EPA 600/D-81-067,
February 1981
Evaluation and Control of Asbestos-Cement Pipe Corrosion
by
Michael R. Schock, Gary S. Logsdon, and Patrick J. dark
U.S. Environmental Protection Agency
Municipal Environmental Research Laboratory
Drinking Water Research Division
Cincinnati, Ohio 45268
To be presented at the International Corrosion Forum
i
Sponsored by the National Association of Corrosion Engineers
April 6-10, 1981
Toronto, Ontario, Canada
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EVALUATION AND CONTROL OF ASBESTOS—CEMENT PIPE CORROSION
MICHAEL R. SCHOCK, GARY S. LOCSDON and PATRICK J. CLARK
Drinking Water Research Division
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
ABSTRACT
In order to properly evaluate the corrosiveness of water supplies to
asbestos—cement (A/C) pipe, several different analytical methodologies
are being compared with regard to their cost, ease of use, type and
amQunt of information gathered and accuracy in describing the pipe
condition under field and laboratory conditions. Reported here are
experiences gathered thus far from the use of water chemical analyses
coupled with.computer—assisted calculation of aqueous and solid
speciation, reflected—light optical microscopy, scanning and trans-
mission electron microscopy and energy—dispersive x—ray spectroscopy.
References are made to more detailed theoretical interpretations of
results of experimental and field studies, and compilations of the
experiments.
INTRODUCTION
Because of concern about the possible problem of asbestos fibers being
released from the walls of asbestos—cement (A/C) pipe, the American Water
Works Association Research Foundation reviewed the problem and in September,
1974(1) suggested several research needs in this area. As a response to this
call for research, several projects were designed by the Drinking Water Research
Division (DWRD), U.S. Environmental Protection Agency’, to determine whether
A/C pipe would be attacked and asbestos fibers would be released from the pipe
under various conditions of water quality. In general, this research has been
divided into four general phases. The phases are: a field evaluation of 10
public water supply systems that used A/C pipe, an A/C pipe loop system
operated under controlled conditions, numerous pilot plant tests of A/C
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‘pipe coupons,” and research projects that are attempting to rehabilitate
deteriorated pipe in place. Buelow et al( 2 presented results from the first
three phases of the research, and Schock and Buelow( 3 ) presented additional
detail on the laboratory experimentation, and proposed a theoretical chemical
framework upon which a more accurate assessment of A/C pipe behavior in
drinking water can be based. Presently, as an adjunct to several studies
focusing on exposure assessment and investigation of possible human health
effecr s., 4 ’ 5 more field chemical data is being gathered to correlate with
the chemical model of naturally—occurring and synthetic corrosion inhibitory
factors. Additionally, DWRD has recently begun investigation and evaluation
of various methods for quantitatively and qualitatively describing A/C pipe
surf icial condition, and this paper reports some of the experience gathered
thus far with those techniques.
CHEMICAL EVALUATION OF A/c PIPE CONDITION
Limitations of the “Aggressiveness Index ”
Classically, the tendency of a water to deteriorate the structure of
asbestos cement pipe has been described by the Aggressiveness Index”
(AI) ( 6 ’ 7 given as
Al pH ÷ log (AK)
where
pH —log aff (—log of the hydrogen ion activity)
A total alkalinity in mg/L as CaCO 3
H calcium concentration in mng/L as CaCO 3
Waters possessing an Al equal to or in excess of 12.0 are considered to
be “nonaggressive;” those where AX < 10.0 are said to be “highly aggressive,”
and those with an AZ between 10 and 12 are -“moderately aggressive.” The Al
is derived 6 from a simplified form of the Langelier Index of calcite
sacuration ( 8 , 9 ) with factors introduced to compensate for the temperature
dependency of• the solubility product constant (Kso) of calcite and for the
ionic strength ( ° 11 of the solution.
The use of the Al as a predictor of the condition of the interior surface
of the pipe in contact with the drinking water and its tendency to retain or
release asbestos fibers has come about in spite of the fact that the original
intention of the index was to outline water’conditions that might cause
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structural failure of the pipe. ( 12 ) The difference in application is very
significant.
Substantial field and pilot plant data, combined with a comprehensive
evaluation of many of the important chemical complexation and precipitation
reactions occurring in a drinking water, give compelling evidence that the Al
has immense shortcomings with regard to use as a predictor of fiber release
and interior surficial pipe condition that enjoin against its use under most
circumstances. Schock and Buelow have discussed many limitations in detail, ( 3 )
and they may be briefly summarized as follows:
1. The temperature dependence of the solubility constant for calcite
used appears to be in substantial error. The original experimental
work did not account for the existence of ion pairs of calcium and
carbonate species. It is also not clear that the first—precipitated
calcium carbonate solid phase can be accurately characterized by the
solubility product constant of calcite.
2. There is no a priori reason to expect the dissolution of a primarily
silicious material, such as portland cement, to be accurately
represented by calcite (or any calcium carbonate solid, for that
matter) solubility.
3. The Al does not include any provision for the consideration of com—
plexation reactions (such as with polyphosphate additives) that can
limit the free ion activities of calcium and carbonate ions, and
either inhibit calcium carbonate precipitation or enhance the pipe
dissolution rate.
4. The Al does not consider the formation of protective precipitates of
ferric iron, manganese, zinc or silica that have been observed to be
the corrosion inhibiting agents in field and laboratory studies.
Other, less common constituents such as copper, ferrous iron and
orthophosphate also can form protective coatings under the proper
chemical conditions.
5. Certain coatings formed on the A/C pipe tend to allow some continued
dissolution or alteration or both, of the pipe surface below, although
the coating is tenacious enough to continue to bind the asbestos
fibers against release into the water. Ferric oxyhydroxide coatings
seem to operate in this manner in many instances. Therefore, there
should be a differentiation in the effectiveness of a coating with
regard to fiber retention and structural protection.
In most cases the dependence upon the Al has resulted in more pessimistic
projections of the deteriorative nature of the water than actually exist, so
the hunan exposure to released fibers and the number of utilities encountering
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large—scale pipe degradation is less than it otherwise might be. However,
the concern over the health implications of ingested fibers has lead to
numerous instances of strong public reaction to the presence of A/C pipe in
water systems possessing a “low” Al (less than 10), though the water in fact
may not be aggressive in the true sense. By considering the trace metal
equilibria and redox potential of the water, along with the calcium and carbonate
speciation, a much more reliable estimation of the pipe condition and potential
for asbestos fiber release can be obtained,( 3 ) and a later section will
correlate the refined water chemistry—based interpretation with other methods
of pipe condition assessment.
