(EPA Office of Enforcement and General Counsel letterhead)
August 28, 1974
TO: All Regional Permit Branch Chiefs
FROM: Chemist, Permit Assistance Branch
SUBJECT: Application of Electroplating Guidelines to NPDES
Permits
Summary and Introduction
This memorandum is written to help explain the application of
Electroplating Guidelines to writing NPDES permits. It is
considered that the guidelines are essentially formulated on the
use of effluent flow X treated pollutant concentration logic.
The effluent flow is rated and used on a flow per area plated
basis. A generalized approach is given to understanding what is
meant by area plated in the guidelines and three possible methods
of calculation of area plated to obtain pollutant limits are
outlined. Finally, it is suggested that a direct total flow X
concentration calculation to made to assure reasonableness of
assigned permit limits.
The Electroplating Guidelines, Phase 1, covering the copper,
nickel, chromium and zinc subcategories, were issued in the
Federal Register on March 28, 1974. During that same month, the
final version of the Effluent Guidelines Division support
documentation for these guidelines were published as EPA Report
440/1-74-003-a. In recent months there have been three workshops
on the subject co-sponsored by Effluent Guidelines Division and
the Permit Assistance and Evaluation Division; they were held in
Washington, D.C., Boston, Massachusetts, and Philadelphia,
Pennsylvania and all were well attended by invited, interested,
State and Regional permit writing personnel. Specifically, the
subject matter of the meetings emphasized the justification of
the guidelines as well as their application to permit writing.
Significantly, the latter was explained by use of a number of
different examples. Apparently, most if not all of the
attendees' questions were answered to their satisfaction during
these meetings.
Unfortunately, the diverse nature of the Electroplating Industry
makes it extremely difficult, if not impossible to write down a
discrete, concise set of rules and examples to follow for the
facile writing of permits. The essential problem is that it is
absolutely necessary to correctly determine the total area plated
as required by the guidelines to obtain the basis of production
for the plant.
This memorandum is written in response to Regional requests I am
still receiving at this point in time for assistance in helping
to properly interpret the application of these guidelines. On
this subject matter, I have had numerous discussions with Carl
Schafer and participated in all of the Effluent Guideline
Division technical working group meetings. The contents are
based on these experiences as well as my own considerations and I
hope will clarify the picture enough to better expedite permit
preparation.
I. Underlying Premises and/or Assumptions
(a) Justification of the actual guideline limitations themselves and
the use of area as the unit-of-production base is not the object
of this memorandum. It must now be accepted as the Law and all
permits covered by these guidelines must be written accordingly.
(b) The treatment model is that of a common treatment plant wherein
the involved metals are coprecipitated and removed by settling,
clarification and/or filtration.
(c) The area plated is directly proportional to water use.
Essentially, the entire volume of process water used by an
electroplating plant is for rinsing the plated part after each
separate or individual operation. The explanation of what is
meant by a bona fide operation has been confusing, if not
misleading. In my opinion, it should mean any form of metal
finishing step that is followed by a rinsing procedure requiring
approximately the same amount of rinse water used after a
specific plating step. Certain metal pre-plating steps such as
acid-alkaline cleansing (or pickling) and on-line plating steps
such as the so-called metal "strike" may or may not require the
usual amount of rinse water, if any at all, after the specific
treatment step. It is essential that the permit writer establish
this through appropriate dialogue during the permit writing
process with the discharger. In this regard, a rule-of-thumb is,
the cleaning steps preceding plating are bona fide operations and
are to be counted as such, whereas the usual "strike" is not.
(d) The guideline limits are given in terms of mg or lbs of pollutant
per unit area plated (m2 or ft2). However, the logic is based on
the product of total flow into the treatment plant X treatment
concentration for each pollutant, in view of the treatment model
expressed in Item (b), above. This means that for each pollutant
the following relationships hold (for purposes of clarity, we
shall use the metric system only, hereafter).
Guideline Limitation: L/m2 X mg/L - mg2 (1)
In Equation (1) the term L/m2 actually represents either the
total flow in liters into the common treatment plant divided by
the total area plated or else, ideally, this ratio would be equal
to the ratio of amount of rinse water used for a particular
plating operation divided by the area plated during that
operation. The element of time is considered constant throughout
these discussions and, therefore, its actual amount is
irrelevant. Expressed analytically,
L (single operation/m2 (single operation) = L (total
flow)/m2 (total area plated) (2)
Therefore;
m2 (total area plated) = m2 (single operation) X No. of
operations (3)
Since the guideline limitation in mg/m2 is based on flow x
concentration logic as expressed in Equation (1), in order to
obtain mg as required for each pollutant in the permit (on a
daily basis) the following calculation must be used for each
pollutant:
m2 (total area plated) X mg/m2 (4)
This means that as long as there is a common treatment plant,
coefficient m2(total area plated) in Equation (4) is common to
all pollutants.
The above description applies to a single metal finishing line,
representing a number of separate operations in series. When
there is more than one line and regardless of whether or not
these additional lines plate at similar rates or plate different
objects with different metals, the total area plated and total
accompanying water use (if necessary) is calculated for that line
separately. Finally, and assuming the effluent from all plating
lines enter the same treatment plant concurrently, the total area
plated for all lines is summed up arithmetically to arrive at the
grand total m2 term used in Equation (4). If necessary, the
total effluent volume entering the treatment plant is arrived at
in the same manner.
