponent  is  vegetation.  It is within this component -that
mineral content of the water  and  lake  bottom  interact
with sunlight to form the first trophic level of the sys-
tem,   The lake vegetation se.rves a wide variety of func-
tions such as food sources 'for aquatic life, habitats for
aquatic fauna,  benthic  stabilizers  frow  the  scouring
forces of currents, and a source of dissolved oxygen,

     Inherent  in the nature of plant life is its ability
to selectively take minerals  from  the  environment  and
include  them  within its organic structure.  Such action
causes the lake flora to concentrate many of  the  radio-
active elements discharged into the lake as wastes.  Such
storage  action is only temporary since the radionuclides
following the patterns of cycling elements transfer  from
one  component  to  another  until they have decayed to a
stable elemental form and become a respectable member  of
the natural nutrient pool .

     The  vegetation found in lake Bobinson is typical of
dark water lakes of that  region.   Table  13  lists  the
major  aquatic weeds that were observed indigenous to the
lake.  Of the many species found  there  Mygyphae  odorata
(white   water   lily) »   gap as   flexilis  (naiad) ,  and
             (water milfoil)  were most often  chosen  for
field sampling,  sampling instructions were to find about
1  kilogram  of vegetation in the vicinity of a 200-liter
water sampling site.  The* preferred vegetation type was a
submersed weed.   The  second  preference  was  given  to
emersed  weeds  which  had only floating leaves above the
water surface,  Emergent weeds were taken only as a  last
resort.

     The  agtiatic  vegetation  appeared to be a sensitive
monitor of  the  presence  of  some  radioactive  wastes.
Table  1t  compares the confirmation of radioactive waste
nuclides in the water and vegetation of the lake.   These
data  suggests  that  vegetation  might  be  particularly
effective for detecting cobalt,  manganese,  and  iodine,
Chromium and cesium seemed to be more readily detected by
water sampling,
                          44

-------
                         Table 13
Genus
Aquatic weeds observed

   in Lake Robinson

         Common Name
Character
Nymphae

Najas

Myriophyllum

Graminea (family)

Brasenia

Vallisneria

Juneus

Eleocharis

Typha

Potomogeton


Pontederia
        White Waterlily

        Naiad

        Watermilfoil

        Grass

        Watershield

        Valisneria

        Creeping Rush

        Spike Rush

        Cattail

        Pondweed


        Pickeral Weed
emersed

submersed

submersed

emersed

emersed

submersed

submersed

emersed

eutersed

emersed and
  submersed

emersed
                            45

-------
                             Table 14

           Environmental confirmation of radionuclides

                    released in liquid wastes*
Times
Observed in
Radionuclide Liquid Waste
seCo 10
60Co ' 10
5 "*Mn 8
stCr 5
I311 6
1 3 7Cs ** 6 **
13 £i
v ~ iTi « jr
Tiroes
Observed
in Water
7
7
4
4
1
5 **
4
Times
Observed
in Vegetation
10
10
7
1
3
2 **
1
*   Confirmation over 10 trips,
**  Occurs - in-detectable quantities in the environment independent
    of reactor releases,    ,
       Tables  15,  16»•  17, and 18 show the average radio-
  nuclide contents of aquatic vegetation.  The data  demon-
  strate  that radionuclide content increases and decreases
  with  releases • of  'radionuclides.    (See   figure   A~3»
  Appendix I.)  The  rates of decrease appear to exceed the
  decay rates  of  the  longer-lived  radionuclides.   Such
  behavior  implies  the  presence of a removal action from
  •the vegetation ether  than  that  of  radioactive  decay.
  Apparently the radionuclide content of vegetation is more
  a  function  'of  the  recent  history  of liquid releases
  (releases in the last 1 to 6 months) than it is of  prior
  releases, .  . The vegetation•does appear to be an effective
  integrator of- some radionuclide releases and, as such, an
  effective biological monitor of certain radionuclides  in
  water.
                            46

