HomeMy WebLinkAboutAgenda Packet 10/11/2011Presented by Michael Puntenney, City Engineer since 10/7/2010. Presentation for the
City Council and Council Candidates, 10/11/2011.
Guest Participants: Jack Warburton, Senior Vice President, Brown and Caldwell, Inc.,
and Greg Zentner, Supervisor of the of the Municipal Operations Unit, Water Quality
Program, Department of Ecology
Introduction:
This presentation characterizes the historic basis of the City of Port Angeles’ CSO
problem and the solutions to fix it. Each city’s infrastructure historically developed
differently, has different geographical and geological conditions, are in different
economic straits, and each must be evaluated for which solution will work best for that
community. We often read in the Press that this is the most expensive project ever
undertaken in the City’s history, with little emphasis on the elegant, efficient, and
economical engineering accomplishment that Brown and Caldwell has created in
developing the current CSO designs. I am certain that this project ‘s estimated cost of
just under $40M feels extremely burdensome to the citizens of Port Angeles, and
should not be taken lightly. However, the project’s approach is truly the most
inexpensive way to solve the problem, which we will show in this presentation. At the
end of it, I hope that the Council, council candidates, and citizens of Port Angeles will
have the necessary information and be in a position to confidently make a decision on
this project, both for what it does for Port Angeles and what it doesn’t cost. For any
other approach will certainly cost the citizens a great deal more.
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Photo from Emeryville Tattler, California for an outfall in the San Francisco bay area.
From an separate article in “Pollution Engineering” based on the Bremerton CSO experience, when a discharge occurs, receiving waters become
polluted with as much as 95 percent untreated sanitary sewage. This could certainly be the case for the first flush of the system at the beginning of
the storm event causing it.
Solving the CSO issue is important for Port Angeles. I truly believe this. The main pollutants in raw sewage are:
Bacteria
Viruses
Pathogens
intestinal parasites and other microorganisms
excessive nutrients
light industrial wastes for Port Angeles
toxic pollutants such as oil and pesticides
wastewater solids and debris
These can cause serious illness such as:
cholera
dysentery
hepatitis
The most common effects of sewage-related illness are:
Gastro intestinal problems
skin rashes
infection of open cuts.
Often symptoms can be treated, but no curative medical treatment is available for some sewage -related illnesses.
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The main pollutants in raw sewage are bacteria, viruses, pathogens, excessive nutrients, industrial wastes, toxic pollutants such as oil and pesticides,
and wastewater solids and debris. SSOs and CSOs are of special concern to public health because they expose citizens to bacte ria, viruses, intestinal
parasites, and other microorganisms that can cause serious illness such as cholera, dysentery, hepatitis, cryptosporidiosis, and giardiasis. Sensitive
populations - - children, the elderly and those with weakened immune systems - - can be at a higher risk of illness from exposure to sewage.
The most common effects of sewage-related illness are gastroenteritis, which is an infection of the gastrointestinal tract, skin rashes, and infection of
open cuts. Gastroenteritis affects the entire gastrointestinal tract, including the stomach and small and large intestines. Symptoms typically include
abdominal cramps, watery diarrhea and vomiting which can last from one to ten days, depending on the severity of the illness and the sensitivity of
the individual. Infected cuts and rashes can become swollen and red, and in some cases can result in septicemia or blood pois oning. Although
symptoms can be treated, no curative medical treatment is available for some sewage-related illnesses.
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The most common effects of sewage-related illness are:
Gastro intestinal problems
skin rashes
infection of open cuts.
Often symptoms can be treated, but no curative medical treatment is available for some
sewage-related illnesses.
The main pollutants in raw sewage are bacteria, viruses, pathogens, excessive nutrients,
industrial wastes, toxic pollutants such as oil and pesticides, and wastewater solids and debris.
SSOs and CSOs are of special concern to public health because they expose citizens to bacteria,
viruses, intestinal parasites, and other microorganisms that can cause serious illness such as
cholera, dysentery, hepatitis, cryptosporidiosis, and giardiasis. Sensitive populations - - children,
the elderly and those with weakened immune systems - - can be at a higher risk of illness from
exposure to sewage.
