United States
                       Environmental Protection
                      Office of Water
                      Washington, D.C.
EPA 832-F-99-034
September 1999
Combined Sewer Overflow
Technology  Fact Sheet
Chlorine  Disinfection

Combined sewer overflows (CSOs) tend to occur
during periods of rainfall or snowmelt, when total
wastewater flows exceed the  capacity  of the
combined sewer system (CSS)  and/or treatment
facilities. When this occurs, the CSS is designed to
overflow directly to surface water bodies, such as
lakes, rivers, estuaries,  or coastal waters.   These
overflows can be a major source of water pollution
in communities served by CSSs.

CSOs typically  discharge a variable mixture of raw
sewage, watershed runoff pollutants,  and scoured
materials that build up in the collection  system
during dry weather  periods.   These discharges
contain pollutants  that  may adversely impact the
receiving water body.  These pollutants range from
suspended  solids, pathogenic  microorganisms,
viruses,  and cysts,  to  chemical  and floatable
materials. Dermal contact with the discharge or
ingestion of water or contaminated shellfish may
result in health risks.

Consistent with the U.S. Environmental Protection
Agency (EPA) 1994  CSO Control Policy, cities
with CSSs are  implementing controls that will
provide for attainment of water  quality standards
that protect the beneficial use of streams and other
receiving water bodies.  To help  meet site-specific
bacterial  water quality standards,  pathogenic
bacteria in the  CSO discharge will most likely
require inactivation or destruction.  The process of
selective   inactivation and/or destruction  of
pathogenic  microorganisms  is  known   as
                     CSO disinfection occurs through the reduction of
                     solids and through the oxidation or radiation of
                     pathogens. Physical reduction of bacteria in CSOs
                     is accomplished through sedimentation, flotation
                     and filtration, while common chemical oxidizing
                     agents include chlorine, bromine and hydrogen
                     peroxide or their compounds.   In addition to
                     chemical oxidants, there  are several  alternative
                     disinfectants, such as ultraviolet light (UV) radiation
                     and ozonation. These are further described in the
                     EPA CSO Technology Fact Sheet 832-F-99-020,
                     Alternative Disinfectants for Treating CSOs. The
                     remainder of this fact sheet focuses on chlorine as a
                     CSO disinfectant.

                     Chlorine may be applied to a  CSO  in either a
                     gaseous  form  (C12)  or as an  ionized  solid
                     [Ca(OCl)2,NaOCl]. Each compound reacts in water
                     to produce the disinfectants  HOC1 (hypochlorous
                     acid) and OC1" (hypochlorite ion) as illustrated in
                     Figure 1. Together, these compounds contribute to
                     what is know as the CSO's  free residual chlorine
                     concentration. As chlorine is added to  the CSO, it
                     reacts with ammonia and organic matter to form
                     chloramines and chloro-organic compounds. The
                     addition  of more chlorine oxidizes some  of the
                     chloro-organic  compounds  and  chloramines,
                     resulting in the conversion of monochloramines to
                     dichloramines and trichloramines.
                              C12 + H2O
                              Ca(OCl)2  -
- HC1
+ HOC1
                                               FIGURE 1  COMMON REACTIONS OF
                                                     CHLORINE PRODUCTS

As more chlorine is added, the residual chloramines
and chloro-organic compounds  are reduced  to a
minimum value and free chlorine residuals result.
The  point  at which the formation  of residual
chlorine  compounds  occurs  is known  as the
"breakpoint."     Thus,  the  term   "breakpoint
chlorination"  describes  the  process  whereby
sufficient chlorine is added to the CSO to obtain a
free chlorine residual. If sufficient chlorine cannot
be added to achieve the breakpoint reaction and
thus ensure that disinfection of the CSO is occurring
through saturation with chlorine, care should be
taken to  ensure  that disinfection  is  occurring
through extended chlorine contact time with the
CSO  (see  discussion  of  the  relationship of
disinfection  dose vs. contact time below).

Various theories have been put forth to explain the
germicidal  effects of chlorine.    These  include
oxidizing the germ cells, altering cell permeability,
altering cell protoplasm, inhibiting enzyme activity,
and damaging the cell DNA and RNA.  Chlorine
appears to react  strongly with  lipids in the cell
membrane,  and   membranes having  high  lipid
concentrations appear to be more susceptible to
destruction.  For this reason, viruses, cysts, and ova
are more resistant to disinfectants than are bacteria.