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              Table 15





Radioactive cobalt in Lake Robinson



         aquatic vegetation



               pCi/kg
Trip
Date
I
12/01/70
II
03/09/71
III
09/21/71
IV
03/14/72
v
07/10/72
VI
10/31/72
VII
02/06/73
VIII
06/05/73
IX
11/05/73
X
05/14/74
Dry Wt
5,000
44,000
2,500
5,200
74,000
6,200
1,900
4,500
470
260
Cobalt-58
Wet Wt.
570
3,200
250
770
14,000
900
350
380
30
40
Dry Wt
290
9,200
1,400
1,200
12,000
3,100
1,400
4,900
2,100
1,500
Cobalt- 60
Wet Wt.
40
640
100
200
2,100
400
250
420
150
220
                 47

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               Table 16





Radioactive cesium in Lake Robinson



          aquatic vegetation



                pCi/kg
Trip
Date
I
12/01/70
II
03/09/71
III
09/21/71
IV
03/14/72
V
07/10/72
VI
10/31/72
VII
02/06/73
VIII
06/05/73
IX
11/05/73
X
05/14/74
Cesium-137
Dry Wt. • Wet Wt.
2,160
3,500
1,000
580
3,200
1,400
, 510
1,200
9,400
7,800
240
240
90
50
550
100
100
110
800
1,100
Cesium-134
Dry Wt. Wet Wt.
< 50
< 40
< 50
< 50
< 50
<100
< 60
< 20
6,700
3,500
< 10
< 3
< 3
< 5
< 6
< 5
< 13
< 5
570
760
                   48

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              Table 17

  Radioactive iodine and strontium
in Lake Robinson aquatic vegetation
               pCi/kg
Trip
Date
I
12/01/70
II
03/09/71
III
09/21/71
IV
03/14/72
V
07/10/72
VI
10/31/72
VII
02/06/73
VIII
06/05/73
IX
11/05/73
X
05/14/74
Strontium- 8 9
Dry Wt, Wet Wt.
< 50
<400
<100
<100
<100
<200
100
<100
160
280
< 5
< 30
< 5
< 10
< 10
< 20
< 10
< 10
20
40
Strontium-90
Dry Wt. Wet Wt,
< 10
620
850
210
870
1,700
780
1,000
3,700
280
< 1
40
50
30
150
130
140
90
70
40
Iodine-131
Dry Wt. Wet Wt.
< 50
1,000
< 50
< 50
< 50
<100
< 50
< 50
3,400
4,200
< 10
70
< 5
< 5
< 5
< 6
< 20
< 5
280
590
                 49

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              Table 18

 Radioactive chromium and manganese
in Lake Robinson aquatic vegetation
               pCi/kg
Trip
Date '
I
12/01/70
11 • -
03/09/71
III
09/21/71
IV
03/14/72
V
07/10/72
VI
10/31/72
VII
02/06/73
VIII
06/05/73
IX
11/05/73
X
05/14/74
Chromium- 51
Dry Wt. Wet Wt.
< 500
< 500
2,000
< 500
4,100
<1,000
<2,OQO
1,200
< 500
< 500
< 50
< 50
130
< 50
710
< 60
<200
100
< 50
< 50
Manganese-54
Dry Wt. Wet Wt.
< 50
2rOOO
< 50
< 50
2,100
410
490
2,100
910
520
< 10
140
< 5
5
360
130
90
180
60
70
                  50

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                       SECTIOW ¥1

                    BENTHIC S1DIMENTS
     The  lake  benthos comprises a component of the lake
system which could receive and store significant  quanti-
ties  of  radioactive  material through sedimentation and
through direct chemical transfer from the water  such  as
chemical  reaction,  ion  exchange,  and  other  adhesion
actions,  sedimentation is considered to be  the  primary
action contributing to the accumulation that takes place.
It  consists of suspended solids which have grown through
agglomeration to a density sufficient to cause  settling,
Agglomeration is a scavenging process by which ions, some
molecules,  and  smaller particles are attracted by elec-
trostatic , magnetic, and gravitational forces.  Such  ac-
tions  are  not unique to radio!sotopes, but do effect an
accumulation of them and thereby remove some  radioactive
material  from  the liquid medium.  In addition„ dead or-
ganic material, detritus, falls to  the  bottom  carrying
with  it  the  radioactive material it accumulated in its
growth and other active biological processes.