The most common effects of sewage-related illness are gastroenteritis, which is an infection of
the gastrointestinal tract, skin rashes, and infection of open cuts. Gastroenteritis affects the
entire gastrointestinal tract, including the stomach and small and large intestines. Symptoms
typically include abdominal cramps, watery diarrhea and vomiting which can last from one to
ten days, depending on the severity of the illness and the sensitivity of the individual. Infected
cuts and rashes can become swollen and red, and in some cases can result in septicemia or
blood poisoning. Although symptoms can be treated, no curative medical treatment is available
for some sewage-related illnesses.
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CSO cities in the United States. Notice that they consistently are the older historic cities. They
are the ones that are having to contend with this problem. New cities in the United States that
have been created that you’d recognize in urban sprawl are not those that you’d find having
this. So it is that that have the very old infrastructure. That is also the case for Port Angeles.
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CSO control is a vital part of the statewide effort to reduce and control stormwater discharges.
CSO reduction programs are in place in 11 cities in Washington. Ecology estimated that, in
1988, the average volume of untreated CSOs discharged to the state waters was 3.3 billion
gallons of untreated discharges per year. Since then, Washington has made progress with a
reduction of CSOs to less than one billion gallons in 2009.
CSO Communities in Washington
NPDES Permittees with CSO Outfalls CSO Outfalls
Anacortes 3
Bellingham 2
Bremerton 15
Everett 13
King County- West Point Treatment Service Area 34
LOTT (Olympia) 1
Mount Vernon 2
Port Angeles 4
Seattle Public Utilities – City of Seattle 92
Snohomish 2
Spokane 22
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Note that San Diego is on its 3rd large settlement. We want to solve this once.
In 1972, Congress enacted the first comprehensive national clean water legislation in response
to growing public concern for serious and widespread water pollution. The Clean Water Act is
the primary federal law that protects our nation's waters, including lakes, rivers, and coastal
areas.
The Clean Water Act focuses on improving the quality of the nation's waters. It provides a
comprehensive framework of standards, technical tools and financial assistance to address the
many causes of pollution and poor water quality, including municipal and industrial wastewater
discharges, polluted runoff from urban and rural areas, and habitat destruction. The Clean
Water Act:
- requires municipalities and major industries to meet performance standards to ensure
pollution control;
- charges states and tribes with setting specific water quality criteria appropriate for their
waters and developing pollution control programs to meet them;
- provides funding to states and communities to help them meet their clean water
infrastructure needs; and
- protects valuable wetlands and other aquatic habitats through a permitting process that
ensures development and other activities are conducted in an environmentally sound manner.
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A recent settlement in Cleveland. Notice their solution involves tunnel storage. Of most
of the cities with large CSO volumes, storage and treatment becomes an essential part
of the solution.
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Even in Washington, D.C., a city that has been touted as having a “greener” CSO
approach, the workhorse of the solution relies on conveyance to treatment.
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The City currently has until December 31, 2015 to complete the CSO Phase 1 and 2
projects. $10,000 per day fine equates to $3,650,000 year, a sizeable sum.
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Note: The following series of slides depict another Washington State CSO City and how they solved their
problem. They are shown to illustrate what it takes to solve CSO problems of this magnitude. Many
parallels can be drawn and lesson can be learned from their experience.
POC: Combined Sewer Overflows (CSOs) / Water Conservation – (360)473-5929 – Chance Berchiaume
Combined Sewer Ordinance:
1.Extra fee based on additional impervious area such as roofs or parking area drains if a residence or
commercial activity chooses or is not able to disconnect.
2.Downtown area, a number of businesses have disconnected. Disconnects are typically taken to the
curb line. In numerous cases, if there is no separated stormwater system, it goes back to the
combined sewer system. There may be future stormwater separation projects that can then pick this
up.
CSO Strategy.
1.Basic storage in tanks and existing pipes, transfer, and treat at west WWTP or CSO Treatment Plant.
2.Storage occurs in tank and transmission pipes.
3.Both primary transmissions lines, the cross-town and the Naval Ave, are at capacity during large
storm events.
4.Both plants provides most of the capacity for handling CSOs.
5.Disconnection program provided some reduction; but most CSO water is handled through the
plants.
6.A variety of pipelines were increased in capacity for transmission to the plant; some realignment to
transfer surplus CSO to pipes with residual capacity, and some separation.
7.West WWTP was increased in capacity to handle more CSO water.
8.Bremerton received a federal grant for some of the work.