Chemical Monitoring of Pipe Dissolution
Attack upon A/C pipe by drinking water may generate two quite different
problems. Dissolution of the pipe matrix material will lead to structural
deterioration, which causes economic and service problems for the water
utility. Additionally, deterioration of the interfacial fraction of the interior
pipe surface will lead to the release of asbestos fibers, over which there is
considerable concern for possible human health effects. As will be discussed
later, it has been shown that it is possible to form adherent coatings on the
pipe that will prevent fiber release, but which may or may not totally prevent
some surf icial softening.
The cement matrix of asbestos cement pipe is a very complicated combina-
tion of compounds and phases, some of which are poorly identified or are of
indefinite composition. Over 100 compounds and phases important to the
chemistry of portland and related cements have been described and identified,(U)
and because of solid solution possibilities, probably many more exist. The
state of knowledge of the solubilities in water of the individual predominant
compounds of the cement lags far behind that of minerals and related man—made
compounds important to drinking water chemistry. Until more research is
done, only some qualitative generalizations can be made.
The corrosion of A/C pipe is governed virtually completely by solubility
considerations, and therefore, the dissolution and coating processes of the
pipe can largely be described and predicted by bulk—solution chemical parameters
and straightforward solid solubility reactions.
The effects of pipe dissolution on the distribution system water quality,
in addition to fiber release, are several.
The “free lime” component of the pipe (essentially equivalent to the
solid portlandite) can dissolve, which would increase the pH, titration
alkalinity and the calcium content of the water during its passage through the
pipe (and, therefore, the Al). The pH increase would enhance the ability of
the water to absorb and hydrate any CO 2 gas present. Subsequently, the
reaction of any absorbed CO 2 with the hydroxyl ions present would lead to the
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formation of bicarbonate ions, a step that would favor increased dissolution
of Ca(OH) 2 (s) by the mass—action effect. In the present commercial autoclaved
type II A/C pipe, the free lime phase is regulated to be < 1.0% by weighc.( 7 )
Three of the predominant phases of the matrix of A/C pipe are tricalcium
silicate (nominally Ca 3 SiO 5 ) a ium silicate (nominally Ca 2 SiO 4 ) and tn—
calcium aluminate (Ca 3 A1 2 0 5 ).’ ‘ /
An estimate of the solubility constants for Ca 3 SiO 5 and Ca 2 SiO 4 has been
made, ( 3 ) utilizing an internally—consistent set of Gibbs free energy of
formation data, and the calculations indicate a very high solubility.
Dissolution would produce three major effects. First, the levels of
calcium, aluminum, and silicon species (as well as any substitutional elements)
will increase with time upon standing, or with distance of passage through
a pipe line, unless threshold conditions are met for saturation and precipitation
of another less soluble phase.
Second, the pH of the system would tend to increase because of several
dissolution reactions and the two dissociations of silicic acid. The dis-
solution of calcium hydroxide would provide hydroxyl ions directly, and it
could be a strong influence by virtue of its high solubility. The presence of
carbonate, as in a drinking water, could lower the magnitude of p}l increase
possible resulting from calcium hydroxide dissolution by pH buffering or if
calcium carbonate saturation were attained. The overall solution pH may also
be increased by dissolution of the asbestos fibers themselves, though the impact
of this factor would be quite small except for small water volumes and stagnant
flow conditions.
One would not ordinarily expect large p11 gradients between the pipe surface
and the bulk solution. The water in a distribution main would have minimal
periods of suspended flow, such as in a household system during overnight
standing, except at dead ends. Also, the buffer capacities of most, even
“aggressive,” water should be sufficient to substantially moderate a pH rise,
especially when combined with constant water flow. Additionally, a very large
local rise in pH would often cause CaCO 3 deposition and subsequent protection.
This would tend to conflict with the observation of continual Ca 2 + leaching
in field and laboratory tests discussed by Buelow et al.( 2 ) and Schock and
Buelow. (3)
Third, the alkalinity of the system may also show à n increase. Considering
that alkalinity is a charge—neutralizing capacity, the dnly new1y—fo med
directly—contributing entities would be 0H, Si0(OH) 3 and Si 92 (OH) 2
However, a pH increase favors the production of HCO 3 and CO 1 , which
are the significant contributors to alkalinity in most drinking waters of pH
less than approximately 9 to 10. It must be emphasized that the alkalinity
increases observed in field studies ( 2 ) do not necessarily indicate input
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of dissolved carbonate fran pipe materials. That possibility may be checked
by carefully obtained, analyzed and preserved samples for potentiomecric total
alkalinity, pR, temperature and major constituents.
Precipitation reactions in a field situation nay obscure some of the three
major dissolution indicators, though pH and calcium increases with increasing
distance of travel (or recirculation in a closed loop) are generally good
evidence of pipe softening. Decreases in the total concentrations of various
constituents (such as calcium, zinc, manganese, iron, silica or orthophosphate)
with travel through a system tend to indicate the formation of a pipe coating,
provided that the analytical procedures are sufficiently precise to accurately
find those trends. Some constituents such as iron and manganese that may
exist as colloidal or particulate species in many cases frequently show large
analytical variability because of the inhomogeneity of the samples.
Laboratory Experimentation
The apparatus and experimental procedure utilized in DWRD coupon tests has
been given in detail by Buelow and Buelow et al. ( 2 ) Table 1 presents a
summary of the major constituent water qualities of the DWRD small—scale pipe
loop studies, along with the concentrations of additional primary corrosion—
control constituents (zinc, orthophosphate, and silica). Table 2 gives
qualitative information on the physical conditions of the coupons at the end of
the experiments. The test periods were of approximately six months duration
(ii months for experiment 22), and more detailed analytical information has been
provided by Schock and Buelow. ( 3 ) Earlier, larger—scale tests have been
described by Buelow at a l.( 2 )
The Solubiliry Modeling Approach
Just as calcium carbonate may precipitate and adhere to a pipe surface to
form a protective coating, so too could any other reasonably dense solid. Few
combinations of cations and anions are present in drinking water in sufficient
quantity to provide enough mass for precipitation and effective pipe coating.
Four elements that can be useful in this regard are iron, zinc, manganese and
silicon.
In order to fans a generalized chemical model that can take into account
the many chemical reactions in a drinking water, the computer program
R.EDEQL.EPAK( 16 17 ) was used. Two types of diagrams have been prepared,
primarily to explain and predict conditions under which A/C pipe will become
protected by zinc or iron compounds.( 3 ,18) The 5atur’ation Index” (SI)
diagrams are a plot of the saturation indices of solias of interest defined as
the common logarithm of the quotients of the scoichiometric ion activity
products (tAP) and the thermodynamic solubility constants (K 0 ), versus P 1
for a system of a given composition. If a solid at equilibrium is oversatur red,
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SI >0. If the solid is undersaturated SI < 0, and if the solid is exactly
at saturation, SI 0. Figures 1 — 4 show example SI diagrams for the system
compositions given in Table 3.
