United States
Environmental Protection
Agency
Municipal Environmental Research -
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-83-056 Oct. 1983
SERA Project Summary
Seattle Distribution System
Corrosion Control Study:
Volume IV. On-Site Evaluation of
Corrosion Treatment
Carlos E. Herrera, Karen S. Nakhjiri, and Brian P. Hoyt
The Seattle, Washington, Water De-
partment conducted an 8-month pilot-
plant study on the treatment of Tort
River water with lime and sodium car-
bonate to prevent pipe corrosion. Pipe
loop tests were conducted with the
following objectives: (1) to determine
the appropriate chemical startup pro-
cedures for two full-scale corrosion
treatment facilities, (2) to document
the effectiveness of the corrosion treat-
ment program in suppressing corrosion,
metal leaching, and tuberculation in
older, galvanized-steel premise plumb-
ing systems, (3) to document the ef-
fects of the corrosion treatment pro-
gram on bacteria in water, and (4) to
anticipate any possible customer prob-
lems caused by implementing the cor-
rosion treatment program.
The study monitored the effects of
simulated corrosion treatment startup
on chemical and microbiological water
quality from an old galvanized plumbing
system. Standing water samples col-
lected after treatment startup displayed
increased iron deposits, organic debris,
and bacterial populations compared
with untreated standing-water samples.
Zinc leaching was reduced during treat-
ment at pH 6 to 7 and increased at pH 7
to 8. Iron leaching increased by approxi-
mately 38% during treatment startup,
whereas copper and lead leaching were
reduced by 53% and 57% respectively.
Corrosion treatment also reduced the
tuberculation rate by about 32%.
Based on this pilot study, a full-scale
corrosion treatment schedule is recom-
mended that minimizes possible water
quality problems caused by implemen-
tation. The recommended approach in-
cludes the gradual addition of lime and
sodium carbonate to a final treatment
pHof8.3.
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 persons in the
greater Seattle area The water originates
in the Cascades from two mountain sources
- the Cedar and Tolt Rivers. The watersheds
are well protected, and the water requires
only disinfection with gaseous chlorine to
meet Federal standards. The Cedar River
system, developed in 1901, serves about
two-thirds of the area; the remaining third
is served by 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 sys-
tems and the associated water quality
degradation has been a major concern of
the Seattle Water Department for many
years Corrosion has caused aesthetic,
economic, and health problems. This sum-
mary discusses these problems and an
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Customer complaints of aesthetically
undesirable rusty water, red- and blue-
stained fixtures, and metallic tastes are
frequently received from within the Cedar
water distributrion system. These problems
have been documented by accurate com-
plaint records and by a questionnaire sur-
vey conducted by the Seattle Water De-
partment in 1973. The survey, which was
distributed to 1096 of all service units
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 plumbing
systems served by the Cedar supply also
places a significant economic burden on
the homeowner. The average estimated
life span of hot water galvanized and
copper pipes is approximately 35 years.
The average annual cost forecast in 1 978
for maintaining serviceability in these pipes
is estimated to be approximately $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 Regulations Cadmium and
zinc also increased after standing over-
night in home plumbing, but they rarely
exceeded permissible levels. These metals
originate from the copper and galvanized
pipes and the solders used in home plumb-
ing systems. Though the health impact of
metal contaminants in overnight-standing
water is not an acute problem, it is certainly
desirable to reduce exposure where possi-
ble.
Causes of Corrosion
The corrosiveness of Cedar water results
from several related factors, including:
• Acidity, as indicated by low pH (the
raw Cedar water pH is approximately
7.6; after chlorination and fluoridation,
pH is reduced to 6.8 to 7.2);
• Dissolved oxygen concentration at
saturated conditions;
• Insufficient calcium and bicarbonate
alkalinity in the water to form protec-
tive calcium carbonate films on pipe
surfaces;
• A relatively high [halogen + sulfate]/
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, the chlorine dosage at the
open distribution reservoir outlets was
increased to decrease the occurrence of
positive bacteriological samples within the
distribution systems. Second, ammoniation
of the water supply was stopped at the
request of the U.S. Public Health Service
to enable a free chlorine residual to be
maintained throughout the distribution sys-
tem. This change from combined to free
chlorination was implemented to provide
quicker, more effective disinfection of the
unfiltered water supply. The third factor to
intensify the corrosiveness of the water
supply was the implementation of fluorida-
tion with hydrofluosilicic acid in 1970
after a vote of the Seattle citizens in 1968.