Since the effluent limitations are fundamentally based on flow X
concentration logic, then it can readily be seen that the m2
(total area plated) term in Equation (4) is the same for all
pollutants in a complex plating plant regardless of how many
operations a particular pollutant is involved in, in the
different plating lines. Thus, assuming the pollutant is zinc.
whether or not it is plated in one or more different plating
lines in the same complex plating plant does not matter in
itself; what really counts, is that it is the total number of
operations involved, summed up in the manner described above,
that determines the m2 (total area plated) term in Equation (4).
Significantly, what this really means is that a plant plating
zinc in a solely single plating step (one operation) winds up
getting only one-fifth the total daily allowance of zinc that a
plant plating this same amount of zinc (geometric area being the
same) and plating four other metals (total of five operations) in
a single line, would get. This is due to the precipitation step
being concentration limited; therefore, the magnitude of the
final effluent is directly related to water usage.
II. Methods for Obtaining Total Area Plated
For purpose of emphasis, it is now repeated that each guideline
parameter expressed as mg/m2 must be multiplied by the same total
area plated figure determined for the particular plant.
This figure, in terms of a calendar day rate, can be obtained by
the various alternative methods to be discussed. It should be
possible to use at least two alternative methods as a check on
the reliability of the approach. These methods will now be
discussed.
(a) Geometric: The particular plant in question is likely to be a
captive shop that plates a common part of fixed geometry. The
plant knows the area plated for each part. Then, the total area
plated daily to be used for permitting purposes is:
Geometric Area Plated per Part X No. of Parts X No. of
Operations (5)
Needless to say, the average job shop that plates sundry
shaped parts on a day to day basis is not likely to have
such data.
(b) Electrochemical: The principle involved is the application of
Faraday's Law. The pertinent Law, actually the second of
Faraday's two laws on electrolysis states, in effect, that the
quantity of electricity required to liberate (or deposit) one
gram equivalent weight of a substance is 96,500 coulombs
(ampere-second). Expressed mathematically
W = Ite/96,500 (6)
Wherein
W = weight of metal deposited in grams
I = amperes flowing in plating line
t = seconds (time duration of plating)
e = gram equivalent weight of the metal plated
The gram equivalent weight of each metal can be obtained from
handbooks; however, in order to obtain the true W, one must
multiply the right-hand term in Equation (4) by the known plating
efficiency suggestions are given in the above referenced EPA
document, or else the plant must give its own certified estimate
of its plating efficiency.
Next, it is necessary to convert from W, the weight of metal
plated out to area by dividing by density of the plating
(certified plant estimate), to derive the volume of the plating.
Knowing the thickness of the plating (certified plant estimate),
it would then be possible to readily obtain the area plated if a
simple flat piece is involved. If the geometry of the plated
part is complex, then it is necessary to estimate the area from
the basic rules of solid geometry which are available from
standard handbooks.
It is my considered opinion that, once having gone through all of
these calculations, calculated area plated may still be off by
two or three times. If several metals are plated in the same
line, then possibly some direct averaging could be applied to
derive the best representative area. It is important to note
that the electrochemical approach gives the geometric area plated
per operation in a particular plating line. In order to obtain
the total area plated per plating line, it is necessary to
multiply the geometric area plated per operation as calculated
from Faraday's Law (this may require average if several metals
are plated per line and their respective geometric areas are
calculated individually by the total number operations involved
in that plating line.
In certain cases, such as when hollow cylinders are involved and
only the outside of the cylinder gets plated, the geometric area
plated must be multiplied by two, if both the unplated inside and
plated outside got rinsed. This is due to the fact that the
inside of the cylinder may be non-conductive, but nevertheless
gets exposed to electrolyte.
In summary, it is important to note that the permitter must
approach his estimation of area plated by this method very
cautiously and must be especially cognizant of pitfalls in the
plater's own estimate of area plated by this method, i. e., the
plater himself, especially if it is a job shop, may be incapable
of performing this type of calculation reliably for any one of a
number of reasons. In the past, he has not had to do so since
this has been a labor-based pricing type of industry for the most
part.
(e) Assumed Water Use-Area Plated Ratio: According to information
received from Effluent Guidelines Division, a liberal water use
per unit area plated per operation is
200 L/m2 (7)
This would apply to a plant that does not exercise particularly
good water conservation and could be readily established by a
casual plant visit by the permitter. Then, for each plating
line, the following calculation could be performed to obtain
total area plated:
L [total flow per line] / 200L / m2 = m2 (total area plated
per line) (8)
m2 (line 1) + m2 (line 2) +... = m2 (total area plated) (9)
Finally, total area plated could be substituted in Equation (4)
to yield the allowed pollutant limit in the permit. If a plant
is exercising good water conservation practice, the figure of 160
L/m2 (area plated per operation) would be a more judicious choice
in this calculation.
(d) Direct Flow times Concentration Method. This approach should be
used as a final check as to whether or not the assigned pollutant
limitations seem reasonable. The total flow would be multiplied
by the suggested EPCTCA concentrations in the above referenced
document, i.e., 0.5 mg/l for the heavy metals. If the plant is
using excessive water, these limitations would naturally be
expected to be higher than those obtained by the area-based
calculations. On the other hand, if the plant is using good or
normal water conservation, the pollutant limitations should check
out quite well with those of the other methods. Needless to say,
anything suspicious should lead to a reinvestigation of the
estimated total area plated.
Murray P. Strier
cc: C. J. Schafer
R. D. Schaffer
R. H. Johnson
Director, NFIC Denver
Director, NFIC Cincinnati
W. Hunt
Approved States