United States
Environmental Protection
Agency
Municipal Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-84-066 Mar. 1984
&EPA Project Summary
Seattle Distribution System
Corrosion Control Study:
Volume V. Counteractive
Effects of Disinfection and
Corrosion Control
Karen S. Nakhjiri, Carlos E. Herrera, and Ronald D. Hilburn
This study is the fifth in a series of
corrosion control studies in the Seattle,
Washington, water distribution system.
The present project consisted of three
research phases designed to evaluate
the counteractive effects of corrosion
treatment (pH adjustment) and disin-
fection. These phases consisted of
(chlorination)/electrochemical tests,
onsite treatment tests, and bacteriolog-
ical tests. In the electrochemical tests,
copper corrosion rates were measured
under varying pH, free chlorine resid-
uals, and chloride concentrations using
a rotating disc electrode and linear
potential sweep technique with solution
resistance compensation. The onsite
treatment tests monitored the effects
of simulated corrosion treatment start-
up on chemical and microbial water
quality from an old galvanized plumbing
system. The bacteriological tests deter-
mined the survival of Pseudomonas
aeruginosa. Escherichia coli. and En-
terobacter aerogenes under varying pH
and free chlorine residuals.
The results of the electrochemical
tests showed that copper corrosion
rates increased about 70% when free
chlorine residuals were increased from
0 to 1.0 mg/L. These results indicate
that increases in chlorine dosages may
offset the corrosion reduction benefits
realized with pH adjustment.
In the onsite treatment tests, standing
water samples collected after treatment
startup had larger bacterial populations
than the untreated standing water
samples. Iron-oxidizing and sulfate-
reducing organisms were found in both
standing water and tubercular incrusta-
tions. Opportunistic pathogens and
coliform antagonists (including Pseudo-
monas and Flavobacterium) were de-
tected in standing water samples and
increased in number with treatment
startup.
The results of the bacteriological tests
showed a slower death rate at pH 8 for
all three bacteria than at pH 7 or 6. But
100% mortality was achieved at all pH
values tested for all three species with a
free chlorine residual of 0.2 mg/L or
less and 1 min of contact time. The
Seattle Water Department's present
chlorination practices should therefore
be sufficient to provide adequate disin-
fection at increased pH.
This Project Summary was developed
by EPA's Municipal Environmental Re-
search Laboratory, Cincinnati, OH, to
announce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
The Seattle Water Department serves
an average of 161 mgd of high quality
water to nearly 1 million people in the
greater Seattle area. The water originates
in the Cascades from two mountain
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sources — the Cedar and Toll Rivers The
watersheds are well protected, and the
water requires only disinfection with
gaseous chlorine to meet Federal stand-
ards. The Cedar River system, developed
in 1901, serves about two-thirds of the
area; the remaining third comes from the
newer Tolt supply. These mountain
waters, which are predominantly rainfall
and snowmelt runoff, are very soft and
tend to be highly corrosive to the unlined,
metallic pipes in home plumbing systems.
Corrosion of the plumbing systems and
the associated water quality degradation
has been a major concern of the Seattle
Wat,er Department for many years. Cor-
rosion has caused three types of problems
— aesthetic, economic, and health. This
summary discussed these problems and
the approach to reducing corrosion in the
distribution area.
Customer complaints of aesthetically
undesirable rusty water, red and blue
stained fixtures, and metallic tastes are
frequently received from within the Cedar
water distribution system. This problem
has been documented by accurate com-
plaint records and by a questionnaire
survey conducted by the Seattle Water
Department in 1973. The survey, which
was distributed to 10% of all services
within the direct service area, showed
that 16.7% of customers in the Cedar
water distribution system experienced
corrosion-related problems.
Piping corrosion in the premise plumb-
ing systems served by the Cedar and Tolt
supplies also places a significant eco-
nomic burden on the homeowner. The
average estimated life span of hot water
galvanized and copper pipes is approxi-
mately 35 years in the Cedar system and
25 years m the Tolt system The average
annual cost in 1978 for maintaining
serviceability in these pipes was about $4
million.
Studies performed from 1972 to 1976
demonstrate that the levels of lead,
copper, and iron in overnight standing
Cedar tap water often exceed the levels
defined by the National Interim Primary
Drinking Water Regulations and the
National Secondary Drinking Water Regu-
lations. Cadmium and zinc were also
found to increase after overnight standi ng
in home plumbing, but they rarely ex-
ceeded their limits. These metals origi-
nate from the copper and galvanized pipes
and the solders used in home plumbing
systems. Although the health impact of
metal levels from overnight standing
water is not an acute problem, it is
certainly desirable to reduce exposure
wherever possible.