     As there is transport into this  compartment,  there
is  also  removal  or  disappearance  from  it.  The ever
changing parameters of the water such as pH and ionic and
elemental concentrations cause varying dissolution inter-
actions between the lake water and the  material  at  the
lake  floor  (10),   As radioactive decay takes place the
quantity of radioactive material within  the  compartment
further reduces.

     This  study  did  not attempt to quantify the inflow
and outflow rates of the compartment, but it did  attempt
to  capture  pictures of the existing radioactive - content
of the lake benthos and thereby to infer something of the
nature and significance of the lake benthos as a  storage
compartment.  Table 19 summarizes the radionuclide analy-
     for the dredge sampling locations (figure 11).  This
table presents only those radionuclides which  are  obvi-
ously  originating in the reactor.  The only exception is
cesium-137 which is present in the general environment .as
well as produced as a fission product within the reactor.
The results of the surveys as given in table 19  indicate
that measurable concentrations of these radionuclides not
only  rise  but  fall.   Figures 12 through 17 show a se-
quence of data on cobalt that suggests this action.
                          51

-------
Kilometers
Upstream
of Dam
              Position A
                   .2
                            Table  IS

            Radioactivity in Lake  Robinson  sediments

                     pCi/kg  (dry weight)

             Position B    Position C    Position D
                                                                      Position E    Position F
                                2.4
                                              5,7
                                                           7.5
                                                                         9.1
                                                                                       9.8
Trip I
12/01/70
 7Cs:   543    1>7Cs:   352    1!7Cs;   <20   1>7Cs:'   193   l"Cs:    78  No Sample
Trip II
03/09/71
                'Css  939   I3'Cs:  528   l"Cs;    822  137Cs:   4222  137Cs:    714   13'cs:   1578
Trip III
09/21/71
              '"CS!  266   I37Cs:  442   '3'Cs:   2657  1J7Cs:   1430  vs?Cs:    3S5  ls'Csi    620
Trip IV
03/14/72
 "Co:
  88   15'Cs:  311   1}'Ca:    168  l"Cs:    144  1J7Cs:   1159- l"Cs:   1538
  68                                              !J1I:    202
Trip V
07/10/72
Trip VI
10/31/72
Trip VII
02/06/73
Trip VIII
06/05/73
                7Cs:
 'Css
 "Co:
"Cs:
iBCo:
"CO!
 292   "7Cs: 1584   l"cs:    139  ' "Cs:    730  ls?Cs:   1697   >3'cs:    770
                                    '"Cos    120
                                    5BCo:   1140
                                    5*Mn:    110

 332   "JCS!  794   157Cs:   2380  '37Css   1970  ii7Cs:   1016   '"Css   1879
 124    "Co:  110    "Co:    568   "Cos    340   68Co:     56    60Co:    104
                      58Co;    550   s"Cos    900

4682   137Cs: 1071   137Cs:   1246  I>7Cs:    889  '"ess   3002   JS7Cs:    583
 332                                '"Co;   1165
 102                                S8CO!    755

 3457  ls'Css  1034 'l37Cs:   3626  117Cs:   1183  137Cs:   1388    ls?Css   2544
                      **Cos    213   68Co:    550
Trip IX
11/05/73
Trip X
05/14/74
                'CB:
 'Cs:
 "Co:
 2246  137CS!   1051  l"Css    401  l37Cs:   1735  »"C»»   2686    "7Csi   1048
                      "Cos    241   e°Co:   1140
                                    S«CO!    190

 1438  137Cs:   1051  '"Css    601  137Cs:    403  "'Css   2246    ll7Cs:    192
   75   60Co:    200   68CO!    243   £8Co:    238'   "Co:    107
                                              52

