ADDENDUM TO "ESTIMATES OF POPULATION EXPOSURE
TO AMBIENT CHROMIUM EMISSIONS" OCTOBER 1983 FINAL REPORT
                        Julv 1984
                      Prepared for:

                   Karen L. Blanchard
                   EPA Project Officer
               Pollutant Assessment Branch
           ,  S. Environmental Protection Agency-
            Research Triangle Park, NC  27711
                      Prepared by:

                   Radian Corporation
                  3200 Progress Center
                     P. 0. Box 13000
            Research Triangle Park, NC  27709

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     ADDENDUM TO "ESTIMATES OF POPULATION EXPOSURE
TO AMBIENT CHROMIUM EMISSIONS" OCTOBER 1983 FINAL REPORT
                        July 1984
                      Prepared for:

                   Karen L. Blanchard
                   EPA Project Officer
               Pollutant Assessment Branch
          U. S. Environmental Protection Agency
            Research Triangle Park, NC  27711
                      Prepared by:

                   Radian Corporation
                  3200 Progress Center
                     P. 0. Box 13000
            Research Triangle Park, NC  27709

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1.0  INTRODUCTION

     The purpose of this Addendum is to present chromium emissions and
exposure information that has been developed subsequent to the finalization
of the October 1983 chromium exposure report, "Estimates of Population
Exposure to Ambient Chromium Emissions."  The source categories for which
information is presented include cooling towers and chromium electroplating,
Cooling towers were assessed in the October 1983 exposure study while
chromium electroplating was not.

     An additional examination of these two source categories was made
primarily because both are sources of hexavalent chromium emissions.   For
the cooling tower source category, the Addendum presents data on the
estimated total quantity of chromium that could be emitted into air
nationwide.  An approach to estimate total national emissions is explained,
key assumptions and input data are presented, and calculations leading to
the final chromium emission estimate are shown.  No exposure assessments
were conducted for cooling towers because of a lack of key data such  as the
number, sizes, and locations of sources, and the number of towers using
chromium corrosion inhibitors.

     The discussion of chromium emissions from chromium electroplating is
organized very similar to the cooling tower discussion.  Total national
chromium emissions from chromium electroplating are estimated and the
accompanying estimation methodologies, assumptions, and calculations  are
presented.  In addition, an attempt has been made to assess the national
exposure to chromium emissions from chromium electroplating using the Human
Exposure Model, a chromium electroplating model plant, a representative
subset of source locations, and an extrapolation of the subset to the total
population of approximately 10,000 platers.  All information pertinent to
the exposure assessment is presented in the Addendum.

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2.0  COOLING TOWERS

     This section of the Addendum presents the methodology used to calculate
an estimate of national chromium emissions from cooling towers and the
results of that calculation.  The primary method used to calculate chromium
emissions from cooling towers is based on an analysis of the energy consumed
by utilities and industry, the waste heat produced by this energy
consumption, and the quantity of water required to reject this heat.   Each
step of the emission estimating process is described below.

     The first input to the chromium emission estimating process is to
determine fuel consumption in the utility and industrial sectors.  These
data for 1983 are as follows.

     Utilities

     Coal - 13.226 x 10   Btu consumed
     Oil - 1.544 x 10   Btu consumed
     Gas - 3.011 x 10   Btu consumed
     Nuclear - 3.235 x 10   Btu consumed

     Industry

     Coal - 2.458 x 10   Btu consumed
     Oil - 6.763 x 10   Btu consumed
     Gas - 7.733 x 10   Btu consumed

For utilities the assumption was made that all consumed energy went to
produce electricity.  The efficiency of the electricity-generating process
is only about 30 percent, such that 70 percent of the consumed heat energy
is lost as waste heat.  Of the 70 percent waste heat fraction, 10 percent is
heat losses in the plant and 60 percent is heat rejected in cooling towers,

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                                          2
cooling ponds, or by once-through cooling.   The total quantity of waste
heat from utilities to be rejected by cooling is calculated as follows.