Eastern CSO Treatment Plant
1.Solids/sediment removal process (similar to actiflo).
2.Ultraviolet disinfection.
3.Stores solids until west WWTP can accept; transferred in the cross-town pipeline; will spike solids at
the west WWTP when this occurs.
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The run up to solving the CSO problem in Bremerton was as controversial there as it is
for Port Angeles.
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99% reduction was achieved required. This is a phenomenal amount to reduce.
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In discussion with the Engineering Tech overseeing the disconnection program at Bremerton, it
wasn’t feasible to disconnect all CSO connections. In numerous other instances, health codes
determined that it wasn’t allowed such as sumps or drains from within buildings due to the
potential for disease or pollution transmission. They also found that foundation drains and
driveway drain systems were difficult. Essentially, if a facility wasn’t reasonably able to
disconnect, they owner had to pay either a 50% or 100% surcharge on there stormwater fee.
In some instances such as parts of the commercial district where separated stormwater
systems didn’t exist, disconnections were made to the street curb, where the water would
travel along the gutter to the next catchbasin and back into the combined sewer system.
Nevertheless, the business would then qualify for the lower rate. Even this strategy has
potential, because when the opportunity occurs to put in a separate stormwater system in
those locations, those facilities will already be in compliance.
Smoke & dye testing occurred for the CSO drainage basins from 1991 – 1993. A few thousand
were identified; ultimately, only 390 were resolved.
Bremerton’s incentive program provide $25 per downspout for residential disconnections only.
Commercial received nothing. Residences could also receive up to $500 for an infiltration
system such as a wet well.
Bremerton’s base residential stormwater fee is $8.67 per month per impervious surface unit
(ISU) equivalent to 2,500 SF.
Note that the 300,000 SF of imperious surface is less than the area of Civic Field Park in Port
Angeles.
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Note that the 300,000 SF of imperious surface is less than the area of Civic Field Park in
Port Angeles. It would require a lot more than this alone to solve the magnitude of CSO
volumes experienced in significant storm events for either Bremerton or Port Angeles.
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Statistics:
1.11/16 & 11/17 event:
- 2 days of continuous rain
- 32.1 MGD instantaneous peak for CSOs’ occurred at 8:46 pm on 11/16
- 42.5 MGD instantaneous peak flow was experienced for the entire
system (WWTP treatment plus CSOs)
- 2.25 inch rain event
- 8.4 MG of overflow volume occurred 11/16
- 6.7 MG of overflow volume occurred 11/17
2.12/12/2010 Event:
- 13.75 MG of overflow volume occurred 12/12
- duration of the CSO event was only 24 minutes
- less than 1 inch rain event
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Inverted siphons at Port Washington Narrows include a 16” cast iron pipe placed in
1946 and a 24” ductile iron pipe place in 1983.
Photo shows the Pacific Ave Trunk sewer
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Even to this day, Bremerton still characterizes much of their system as a “Combined
Sewer Collection System”
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Yes, even back in 1863, without all the impervious surfaces and pavements we have
now, storms were an issue. Its not surprising due to Port Angeles’ soils. Storm’s and
flooding can be powerful, that’s why we need to be attentive to them also. So not only
do you have to worry about sewage, but storms also. Let’s refresh on recent storms.
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From Peninsula Daily News
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From Peninsula Daily News
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From Peninsula Daily News
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From Peninsula Daily News
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From Peninsula Daily News
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From Peninsula Daily News
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From Peninsula Daily News
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Note that a 100 year storm is only about twice the quantity of that of a 2 year storm for
Port Angeles.
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From 2003 storm. The City’s stormwater system has many capacity issues.
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4th & Jones
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From a 2008 storm. Stormwater systems limitations exist to this day.
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Note that the yellow area is the Clallam Hyopus and the orange area is the variegated
Clallam Gravelly Sandy Loam. So, Port Angeles has soils with either moderately high
runoff characteristics (yellow) or a variegated soil of moderately high runoff
interspersed with soil with low runoff characteristics (orange). It is about 2/3
probability that you will encounter the poorer draining soils than the better soil. This
will make if more costly to effect LID solutions in Port Angeles. Generally described,
significant rainfalls saturate the ground, and runoff. For Port Angeles, many of the LID
systems will have to be backed up with gray infrastructure, that is, piped overflow
systems to the City’s stormwater system. With many parts of the stormwater system
already at capacity, the City would need to invest in upsizing that system.