-------
Based on these results it is believed that buildup of  ra-
dioactive materials in the benthos  sediments of the  lake
is  reduced   by  an  additional  removal action other than
radioactive  decay.
     scale
     1 km.
                                                             D
                                                      visitors center
                       legend

                    &s Dredge sampling  locations (a-f)

                       in Lake Robinson


Figure  11.   Dredge sampling locations in Lake Robinson

                         .  53

-------
    100CH
U t 500-
°- Q
                                                     legend
                                                  0-58Co
           1971
1972
                                 year
                                        1973
1974
Figure 12.   Radioactive  cobalt  in sediment  (position  a)
    1000'
 o»
  £?  500-
  o
                                                   legend
                                                0--58Co
            1971
 1972     year    -1973
                                                       1974
Figure 13.   Radioactive  cobalt  in sediment  (position b)
       1000'
                _JL
                                     i >A»




                                  f\
             1971
                          1972
                                             O
                                year
                                       1973
                                                  legend
                         o .     o	
                          1974
Figure 14.   Radioactive cobalt in sediment (position c)



                              54

-------
                                                        legend
                                                     0-~58Co
     1OOCH
      500'
            1971
19*72
                                year
                                        1973
1974
Figure 15.   Radioactive cobalt in sediment  (position d)
     100CH
 en
u  •
a Q  5QO
                                                      egena
                                                   0-58Co
                                                              -A

                                                              _Q
            1971
                                  year
                                                         1974
Figure 16.   Radioactive cobalt  in sediment  (position e)
    1000
    50O-
                        legend


                      A 60_
                      A—  Co



                      0-58Co
           1971
1972            1973
       year
                                                        1974
Figure  17.  Radioactive  cobalt  in sediment (position f)



                              55

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                       SECTION VII

                          FISH  •
     In spite of the dark water nature of Lake  Robinson,
the  productivity  in  the lake appeared to be relatively
low.  Nutrient levels as  recorded  in  STORET   (11)  and
other  qualitative  observations  seemed to predict this.
Conversations with the area game  warden  suggested  that
sport  catches  from the lake were relatively low.  There
was considerable difficulty  in  obtaining  fish  samples
from  the  lake with any consistency.  The method of col-
lection was by electrical shocking.  The conductivity  of
the  lake water was sufficiently high to restrict the ef-
fectiveness "of this procedure.   As  a  result  of  these
problems,  the  available  data  were  limited.  Table 20
shows the cesium-137, cobalt-58, cobalt-60,  chromium-Si,
and manganese-5*J observed in the samples.

     The  samples  were prepared by grouping the fish ac-
cording to species.  The fish were  then  dissected  into
meat,;  bone,       viscera.  In the case of larger speci-
mens J hearts and livers were  separated  from  the  other
entrails  for  analyses.   Cobalt-58  was  identified  in
specimens of catfish, bream,  suckers,  largemouth  bass,
crappie,  and drum in the second survey trip.  The appar-
ent absence of this radionuclide in Trip I  may  indicate
that accumulation of cobalt in the fish of the lake is at
a relatively slow rate; thus, fish are a slow integrating
storage component for this radionuclide in this lake.

-------
                                                 Table  20

                                    Radioactivity in  lake Bobinson  fish,


                                            pCi/kg Wry weight)
Shiners
   »"Ca

Catfish
    a'
      Co
Carp
            Trip I  Trip II  Trip III   trip  IV  Trip V  Trip VI  Trip VII   Trip  VIII   Trip  IX  Trip X
             2430
T"C« 442
Breara
l*'Cs 431
»»CO
Pike
1>TC» 965
Suckers
>"C« 503
5*Co '
"CO
Sicr
Large Bass
»»*C» 776
*«CO
"CCS
Baby Bats
C* 51«
Crappie
^Cs
"Co
Dram
***C»
**CO


453
127

610

419
64

211 •

897
103




722
5»

301
103


320




186




620
(5)
m

436

278




                                         274
                                         382
                                         435
                                                         152
                                                            S
                                                         m
                                                                 309
                                                                 1S3
Shad