     (21.016 x 1015 Btu) x 0.60 = 12.6096 x 1015 Btu
     The fraction of heat rejected by various cooling means at utilities is
shown below.
     Cooling towers - 70 percent
     Cooling ponds - 20 percent
     Once-through cooling - 10 percent

     For industry the assumption is not made that all energy consumed goes
to produce energy in the forms of steam and electricity.  In industry,
energy (as coal, oil, and gas) is consumed as a process raw material and
there are direct fired sources that just burn fuel for heat.  The estimated
fractions of industrial energy consumption that are used for energy (steam
                                          4
or electricity) production are as follows.

     Coal - 30 percent
     Oil - 70 percent
     Gas - 50 percent

The energy conversion efficiency in the industrial sector is assumed to be
about 40 percent.  Like the utility sector, 10 percent is lost within the
plant as heat and the remaining 50 percent is rejected as waste heat in
cooling towers.

     For industry, the amount of waste heat to be rejected in cooling towers
can be calculated as shown below.

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     Coal:     2.458 x  1Q15 Btu
                     x  0.30
               7.374 x  10   Btu to Energy
                     x  0.50
               3.687 x  1014 Btu as Waste Heat
     Oil:      7.733 x 1015 Btu
                     x 0.70
               5.413 x  1015 Btu to Energy
                     x  0.50
               2.707 x  1015 Btu as Waste Heat
     Gas:      6.763 x  1015 Btu
                     x  0.50
               3.382 x  1015 Btu to Energy
                     x  0.50
               1.691 x 1015 Btu as Waste Heat
     Total as Waste Heat = 4.766 x 10   Btu
     To determine the quantity of water required to reject the heat loads in
the utility and industry sectors, the following equation is used.

     Heat Rejected  (Q_) = Mass Water (W) x (1 Btu/lb  F) x Temperature
                     K
          Change to be Effected  (AT0)

The AT0 value in the equation represents the temperature differential
between the incoming hot water containing waste heat from combustion and the
effluent water stream to be discharged or recycled to the plant.  The AT to
be achieved varies from plant to plant.  For the purposes of these emission
estimation calculations, AT0 is assumed to be 40F, i.e., water temperature
is being decreased from 120F to 80F.

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     The results of applying this equation to the waste heat loads
calculated from the utility and industry sectors is given below.

Utilities

     QD = 12.6096 x 1015 Btu
      K

     (12.6096 x 1015 Btu) = W  (1 Btu/lb  F) (40F)

     W  = 3.1524 x 1014 Ib water
      u

Seventy percent of W  in the utility sector goes to cooling towers and is
expressed as W'.

     W = (3.1524 x 1014 Ib) x 0.70 = 2.2067 x 1014 Ib water
     Of the total quantity W, some fraction occurs as cooling tower drift.
Drift is entrained water droplets that are mechanically formed in the tower
and carried out into ambient air by the cooling tower air flow.  The
quantity of drift formed and released is a function of several factors
including:

          the quantity of heat to be rejected,
          tower air flow,
          tower design, and
     -    ambient meteorological conditions.

The amount of drift occurring from a tower is generally designed to be a
percentage of the total quantity of water recirculating in the tower.  Drift
fraction like the AT0 value is site specific and very difficult to typify
for all sources.  Drift losses reported in the literature range from 0.002 -
0.2 percent.  For the purposes of these calculations a drift fraction of
0.01 percent is assumed.

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     (2.2067 x 1014 Ib water) x 0.0001 = 2.2067 x 1010 Ib water emitted
                                                       as drift

                10                              9
     2.2067 x 10   Ib water x 1 gal = 2.659 x 10  gal water as drift
                              8.3 Ib

     This quantity of drift is assumed to contain 20 ppm chromium (as
chromates) based on typical values reported in the literature.

     (2.659 x 109 gal) x 0.00002 = 5.318 x 104 gal chromium

     To calculate the mass of chromium emitted in the drift, the typical
density of the various proprietary chromate corrosion chemicals would have
to be known.  This value is unavailable, therefore, the density of sodium
chromate was used for the purposes of these calculations since  it is a raw
material in the production of the corrosion inhibiting chemicals.  The total
quantity of chromium calculated to be emitted from utility cooling towers is
shown below.

     (5.318 x 10  gal) x 22.67 Ib/gal = approximately 600 tons  of chromium
                                        as sodium chromate

The quantity of hexavalent chromium contained in this 600 tons  is
approximately 192 tons.