By examining the areas where the curves are above the SI = 0 line, a
domain of pH is given where pipe protection can be predicted. St diagrams
can often be prepared for general classes of waters, acid a relatively small
number of diagrams can be used to cover a wide range of concentration extremes
that would likely be encountered, and therefore they can yield a large amount
of semi—quantitative information on the occurrence and identity of pipe coatings.
Precipitation diagrams were calculated by the same computer program, by
“allowin supersaturated solid phases to precipitate to their saturation
ieveis. ( While it is just as easy to plot the concentration of each solid
phase versus pH, a plot of total dissolved constituent concentration(s) versus
pH was selected. Figures 5 — 8 illustrate the Precipitation diagrams corres-
ponding to the previously given SI diagrams. The selection of dissolved total
constituent concentration as the variable to plot versus pH was made because
it is representative of the practical situation of the addition of known con-
centrations of soluble corrosion—control compounds. The minimum dosage level
is easily estimable, by observing the dissolved concentration of the constituent
of interest (zinc or ferric iron, in this case) in the pH region where
precipitation would be taking place.
The relationship of effective zinc coating on A/C pipe to pH and carbonate
levels in a water have been extensively studied by DWRD using these types of
diagrams, and the results have been reported by Schock and Buelow, along with
the thermochemical data used. ( 3
The aqueous and solid species included in the DWRD chemical model calcula-
tions are listed in Tables 4 and 5. Subsequent to the completion of the
modeling calculations previously reported, the observation was made that the
projected zinc solubility in systems of much greater carbonate concentration
(approximately 0.08 U) is much lower than that observed in precipitation
experiments by P 4 ttersort et al.( 20 The addition of a dicarbonate complex
of zinc (Zn(C0 1 ) ) and the adoption of the formation constants suggested
by Hattigod ana Sposito 20 lead to still worse agreement, but this time
by overestimating the zinc solubility. A careful examination of the published
stability constant data of Bilinski et al. ( 21 ) originally used in the modeling
revealed that their polarographic a ta could alternatively be explained by
the formation of ZnCO 3 nd Zn(C0 3 ) complexes. A graphical extrapolation
yielded log B 11 5.2 and log B 12 2 7.5 (corrected for ionic strength).
Until the formation constant issue is decided, the latter values have been
incorporated into the model, and excellent agreement is obtained in comparison
with both the precipitation data ( 19 and the DWRD coupon studies. ( 3
Inclusion of the ZnHCO+ omplex suggested by Zirino and Yamamoto 22
would have mostly minor impact 3 throughout the carbonate range examined.
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Evaluation Using Field Chemical Data
Some of the interactions observed to provide either total corrosion inhibition
or fiber retention by a soft surficial deposit are summarized in Table 6. The levels
in the table are mutually related, so the numbers are semi—quantitative at best.
Other interactions such as calcium and zinc with silica, or silica with iron and
organic material are not covered here, but some aspects have been covered else-
where. (3)
In order to interpret the chemical data in a more quantitative manner, the
saturation states of several solids that can have an inhibiting effect on A/C pipe
deterioration can be used. Unfortunately, the use of the Al (and Langelier Index)
as the dominant indicators of corrosivity toward A/C pipe has lead to the recording
of data for only a few chemical parameters (mainly pH, alkalinity and calcium
hardness). Therefore, complete enough information is rarely available that one
could use to compare fiber Counts with the saturation indices and assess the
accuracy of the multiple—SI method of estimating corrosivity.
Table 7 shows how various saturation indices can be used to predict protection
or deterioration of pipe. It is necessary to either know or estimate the redox
potential of the water in order to determine the saturation states of solids
possessing more than one stable valence state in drinking water. A value of the
redox potential representing moderately oxidizing conditions was chosen in Table
7, for all waters that were chlorinated. The interrelationship of the redox
potential, pH and the domain of water stability to chlorination species is shown
in Figure 9.
It is important to select solids that represent precipitation reactions that
are not inhibited under drinking water conditions. 18 ) For example, spontaneous
precipitation of amorphous silica probably would not be achieved in water distri-
bution systems. Therefore, quartz was chosen to represent observed behavior of
silica in the hardening of A/C pipe, though the role of the dissolved silica in
pipe protection is not yet understood in detail. ( 3 ) On the basis of the observa-
tion that the Mn0 2 phase birnessite is common in stream deposits, it is chosen
as the representative manganese solid.(2 3 ) Figure lO, ows the thermodynamic
potential—pM relations of manganese species in water.” Although the Mn0 2 solid
used in the calculation of the diagram was pyrolousite, the boundary between
s 9 lid a ,4issolved species is little changed by the identity of the solids
chosen.” 4? The calculated saturation state of Mn0 2 is extremely sensitive to the
redox potential of the water, and it is therefore very imprecise without precise
and accurate analytical redox potential measurements.
Note that the system with the highest Al (least’aggressive) also contained
the highest fiber count, whereas systems with high SI values for quartz, 1nO 2 and
amorphous Fe(OH) 3 generally show fiber counts near or below detectable levels.
Some calcium Leaching in systems 1 and N is evident, but there is also the sug-
gestion of iron and manganese deposition, perhaps binding the fibers. The increased
iron level in system P could be the result of corrosion of iron or steel piping,
and the increased iron hydroxide saturation could actually be removing some fibers
from the water as well as providing a coating on the A/C pipe.
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Obviously, the sample number is too few, and the documentation is not
sufficient to make many definitive statements. However, the broader—spectrum
look at water chemical interactians certainly provides much more information
that can be applied to determine pipe conditions and the potential for human
exposure than the traditional approach that only considers the calcite saturation
state.
The cost of the sampling and analyses involved in this type of approach
is extremely variable, and cannot be generally estimated. The computer programs
used on the EPA computer system (IBM 370/168) typically cost in the range of
$5 — $50 to compile at a low—level time priority. Calculations performed on
analytical data typically cost in the range of $5 — $20 for several sites run
at a fairly high—level time priority, once the programs have been compiled.
Sampling Considerations for Chemical Data
The most obvious, and yet often most neglected aspect of any theoretical
chemical interpretation of factors influencing corrosion, is the sampling
procedure itself. Because of the complex nature of the chemical equilibria
involved in A/C pipe protection, the chemical analyses must include metals such
as Fe, Zn, Mn and Cu plus the anions with which they can complex or form solids
(ortho and polyphosphates, sulfate, fluoride, etc.) and silica, in addition to
the major constituents and parameters (pH, total alkalinity, calcium, magnesium,
sodium, chloride, etc.). Samples for certain constituents must be properly
preserved( 25 ’ 26 ) on site.
To properly determine the conditions in a distribution system, a sample
should be taken from the finished water tap at the plant to represent initial
conditions. Additional samples must be taken from locations of frequent use,
in order to prevent misleading constituent concentrations that result from
contact with metal pipes. Household taps (inside or outside) that are the
closest to the service connection would be the most suitable in this regard,
and the water should be run at approximately half—maximum for five minutes
before sai:iple containers are filled. ( 27 No aerators should be in taps used
for sampling, and no samples should be taken of waters treated by home or
building water softeners.