The  predominant disinfection  mechanism  will
depend  on  the microorganism  in  question, the
wastewater  characteristics,   and  the   chlorine
compound used.  When the physical parameters
controlling  the   chlorination  process  are   held
constant, the  germicidal  effects of chlorine as
measured by bacterial survival depend primarily on
dosage (and form) and the contact time. It has been
found that increasing either dosage or contact time,
while simultaneously decreasing the other, can
achieve  approximately  the  same  degree  of
disinfection.   When  breakpoint chlorination  is
practiced  properly,   the  bactericidal  effect  is
considered good and viricidal  effect is considered


The selection of a disinfection method for a specific
CSO outfall depends  on many factors, including:
the quality of the wastewater being discharged; any
potential toxic effects; the ease  of operation and
maintenance; and any regulations governing residual

As discussed above, the disinfection capability of a
system is heavily dependant on the  contact time
between  the  chlorine  and  bacteria.    Because
suspended solids can inhibit the disinfecting agent
from  reacting with the  bacteria,  disinfection  is
usually used in conjunction with an additional
technology that specifically reduces the suspended
solids in solution.


CSO  disinfection  systems must  be designed  to
handle variable  pollutant  loadings  and  large
fluctuations in flow. Because CSOs are intermittent
and  are  characterized by  short  durations  and
relatively large flow rates relative  to base sewage
flow,  bacterial and organic loadings from the
collection system may vary greatly, both within and
between storm events.  Loadings can be extremely
variable from  the beginning  to the end of a wet
weather event.  The beginning of a CSO event will
typically exhibit high solids and bacterial loadings as
the system is flushed.    The concentration  of
pollutants will typically trail off as the storm event
continues.  Loadings will also be  affected by the
characteristics of the watershed, the dynamics of the
collection  system,  the antecedent  dry  weather
conditions, and the regional rainfall rate.  A CSO
disinfection system  should be designed with site-
specific loading characteristics in mind, and should
be capable of handling a large first-flush pollutant

The intended  or designated use of the receiving
water body may also affect the disinfection process
design.   For  example, the presence of sensitive
aquatic species may limit the allowable residual
disinfectant concentrations in the receiving water,
thereby limiting the amount of disinfectant that can
be added to the CSO.

An additional baseline  consideration  for  the
successful design of a CSO disinfection process is
solids  reduction.  Since  bacteria embedded  in
paniculate  matter  can  be  shielded from  the
disinfectant, solids must be removed from the CSO
to ensure effective disinfection.  Therefore, even if

the water quality requirements for the receiving
water  body  do not dictate  the need for  solids
reduction, the disinfection process itself may require

After these general considerations are resolved, the
designer can begin to evaluate specific disinfection
processes to determine which potential processes
may be most appropriate.  Generally, disinfection
processes can be broken into "high rate" processes
and  extended  detention  processes.   High rate
processes using breakpoint chlorination (described
above) are often chosen over extended-detention
systems because the cost differences between the
systems are minor (the two systems have similar
capital costs, but the high rate systems often incur
additional O&M costs for  chemicals and power),
and the decreased retention time characteristic of
the high rate processes makes them more attractive.
In order to design a breakpoint chlorination system,
it may be necessary to determine the amount of time
that the chlorine must be in contact with the CSO to
achieve the desired disinfection.   This "contact
time," or CT, relationship should be developed for
treatment of the design CSO event for a significant
antecedent dry weather  period.   This will  likely
provide worst case conditions for determining vessel
size and disinfectant supply rate.

The reactor should be designed for as close to ideal
plug flow as possible and should include effective
initial mixing of the chlorine solution. Strong initial
mixing is critical in high rate disinfection processes
where contact times are short.   Mixing  occurs
through   mechanical  means   (mixers,  pumps,
spargers)  or through the utilization of the energy
available  in the  storm  water gradient (hydraulic
jumps, flumes, high velocity segments).