       Utility Cooling Tower Emissions of Cr   = 192 tons

This estimated total of 192 tons is an upper bound because it assumes that
all towers use chromium corrosion inhibitors.  No information could be
developed to approximate the fraction of utility towers using chromium.

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Industry

     The same methodology described above for utilities was also applied to
the waste heat load estimated for industry of 4.766 x 10   Btu.  The
calculations are briefly illustrated below.

     (1)  (4.766 x 1015 Btu) = W. (1 Btu/lb  F) (40F)
                          14    x
          W. = 1.1915 x 10   Ib water to cooling towers

     (2)  (1.1915 x 10U Ib) x 1 gal = 1.4355 x 1013 gal water
                               8.3 Ib
     (3)  (1.4355 x 1013 gal) x 0.0001 = 1.4355 x 109 gal water as drift

     (4)  (1.4355 x 109 gal) x 0.00002 = 2.871 x 104 gal chromium

     (5)  (2.871 x 104 gal) x 22.67 Ib/gal = approximately 325 tons of
                                             chromium as sodium chromate
     The quantity of hexavalent chromium contained in this 325 tons is
     approximately 104 tons.

       Industrial Cooling Tower Emissions of Cr   = 104 tons

     This estimated total, like that from utility towers, is an upper bound
     because it assumes that all towers use chromium corrosion inhibitors.

     The total amount of Cr   estimated to be released from utility and
industrial cooling towers, assuming all use chromium corrosion inhibitors,
equals 296 tons/yr.

     Additional information is available in reference 2 from which to
calculate another estimate of chromium emissions from utility cooling
towers.  The different estimate is based on a cooling water requirement

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presented in the reference that is different from that calculated by the
                                                        o
heat capacity equation.  Reference 2 reports that 0.16 m  water are needed
for cooling at utilities per kWh of power produced.  According to Department
of Energy statistics, power plants producing electricity and requiring
cooling water generated 1,971,698 x 10  kWh of electricity in 1983.  Total
water requirements can be calculated as follows.

     (1)  (1,971,698 x 106 kWh) x 0.16 m3 = 3.1547 x 1011 m3
                                    kWh
     (2)  3.1547 x 1011 m3 x 264.2 gal = 8.3347 x 1013 gal water
                                     3
                                    m
Of this amount of water, 70 percent is used for cooling towers.

     0.70 x (8.3347 x 1013 gal) = 5.8343 x 1013 gal
Assuming a 0.01 percent drift fraction, total drift can be calculated as
follows.

     0.0001 x  (5.8343 x 1013 gal) = 5.8343 x 109 gal

By applying the chromium concentration in drift of 20 ppm and the sodium
chromate density factor used in the previous emission estimating
calculations,  a chromium (as Cr  ) emission rate from utility cooling towers
of approximately 423 tons/yr can be calculated.  This emission rate, like
that in the previous calculations, represents an upper bound because it
assumes that all utility cooling towers use chromium corrosion inhibiting
chemicals.

     If the 423 tons/yr chromium emission number for utility cooling towers
is used in the emission estimating assessment, the range of hexavalent
chromium emissions from utility and industrial cooling towers would be
296 - 527 tons/yr.

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     It is expected that this range overstates emissions because it assumes
all utility cooling towers use chromium, but most references indicate that
                                               811
utilities use much less chromium than industry.      Quantitative data on
chromium usage is generally not available; however, the Electric Power
Research Institute (EPRI) has indicated that it has such data on its member
                                                                     12
utilities but the information is confidential and cannot be released.
                                      10

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3.0  CHROMIUM ELECTROPLATING