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Glacial till forms a barrier to water at about the 20 inch to 40 inch depth.
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New Proposed Language for the 2012 reissuance for the Municipal Stormwater General Permit.
Expect greater mandates for LID.
Permittees shall review and revise their local development-related codes, rules, standards, or
other enforceable documents to incorporate and require LID principles and Best Management
Practices (BMPs) to the maximum extent practicable. The intent of the revisions shall be to
make LID the preferred and commonly-used approach to site development. In reviewing the
local codes, rules, standards, or other enforceable documents, Permittees shall look for
opportunities to minimize impervious surfaces, native vegetation loss, and stormwater runoff
in all types of development situations. Permittees shall conduct a review and revision process
similar to the steps and range of issues outlined in the following document: Integrating LID into
Local Codes: A Guidebook for Local Governments (Puget Sound Partnership, 2011).
City Staff is evaluating these requirements, but expect to have to infiltrate and/or treat
stormwater on site at least (if not more) to the extent that it occurred on pre-development (or
native) land.
Underground utility projects Exemption: Underground utility projects that replace the ground
surface with in-kind material or materials with similar runoff characteristics are only subject to
Minimum Requirement #2, Construction Stormwater Pollution Prevention.
Road Maintenance Exemption: The following road maintenance practices are exempt: pothole
and square cut patching, overlaying existing asphalt or concrete pavement with asphalt or
concrete without expanding the area of coverage, shoulder grading, reshaping/regrading
drainage systems, crack sealing, resurfacing with in-kind material without expanding the road
prism, and vegetation maintenance.
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The Portland rain gardens do not have under drains. Generally the soils in Portland have
sufficient permeability.
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Some Portland rain gardens designed by Brown & Caldwell. These didn’t require
overflow drains to the stormwater system since the soils were good, and would
accept the expected stormwater flows. For Seattle where the soils are much
tighter Brown and Caldwell looked at a number of options to increase capacity:
– Over excavating and filling with granular material ( this increases the volume
of storage and increases the vertical interface for infiltration and in some cases
excavating down to a more permeable layer).
– Installation of ‘rock’ columns below the treatment soil layer (facilitates a greater
depth than #1 above)– to increase volume and potentially to penetrate a layer of
more permeable soils.
– Installation of an under drain system connected to either a catch basin or
manhole with an orifice controlled release. The effectiveness of this approach is
a function of being able to attenuate the peak flows
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Portland rain garden by Brown & Caldwell (left). Parking lot rain garden at Peninsula
College (right); note the overflow drain system that was required due to the poor soils
that are prevalent in the area of the college.
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Peninsula College Systems (left) and Family Medicine (right). These systems tie to the
City’s stormwater system through overflow piping.
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A recent news story of the difficulty of some rain gardens in Seattle. Designing rain
gardens where soils don’t drain well requires careful consideration and typically
additional control features. The following is some of the comments in the news story:
The gardens, which look sort of like shallow, sparsely planted ditches running
between the road and sidewalk, fill with water – and stay filled. Some of the
rain gardens drain over the course of hours or days, but some become
miniponds until the city comes to pump them out.
Now the financially pressed city will have to spend $500,000 to fix the rain
gardens. And after the fixes, the gardens will do less of what they were designed
to do: keep runoff from sewers to prevent overflows.
Many of the residents are not pleased. They worry that the swamped gardens
are a drowning hazard for young children, a breeding ground for mosquitoes
and a flaw that will lower property values. There’s even a neighborhood blog
calling for their removal.
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Peninsula College rain gardens. Note wet area on lower-right picture. This spot has
been there for over a month. While it has reduce in size in the more recent dryer
weather, it still exists. Due to the poorer draining soils and all of the water sent to the
ground from their LID improvements, water is naturally finding locations of least
resistance that were unanticipated. Similar unintended consequences could occur in
Port Angeles if rain gardens aren’t carefully considered for location and permeability of
soil.
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Infiltration Test & Certification (From Seattle Public Utilities; required for their LID program)
How water flows through soil plays a significant role in how large to build a rain garden. Subsoil
characteristics can also play a role in water movement. A glacial till or clay subsoil can act as a
seal
underneath the topsoil. If there is enough rain, the topsoil will become saturated and there will
be no
place for the water to go regardless of the characteristics of the topsoil.