Internal Corrosion Study
In December 1975, the City of Seattle
retained a consulting engineering firm to
perform a detailed analysis of the corrosion
problem and to recommend possible solu-
tions. The Internal Corrosion Study, which
included a 9-month pilot-plant investiga-
tion, confirmed the corrosiveness of Seattle
water, the causes of corrosion, and the
impacts associated with the corrosive
water, and evaluated alternative measures
to reduce the corrosiveness of the water
supply. The latter included changing the
methods of disinfection and fluoridation,
blending the water supply with ground-
water supplies, and adding corrosion-in-
hibiting 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 water's
corrosiveness, this plan was designed to
correct the natural deficiency of minerals
in Seattle's water through chemical addi-
tion.
The consultant recommended water
quality goals using various chemical com-
binations that included the addition of lime
and sodium bicarbonate. The actual selec-
tion of chemical combinations and optimum
dosages became the task of the Seattle
Water Department.
Tolt and Cedar Pi lot-Plant
Studies
The Tolt and Cedar pilot-plant studies
were conducted in 1979-80 to define
precisely the chemical treatment and dos-
ages needed for corrosion control in both
water supplies, and to document further
the effects of such treatment.
These studies recommend the addition
of lime only to the Cedar supply and lime
plus sodium carbonate to the Tolt supply
for internal corrosion control. The treat-
ments were designed to achieve the water
quality characteristics listed in Table 1.
Study Objectives and Scope of
Work
The objectives of this research were as
follows:
1. To determine appropriate chemical
startup procedures for the Tolt and
Cedar full-scale corrosion treatment
facilities,
2. To document the effectiveness of the
corrosion treatment program in sup-
pressing corrosion, metal leaching,
and tuberculation in older galvanized-
steel premise plumbing systems,
3. To document the effects of the cor-
rosion treatment program on bacteria
in water, and
4. To anticipate any possible customer
problems caused by implementing
the corrosion treatment program.
From January 1981 to August 1981,
tests designed to simulate corrosion treat-
ment startup were conducted at the City of
Seattle Fire Station No. 35. This test site
was chosen because it contains older
galvanized plumbing that experiences
severe corrosion-related waterquality prob-
lems. Also, the test site was located in the
Tolt distribution system because the
changes in water quality caused by corro-
sion treatment will be greater there than in
the Cedar distribution system.
The corrosion tests documented the
effects of corrosion treatment startup
based on metal leaching, bacteriological
water quality, aesthetic water quality, and
pipe tuberculation. Running-water samples
and 24-hr-standing samples were collected
from an 8.5-m pipe loop system. The
samples were collected before treatment
(to establish baseline data) and during the
simulated treatment startup.
Operation, Results, and
Evaluation
The pilot test apparatus consisted of a
chemical feeding and mixing system and a
1.9-cm-diameter old galvanized pipe test
loop (Figure 1).
The pipe loop system was made from
10-year-old galvanized hot-water pipe col-
lected from the University of Washington.
When the pipe loop was installed, it was
highly tuberculated. The pipe loop was 8.5
m long and contained five elbows. Pressure
test gauges were located at the beginning
and end of the loop to determine headloss
in the loop. A flow of 10.5 L/min was
maintained through the loop using a throt-
tling valve at its end. Also at the end of the
loop was a flowmeter. The throttling valve
was periodically shut off to collect 24-hr-
standing samples.
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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 (mg/LfCaCOJ
(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
Throttling
Pressure
Gauge
Flowmeter
To Drain
Pressure
Gauge
From Building
Plumbing
To Building
Plumbing
Static
Mixer
1.9-cm-Diameter Pipe
Total length = 8.5 m
(a) Test Loop
Static
Mixer
I Flowmeter
Figure 1. Pilot plant flow schematic.
The test treatment conditions were
chosen to simulate average distribution
system levels of pH and alkalinity during
full-scale treatment startup. Target water
quality for the test conditions appears in
Table 2.