3.1  PROCESS DESCRIPTION

     Chromium is plated onto various substrates in order to provide a
decorative and corrosion resistant surface.  Steel, brass, aluminum,
plastics, and zinc die castings may serve as substrates.  The two major
types of chromium plating are decorative and hard.  Decorative plate
consists of a thin (0.25 ym thick) layer of chromium which is applied over a
layer of nickel to provide a bright, tarnish-resistant surface.  Decorative
chrome plate is popular for consumer items such as auto trim.  Hard plating
produces a thicker chromium layer (10 to over 300 urn thick) which has
excellent hardness and wear-resistance and a low coefficient of
         13 14
friction.  '    Applications include drills, reamers, burnishing bars,
drawing plugs or mandrels, drawing dies, plastic molds, gages, pump shafts,
rolls and drums, hydraulic rams, and printing plates.    The electroplating
process used to produce the two types of chromium plates are similar.
     Figure 1 provides a generalized flow chart for decorative chromium
plating on a steel substrate.  Figure 2 shows the hard plating process, for
which steel is the usual substrate.  Possible variations on the processes
shown in Figures 1 and 2 are discussed below.  Plating operations generally
involve dipping the substrate into tanks containing various solutions.   The
substrate items may be moved between tanks manually or using automation.
The decorative and hard plating processes both involve cleaning and
preparing the substrate followed by the electrodeposition of chromium.   It
should be noted that rinsing is carried out between every cleaning and
plating step.  When a part being plated is moved from one tank to the next,
some of the solution from the first tank will remain on the part and be
transferred to the next tank.  This process is termed drag-in, and rinsing
between plating steps is necessary to reduce contamination of plating
solutions by drag-in.
                                     11

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                                        Steel Substrate
                                        To Be Plated
                                    Pretreatment Step
                                   (polishing, grinding,
                                    degreasing)
                                   Alkaline  Cleaning
                                                Rinse
                                         Acid  Dip
                                                Rinse
                                  Strike Plating of
                                       Copper
                                                Rinse
                                        Acid Dip
                                                 Rinse
                                   Electroplating of
                                       Copper
                                                 Rinse
                                   Electroplating of
                                   Semibright Nickel
                                                 Rinse
                                   Electroplating of
                                   Bright Nickel
                                                 Rinse
                                   Electroplating of
                                      Chromium
                                                 Rinse

                                           I
                                      Decorative Chromium
                                         Plated Product
Chromic Acid
Emissions
Figure   1.   Flow chart  for  decorative chromium plating on a  steel  substrate,
                                                                                              15
                                             12

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             Substrate to be
                  Plated
                    i
          Pretreatment Step
          (Polishing,  grinding,
          degreasing)
                     \
         Alkaline Cleaning
                         Rinse
                 Acid Dip
                         Rinse
           Chromic Acid
           Anodic Treatment
                         Rinse
           Electroplating of
               Chromium
                         Rinse
              Hard Chromium Plated
                    Product
Chromic Acid
Emissions
Chromic Acid
Emissions
Figure 2 .   Flow chart for hard chromium plating.
                     13

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     The chromium plating processes start with a pretreatment step
(Figure 1, pt. 1 and Figure 2, pt. 1) which can consist of mechanical
buffing, polishing, and vapor degreasing or soaking in an organic solvent.
Alkaline cleaning (Figure 1, pt. 2 and Figure 2, pt. 2), removes surface
soil and is accomplished by soaking and/or electrolytic processes.  Gas
evolution on the surface of the substrate aids the cleaning agent's action
in electrolytic alkaline cleaning.  More details on electrolytic processes
are given in reference 14 in connection with chromium electroplating tanks.
After cleaning, the substrate is dipped in acid (Figure 1, pt. 3 and
Figure 2, pt. 3) to remove tarnish and to neutralize the alkaline film on
its surface.  At this point, the steel substrate is clean and ready to
accept a metal deposit.

     In the case of decorative chromium plating, an undercoat of copper is
applied to the steel in two plating steps, with an acid rinse between each
step (Figure 1, pts. 4-6).  Next a nickel plate is applied by
electrodeposition (pts. 7 and 8).  These undercoats prohibit undesirable
reactions between the substrate and the final plate which could embrittle
the final product.  Nickel also provides the basic protection and
wear-resistance of the plated part since the decorative chrome layer is very
thin.  The final step in the decorative plating process is the
electrodeposition of a thin layer of chrome (pt. 9).

     In the hard chromium plating process, the cleaned substrate undergoes
an anodizing treatment (pt. 4).  This puts a protective oxide film on the
metal by an electrolytic process in which the substrate serves as the anode.
Then the hard chromium layer is electrodeposited (pt.  5) without any
                           . .  . 13-15
undercoating of copper or nickel.