To properly size your rain garden perform the following infiltration test:
1)Dig a hole 24 inches deep and at least 10 inches across. Add a stake with a ruler attached to
it. (Duct tape works for this.)
2)Fill with a hose, and let drain completely.
3)Repeat fill and drain a second time. This may take overnight.
4)On the third fill:
– Measure the water height every hour. Note your results.
– Continue until the rate of fall stabilizes. (Same amount of fall for 2-3 hours)
– Use that as the infiltration rate. (inches/hour)
If you find any of the following conditions during your test
You hit hard pan
Your test hole does not drain at least .25” per hour
Your test hole fills with water
Do not attempt to install a rain garden or other infiltration system!
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The City’s website host a number of programs led by Terri Partch, the City’s stormwater
engineer.
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Olympian House right and Globe Hotel left
Note: Historic photos cannot be redistributed without permission of the North Olympic
Library System
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Olympian House right and Globe Hotel left
Note: Historic photos cannot be redistributed without permission of the North Olympic
Library System
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Perched at the end of a ramp leading from the hotel, the lower portion of the unique
outhouse was cleansed regularly by the rise and fall of the tide.
Note: Historic photos cannot be redistributed without permission of the North Olympic
Library System
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Note: Historic photos cannot be redistributed without permission of the North Olympic
Library System
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Note: Historic photos cannot be redistributed without permission of the North Olympic
Library System.
At the turn of the century, you can see the early development. The alleys are
developing between the two unpaved streets. At this point, sanitation would be
becoming a larger issue. I would expect that the early plans for the eventual sewer
system began because of issues that can be imagined in this photo. Also, note the
general lack of trees for the Olympic Peninsula.
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Note: The first project to be undertaken in 1914 required tunneling through the “hog
Back” hillside at Lincoln Street Between First and Front Streets, changing the course of
Peabody Creek so that it would enter the bay near what is now the City Pier. The old
east-west creek bed winding through the downtown business district was then filled to
allow more construction there.
Note: Historic photos cannot be redistributed without permission of the North Olympic
Library System
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Note: Historic photos cannot be redistributed without permission of the North Olympic
Library System
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Note: Historic photos cannot be redistributed without permission of the North Olympic
Library System
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Note: Historic photos cannot be redistributed without permission of the North Olympic
Library System
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Note: Lincoln Street just before construction of the planked thoroughfare was finished.
The trestle spanned a tributary gully to Peabody Creek which has since been filled. A
streamlet ran down the gulch parallel to Lincoln Street. Near Third Street, the stream
entered Peabody Creek behind the Library.
Note: Historic photos cannot be redistributed without permission of the North Olympic
Library System
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Notice the alleys in this 1919 construction drawing. The combined sewer system was
originally created there, being used to drain low areas as well as being the sanitary
sewer system. Area is Cherry thru Laurel between 8th St and 15th St.
Combined sewers were not without rational. It was cheaper to build one pipe,
especially when retrofitting an urban area, as many where doing (first we had cities –
then we had sewers). At a time when the goal was to get the stuff away from people to
minimize public health risks and treatment systems were not common, combined
systems with overflows were a significant improvement and probably made sense.
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Note: Historic photos cannot be redistributed without permission of the North Olympic
Library System
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Note: Historic photos cannot be redistributed without permission of the North Olympic
Library System
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Note: Historic photos cannot be redistributed without permission of the North Olympic
Library System
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Back in 1969, this project was receiving as much controversy as the CSO project is
receiving today.
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Note that the stormwater system was largely installed to replace road stormwater
ditches. It was designed to handle surface run-off, predominantly from streets and
driveways. It didn’t replace the alley drainage system that was handled through the
sewer system.
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Map depicting the sewer (green) and the stormwater system (red) with line thickness
representing increasing pipe sizes.
