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

-------
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

-------
 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.

-------
       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

-------