     A typical chromium electroplating tank is pictured in Figure 3.    The
system consists of a cathode and an anode, both immersed in electrolyte.
Generally the part to be plated functions as the cathode, and the anode is a
bar of lead-antimony or lead-tin alloy.  The electrolyte contains ions of
                                     14

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                    Anode bar

                Anodes
    Insulating
    block
Cathode
     bus
  Flexible
  conduct
    Anode bus
                                        'Work bar
  Low-rpm drive motor
  to move work bar
  in oscillating
  motion

   Connecting rod
                                                     Cooling  or  heating
                                                     coil
Rack load of parts
suspended from work
bar
                Tank
      Figure 3 .   Cut away view of  electroplating  tank.
                               15

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hexavalent chromium (from chromic acid) and small amounts of another anion,
usually sulfate.  The sulfate, or sometimes flouride, improves the
electrical conductivity of the electrolyte bath.

     To accomplish the plating process, low voltage direct current process
electricity is charged through the electrolyte bath.  Electrolytic
decomposition of water in the bath releases hydrogen gas at the cathode and
oxygen at the anode.  As these gases rise to the surface of the bath, a mist
of electrolyte is formed and chromium metal is deposited on the substrate.

     Table 1 shows the composition of conventional chromium plating
solutions, and the temperature and current densities in a typical tank.
Recently developed proprietary processes substitute flouride or flousilicate
ions for sulfate ions in the electrolytic plating solution, resulting in
more efficient chromium plating.  Another area of present investigations
involves using trivalent chromium baths as an alternative to hexavalent
chromic acid plating baths.  The extent of use of trivalent chromium plating
solutions is unknown.

     Current efficiency of chromium deposition is low, about 8 to 12 percent
for conventional baths and up to 20 percent for newer flouride ion
solutions.  This and other factors combine to require long plating times for
depositions of the thickness required in hard chromium plating.  Table 1
gives typical chromium plate deposition rates.

     The chromium electrodeposition step is the same no matter what
substrate material is used.  However, the cleaning and preparation of other
metal substrates may differ from those discussed for steel (Figures 1 and
2).  For example, the copper undercoat may be applied in one plating step
rather than the two copper plating steps for steel substrates shown in
Figure 1.  Similarly, nickel underplate may be applied in one rather than
two steps.  On aluminum substrate, a zinc plate is usually applied before
the copper plate.  When plating on plastic, the cleaned surface must be
                                     16

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             TABLE 1.  TYPICAL CHROMIUM-PLATING CONDITIONS USING

                       CONVENTIONAL BATHS15
                                                         Hard Chromium
                               Decorative Plates    Dilute
                              Concentrated
Chromic acid (CrO ), g/1


Sulfuric acid (H2S04), g/1

                            2
Cathode current density, A/m


Temperature, C


Deposition rate, ym/hr
  250-400


   2.5-4


1,250-1,750


   38-43


    8-13
  250


    2.5


3,100


   55


   25
  400


    4


2,200


   50


   13
                                     17

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activated, rendered catalytic, and given an electroless deposit of nickel or
                                                                          1 "3
copper before the electrolytic deposition of copper, nickel, and chromium.
These process variations, however, do not affect the procedures used in or
emissions from the final chromium electroplating step.

Emission Factors                                           *
     The potential source of chromium emissions from the decorative chromium
plating process is the electroplating step (Figure 1, point 9).  Chromium
emissions from the hard plating process (Figure 2) are generated in the
electroplating step and in the chromic acid anodizing treatment step.   In
the chromium electroplating steps of the decorative and hard plating
processes, mists or aerosols of the electrolyte (primarily chromic acid)  are
generated.  Variables that affect electroplating emission rates include the
bath temperature, the concentration of bath constituents, the amount of work
being plated, and the plating current.  The chromium plating tank in the
hard chromium process generates more chromic acid mist than the plating tank
in the decorative process because a higher current density is used for metal
deposition (see Table 1).  The higher current density causes higher rates of
gassing thereby generating more chromic acid mist.

     Hooding is generally used on chromium electroplating tanks to collect
chromium containing gases and convey them out of the plating building.   Wet
scrubbers are often used to control chromic acid emissions from plating
operations.  The efficiency of wet scrubbers in collecting chromium
emissions from electroplating tanks is reported to be 95 percent.   '    A
system developed at one plating operation combines a wet scrubber, multiple
stages of electrostatic precipitators, and an activated carbon filter.   The
tested chromium removal efficiency is 99.7 percent.