The alleys and streets alternate for those running in the east – west direction. Note
that in many areas, the stormwater lines only run north – south. Because of the general
topography, the stormwater system was designed to rely on the streets surfaces in the
east-west direction to surface drain to the catchbasins located at the intersections with
the north – south running streets where it enters the stormwater piping system. Alleys
can also surface drain to the north – south intersections, but on many alleys, there are
low lying areas in the alley that cannot reach one of the intersections. In those
locations, grated manholes or catchbasins are found attached to the sanitary sewer
system to drain them. In many of these locations, the surface area draining to the
sanitary sewer can be quite significant. Typically, you will find backyard driveways,
ground and lawn surfaces, garage and house downspouts, and other drainage features
all draining to these catchments. Because of the prevailing soils types encountered, the
soils would be inadequate to handle all of this stormwater, particularly after successive
storms when the ground is saturated. To remove these from the sanitary stormwater
system would require new stormwater lines to be installed to these manholes and
catchments. That would be expensive.
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Real view of north – south direction where stormwater lines generally run.
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Port Angeles Wastewater Treatment Plant as it exists today. The initial plant was
constructed in 1968 and was primary treatment only. It was expanded to secondary
treatment, completing construction in 1993. The photo above is after completion of
this upgrade. Again, controvery ensued for the need to go to secondary treatment.
- The average daily flow rate is about 0.117 MGH and the average dry weather flow
rate is about 0.083 MGH (million gallons per hour)
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Map showing route of main sanitary sewer interceptor line installed in 1968. Many
outfalls on the line have been removed. Four remain.
Map showing CSO drainage basins to their outfalls.
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Note the alternating street/alley structure in the east – west direction that is common
in Port Angeles. In the very center of the map is a grated manhole depicted as a green
circle and a catchbasin attached to the sewer system shown as a red square. Note the
nearest storm water mains (red lines) run in the south-north direction and are half a
block away. Removing these from the sewer system would require putting a new
stormwater main down the alley to separate it from the sanitary sewer system. This is
found in a multitude of locations throughout the City’s alley system.
(To avoid misinterpretation, the sewer lines have been painted in this map over the top
of the stormwater system by the GIS. In some cases such as at the street intersections,
some stormwater lines appear to interconnect with the sewer. They do not; due to
resolution in the drawing, one system is covered up by the other pictorially.)
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Typical alley structure with internal grated manholes and/or catchbasins directly
attached to the sewer. Note the nearest storm water mains run in the south -north
direction and are half a block away which requires putting a new stormwater main
down the alley to separate it from the sanitary sewer system. The City is replete with
this situation.
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Hancock/Dolan Area. Alley grated manhole on sewer line. Hillside draining water to
alley. Large surface area to pick up.
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Hancock/Dolan Area. Note drainage from hillside which is prevalent in many locations
of Port Angeles due to its geology.
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Downspouts, parking areas, and drainage at alley locations. Requires new storm lines
to be installed down the alleys to the nearest stormwater trunk line.
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Downspouts, parking areas, and drainage at alley locations. Large drainage areas.
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Downspouts, parking areas, and drainage at alley locations.
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Downspouts, parking areas, and drainage at alley locations. Note inundated soil.
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Downspouts, parking areas, and drainage at alley locations.
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Areas with catchment inflow into the sanitary sewer system, primarily at the alleys. Size
of circle is relative to amount of inflow area. (Map still under development)
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Stormwater system mains evaluated to be at capacity. Source: 1990 B&C Stormwater
Plan.
This shows that the City already has capacity issues in its main trunk lines for its
stormwater system. This is also true for its smaller stormwater lines in many locations,
though not evaluated for this presentation. In many locations, the capacity of the
stormwater piping system is inadequate to accept additional stormwater that was
originally designed to be handled by the sewer system.
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House disconnection represents only 13.7 percent of the CSO volume. The City ran a
pilot disconnection program in 2003. Additional houses were added late in the program
that skewed the actual cost to a larger number than was originally estimated. This was
because of the area involved and its soil conditions, which required additional piping to
curb outlets at the street to be installed.
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Downtown area (about 1.75 million SF).
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Downtown business alleys. Low lying areas will require pumping are a deep storm line.
Lots of impervious surface to capture.
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Downtown business alleys. Low lying areas will require pumping are a deep storm line.
Lots of impervious surface to capture.
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Downtown business alleys. Lots of impervious surface to capture.
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Picture taken from atop Naval Elks Lodge. Downtown roofs.
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Downtown roofs. Many historic buildings with non-exterior roof drain systems.
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Downtown roofs. Many historic buildings with non-exterior roof drain systems.
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Downtown roofs. Many historic buildings with non-exterior roof drain systems.