Jack

   "'C»                         411      361


f - Trace detected but !«•• than quantitative Mneitivity,
                                                                    263



                                                                    188
                                              57

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                      S1CTIQN VIII

                         AND CONCLUSION
'BjsjmyjLoi: of Lake Components

     In  the  review  of  data  collected from the system
tinder study, it is clear that  measurable  quantities  of
radioactivity accumulate in the lake and its various com-
partments.   Frequently  the  concentrations are so small
that exceptional techniques are required to determine the
concentration of radioactivity.  This is especially  true
in  the measurement of radioactivity in water.  It is im-
portant to note that although many samples yielded no de-
tectable content of radioactive waste from  the  reactor,
there did occur some occasions when measurable quantities
of  such  radioactivity  were present in each of the lake
system  compartments;  lake  water,  aquatic  vegetation,
fish,  and benthic sediments.  It wasf therefore* evident
that accumulation did take place.

     The lake volume, the rate of cooling water flow from
the lake through the reactor and  return,  and  the  lake
discharge  rates  all cause the lake water to perform ac-
cording  to  a  simple  mathematical  equation.   Several
unique  features  of the lake probably aided in effecting
the predictable behavior.  The low pH of the  dark  water
lake  tends to increase the solubility of many waste ele-
ments and compounds.  The apparent  low  productivity  of
the  lake  limits  the  storage capacity of the fauna and
flora components.  The sandy nature of much of  the  ben-
thic  soils  limits  its  ion  exchange capacity, thereby
reducing the capacity of the benthos to store radioactive
wastes.  As a result, the mathematical model should  pro-
vide  good  predictive  values  of  concentrations.   The
deviation of the model values from observed concentration
values may be attributed to  the  errors  in  the  liquid
waste  release data and lake flow data.  Therefore, it is
believed that the equation 2 is a  good  model  for  this
system.

                             it
                    fl-e
                          58

-------
Further downstream dilution can be simulated by;

               c  = CT   e-
Due to the variability of lake flows and liquid waste re-
lease  rates, it is difficult to define a maximum concen-
tration value expected for any  radionuclide.   Table  21
summarizes  expected  ranges  of  concentration in water,
using   the   release   parameters   presented   in   the
Environmental  Impact  Statement  (9),   The  upper range
limit is calculated on a lake flow of 2.8 m3/sec a  typi-
cal "dry" month flow; the average on a flow of H.l m3/sec
an  average  flow;  and  the  lower  value  for  flows of
11.3 in3/sec typical of a "wet" month flow.  This table is
not designed  to  express  maximum  concentrations  which
might occur but is to demonstrate a set of typical values
which might reasonably be expected.

     Table 22 expresses the dose to a swimmer swimming 50
hours  in  the  water  at the concentrations of table 21.
Fifty hours was chosen as a realistic and convenient sea-
sonal exposure for an individual.  The dose expressed  in
table  22  also  represents that of 100 hours of fishing,
boating, and/or water skiing  on  the  lake  since  these
activities  represent  a 2 ir geometrical exposure as com-
pared to a 4 w exposure from swimming.

     The concentrating effects of vegetation appeared  to
be quite significant for many of the radionuclides occur-
ring  in  the liquid wastes.  On several survey trips the
radionuclides were easily detectable  in  vegetation  but
not detectable in the water directly.

     The apparent concentration factors of the vegetation
demonstrated  a high degree of variability which was dif-
ficult to interpret.  The obvious  behavior  demonstrated
by the vegetation was an apparent transfer of radioactiv-
ity  back  to the water as the water concentration of ab-
sorbed radionuclides decreases,  such action modifies the
extent of a long-term buildup over the years,

     Fish data, like vegetation,  indicate  a  responsive
rise  and  fall of radionuclide concentrations with those
of water.  Again such behavior suppresses a gradual long-
term rise in radionuclide concentrations  independent  of
lake water concentrations.
                          S§