As discussed  above,  control  of  the  chlorine
disinfection process  for CSOs is  complicated
because of the highly variable nature of the flow.
Measurement  of the CSO flow rate is therefore
critical in  determining  the rate at which to add
disinfectant. Often a combination of weirs or flumes
(for  lower  flows)  and open  channel   flow
measurement (for high flows) is required to cover
the varying flow rates. Sonic devices, bubblers, and
pressure-type level sensors have all been used in
conjunction with flumes, weirs and open channels to
measure CSO  rates  and volumes. In  addition,
because CSO chlorine  disinfection will typically
include short contact times (one to ten minutes), be
applied to  relatively  dirty  water, and  operate
intermittently, the use  of feedback systems  and
chlorine residual analyzers to pace the chemical feed
is  difficult.  Membrane and probe type chlorine
monitors have  been used, but neither has been
proven to date to be effective and reliable.

A   flow-paced   control  system  with  a  fixed
chlorination feed concentration has been found to be
simpler and  more reliable  than  feedback-based
systems, although flow-paced systems will require
some trial and error adjustment  after installation to
develop   proper  dosage-to-flow  relationships.
Chlorine feed rate is based on the required dosage
and the flow rate.

The flow-paced system may result in higher chlorine
residual concentrations relative to feedback-based
systems. While these higher residual concentrations
may be more effective  at inactivation of viruses,
spores and cysts, these residuals and their various
chlorinated byproducts can have an adverse impact
on the quality of the receiving waters.  Although
chlorine  dissipates rapidly  downstream of  the
application point, in some cases it may be necessary
to dechlorinate the disinfected effluent to protect the
receiving water bodies.  Gaseous sulfur dioxide or
liquid sodium bisulfite can be used for this purpose
and   dechlorination  is  achieved   at  almost
instantaneous  contact  times.    Control  system
difficulties similar to those described for the flow-
paced chlorination system can lead to overdosing of
dechlorination chemicals.

Several chlorine forms  can  be  used  to provide
disinfection. When choosing a form of chlorine for
a specific application, consideration should be given
to  safety, stability, availability, deodorizing ability,
corrosiveness,  solubility and ability to respond
instantaneously to initiation and rate changes.

Because of concerns over accidental  releases in
developed areas or from unstaffed facilities, gaseous
chlorine  is  not utilized as  frequently  in  CSO
applications as is liquid chlorine. However, gaseous

chlorine  may be  appropriate  for  use in CSO
treatment facilities that are located at Wastewater
Treatment Plants (WWTPs) because the chlorine
application can be carefully monitored.  Gaseous
chlorine-based  systems will require evaporator
equipment and potable water, and possibly chemical
scrubbing facilities.

The most common forms of chlorine used in CSO
applications are chlorine gas, sodium hypochlorite,
and   calcium  hypochlorite.    The  following
paragraphs describe these  compounds in more

Liquid forms of chlorine  appear to be the most
appropriate  choice for wet weather treatment
because  they  are  comparatively easy to  handle
relative to other forms of chlorine, such as gaseous
chlorine.  In general, liquid chlorine will be applied
from on-site chemical storage tanks using metering
pumps. Because of potential problems in delivering
liquid chlorine to remote sites after suppliers' hours,
chlorine should be stored on-site. The chlorination
system  should  have  adequate on-site  storage
capacity  to feed the design dosage for the design
overflow event. Extra volume may also be stored to
allow for chemical degradation. Feed equipment
should be sized to  deliver the required dose under
peak flow conditions.  Consideration  of the time
required  to replenish chlorine should  be factored
into sizing of storage tanks.

Chlorine gas:

Gaseous  chlorine (C12) is relatively inexpensive and
has the lowest production  and operating costs for
large  continuous disinfection operations.   It is a
stable  compound  which may  be  stored  for  an
extended period of time, but only as a liquefied gas
under high pressure. Storage containers vary in size
from 150 pound cylinders to 55 ton tank cars. The
size of the storage containers used at any given site
will be dependent upon the facility design as well as
the anticipated treatment capabilities of the system.
Because  chlorine gas is hazardous, it should not be
stored in areas accessed by the public and  any
transportation of the gas should be continuously
monitored.   Chlorine gas  is extremely toxic  and
corrosive and because it is such a strong oxidant, it
reacts with almost any organic  material found in
wastewater.   Organics, ammonia,  and phenolic
compounds will often react with the chlorine before
it has  a chance to react with pathogens.   For
example, chlorine  reacts with ammonia to form
chloramines and phenols to form chlorophenols.
Chloramines and chlorophenols are  referred to as
combined chlorine residuals and together with free
chlorine  residuals  constitute  the  total residual
chlorine (TRC).   Therefore, use of chlorine  gas
should  be  closely   monitored  to  ensure   its
effectiveness as a disinfectant.