Causes of Corrosion
The corrosiveness of Cedar water re-
sults from several related factors, includ-
ing:
• Acidity as indicated by low pH (the
raw Cedar water pH is approxi-
mately 7.6; after chlorination and
fluoridation, pH is only 6 8 to 7.2);
• Dissolved oxygen concentration at
saturated conditions;
• Insufficient calcium and bicarbon-
ate alkalinity in the water to form
protective calcium carbonate films
on pipe surfaces; and
• A relatively high [halogen + su/fate]/
alkalinity ratio of 0.5 to 0.8 that
results in conditions favorable to
pitting corrosion.
In 1970, three factors combined to
intensify the corrosiveness of this water
supply. First, to decrease the occurrence
of positive bacteriological samples within
the distribution system, the chlorine
dosage at the open distribution reservoir
outlets was increased. Second, at the
request of the U.S. Public Health Service,
ammoniation of the water supply was
stopped to enable a free chlorine residual
to be maintained throughout the distribu-
tion system. This change from combined
chlorination to free chlorination was
implemented to provide quicker, more
effective disinfection of the unfiltered
water supply. And third, as the result of a
1968 vote of the Seattle citizens, fluorida-
tion of the water supply with hydrof luoro-
silicic acid began in 1970.
Internal Corrosion Study
In December 1975, the City of Seattle
retained a consulting engineering firm to
perform a detailed analysis of the cor-
rosion problem and to recommend possi-
ble solutions. The Internal Corrosion
Study, which included a 9-month pilot-
plant investigation, confirmed the corro-
siveness of Seattle water, the causes of
corrosion, and the impacts associated
with the corrosive water, and it evaluated
alternative measures to reduce the corro-
siveness of the water supply. Alternative
methods to reduce corrosion included
changing the methods of disinfection and
fluoridation, blending the water supply
with groundwater supplies, and adding
corrosion-inhibiting chemicals.
Based on the findings of this study, an
Internal Corrosion Control Management
Plan was developed. Because the very
low levels of mineral solids, pH, and
alkalinity constitute the major causes of
the waters' corrosiveness, this plan was
designed to correct the natural deficiency
of minerals in Seattle's water through
chemical addition.
The consultant recommended water
quality goals using various chemical
combinations that included the addition
of lime and sodium bicarbonate. He also
suggested that because of the addition of
these chemicals, chlorine dosages might
need to be increased to provide adequate
disinfection. The actual selection of chem-
ical combinations and optimum dosages
became the task of the Seattle Water
Department.
Tolt and Cedar
Pilot-Plant Studies
The Tolt and Cedar pilot-plant studies
were conducted in 1979 and 1980 to
define a precise chemical treatment and
dosages needed for corrosion control in
both water supplies, and to document
further the effects of such treatment.
These studies recommended the addi-
tion of lime only to the Cedar supply and
lime plus sodium carbonate to the Tolt
supply for internal corrosion control. The
treatments were designed to achieve the
water quality characteristics listed in
Table 1.
Study Objectives and
Scope of Work
The objectives of this research were to:
1. Document the effects of the free
chlorine residual on corrosion rates.
2. Determine whether chlorine dosages
should be increased to provide ade-
quate disinfection when pH adjust-
ment is implemented.
3. Document the effects of the corrosion
treatment program on bacteria in the
water.
The study was divided into the following
research phases:
Electrochemical Tests
Corrosion rates were determined elec-
trochemically for copper in Cedar River
water under various pH, free chlorine
residuals, and chloride concentrations to
determine the effects of chlorination on
corrosion rates. Corrosion rates were
determined with (1) a standard linear
potential sweep method modified to in-
clude positive feedback compensation for
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Table 1. Present and Proposed Water Quality Characteristics
Present Quality of Chlorinated
and Fluoridated Water
Proposed Water Quality
After Corrosion Treatment
Parameter
Cedar
Tolt
Cedar
Tolt
pH
Alkalinity
(as mg/L CaCOJ
(Halogen + sulfate)/
alkalinity ratio
6.8-7.4
15-18
0.5-0.8
5.8-6 2
2
2.5-4.5
7.8-8 3
20
0.5
7.8-8.3
14
0.5
potential drop resulting from solution
resistance, and (2) a rotating disc elec-
trode to eliminate mass transport limita-
tions.
Onsite Corrosion
Treatment Tests
During the period January to August
1981, tests designed to simulate corro-
sion treatment startup were conducted at
the City of Seattle Fire Station No. 35.