-------
                            Table 21


         Projected range of equilibrium concentrations

                     at various lake flows

                            pci/1
           2.8 m3/sec
4.8 m3/sec
11.3 m3/sec
Highest Lake
Average
Nuclide
3e
sicr
"Mn
58Co
60Co "
89Sr
90Sr
I 3 1 j
13 kCS .
137Cs
(dry month)
1.1 x 103
.10
.12
1.9
.47
.05
.005
7.38
9.89
10.1
(avg. month)
.55 x 103
.08
.07
1.36
.24
.04
.0024
6.91
5.62
5.06
{wet month)
.25 x 10s
.06
.04
,87
.12
.03
.0012
6.12
2.73
2.54
Observed .. .
3.7 x 103
2.2
.15
1.8
.2
.27*
< 5*
4.5
2.4
3.2
*This concentration is found in the general environment and cannot
 be wholly attributed to releases from this facility.
                              60

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                              Table 22
                Projected range of doses to an adult
                            *
           swimming 50 hours  in expected concentrations

                       (mrem to whole body)
                                                        Highest Lake
                                                        Concentrations
Nuclide
Dry Month
Avg. Month
3H -0-
5lCr
slfMn
58Co
60Co
"Sr
90Sr
1 3 1 T
13*CS
137Cs
2.
9.
1.
1.
1.
1.
2.
1.
5.
6 x
0 x
7 x
,1 x
2 x
4 x
5 x
4 x
1 x
1Q-7
1Q~6
10-4
„ . am, tl
io-8
io-l°
lo-"
1Q_3
10-*
2.
5,
1.
5.
9.
6.
2.
8.
2.
-0-
1 x 1Q~7
3 x 10~6
2 x 10~*t
5 x 1G~S
2 x ID"9
5 X ID"11
3 x 10-1*
1 x 10"""*
5 x 10~%
Wet Month

1
3
7
2
6
3
2
4
1

.6
.0
.8
.8
.9
.2
.1
.0
.3
-0-
x ID"7
x IO"6
x 10~5
x 10~5
x 1Q-9
x IO-11
x 10"1*
x 10-*
_ _ „_ u.
x 10
Observed
-0-
5.
1.
1.
4.
6.
1.
1.
3.
1.
7
1
6
6
2
4
5
5
6
x IO""6
x 10~s
x 10"**
x ID'5
x 10~8
x IO""7
x 10""**
x ID"1*
x io-*
   Total  2.4 x 10"3
1.5 x 10
                                  -3
8.5 x 10"
'.8 x 10*
* The dose expressed also represents that of 100 hours of fishing,
  boating or water skiing.
                                 61

-------
     Benthic  sediments demonstrate an ability to release
their stored radionuclid.es.  Such  action  again  reduces
any extended storage in this component of the system.

     This  particular  lake system stores the bulk of the
liquid radioactive waste in the same manner that it would
any solute.  As such, it tends to  make  maximum  use  of
downstream  .transport  and dilution.  If one assumes that
dispersion and dilution are desirable qualities of such a
system, this particular system offers many advantages.

     1.   The low  pH  probably  increases  the
          solubility  of  many  of  these waste
          products and thereby insures a longer
          retention in the soluble state.

     2.   The  low  productivity  of  the  lake
          limits the fish available for sports-
          men and human intake.

     3.   The  water  is  not  of   a   quality
          desirable- for potable uses.  Since it
          is  not  used  in this manner another
          potential pathway of  human  exposure
          is avoided.

     ft.   The region does not generally require
          this water for  agricultural  irriga-
          tion and thus avoids another radionu-
          clide pathway to man,

Suryei1Iance Techniques

     From experiences in the conduct of this study sever-
al  surveillance techniques were found effective in eval-
uating the aquatic environment.  It was demonstrated that
in-plant source monitoring was of great value in  guiding
the  analytical techniques to achieve a maximum sensitiv-
ity for the radlonuclides released.  It was invaluable to
know the relative probability of the presence of volatile
nuclides like iodine in advance of sample preparation  to
preclude  any  loss of activity by the sample preparation
procedures.  The procedure  of  proportional  compositing
liquid  wastes as an independent monitor of waste release
rates was of similar value.   Such  procedures  validated
the operatorfs waste release data.
                          62

-------
     In  the  analysis of lake water the advantage of ion
exchange columns to improve sensitivity was demonstrated.
This technique was reported by Hasuike and Windham   (12).
This  technique  increased  analytical  sensitivity  by  a
factor of eight or more  compared  to  usual  techniques.
Such increased sensitivity provided crucial positive mea-
surements  which  otherwise  would have been missed using
former techniques.