Sodium hypochlorite:

Chlorine  may  also  be   supplied  as   sodium
hypochlorite (NaOCl), otherwise known as liquid
bleach. Sodium hypochlorite can be generated from
sodium hydroxide  and chlorine,  or it  can  be
generated  electrolytically  from  brine.   Sodium
hypochlorite can be manufactured on site, or it can
be purchased in liquid form generally containing 3 to
15 percent available chlorine. Decay  of the original
product will occur as a result of exposure to light,
an  increase   in  temperature,  or   because   of
concentration  of the compound.  Product decay
occurs  more  rapidly  at  higher  concentrations;
therefore sodium hypochlorite is typically stored as
a 5  percent solution of available chlorine. Sodium
hypochlorite should be stored at temperatures below
85 degrees Fahrenheit in a corrosion-resistant tank.
Sodium hypochlorite is the most expensive of the
three forms of chlorine compounds.  It produces a
free chlorine residual, and forms chloramines  and
chlorophenols.  Sodium hypochlorite is safer to
handle than gaseous chlorine, and can be generated
and stored on site.

Calcium hypochlorite:

Chlorine may  be supplied in the form of calcium
hypochlorite, Ca(OCl)2,  in either wet or dry form.
High grade calcium hypochlorite contains at least 70
percent available chlorine, and is readily soluble in
water.   It is  a strong oxidizer and is extremely
hazardous.    Calcium  hypochlorite tends to  be
unstable and therefore should  be  stored in a  dry
place inside a corrosion-resistant container in order
to reduce product breakdown.  Like chlorine  gas
and sodium  hypochlorite,  calcium  hypochlorite
breaks down into free chlorine residuals and will

react  to form chloramines  and  chlorophenols.
Calcium hypochlorite  is more  expensive than
chlorine gas and will  degenerate as a result of
storage. Calcium hypochlorite also crystallizes and
can clog pipes, pumps, and valves.


A long record  of historical data has shown that
chlorine is the best and most successful means of
disinfecting water. Clean drinking water is a global
necessity and the residual addition of chlorine to
water in controlled amounts prevents the spread of
life-threatening diseases and the growth of living

However,  chlorine  disinfection  also  has  its
disadvantages.  Numerous toxicity  studies have
shown adverse effects  due to chlorination (Rein,
1992; Hall, 1981; Ward, 1978).  Any discharge of
chlorinated effluent into a receiving water body
may involve some release of chlorine residuals and
chlorine byproducts.  Free chlorine and combined
chlorine residuals are toxic to aquatic life at certain
concentrations. The lethal effects of free chlorine
are more rapid and occur at lower concentrations
than chloramines.  Chlorine  will also  react with
organic  material  to  form  trace   amounts  of
chlorinated  hydrocarbons called trihalomethanes
(THMs). THMs are suspected as being carcinogens
and are strictly monitored in drinking water.

Environmental  variables  affecting the toxicity of
residual chlorine include pH and temperature of the
receiving water. Due to increases in available free
chlorine, toxicity increases with decreasing pH.
Toxicity also tends  to  increase with  increasing
temperature.  Mean acute toxicity values for several
species are given in Table 1.

Intermittent  discharges of total  residual  chlorine
have  been  recommended  not  to  exceed 0.2
milligrams per liter for a period of 2 hours per day
where more resistant species of fish are known to
persist, or 0.04 milligrams per liter for a period of 2
hours per day for trout or salmon (Brungs, 1973).
In addition, chlorine may inadvertently enhance the
growth of pathogenic microorganisms in receiving
waters,  since  chlorine  breaks  large   protein
molecules into  small proteins, peptides, and other
Daphnia magna
Fathead minnow
Brook trout
Mean Acute Value ( g/l)


Source: U.S. EPA, 1985.

amino acids  that can  be more readily used by
coliform bacteria.

Using chlorine as a disinfectant does have certain
health and   safety   limitations  that  should  be
evaluated before implementing any CSO plan.  The
transport of chlorine can pose serious hazards and
in some  states,  transport  of chlorine is severely
restricted. Some of the health risks include:

      Irritation of mucous membranes, respiratory
      tract and eyes.

      Prolonged exposure to  the gas may cause
      coughing,  gagging,  and  may result in
      pulmonary edema and death.