     Chromium emission factors for electroplating operations are limited,
particularly for the decorative plating process.  Table 2 shows chromium
emission factors developed from the testing of one hard chromium plating
          I Q
operation.    Emission factor data for decorative plating are much more
                                     18

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    TABLE 2.  UNCONTROLLED EMISSION FACTORS FOR CHROMIUM ELECTROPLATING18
                                            Chromium Emission Factor


     Source of Emissions                     Ib/hr  ft  tank area
Hard Plating Tank                                   0.000044



Hard Plating Tank                              0.000028 - 0.00015



Hard Plating Tank                              0.000046 - 0.00013
a                                                         +6
 Factors are expressed in terms of hexavalent chromium (Cr  ).
                                     19

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limited; however, uncontrolled emissions from one 4,920 liter (1,300 gallon)
tank used for decorative chromium plating were reported to be 0.20 kg
(0.45 Ib) of chromic acid per hour.

3.3  NATIONAL EMISSIONS

     National chromium emissions from chromium electroplating operations
were estimated using the emission factors in Table 2 and assumptions
generated from contacts with the plating industry.  The key assumptions to
estimating national emissions involve the following factors.

          number of shops plating chromium
     -    number of chromium tanks per shop
          size of chromium plating tanks
          operating schedule of chromium plating shops

The number of shops plating chromium was estimated using data generated by
EPA in its characterization of the electroplating industry for wastewater
                      19
pretreatment standards   and using estimates from the electroplating
         20-23
industry.       The total number of electroplating shops in the U.  S.  has
                            19
been estimated to be 13,000.    Of this 13,000, approximately 75 percent are
                               20-23
assumed to be plating chromium.       The 9,750 shops assumed to be plating
chromium includes both captive and job shop platers.  Contacts in the
plating industry stressed that there are no complete or well developed data
bases for this industry in regard to the number of shops,  the number of
tanks per shop, tank sizes, and shop locations.  The estimates used in this
assessment for these parameters were judged by the people  contacted to be
reasonable.  Therefore, the following assumptions were applied for the
purpose of calculating national chromium emissions from chromium
electroplating.

     Number of shops plating chromium - 9,750
     Number of chromium tanks per shop - 2
                                     20

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     Size of each plating tank - 32 ft2  (4* x 8')
     Operating schedule - 8 hrs/day, 250 days/yr

     From the data presented in Table 2, an average chromium emission factor
of 0.000080 Ib/hr  ft  (as Cr+ ) was estimated.  Using this factor and the
assumptions given above, a national emission estimate can be calculated as
follows.

     (1)  2 tanks x 9,750 shops x 32 ft2  = 624,000 ft2
            shop                     tank
     (2)  624,000 ft2 x 0.000080   Ib     = 49.9 Ib
                                 hr  ft2         hr

     (3)  49.9 Ib x 250 days x 8 hrs = 99,800 Ib = 49.9 tons Cr+6
               hr        yr      day          yr         yr

National chromium emissions (as Cr  ) from chromium electroplating are
estimated to be approximately 50 tons/yr.  This estimate is based on the
average emission rate.  The range of potential emissions is 17.5 -
93.6 tons/yr Cr  .  All the national chromium emission estimates presented
here are for uncontrolled emissions.  A vendor of control systems for
electroplating shops indicated that shops built in the last 10 years
                                                20
probably have some type of chromic acid control.    He expects, however,
that the majority of the chromium plating shops are uncontrolled.  No
quantitative estimate is available on the percentage of chromic acid
                         in , 20
emissions that are controlled.
3.4  POPULATION EXPOSURE TO CHROMIUM FROM CHROMIUM ELECTROPLATING

     In this section, the ambient chromium concentrations attributable to
chromium electroplating sources are estimated and the level of population
exposure to these estimated concentrations are determined using the EPA's
                                     21

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Human Exposure Model  (HEM) .  A description of the HEM is provided in
Appendix A of the original October 1983 final report.

     Source-specific  input data for the HEM analysis could not be determined
for the chromium electroplating source category because of the large number
of individual sources.  As an alternative, a chromium electroplating model
plant was developed for use in the HEM analysis.  The source parameters of
the model plant are presented in Table 3.  A model plant of the type given
in Table 3 was assumed to be located in 117 cities in the country where
chromium plating is expected to be found.  The locations of these platers
were obtained from the Thomas Register industrial directory.  It is assumed
that these 117 model  plant sites are representative of the total population
of chromium platers and that the HEM results for the subset can be
extrapolated to the total population.