     The analysis of vegetation tended to  indicate  that
qualitative monitoring of a body of water might be accom-
plished  from  this  data.   It was observed that aquatic
vegetation should be  surveyed,  mapped,  and  identified
prior  to establishing the sampling protocol.  In the ac-
complishment of this, divers should be used  to  acquaint
surveyors  with the location, prevalence, and identity of
submerged vegetation.  The latter is  probably  the  most
desirable sample source and is often ignored otherwise.

     Representative  sampling of the aquatic fauna proved.
to be the most difficult task to  achieve.   Due  to  the
mobility  of  the  fish,  the wide variety of species and
habitat preferences, and apparent paucity of  population,
this  task  was  not  accomplished to the degree desired.
The conductivity of the water in this  lake  limited  the
effectiveness of electrical shocking.  Rotenone poisoning
appeared too drastic a procedure.  Netting or other trap-
ping  techniques would have provided an insufficient sam-
ple size and a highly biased species distribution.

     Sampling of benthic  sediments  offered  significant
problems  in portions of the lake where submerged sticks,
limbs, and debris lined the bottom.  This material caught
in the jaws of the Peterson dredge and prevented its con-
tainment of a sediment sample.  In  many  cases  numerous
dredging  attempts  were performed to collect the sample.
Operationally, a wench system to operate the dredge was a
necessity.  It is felt that use of a diver to  locate  an
underwater marked location and perform a stringently con-
trolled  sample  collection  procedure might have reduced
some sample variability,

     An underwater gamma probe was used to survey regions
where  elevated  concentrations  of  sediments  might  be
found.   In  this  particular lake this procedure was not
sufficiently productive  to  warrant  discussion  of  any
positive  results.  Such procedures in other studies (13)
have been extremely helpful and should  be  evaluated  in
any similar surveillance activity.


                          63

-------
Conclusion

     The    buildup    concentrations    of    long-lived
radionuclides observed in Lake Robinson are  detailed  in
the   appropriate   tables.   The  rate  of  radionuclide
turnover in the components other than the water  was  too
rapid to quantitatively determine in this study.

     Since  the  buildup  rates appeared to be highly re-
sponsive to waste discharge rates,  lake  flow,  and  ex-
change  rates  between  the  component and the system, no
"life-of-the-reaetor"   effect   could   reasonably    be
evaluated.   At any given point in time concentrations of
radionuclides from the reactor as they occur in the  lake
water  and other lake components are primarily a function
of the history of the parameters for  the  previous  year
and are essentially independent of any older history.

     Table  22  summarizes reasonably expected annual ex-
ternal radiation doses to individuals engaging  in  swim-
ming,  boating, or fishing,  These data are calculated on
release rates presented in the  EIS  (9).   A  reasonable
estimate  of  dose  to  an  individual  who -swam, fished,'
and/or water skied in the lake would be about 5  microrem
per  year,  an  imperceptable  quantity  when compared to
background and other potential exposures.
                          64

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                       REFERENCES
1.   UNITED STATES NUCLEAR REGULATORY COMMISSION.   Title
     10,  Code of Federal .Regulations, Part 50, Licensing
     of Production and Utilization  Facilities,  Appendix
     I.   United  States  .printing Office, Washington, DC
     20402 (April 1975).

2.   UNITED STATES ATOMIC ENERGY COMMISSION.   Title  10,
     Code  of Federal Regulations, Part 20, Standards for
     Protection  Against  Radiation,  par.  20.105    (a).
     Division  of  Radiation Protection Standards.  U. S.
     Atomic  Energy  Commission,  Washington,  DC   205*15
     (August 1969).