      Gaseous  chlorine   has  a  tendency  to
      hydrolyze  in the  presence  of moisture,
      forming hydrochloric acid, which irritates the
      eyes and skin.

      Liquid chlorine removes body heat, freezing
      exposed skin.

      It  should be noted, however, that sodium
      hypochlorite  is  considered to be safe for
      storage and handling in systems for remote
      disinfection of CSOs, and there is currently
      no  definitive scientific evidence that the
      intermittent  use  of  chlorine  for   CSO
      disinfection poses a significant environmental


The  performance of a  CSO disinfection system
depends on its ability to kill bacteria, viruses, and
other pathogenic organisms. In  CSOs with low
suspended  solids concentrations, pathogens  are
killed with a quick dose of disinfectant. However,
when suspended solids concentrations in the CSO
are high, the disinfection process is controlled by
two different mechanisms.  The initial disinfection
phase kills individual and small clumps of bacteria.
The majority of the bacterial kill occurs in this step;
however, residual bacteria entrapped in solids are
usually  not  affected.   The  amount  of bacteria
remaining in the CSO after the initial disinfectant
dose is a function of the concentration of suspended
solids and their particle sizes.   If low levels of
bacteria  are required  to  meet the treatment
objectives, the disinfection process may require a
higher level of solids removal, longer contact times,
or larger disinfectant dosages to kill these remaining
bacteria. The first two of these options will require
larger treatment vessels.

Disinfection performance is often assessed through
changes in concentrations of indicator organisms
(primarily fecal and total coliform) over time. This
assessment  is  often  made  using mathematical
equations that  predict  future  concentrations of
indicator  organisms  based  on   system-specific
variables. For example,  the Collins model predicts
the reduction in bacterial concentration as a function
of chlorine  residual  concentrations  and system
contact  time according to the following equation:
             Y, = Y0 (1+0.23CT)
       Yt = bacterial concentration after time T

       Y0= original   bacterial    concentration

       C = chlorine  residual concentration after
            time T (mg/1)
At lower values of CT, a modified model (Collins-
Selleck) was developed to define the relationship
between  Y/Y0 and  CT.  Several  other  factors,
including  the chlorine  dose, contact time, flow
characteristics, and mixing intensity, also influence
the effectiveness of chlorine disinfection.

As described above, the effectiveness of chlorine in
disinfecting CSOs is usually measured in terms of its
effect on reducing fecal coliform or total coliform
bacteria.   Table 2 presents the results of several
studies that evaluated the effectiveness of chlorine
gas in reducing pathogens from CSOs and simulated


Maintenance for a CSO treatment facility is typically
performed similarly to maintenance performed at a
batch operation.  Properly designed facilities will
operate automatically; however, after a storm event,
most facilities will require maintenance to remove
residuals (screenings, floatables & grit) and to check
and replenish chemical  supplies.  Maintenance  of
disinfection equipment can occur during the post-
event visit and includes the following:

      All copper tubing from lines and fittings must
      be  checked routinely.   The lines  can be
      checked for corrosion by bending them; if the
      lines give off a screeching noise when they
      are bent, they are corroded  and the tubing
      must be replaced.

     Tubing and  vessels   should be  checked
      routinely for moisture accumulation or metal
      discoloration,  both of which are signs  of
      incipient leak development.

      Evaporator vessels should be inspected for
      sludge  accumulation  either every year  or
      after every 200 tons of chlorine use. Piping
      and connections to the evaporator should be
      inspected  every six months.
       T =  contact time (min)

Dosage CI2
Total Coliform
Fecal Coliform
Philadelphia1       5 mg/l       before: 1,000,000 units/
                           100 ml after: 5-10 units
                                   before: 1,000,000
                                  units/100 ml after: 5-
                                   10 units/100 ml
Grosse Point
Grosse Point
New York4

New York4
New York4
New York5
2.6 mg/l
5 mg/l
1-5 mg/l
25 mg/l

25 mg/l
16 mg/l
0-24 mg/l
12 mg/l
12 mg/l
99.9% reduction
<200 units/1 00 ml
4 log reduction 4 log reduction
3-4 log reduction 3-4 log reduction
1 000 units/1 00 ml 200 units/1 00 ml 200/1 00 ml fecal
strep 5 log
poliovirus &
Sabin K-1 5 log
200 units/1 00 ml 2min.
Fecal Strep
1000 units/1 00 ml
1-6 log reduction 5-9.8 mg/l
3-4 log reduction to CI2 residual
200 units/1 00 mg/l 5-8 mg/l
2-4 log reduction to CI2 residual
?00 units/100 mn/l
3 min.
4 min.
6 min.
2 min.
2 min.