     The summary results of the HEM analysis for the subset of chromium
platers are presented in Table 4.  Problems exist in extrapolating these
results to the total  population of chromium platers due to a large amount of
double-counting of exposed people.  Double-counting occurs because the
number of sources is  large and the sources are concentrated in mostly urban
locations such that the population grids defining exposure overlap.  The
overlapping occurrence is easily illustrated in that about twice as many
people as are in the  country are predicted to be exposed to chromium from
plating, and this estimate only represents 1 percent of the sources.  The
public exposure results should likewise be evaluated cautiously because they
are related directly  to the population exposed numbers.

     The most meaningful results from the HEM analysis of the subset of
chromium platers appear to be the chromium (as Cr  ) concentrations
predicted to occur in ambient air around plating shops.  The maximum
concentration to which anyone is estimated to be exposed to is
            o
0.00539 yg/m .  This  exposure concentration ranges from one to about four
orders of magnitude less than the maximum exposures estimated for the other
                                     22

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        TABLE 3.  SOURCE CHARACTERIZATION PARAMETERS OF THE CHROMIUM
                  ELECTROPLATING MODEL PLANT
     Parameter
          Value
Chromium Emission Rate

Stack Height

Stack Diameter

Stack Gas Velocity

Stack Gas Exit Temperature

Cross Sectional Area

Vertical Stack
4.6 kg (10.2 lb)/yr

6.1 m (20 ft)

0.31 m (1 ft)

18.6 m/sec (61.1 ft/sec)

305K (32C)

100 m2 (1076.4 ft2)

Not Applicable
Emissions expressed as hexavalent chromium (Cr  ) .
DThis represents the vertical cross sectional area of the emission point  to
 the mean wind direction for the purpose of calculating downwash.
                                     23

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   TABLE 4.  POPULATION EXPOSURE TO CHROMIUM FROM CHROMIUM ELECTROPLATING

             SHOPS AS PREDICTED BY THE HUMAN EXPOSURE MODEL3
Concentration Level           Population Exposed            Public Exposure
          Q                                                              Q
           )                       (Persons)                (Persons-yg/m )
0.00539
0.0050
0.0025
0.001
0.0005
0.00025
0.0001
0.00005
0.000025
0.00001
0.000005
0.0000025
0.000001
0.0000005
0.00000025
0.0000001
0.00000005
0.000000046
1
1
5,710
50,300
162,000
391,000
1,150,000
2,670,000
6,190,000
18,600,000
41,000,000
84,500,000
201,000,000
328,000,000
416,000,000
437,000,000
438,000,000
438,000,000
< 1
< 1
18
83
161
240
355
460
582
770
924
1,080
1,260
1,350
1,380
1,380
1,380
1,380
aThese results apply only to the 117 model chromium electroplating shops
 analyzed as a representative subset of the total population of plating
 shops.
 This column displays the computed value, rounded to the nearest whole
 number, of the cumulative number of people exposed to the matching and
 higher concentration levels found in column 1.  For example, 0.5 people
 would be rounded to 0 and 0.51 people would be rounded to 1.
Column 3 displays the computed value of the cumulative exposure to the
 matching and higher concentration levels found in column 1.
                                     24

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chromium source categories given in the October 1983 report.  The minimum
ambient chromium concentration to which people are predicted to be exposed
                                                             3
to from chromium electroplating emissions is 0.000000046 yg/m .  Although
precise quantification is not possible with the results of the HEM analysis,
it is probable that a large distinct number of people (on the order of tens
of millions) are exposed to ambient chromium levels equal to this minimum
level or greater.  This estimation is based on the raw HEM results which
showed that the population affected by each model plant ranged from 10  -
10  people and the consideration that most sources are in or located close
to urban areas.
                                     25

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4.0  REFERENCES FOR ADDENDUM

1.   Monthly Energy Review - January 1984.  DOE/EIA-0035(84/01).  Energy
     Information Administration, Washington, DC.  April  1984.

2.   Davis, G. H. and Wood, L. A.  Water Demands for Expanding  Energy
     Development.  U. S. Geological Survey.  Geological  Survey  Circular 703.
     1974.