3.   INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION.
     Report of  Committee  II  on  Permissible  Dose  for
     Internal Radiation (1959) .  ICRPf Publication  2, pp.
     27-34.   International  Commission  on  Radiological
     Protection.  Pergamon Press, Oxford  (1967).

<*.   CAROLINA POWER AND LIGHT  COMPANY.   Final  Facility
     Description  and  Safety  Analysis Report, Volumes  1
     and 3, USAIC Docket No. 50-261.  Carolina Power  and
     Light company (November 1968).

5.   RUTTP1R, FRANZ.   Fundamentals of Limnology, pp. ISO-
     IS?.  University of Toronto Press.  Toronto (1953).

6,   U,  S,  DEPARTMENT  OF  INTERIOR.   Daily  Discharge
     Tables  of Gage- Station 02130910 at Black Creek near
     Hartsville, SC,   October  1966  to  September  197ft.
     Geological  Survey,  Water Resources Division, U. S.
     Department of the Interior, Columbia, SC,

7.   CAROLINA POWER AND LIGHT COMPANY.  H.  B.  Robinson,
     Unit No. 2g Operating Reports 1-9.  Carolina Power
     and Light Company (1970 - 1974),

8.   U. S.  DEPARTMENT OF HEALTH, EDUCATION, AND  WELFARE,
     Public   Health   Service,    National   Center   for
     Radiological Health.   Public Health Evaluation of H,
     B. Robinson Unit No.  2,  NF-67-2.   National  Center
     for  Radiological Health, Rockville, Maryland  20852
     (January 1967).
                          65

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9.   ONITED STATES NUCLEAR REGULATORY COMMISSION,  Office
     of    Nuclear   Regulation.    Final   Environmental
     Statement related to the operation of H, B. Robinson
     Nuclear Steam-Electric Plant  Unit  2f  NOREG-75/024
     (April 1975).

10.   SALQ, ANNELI, and RITVA SAXEN.  On the Role of Humic
     Substances in the Transport of Radionuclides, Report
     SFL-A20.   .Institute of Radiation Physics,  Helsinki,
     Finland (December 1974).

11,   ENVIRONMENTAL PROTECTION AGENCY,  Preliminary Report
     on  Lake  Robinson,  Darlington,  and   Chesterfield
     Counties,   South Carolina, (Draft)  STORET No.  4508.
   .  National     Eutrophication     Survey,     National
     Environmental   Research   Center,    Las  ¥egas,  NV
     (November 1974) ,

12.   HASUIKE,  J.  K.  and, S. T. WIWDHAM.  Construction  and
     Operation   of    an   Ion   Exchange  Cartridge  for
     Monitoring   Radionuclides   in   the   Environment,
     ORP/EERF   73-2.   Eastern  Environmental  Radiation
     Facility,     Environmental    Protection     Agency,
     Montgomery,  AL  (June 1973).

13,   WINDHAM,  SAM T,  and C.  R. • PHILLIPS.    Radiological
     Survey of New London Harbor,  Thames River, Ccnn. and
     Environs,   Radiation  Data  and  Reports, 14:659-666
     (November 1973).
                           66

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Appendix I

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   soopoo1
ft
1
en
   300.000'
m

-------
                 1,2'
                 1,0
                f ,6'
                 .2'
                  9/70 1/71
                                          RF- Refueling Period


                                                    RF
         1/72          1/73
             month/year
                                                              1/74
          Figure A-3.
Liquid radioactive waste  releases
non-tritium  (7)
                  14-
                  12'
                  10"
                 4)
                 E1
                 £
                 rt
                 -i 4,
                   9/70 1/71
                                    1/72      .    1/73~
                                         month /year
                                    1/74   6/74
            Figure  A-4.   Lake  Robinson discharge  rates  {6}
*U.S. SOVEBBBW MtOTBB WWCi! »»-449-161/WlZ legion Ho, 4      &— 3

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