REFLECTED LIGHT MICROSCOPIC ANALYSIS
Sample Preparation
When badly corroded A/c pipes are viewed in cros section, the deteriorated
portion of the pipe wall often can be distinguished by the differences in
appearance between undamaged pipe and deteriorated pipe. When the pipe has been
severely attacked and softened by aggressive water, the depth of attack on the
inner pipe wall may be difficult to determine because cutting the pipe to examine
it may disturb the condition of the softened pipe wall. So that A/C pipe condition
could be evaluated in a manner less likely to damage a softened pipe wall, pipe
specimens were cut and mounted in netallographic riounts by a testing laboratory.*
*Gladstone Laboratories, Inc., Cincinnati, Ohio
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Pipe segments were mounted in cylindrical bakelite mounts about 3.1 cm in diameter
and 2.3 cm high, with the pipe segment oriented so that the cross section of the
pipe wall was visible.
Bakelite Mount
Pipe Specimen
Softened Inner Wall
This orientation permitted observation of both the interior and exterior walls of
the pipe. tiounts are polished with progressively finer materials, ending with
#600 grit or aJ.uminum oxide polish.
The particular advantage of the bakelite mounting technique is that the mount
holds the softened asbestos cement layer in place next to the sound portion of
the pipe while the mount and pipe are being ground and polished. The soft pipe
does not flake off or develop feathered edges during the grinding and polishing,
so when these steps are completed, the thickness of the softened layer should be
representative of the condition of the undisturbed pipe.
Evaluation of Corrosivity
In most cases the softened, deteriorated portion of the inside wall could
be seen when illuminated by unpolarized light incident at a shallow angle, and
viewed through an optical microscope at 50X magnification. In some cases the
gradient of color and texture change was not sharp and assessIng the degree of
damage was difficult or impossible. Most specimens could be evaluated in this
nanner though, and in 14 of 20 cases results of visual inspection at 50X agreed
with photomicrograph interpretations.
The optical microscopy technique of cross—sectional viewing can be partic-
ularly advantageous in showing the effects of the interaction of the pipe with
the water over tine. Pipes that have undergone attack in the past but are now
coated with a solid deposit (such as a zinc compound) will show the alteration,
whereas only the surficial coating will be visible to the scanning electron
microscope. One limitation of the optical examination is that it is sometimes
difficult to tell if a visible alteration of the pipe represents actual deterio-
ration, unless the hardness of the surface is tested.
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METHODS BASED ON THE ELECTRON MICROSCOPE
Fiber Counting
One obvious method to test for deterioration of A/C pipe is to determine
the number of fibers input into the water during passage through the pipe. tn
order to determine whether or not fibers are leached from the walls of the pipe,
a sample must be taken at the point of finished water inflow into the system in
addition to any samples taken at other sites. Systems that contain several
different water sources and that do not combine them before distribution require
additional samples at each different location of water input.
In order to accurately represent distribution system conditions, samples
must not be taken from dead ends or locations of infrequent flow such as fire
hydrants, both of which tend to give very erroneous high results. Care must
also be taken to assure that samples not be taken down flow of any system
maintenance, drilling or tapping and that drilling and tapping operations flush
fibers out of the system to avoid contamination. If chemical analyses and
interpretation are to accompany fiber counts, the appropriate sampling consid-
erations must be added to those just discussed.
In order to determine the number of fibers in the water, the method of
ii1lette, et al. 28 was used. At the start of ther procedure, aliquots of
100 to 250 oL from each sample were filtered by suction through a 0.1 pm pore
size Nucleopore’ filter backed by a 0.45 im pore size Millipore filter. A
backing filter was used to insure uniformity of deposition of the particulate
material on the filter surface. A quarter section of the filter was cut while
wet, attached to a glass slide, dried, and coated with carbon in a vacuum
evaporator. A small portion (approximately 2 sam 2 ) of the carbon—coated filter
was cut Out with a razor blade and placed on a 200—mesh copper electron microscopy
grid. A few drops of chloroform were placed on the filter with a 50 iL micro—
syringe to affix the filter to the copper grid. The filter was dissolved using
a modified Jaffe wick apparatus.
After the filter was dissolved, the grid containing the particulates
embedded in the carbon film was placed in a carbon specimen holder in the trans-
mission electron microscope (TEM), operated at an accelerating voltage of 80 kV
and 70 pA beam current, and viewed at a magnification of 17,000 times. At
least 15 grid openings from each of two grids was examined for each sample.
Identification of asbestos fibers, was made on the basis of iaorphology (size,
shape, appearance), crystal structure, and elemental composition. When examined
at 170,000 times through the use of lOX binoculars attached to the TEM, chryso—
tile fibers usually have a distinctive central channel running the length of
the fiber. The crystal structure of a fiber is revealed through the use of
selected area electron diffraction (SAED). Chrysocile provides a distinctive
three double—dot diffraction pattern while amphibole asbestos fibers form rows of
uniformly spaced dots.
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Energy dispersive x-ray ariaJ.ysis (EDXA) is used to obtain information
about the chemistry of the fiber. An electron beam is focused on an individual
fiber, producing x—rays as a result of the interaction between electrons and
the atoms on the surface of the fiber. Atoms of different elements produce
x—rays of different energies, which are displayed graphically as a spectra of
peaks on the DXA unit. The elements present are determined by the position
of the peaks and the relative amount of an element is calculated from the peak
height.
Chryso tile fibers contain silicon, magnesium and some iron. The amphiboles
have a basic silicate structure but differ in the amounts of silicon, magnesium,
iron, calcium, and sodium depending on mineral type.
During sample analysis, fibers are generally sized on circles inscribed on
the TEM fluorescent screen. In some samples where there are high numbers of
fibers or where accurate information about fiber diameter is needed, fIbers are
measured from electronmicrographs taken in the TEM. The concentration of
millions of fibers per liter (MFL) is calculated using the following formula:
(F) x (EFA)
MFL ____________ X 1O
(A) x (v)
in which F • average number of fibers per grid opening
ETA • effective filter area
A area of grid opening, and
V sample volume (in liters).
More information on the development of a standardized method of asbestos analysis
is given by Anderson and Long.’ 29
An effort has begun to store water chemical data in a computer data bank
along with the corresponding fiber counts and physical descriptive informa-
tion, in order to correlate the information on a larger scale when enough samples
are analyzed for both chemistry and fiber counts.
Thus far, good correlations have been found between low fiber Counts and
high states of saturation of the solids given in Table 7. Many other systems
have shown low fiber counts, and pipe inspections have revealed coatings of iron,
manganese, silica and carbonate solids even though chemical analyses of the water
were not performed.
At present, the cost of sample preparation and analysis by TEM and EDXA is
approximately 300 — 600, and B to 10 man hours are usually spent per sample.