1 min.
1 min.
1 min.
1. U.S. EPA, 1973.
2. U.S. EPA, 1974.
3. Rouge River National Wet Weather Demonstration Project, 1999.
4. U.S. EPA, 1975.
5. U.S. EPA, 1979.
      The chlorine gas filter should be inspected
      and the filter element should be replaced
      every six months. At this time, the sediment
      trap should also be washed and dried, and
      lead gaskets should be replaced.

      Chlorine pressure reducing valves should be
      cleaned   with  isopropyl  alcohol   or
      trichloroethylene.  Spring valves should be
      replaced every two to five years.

      Ejectors  should  be   cleaned   every  six
                                           Booster pumps should follow regular pump
                                           maintenance schedules.

                                     To prevent any health  threats, the facility using
                                     chlorine should provide:

                                           Adequate ventilation.

                                           Safety equipment.

                                           Eye wash fountains and deluge showers.

                                           Emergency respiratory protection.

      Emergency kits.

      Information and telephone numbers on the
       Chlorine  Institute   and  the   Chlorine
       Emergency Plan response team.

      Employee training for safe operations.

      Material Safely Data Sheets.

Finally, using chlorine  in CSO applications may
present serious hazards. As mentioned previously,
chlorine  is  extremely  corrosive. The following
recommendations do not cover every aspect of
chlorine  safety, but should  be considered  when
designing a CSO chlorination facility:

      Facilities housing chlorine  require heavy
       ventilation at floor level, since chlorine gas
       is heavier  than air.   Ventilation  should
       provide at least 60 air changes per hour.

      Chlorine  leakage  detection  equipment
       should   be   located   near   chlorinating

      An emergency scrubbing system may  be
       installed to neutralize  any leaking chlorine.

       All  storage  and  chlorinator  equipment
       should be separated  from the rest of the

       Chlorine  storage  tanks  should  not  be
       exposed to  direct  sunlight  to   avoid


Costs for designing a CSO treatment facility are
highly variable, and will depend on the number of
CSOs to be treated,  the drainage area being served,
the anticipated fluctuation in flow rates, and the
sensitivity of the surrounding areas (residential or
habitat).  Costs for a treatment facility may include
the following: planning  costs, capital costs for
construction of the facility,  chemical costs,  and
yearly maintenance costs. The designer may reduce
capital costs by using one vessel or basin for both
suspended solids reduction  and disinfection.  As
most  vendors  typically  base  costs  on  flow
conditions, it is not practical to provide generalized
cost estimates for a chlorination system in this fact
sheet.   Chemical costs will  fluctuate  based  on
current market prices.  Chlorine gas delivered in a
2000 pound cylinder currently sells for $0.57 per
pound.    A  25  percent  solution  of  sodium
hypochlorite  currently  sells for $2.58 per pound.
Calcium hypochlorite can be purchased for $1.29
per pound.  All chemicals delivered in containers
require a deposit which will vary depending on the
vendor.  Table 3 summarizes some of the typical
costs that  can be  encountered by systems  with
specific peak design flows.

                    Peak Design Flow (cfs)

                1,250      2,500       5,000
              $854,000   $979,000  $1,142,000

Capital       $87,000    $100,000  $116,000
 O&M Cost
             $239,000   $239,000  $239,000
 Annualized   $326,000   $339,000  $355,000
Source: NYDEP, 1997.

1.  Costs are present worth in 1997 dollars.
2.  Capital costs are based upon sizing to meet peak design
   flow and a 4-log reduction in fecal coliform.
3.  Capital costs are for installation at Spring Creek and are
    for process equipment only.  Costs do  not include
   additional  contact  tankage  (if required)  or support
4.  Annual operating costs are  based upon  an assumed
   typical 40 CSO events/year at a volume treated of 15
   million gallons per event.
5.  Annualized costs are based upon a period of 20 years at
   an interest rate of 8%.

       Brungs, W., 1973.   "Effects of Residual
       Chlorine on Aquatic Life."  Journal of the
       Water Pollution Control Federation,  Vol.
       45, No. 10.  pp. 2180-2189.