This test site was chosen because it
contained older galvanized plumbing that
experiences severe corrosion-related
water quality problems. Also, the test site
was located in the Tolt distribution sys-
tem, where the changes in water quality
caused by corrosion treatment would be
greater than in the Cedar distribution
system.
Microbiological
Laboratory Tests
Microbiological laboratory tests were
conducted to determine whether chlorine
dosages should be increased upon imple-
mentation of corrosion treatment. The
'tests measured the effects of various pH
and free chlorine residuals on the survival
of Pseudomonas aeruginosa, Escherichia
coif, and Enterobacter aerogenes. The
tests were conducted at three free chlo-
rine residuals and three pH values.
Results and Conclusions
Electrochemical Tests
The electrochemical tests demonstra-
ted that chlorination (using either NaOCI
or CI2) substantially increases copper
corrosion rates. A 1.0-mg/Lfreechlorine
residual increased corrosion rates by
approximately 20%. Also, for free chlorine
concentrations greater than 0.2 mg/L,
the corrosion rate at pH 8 was about
equal to the corrosion rate at pH 7.
Although previous studies have shown
that substantial corrosion reduction can
be achieved by treatment to pH 8.0, the
electrochemical test results indicate that
increases in chlorine dosages would
diminish the benefits received by pH
adjustment.
Onsite Corrosion
Treatment Tests
The changes that occur in overnight
standing and running water quality at the
customer's tap with corrosion treatment
vary depending on the parameter under
consideration.
Assessment of the effects of corrosion
treatment on bacteriological water quality
showed the standard plate counts from
treated, 24-hour standing water were
two to three orders of magnitude higher
than those from the untreated standing
water samples. Standing water samples
collected after treatment began also
displayed increased iron deposits and
organic debris, compared with untreated
standing water samples. Iron-oxidizing
organisms (e.g., Gallionella) and sulfate-
reducing organisms (e.g., Desulfovibrio)
existed within the pipe loop system in
both the standing water and tubercular
incrustations. Both of these organisms
increased with corrosion treatment.
Stalk- or bud-producing microorganisms
(e.g., Caulobacter spp., or iron-precipita-
ting bacteria) were observed in the water
samples and attached to the surface of (or
embedded in) the tubercles. Pseudo-
monas aeruginosa counts increased 47%
in standing water samples during corro-
sion treatment. Opportunistic pathogens
and coliform antagonists (including
Pseudomonas spp. and Flavobacterium
spp.) were detected in standing water
samples, and they increased in number
with treatment startup. Opportunistic
pathogens accounted for approximately
77% of the total standard plate count
isolates in 24-hour standing water sam-
ples, and coliform antagonists accounted
for approximately 71 %.
In running water, reductions occurred
in zinc and iron leaching during treatment
startup. No appreciable change occurred
in lead or cadmium leaching, apparent
color, and turbidity concentrations in
running water.
In standing water, zinc leaching de-
creased during treatment at pH 6 to 7 and
increased at pH 7 to 8. Iron leaching
increased by about 35% during treatment
startup, and copper and lead leaching
were decreased 53% and 57%, respec-
tively. Also, apparent color and turbidity
increased in standing water during treat-
ment startup.
Microbiological
Laboratory Tests
The results of the microbiological labo-
ratory tests indicate that the Seattle Water
Department will not need to increase
chlorine dosages to provide adequate
disinfection when corrosion treatment is
implemented. At pH 8 and 0.2 mg/Lfree
chlorine residual, 100% kill was achieved
for P. aeruginosa and E. coli with contact
times of less than 2 min. The Seattle
Water Department chlorination program,
which maintains a free chlorine residual
of 0.6 mg/L for a minimum contact time
of 10 min will therefore provide a safety
factor sufficient to ensure adequate disin-
fection at pH 8.0.
The full report was submitted in fulfill-
ment of Grant No. R-806686-010 by the
Seattle Water Department under the
sponsorship of the U.S. Environmental
Protection Agency.
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Karen S. Nakhjiri, Carlos E. Herrera. and Ronald D. Hi/burn are with Seattle Water
Department, Seattle. WA 98144.
Marvin C. Gardels is the EPA Project Officer (see belowj.
The complete report, entitled "Seattle Distribution System Corrosion Control
Study: Volume V. Counteractive Effects of Disinfection and Corrosion Control,"
(Order No. PB 84-169 747; Cost: $17.50, subject to change) will be available
only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Municipal Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
•C, U.S. GOVERNMENT PRINTING OFFICE 759-015/7657
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