Therefore, it is a very time consuming and expensive method. Additionally,
very few laboratories across the country have the instrumentation and expertise
to do the work.
Scanning Electron Microscopy and X—Ray Analysis
In order to assess the degree of reliability of using water chemistry and
saturation indices to predict the interior condition of asbestos—cement pipe
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and its tendency to release fibers into the drinking water, additional information
about the pipe surface itself when subjected to various water qualities is
necessary. tt is important to know when asbestos fibers are exposed at the pipe
surface, what changes in surface chemical composition occur, and what inhibitors
best coat the pipe to impede the leaching of calcium with subsequent fiber
release.
Because of the requirement for a more complete physical and chemical
analysis, pipe sections from several of the D(JRD coupon experiments and from
several field samples were studied using the Scanning Electron Microscope
(SEM) and Energy Dispersive X—Ray Analysis (EDXA). The SEM inicrographs showed
the topographic features of the surface of the pipe interior while the EDX
spectra showed the relative changes in chemical composition of the surface
of the pipe.
There are several limitations to any chemical analysis performed by EDXA.
Because the detector is protected from the vacuum chamber by a beryllium window,
many of the soft x—rays are completely attenuated by the window before reaching
the detector. Only the elements heavier than sodium can be detected. Also,
the EDXA is semi—quantitative under the sample preparation and analysis conditions
normally used, so it does not give the exact concentrations of the elements
present on the surface. However, the relative amounts of the elements present may
be important as a means to gain information on the identity of surf icial coatings
and in the monitoring of Ca leaching. One must keep in mind, however, that EDAX
analysis can not identify the compounds present (as would be possible with x—ray
diffraction), or tell whether or not a decrease in x—ray intensity is caused by
depletion of the element or if the element is being masked by a coating.
For EDXA and SEM analysis it is important to observe representative sections
of the pipe, as the same pipe might vary in color and texture. Often, several
sections of the same pipe have to be analyzed.
Pipe sections that were analyzed by EDXA were prepared by the method of
Clark, et al. ( 30 ) Random pieces of each sample, approximately 12 mm by 6 mm,
were mounted on 24 mm by 5 mm copper boats using a conductive graphite adhesive.
These samples were then carbon coated in a Denton* vacuum evaporator. A sample
for determining background counts was also prepared using only a copper boat
and raphite adhesive. Each sample was then placed in a JEOL 1008 Transmission
Electron Microscope (TEM) operated at an accelerating voltage of 40 kV and a
beam current of 55 — 60 }.1A. Using the SEM mode and a magnification of 300X,
the specimen was examined both longLt udinally and laterally in a regularly—
spaced rectangular array with seven to ten consecutive areas the size of 0.1 mm 2
being analyzed by the EDXA. Count rates ranged from 32 to 444 counts per second
(CPS) for a time period of 300 seconds.
* Mention of trade names or commerical products does not constitute endorsement
or recommendation for use.
+ Emission current near filament.
72/13
-------
To examine the surface structure , random pieces from the same samples were
coated with approximately 450 A of gold—palladium in the vacuum evaporator. The
samples were then placed in an ETEC (SE I) operated under an accelerating voltage
of 20 kV, beam current of 150 1A,+ a working distance of 20 — 22 mis and at
magnifications of 100X, 300X, 700X, and l,000X. The samples were examined
for the presence of asbestos fibers and degree of deterioration.
The following examples of the use of SEM—EDXA to evaluate A/C pipe condi-
tion are taken from three D JRD experiments and one field study. Experiment 1
was a • control ” experiment in which no inhibitors were added. The micrograph
(Figure 11) shows fibers present and some pitting of the surface. The EDXA
analysis (Figure 12) shows a large peak for silicon compared to that of calcium.
The difference in peak size may be caused by leaching of the calcium, an inter-
pretation consistent with the calcium increase that was observed in so1.ution.( 3
Also important is the magnesium, the presence of which may indicate exposed
chrysotile fibers at the pipe surface. The magnesium peak has frequently
shown up in analyses of corroded pipe and it is seldom present in EDXA scans
of non—corroded pipe.
Experiment 2 shows a good coating by a zinc compound with very little pitting
and few fibers exposed (Figure 13). The high calcium in the EDXA (Figure 14)
possibly indicates that very little leaching has occurred, an observation chat
would also be consistent with the small increase of calcium level in solution.
The zinc present and the lack of a phosphorous peak shows that it is the zinc
that is responsible for the coating, as would be predicted by chemical theory. (3)
The small magnesium peak seems to indicate that few fibers are exposed.
Experiment 6 shows some pitting and exposed fibers in the tnicrograph
(Figure 15). Here, again, the presence of a strong magnesium peak (Figure 16)
seems to demonstrate the deterioration of the pipe and the presence of fibers
on the surface. An important factor here is that pipe was shown to deteriorate
even when the water was kept just slightly under calcite saturation. The
expense of adjusting many naturally—soft waters to maintain a state of calcium
carbonate saturation, coupled with the undesirability of the harder water to
many consumers may necessitate the use of other treatment methods, such as
zinc addition and pH adjustment.
Two field samples were analyzed by SEM—EDXA in order to determine the degree
of in—situ zinc coating on sections of A/c pipe that had been placed in a
distribution system. Figure 17 shows a section of pipe from far out in the
system where there was a low flow rate and the zinc concentration ranged from
low to just enough to attain saturation with respect ‘to hydrozincite during a
one—year test. The SEll micrograph reveals pitting of) the pipe and a few
fibers exposed at the surface. Figure 13 shows a pipe section that was located
closer to the treatment plant, and that had a better coating. The better coating
correlates well with the exposure of this specimen to a slightly higher level
of zinc, even though adequate hydrozincite supersaturation was not maintained.
721 14
-------
Interestingly, the optical microscopic examination of the bakelite—mounted
specimens from the same two sites showed a zone of alteration 1.1 — 1.2 K
micrometers deep at the pipe surface in the specimen from the site closest to the
plant, and almost no discoloration or alteration could be seen in the specimen
from farther out in the system. The optical examination correctly reveals the
greater attack over time on the specimen in Figure 18, before zinc treatment
was begun. As the pH and calcium concentrations increased from pipe leaching
during travel through the system, the amount of original pipe degradation
decreased, and the specimen shown in Figure 17 was historically under less
attack. Therefore, the different kinds of information obtained by the SEM—EDXA
analysis complement that obtained by optical microscopic observation, although
it is a more costly analytical method. The present cost of SEM—EDXA analysis is
typically $50 — $100 per sample, and each sample requires on the order of 5 — 6
man—hours of labor.