       CXY Chemicals. "Material Safety Data
       Sheet." Internet site at
       ine/chlorine_safety_sheet.html, accessed
       July, 1999.

       Hall, Jr., L., et al., 1981.  "Comparison of
       Ozone  and  Chlorine  Toxicity  to  the
       Development  Stages  of  Striped  Bass,
       Morone  Saxatilis." Canadian Journal of
       Fisheries and Aquatic Science, Vol. 38.

       Hass, C., K.  Longley, and T.  Selfridge,
       1990. "High-Rate Coliform Disinfection of
       Storm Water Overflow." Research Journal
       of the Water Pollution Control Federation,
       V. 62, No. 3, pp.282-287.

       Huang, J.Y.C., R. Warriner, N. Ni,  1985.
       "Pilot Tests of Chlorination Facility for
       Disinfecting Secondary Effluent."  Journal
       of the Water Pollution Control Federation,
       Vol. 57, No. 7. pp. 784-787.

       Rein, D.,  G. Jamesson, and R.  Monteith,
       1992.    "Toxicity  Effects  of Alternate
       Disinfection   Processes."     Water
       Environment  Federation   65th  Annual
       Conference & Exposition.

       Rouge  River  National   Wet  Weather
       Demonstration Project, 1999.   Personal
       communication with  Parsons Engineering
       Science, Inc.

       Tift, E., P. Moffa, S. Richardson, and R.
       Field,  1977.  "Enhancement of High-Rate
       Disinfection  by  Sequential  Addition  of
       Chlorine and Chlorine Dioxide."  Journal of
       the Water Pollution Control Federation.
9.     U.S. EPA,  1973.   Microstraining  and
      Disinfection of Combined Sewer Overflows -
      Phase II. EPAR2-73-124.

10.    U.S. EPA,   1974.   Microstraining  and
      Disinfection of Combined Sewer Overflows-
      Phase III.  EPA 670/2-74/049.

11.    U.S. EPA,  1975.  Bench-Scale High-Rate
      Disinfection of Combined Sewer Overflows
      with Chlorine and Chlorine Dioxide. EPA

12.    U.S. EPA, 1979. Disinfection/Treatment of
      Combined Sewer Overflows: Syracuse, New
      York.  EPA 600/2-79-134.

13.    U.S. EPA,  1985.  Ambient Water Quality
      Criteria for Chlorine-1984.

14.    Venosa, A., 1983.  Current State-of-the-Art
      of Wastewater Disinfection. Journal of the
      Water Pollution Control Federation. Vol.
      55, No. 5.  pp 457-466.

15.    Ward,   R.,  and  G.  DeGraeve,  1978.
      "Residual Toxicity of Several Disinfectants in
      Domestic Wastewater."  Journal  of the
      Water Pollution Control Federation.

16.    Water  Environment  Research Foundation,
      1995.  Comparison  of UV Irradiation  to
      Chlorination:   Guidance for Achieving
      Optimal UV Performance.

17.    Water  Environment Federation,  1996.
      Wastewater Disinfection. Manual of Practice

18.    Water Pollution Control Federation, 1989.
      Combined  Sewer   Overflow  Pollution

19.    White,  G.,  1992. Handbook of Chlorination
      and Alternative Disinfectants. 3rd Ed. New
      York: Van Nostrand  Reinhold.


Bay City, Michigan
Michael Kuhn
Bay City Wastewater Plant
2905 Northwater Street
Bay City, MI 48708

Georgia Environmental Protection Agency
James A.  Sommerville
Manager, East Compliance Unit
Municipal Permitting Program, Georgia EPA
4244 International Parkway, Suite 110
Atlanta, GA 30354

Oakland County, Michigan
Douglas Bouchholz
Oakland County Drain Commissioner's Office
1 Public Works Drive
Waterford, MI   48328

Trojan Technologies Inc.
David Tomowich
Managing Director
3020 Gore Road
London, Ontario N5 V 4T7 Canada

Wayne County, Michigan
Vyto Kaunelis
Chief Deputy Director
Wayne County Dept. of Environment
415 Clifford Street
Detroit, MI 48226
                                                          For more information contact:

                                                          Municipal Technology Branch
                                                          U.S. EPA
                                                          Mail Code 4204
                                                          401 M St., S.W.
                                                          Washington, D.C., 20460

                                                          Exceience fh compliance through optftnal technical sotrtroru:
                                                          MUNICIPAL TECHNOLOGY