The effects of treatment startup were
determined from standing and running
samples and headless determinations col-
lected from the test pipe loop system.
Standing water samples represented 24-
hr stagnant water conditions in the pipe
loop system. Running water samples were
collected after a 2-min flushing of the pipe
loop system at 10.5 l/min following the
collection of the 24-hr standing sample.
The samples were analyzed for metal
concentrations, physical parameters, and
microbiological quality before and after
corrosion treatment. The microbiological
quality of the water and pipe incrustations
Soda Ash Lime
Solution Solution
Ib) Chemical Feed System
were examined with selective enrichment
culture media and scanning electron micro-
scopy. The chemical composition of the
tubercles and suspended paniculate mat-
ter in the water were determined by x-ray,
energy-dispersive microanalysis. Headloss
in the test pipe loop system was used as an
indication of pipe blockage.
The more frequently observed water
quality changes occurring in the pipe loop
before and after treatment were higher
bacterial plate counts in 24-hr standing
water than in running water (by two to
three orders of magnitude), increased levels
of iron concentrations, turbidity, and ap-
parent color in the standing water as
opposed to running water.
Standing-water samples collected after
treatment startup displayed increased iron
deposits, organic debris, and bacterial pop-
ulations compared with untreated standing-
water samples. Iron-oxidizing and sulfate-
reducing organisms were shown to exist
within the pipe loop system in both the
standing water and tubercular incrusta-
tions. Opportunistic pathogens and coli-
form antagonists (including Pseudomonas
and Flavobacterium) were detected in
standing-water samples and increased in
number with treatment startup. The public
health significance of sissile microbial
communities in drinking water was also
considered.
In standing water, zinc leaching decreas-
ed during treatment at pH 6 to 7 and
increased at pH 7 to 8. Iron leaching
increased by approximately 3896 during
treatment startup, whereas copper and
lead leaching decreased by 53% and 5796
respectively.
In running water, reductions occurred in
zinc and iron leaching during treatment
startup, and significant change was noted
in lead or cadmium leaching.
Corrosion treatment reduced the tuber-
culation rate and subsequent pipe blockage
by about 3296.
Conclusions
A full-scale corrosion treatment schedule
(Table 3) based on the test results was
recommended to minimize possible water
quality problems caused by the implemen-
tation of corrosion treatment The recom-
mended approach was first to add lime
and sodium carbonate gradually to the Tolt
supply until the pH equals that of the
Cedar supply and then simultaneously to
add lime to the Cedar supply and sodium
carbonate to the Tolt supply to a final
treatment pH of 8.3.
The full report was submitted in fulfill-
ment of Grant No. R806686 010 by the
Seattle Water Department under the spon-
sorship of the U.S. Environmental Protec-
tion Agency. • - - - - -
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Table 2. On-Site Test Treatment Conditions
Item
Phase
III
IV
pH
Alkalinity (mg/L CaCOJ
Lime Dosage, CaO (mg/L)
Na2C03 Dosage (mg/L)
6.00
2.0
0
0
7.00
9.0
0
7.42
7.60
8.0
2.00
6.40
8.00
14.0
1.70
9.00
Table 3. Corrosion Treatment Plant Startup Procedure for Tolt and Cedar Supplies
Total Cedar
Day
1
8
15
29
42
Lime
Dosage
(mg/L CaO)
0.8
1.7
1.7
1.7
1.7
Sodium
Carbonate
Dosage
(mg/L Na2CO^
0
0
4.0
6.0
9.0
pH
6.3
6.6
7.1
7.5
8.3
Alkalinity
(mg/L CaCOj)
3.4
5.0
8.8
10.7
13.5
Lime
Dosage
(mg/L CaO)
0
0
0
1.0
1.7
pH
7.2
7.2
7.2
7.5
8.3
Alkalinity
(mg/L CaCOJ
16
16
16
17.8
19.0
Carlos E. Herrera. Karen S. Nakhjiri, and Brian P. Hoyt are with the Seattle Water
Department, Seattle, WA 98144.
Marvin C. Gardels is the EPA Project Officer (see below).
The complete report, entitled "Seattle Distribution System Corrosion Control
Study: Volume IV. On-Site Evaluation of Corrosion Treatment," (Order No. PB
83-241 729; Cost: $11.50 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
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