CONCLUSIONS
The several methods of evaluating pipe condition that have been discussed
in this paper can give a very large amount of important information for assessing
the corrosivity of water toward A/C pipe. The chemical methods give a theoretical
understanding of the corrosion or inhibition processes involved. By collecting
more pipe samples and by performing more fiber counts, it should be possible
to calibrate the method to predict pipe condition even more accurately than it
can now. Overall, it is one of the most convenient and least costly methods
of corrosivity evaluation to anyone possessing access to a digital computer
and a water analysis laboratory.
The microscopic methods are seen to complement each other, each one capable
of obtaining a unique type of information. Because the electron microscope
methods are costly, one must carefully decide upon the type of information that
would be of most value.
All of the methods are under development to various extents, and their
rigorous application to A/C pipe corrosion problems is still in its infancy. tt
is clear, however, that the methods discussed are very valuable tools at this
early stage, and they can be expected to become even more informative as more
experience is gained using them.
72/15
-------
REFERENCES
1. The Acierican Water Works Association Research Foundation, A Study of the
Problem of Asbestos in Water 1 Jour AWWA, 66:9:1 (Part 2, Sept. 1974).
2. Buelow, R. W., Millette, J. R., McFarren, E. F. & Symons, J. M., The
Behavior of Asbestos—Cement Pipe Under Various Water Quality Conditions —
A Progress Report Part 1 — E periiuental Results. Jour AWtJA, 72:2:92
(Feb. 1980).
3. Schock, M. R. & Buelow, R. W. The Behavior of Asbestos—Cement Pipe Under
Various Water Quality Conditions, A Progress Report. Part 2 — Theoretical
Considerations. Submitted manuscript (1980).
4. McCabe, L. J. & Ii11ette, J. R. Health Effects and Prevalence of Asbestos
Fibers in Drinking Water. Proceedings of the American Water Works Associa-
tion Annual Conference, San Francisco, California (2)1079—1093 (June 1979).
5. Cooper, R. C. & Cooper, C. W., Public Health Aspects of Asbestos Fibers
in Drinking Water. Jour. AWWA 70:6:338 (June 1978).
6. Certain-Teed Products Corporation, Valley Forge, PA, Definition of
Aggressive Waters.
7. AWWA Standard for Asbestos—Cement Pressure Pipe, 4 in. Through 24 in.,
for Water and Other Liquids. AWWA C400—77, Revision of C400—75, AWWA,
Denver, Colorado (1977).
8. Langelier, W. F. The Analytical Control of Anti—Corrosion Water Tratment,
Jour. AWWA 28:10:1500 (Oct. 1936).
9. Loewenthal, R. E. & Marais, C. R. Carbonate Chemistry of Aquatic Systems:
Theory and Application. Ann Arbor Science, Ann Arbor, titchigan (1976).
10. Stumm, J. & Morgan, J. J. Aquatic Chemistry, Wiley—tnterscience, New York
(1970).
11. Garrels, R. M. & Christ, C. L. Solutions, Minerals, and Equilibria,
Freeman, Cooper & Company, San Francisco (1965).
12. Jackson, J. E. A/C Pipe Producers Association, Arlington, Virginia,
personal communication (1980).
13. Highway Research Board. Guide to Compounds of Interest in Cement and
Concrete Research. Special Report 127 Nat’l Res. Council, NAS, NAE (L972).
14. Troxell, G. E., et al. Composition and Properties of Concrete, Second
Edition. UcCraw—Hill Book Company (1968).
72 116
-------
15. Buelow, R. W. Laboratory Techniques for Determining Corrosivity of Water
to Asbestos—Cement Pipe. Paper presented at the American Water Works
Association seventh annual Water Quality Technology Conference, Philadelphia
(Dec. 9 — 12, 1979).
16. tngle, S. E. et al. A User’s Guide for REDEQL.EPA, A computer Program for
Chemical Equilibria in Aqueous Systems. EPA—600/3—78—024, (Feb. 1978).
17. Engle, S. E. ec al. REDEQL.EPAK Aqueous Chemical Equilibrium Computer
Program. Marine and Freshwater Ecology Branch, Corvallis Environmental
Research Laboratory, Corvallis, Oregon (Draft, 1979).
18. Schock, M. R. Computer Modeling of Solid Solubilities as a Guide to
Treatment Techniuqes. Paper presented at the seminar Corrosion Control in
Water Distribution Systems, Cincinnati (May 20 — 22, 1980).
19. Patterson, J. W., et al. Carbonate Precipitation for Heavy Metals
Pollutants. Jour WPCF 49:2397 (1971).
20. tlattigod, S. W. & Sposito, G. Estimated Association Constants for Some
Complexes of Trace Metals with Inorganic Ligands. Soil Sd. Soc. Am. J.
41:1092 (1977).
21. Billnski, H., et al. Determination of the Stability Constants of
Some Hydroxo and Carbonate Complexes of Pb (II), Cu (It), Cd (II)
and Zn (II) in Dilute Solutions by Anodic Stripping Voltammetry and
Differential Pulse Polarography. Anal. Chim. Acta 84:157 (1976).
22. Zirino, A. & Yainamoto, S. A pH Dependent Model for the Chemical
Speciation of Copper, Zinc, Cadmium and Lead in Sawater, Limnol. Oceanog.,
17:5:661 (Sept. 1972).
23. Potter, R. M. & Rossman, G.R. Mineralogy of Manganese Dendrites and
Coatings. Amer. Mineralogist, 64:1219 (1979).
24. Hem, J. D. Redox Processes at Surfaces of Manganese Oxide and Their
Effects on Aqueous Metal loris. Chein. Geol. 21:199 (1978).
25. Schock, H. R. et al. Laboratory Technique for Measurement of pH for
Corrosion Control Studies and Water Not in Equilibrium With the Atmosphere.
Jour. AWWA 72:5:304 (1980).
26. Methods for Chemical Amalysis of Water and Wastes. EPA 600/4—79—020.
EMSL, Cincinnati, Ohio (1979).
27. Hoyt, B. P. et al. Evaluacing Home Plumbing Corrosion Problems. Jour.
AWUA 71:12:720 (1979).
28. UllIette, J. R. et al. Asbestos in Cistern Water. Environmental Research
Brief, Health Effects Research Laboratory, US EPA, Cincinnati, Ohio (Feb.
1.980).
29. Anderson, C. H. & Long, J. M. Interim Method for Determining Asbestos in
Water. EPA—600/4—80005. US EPA, Athens, Georgia (1980).
30. Clark, P. J. et al. Asbestos—Cement Products in Contact With Drinking
Water: SEll Observations. Scanning Electron Microscopy 1:341 (1980).
72/17
-------
TABLE 1.