3.   Hu, M. C., et_ _al_.  Water Consumption and Costs for  Various Steam
     Electric Power Plant Cooling Systems.  EPA-600/7-78-157.  August 1978.

4.   Summary of unpublished statistical data gathered by Radian Corporation
     during the development of the industrial boiler new source performance
     standard.  Radian Corporation, Research Triangle Park, NC.  1983.

5.   Alkezweeny, A. J., ^_t_ a_l.  Measured Chromium Distributions Resulting
     from Cooling Tower Drift.  Presented at the Cooling Tower  Environment -
     1974 Symposium.  College Park, Maryland, March 4-6, 1974.

6.   Jallouk, P. A., e_t_ _a_l.  Environmental Aspects of Cooling Tower
     Operation.  Presented at the Third Environmental Protection Conference
     of the U. S. Energy Research and Development Administration.
     Chicago, IL, September 23 - 26, 1975.

7.   Taylor, F. G. , _et_ _al_.  Cooling Tower Drift Studies  at the Paducah,
     Kentucky Gaseous Diffusion Plant.  Presented at the Cooling Tower
     Institute Annual Meeting.  Houston, TX, January 22  - 24, 1979.

8.   Telecon.  Brooks, G. W., Radian Corporation with Pucorius, P.,  Pucorius
     and Associates.  March 2, 1983.  Cooling tower emissions.

9.   Telecon.  Brooks, G. W., Radian Corporation with McCloskey, J., Betz
     Laboratories.  February 22, 1983.  Cooling tower emissions.

10.  Telecon.  Brooks, G. W., Radian Corporation with Augsburger, B.,
     Pucorius and Associates.  February 23. 1983.  Cooling tower emissions.

11.  Telecon.  Brooks, G. W., Radian Corporation with Townsend, J.,  Cooling
     Tower Institute.  February 22, 1983.  Cooling tower emissions.

12.  Telecon.  Brooks, G. W., Radian Corporation with Michiletti, W.,
     Electric Power Research Institute.  June 25, 1984.  Chromium use in
     utility cooling towers.

13.  Sittig, M. (Noyes Data Corporation).  Environmental Sources and
     Emissions Handbook.  Noyes Data Corporation, Park Ridge, NJ.  1975.
     pp. 263-270.
                                     26

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14.   Kirk-Othmer Encyclopedia of Chemical Technology.   Third Edition.
     Volume 6.   John Wiley and Sons, Inc.  New York.   1980.   pp.  65-66.

15.   Kirk-Othmer Encyclopedia of Chemical Technology.   Third Edition.
     Volume 8.   John Wiley and Sons, Inc.  New York.   1980.   pp.  826-844.

16.   Daley, P.  S.  Pollutant Generation by Air Force  Electroplating
     Processes.  CEEDO-TR-77-10.  Civil and Environmental Engineering
     Development Office,  U. S. Air Force, Tyndall Air Force Base,  Florida.
     June 1977.

17.   Gothard, N.  Chromic Acid Mist Filtration.  Pollution Engineering,
     Volume 10, Number 8, pp. 36 - 37.  August 1978.

18.   Diamond, P.  Air Pollution Potential From Electroplating Operations.
     Environmental Health Laboratory, McClellan Air Force Base,  California.
     Report Number 69M-15.  April 1969.

19.   Development Document for Existing Source Pretreatment Standards for  the
     Electroplating Point Source Category, EPA-440/1-79/003.  Effluent
     Guidelines Division, U. S. Environmental Protection Agency.
     Washington, DC.  August 1979.

20.   Telecon.  Brooks, G. W., Radian Corporation with  Stewart,  F.,  Lancy
     International.  June 21, 1984.  Chromium plating  air emissions.

21.   Telecon.  Brooks, G. W., Radian Corporation with  Ruhley, K., Metal
     Finishers Suppliers Association.  June 20, 1984.   Chromium plating air
     emissions.

22.   Telecon.  Brooks, G. W., Radian Corporation with  Carey, J.  D., National
     Association of Metal Finishers.  June 20, 1984.   Chromium plating air
     emissions.

23.   Telecon.  Brooks, G. W., Radian Corporation with  Baker, M.,  American
     Electroplaters Society.  June 20, 1984.  Chromium plating air
     emissions.
                                     27

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