Abbreviated qualities of DWRD recirculation experiments. All concentrations
are in mg/L unless noted otherwise. Analyses respresent concentrations at or
near the end of each experiment unless a range is given.
aiglL as CaCOp
Experiment Total Treatment
Number pH Alkalinity Ca Zn P0 4 5102 Chemical
1 8.2 20—27 5—13 — — None
2 8.2 20—26 4—8 0.3—0.5 0.4—1 — zinc orthophosphatea
3 7.0 21—25 10—22 — — — none
4 7.0 20—29 9—17 0.3—0.6 0.4—1 — zinc orthophosphatea
5 8.2 19—22 5—8 0.3—0.7 — 0.1—2 zinc chloride
6 7.5 116—130 133—155 0.03 — 1—4 none
7 7.9 120—131 129—160 0.04 — 1—4 CaCO 3 saturation
8 9.0 38—42 21—30 <0.02 — 0.1—2 CaCO 3 saturation
9 8.2 42—50 9—16 0.02 0.2 15—18 Sodium metasilicate
10 b 7.0 25—27 13—16 0.1 — 14—17 Sodium metasilicate
11 8.2 18—19 0.6—4 0.3—0.4 0.03 3 zinc chloride
12 7.5 18- ’21 9—14 0.3—0.4 0.03 2—3 zinc chloride
13 8.2 19—21 10—15 0.1—0.2 0.03 0.2 zinc chloride
14 8.2 2—4 32—43 0.3—0.4 0.06 1—8 zinc chloride
16 8.2 16—19 7—10 0.3—0.5 <0.2 <0.4 zinc sulfate
19 7.2 18—21 9—25 0.1 0.1 <0.2 zinc chloride &
iron (Ill) chloride
22 8.2 21—25 10—16 0.2—1.0 0.2—0.9 ‘<2.0 zinc orthophosphatea
Notes :
A free chlorine residual of 0.]. to 0.7 mg/L as Cl was nainrained at almost all
times. Iron was less than the lowest calibration standard of 0.1 mg/L except for
experiment 19 in which approximately 0.1 mg/L. of iron was added.
a. Vircheca 93]?, a product of Virginia Chemical Corporation.
b. The same coupon was previously run for almost 1 month at an Si0 2 concen-
tration of 10—30 cag/L and a zinc concentration of approximately 0.2 cng/L.
The pH, total alkalinity and calcium levels were the same.
72/18
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TABLE 2.
Summary of Qualitative Results of DWRD A/C Pipe Treatment Experiments
Experiment Treatment tnner Wall of
Number pH Process Coupon Softened?
1 8.2 none yes
2 8.2 zinc (orthophosphate) 0.3—0.5 aig/L no
3 7.0 none yes
4 7.0 zinc (orthophosphate) 0.3—0.5 aig/L slightly
5 8.2 zinc (chloride) 0.3—0.7 mg/L no
6 7.5 none yes
7 7.9 CaCO 3 saturation very slightly
8 9.0 CaCO 3 saturation slightly
9 8.2 Sodium metasilicate no
10 7.0 Sodium cnetasilicate no
11 8.2 zinc (chloride) 0.4 mg/L; low calcium no
12 7.5 zinc (chloride) 0.4 mg/L slightly
13 8.2 zinc (chloride) 0.1—0.2 mgIL yes
14 8.2 zinc (chloride) 0.4 mg/L; low alkalinity very slightly
16 8.2 zinc (sulfate) 0.5 mg/L no
19 7.2 iron ( L II) 0.1 ing/L; zinc (chloride) slightly
0.1 cng/L
22 8.2 zinc (orthophosphate) 1.0 tng/L for 1 week; no; mottled
zinc (orthophosphate) 0.2 — 0.5 mg/L for grey coating
47 weeks.
Table 3. Chemical compositions of four model systems.
All concentrations are totals in mg/L of the constituents shown.
System Ca Hg Na Zn Fe(tII) CO 3 P0 Cl*
19 4.0 1.0 20 0.15 0 24. 0 18—40
M1OP 4.0 1.0 12 0.5 0 12. 0.5 15—29
Ull 4.0 1.0 12 0.3 0.1 12. 0.5 15—29
M15 4.0 1.0 20 0.5 0 4.0 0 38—42
*Allowed to vary with pH to preserve electroneutrality.
72/19
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Table 4. Aqueous species considered in Saturation Index and Precipitation
diagram preparation.
ZnCl
0
ZnC 1
2
H C0 ZnC].
23 3
HCO ZnC I 2
3 4
0
CO’ ZnC1OH
3
0 0
H 1 PO ZnHPO
J4 4
H P0
24 44
p .po 2 znoIr
4
Zn(OH)°
4 2
Ca 2 Zn(OH)
CaHC0 Zn(OR) 2
CaCO Zn. OH 3
3
0
CaMPO Fe
4
CaP O Fe0H 2
4
CaR.,P0+ Fe(0H)
2
CaO& Fe(OR)°
gZ+ Fe(0L1)
UgIlCO+ Fe 2 (OH )4+
MgOH Fe 3 (0H)
U 8 CO FeSO+
3 .4
1gI{PO, FeCl 2
Na+ FeCl
2
0
NaCO FeC1
3 3
0
U C O FeHPO
3 4
A Zn(C0 3 ) complex is also suggested. See text.
72/20
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Table 5. Solid species considered in Saturation tndex and Precipitation
diagram preparation.
Solid (chemical fo’rtnula) Common name
CaQ) 3 Calcite
Ca(OR) 2 Portlandite
CaHPO 4 .12H 2 0 Brushite
Ca 8 H 2 (I’0 4 ) 6 . 5H 2 0 Octocalciucn phosphate
Ca 5 (P04) 3 0H Hydroxyapatite
Ug 3 Magnesite
Mg(OH) 2 Brucite
Mg 3 (P04) 2 —
ZnCO 3 Smithsonite
Zn 5 (OH) 5 (C0 3 ) 2 Mydrozincite
Z (OH) 2 —
Zrt 3 (P0 4 ) 2 .4H 2 0 CC —Hopeite
Fe(OH) 3 Amorphous iron (III)
hydroxide
FePO 4 . 2H 2 0 Strengite
72/21
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Table 6. Very generalized operation and properties of various
inorganic water constituents in A/C pipe corrosion inhibition.
in conjunction with (at indicated level)
constituent at level —
OH C0 ’ PO function
4
Zn 4 4,5 1,2 H,C
Zn 4 5 3 H?,C
Fe(LII) 4,5 5 3 C
Fe(1I) 4,5 5 1,2 C
Mn(IV) 5 5 C
Mn(II) 5 1,2 C
Cu(II) 4 5 1,2 H?,C
Ca 1 H
Ca 2 4,5 1,2 H, C
Ca 2 4,5 3
si(OH) 4 2 5 H
Notes :
Levels: 1 100—1000 cngft
2 10 — 1.00 ng/L
3 1 — 10 cng/L
4 — 0.1 — 1 Qg/L
5 < 0.1 cng/L
Functions:
H pipe surface hardener
C — coats surface to bind fibers, but pipe surface nay soften
wittiout ocher inhibitive factors.
2/22
-------
Table 7. Saturation Index calculations for several protective solids. The temperature
was assumed. to be 20°C. Concentrations are in mgIL, mg/L as Ca 0 3 for total alkalinity
(TA).
saturation indicesb
Supply pH TA Ca rig Si0 Fe jj C cl CpTe Qf g h Fibers
L—raw 7.52 155 14 2.3 51 0.17 0.27 0.04 11.2 —0.6 —1.1 1.0 —14 1.8 BDL
L—system 7.54 162 14 2.5 49 0.80 0.26 0.03 11.3 —0.6 —1.1 1.0 7.2 2.7 NSS
M—raw 7.64 180 4 1.6 33 0.16 0.12 0.02 10.9 —1.0 —1.5 0.8 —15 1.7 1.0
M—system 8.11 185 6.5 0.9 36 0.80 0.12 0.02 11.6 —0.3 —0.8 0.9 5.9 2.4 2.3
N—raw 7.40 17.2 5.5 2.4 16 0.18 1.3 0.04 9.8 —2.0 —2.5 0.5 —14 2.4 BDL
N—system 8.66 26.8 9.8 2.0 11 0.80 0.05 0.02 11.5 —0.3 —0.8 0.3 3.6 1.7 NSS
0—raw 8.50 210 2.3 0.6 15 0.11 0.03 0.01 11.6 —0.3 —0.8 0.5 —13 1.6 8.4
0-system 8.71 216 2.8 0.5 10 0.80 0.02 0.01 11.9 0.0 —0.5 0.3 3.2 1.3 26.8
P—raw 6.93 130 23 8.4 60 0.21 0.24 0.42 10.8 —1.0 —1.5 1.1 —14 0.8 1.5
P—system 6.82 141 25 9.0 60 0.80 3.8 0.46 10.8 —1.0 —1.5 1.1 5.6 3.3 NSS
Notes:
a. Eh in volts. Estimated at 0.80 volts for distribution system waters,
all of which were chlorinated. For raw waters, Eh was estimated from the
dissolved oxygen concentration measured in the field by the Sato relationship
given by Pluminer, L.N. at al. USGS Water-Resources Investigations 76—13
(1978).
b. SI — log ( lAP/K 90 ). See text.
c. Al — pH + log (AR). See text.
d. C — CaCO 3 , calcite phase.
e. GPT — Fresh CaCO3 precipitate in soils described by Suarez, D.L.
Soil Sd. Soc. Am J. 41:310(1977).
f. Q — Si0 2 , quartz phase
g. • Mn0 2 , birnesaite phase.
h. FH — Fe(OH)3, amorphos fresh precipitate
1. x 106 per liter. NSS — not statistically significant.
BDT.. — below detection limit.
72/23
-------
.
—
a
U,
0
C
C
a
0
U,
*
0
C
C
a
0
0
U)
?I$..t. . L d.* d1. r.. S.? ..I.L I (a. t .b1 3).
pH
3. S.i .x.tLs. Ind. dUqi.. Is .L , i NZ* s . t.bL. 3).
3. kS.nCLOS L .z dLa;rM 1.i .od.L spst UL I,. . tabl. 3).
‘C
0
C
C
0
0
0
U)
. S.tu .tLo. 3M.. dftir.. f t .04.3 •v•i US ( • Tab ). 3).
ic 3 I I
N
S S S. .
1
E
01 • • I I • I
5 6 7 8 9
pH
?1$ .?. S. 41air S., st 3. 4.L •y*I i C... .bI. 3).
0
-S
r
0
C,
pH
t$ r. S. PYscIplullos 41113.0 1.. ILOC. 55335.0 104 .35 1090411041. 15
s .d.L .psi IU P i... laSts 33.
.1
pH
pH
5 6 7
pH
3 9 10
72/24
-------
It.’
a
C
N
Oil
a
E
a
I I
I
ii
F
\
I
• Zinc
o Iron (11$)
‘ a
‘a
\
\
‘a
‘a
a a t I I a - I a -
.01
5 6 7 8 9 10
pH
Pilate 7. Pr.cipitari.s diagra. tar slat arid iron (111) La .od.l .y.iee
Nil (a.. Table 3).
1.0 I I
I I
• S *
.1 ••
‘5’—.. _,
0.1
.01 ‘ • I I I
5 6 7 8 9 10
pH
Vt at. I. Pt.cLpLiatLoa diagraa far cisc La .04.1 sy.tee NL C... Table 3).
2
1
•4
0
a
U i
pH
figure . Potential — pM 41ar.. tar sass .eca.tabl. chlertacattos .pect.s
at 23C with diesotand .cttvitt.a of 1.0 ag/I. as Cl. Dsta La free
r.t.r..c. 3.
0
.1
figure 10. Potential — pM dtqras at asagasa.. La carbonic. — containing
aicar at 2 C. Stability f 1.14. are shown for disa.lv.d .aagasa.e
SpIcLSO activities •f 0.0$ as ’T. arid diusoland carbonata species
acttvicl.. of 10 a g/I. a. CaCO 3 . Data La Ira. ret.r.sca 3.
?1 ure 11. Scaauisg electron sicr.$raph of the pipe c.epee free 0 1 10 ezp.riaent
I shaving p...d fiber. (see Tables 1 and 2). Zr.. and alimlomm
are coesittuests •t the casuaL aetna.
fIgure 12. 1A analyst. .1 the pipe coupon Iron 0110 .zpertassc 1 (a.. Ttbles
1 end 2).
1. -
(I)
0
a
LU
0.0
pH
C
N
he
a
- 4
a ’,
a
E
a
a.
S
7212S
-------
Pi vts 13. $caania$ .lsclrsa .tcro rspn ot tn. p&ps usopa . ti. s
2 .b.WtM a uaLf.l surticisi caacln C. .. T.W.a 1 and 2).
F l Oor. P.&. DZA .ady .i. .1 lbs pip. osupos foes OWI sspsrlasnt 2 ( . .. Isbi.,
1 sad 2). sto lbs pr...&. of sloe, but not of pbo.pboTous.
Fibre 1k. WXA analysiS Of the pipe coupon fm. D’.*D uperta.ni b (see Tabi..
1 and 2). ito. and .losin , are consCltvmnhS •f lb. csssst mainS.
FI$vre 17. Scasnis slectron .icmoraph of a r.sot. pip. s.ctios In a
field ezp.Cioant. 001. lie appsra0.e of plltin re.u lt1os f t c.
pipe dissotutlas.
Vi urs 15. Sc.ns1* 5 electron .icr001aph Of a pipa .octtoa Eros a DuD field
.np.fisunt. SiOVIIt5 substantial coatini by a zinC compound.
Pl ure 13. k...t.s elsctroe .lcfMra,h of the pipe coupon too. DVP.D .zp.m taint
D shouin is.. szps.ed fibers (see Tables 1 s .d 2).
72/26
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