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EPA definitions: “Infiltration” occurs when groundwater enters a sewer system through
broken pipes, defective pipe joints, or illegal connections of foundation drains. “Inflow”
is surface runoff that enters a sewer system through manhole covers, exposed broken
pipe and defective pipe joints, cross connections between storm sewers and sanitary
sewers, and illegal connection of roof leaders, cellar drains, yard drains, or catch basins.
EPA expects “Infiltration” to be managed such that it in not excessive. The October
1991 EPA handbook Sewer System Infrastructure Analysis and Rehabilitation is one
resource available for determining whether the level of I/I in a collection system is
excessive. The 1991 EPA criteria define the non-excessive infiltration as a flow rate that
does not significantly exceed 120 gallons per capita per day (gpcpd). The sum of the
domestic base flow and infiltration based on a 7-14 day average during high
groundwater conditions is used as a basis of comparison when applying the EPA
criteria. This assessment uses readily available information that an agency can
assemble from existing sources. This 1991 handbook Rainfall/Flow Monitoring Program
was again cited in the 2004 EPA documentation as the best available guidance for the
preliminary evaluation of whether a collection system is subject to cost -effective I/I to
pursue. This threshold is further confirmed in EPA’s 1985 document Infiltration/Inflow,
I/I Analysis and Project Certification, No. 97-03. This requirement is cited in the
national Pollutant Discharge Elimination (NPDES) Permit WA0023973, City of Port
Angeles Wastewater Treatment Plant. The requirement is quoted below:
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“Determination of Non-Excessive Infiltration
Based on Needs Survey data from 270 Standard Metropolitan Statistical Area Cities, the
national average for dry weather flow is 120 gallons per capita per day (gpcd). This
includes domestic wastewater flow, infiltration and nominal industrial and commercial
flows. This average dry weather flow should be used as an indicator to determine the
limit of non-excessive infiltration. If the average daily flow per capita (excluding major
industrial and commercial flows greater than 50,000 gpd each) is less than 120 gpcd
(i.e., a 7-14 day average measured during periods of seasonal high groundwater), the
amount of infiltration is considered non-excessive.”
From the City’s NPDES Permit: S4.F Infiltration and Inflow Evaluation
I. The Permittee must conduct an infiltration and inflow evaluation. Refer to the U.S.
Environmental Protection Agency (EPA) publication, III Analysis and Project
Certification, available as Publication No. 97-03 at: Publications Office, DepaJtment of
Ecology, P.O. Box 47600, Olympia, Washington 98504-7600 or at h(11):/
/www.ecy.wa.gov/programs/wg/permits/guidance.html. The Permittee may use plant
monitoring records to aSsess measurable infiltration and inflow.
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From the City’s NPDES Permit: S4.F Infiltration and Inflow Evaluation
I. The Permittee must conduct an infiltration and inflow evaluation. Refer to the U.S.
Environmental Protection Agency (EPA) publication, III Analysis and Project
Certification, available as Publication No. 97-03 at: Publications Office, DepaJtment of
Ecology, P.O. Box 47600, Olympia, Washington 98504-7600 or at h(11):/
/www.ecy.wa.gov/programs/wg/permits/guidance.html. The Permittee may use plant
monitoring records to aSsess measurable infiltration and inflow.
2. The Permittee must prepare a report which summarizes any measurable infiltration
and intlow. If infiltration and inflow have increased by more than 15 percent from that
found in the previous report based on equivalent rainfall, the report must contain a
plan and a schedule for:
a.Locating the source of infiltration and inflow; and
b.Correcting the problem.
3. For any infiltration or inflow identified in segments of the collection system which
are under or adjacent to surface water (100 yards), the Permittee must evaluate these
segments for the existence of exfiltration.
4. The Permittee must submit a report summarizing the results of the evaluation by
May 15, 2009, and annnally thereafter. Any recommendations for corrective actions
must be submitted with the report.
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Dates of predominant sewer system installation.
This and the following map shows that the sanitary sewer system and the stormwater
system were placed in two different eras, and largely were designed for two separate
purposes, and not to replace or duplicate one another. The City of Port Angeles truly
has a combined sewer system and a separate stormwater system.
105
Approximate dates of predominant stormwater system installation.
106
What most residents see today in Port Angeles, but what is under that sewer manhole
cover? The next shot is the same manhole cover, followed by various inside shots of the
old brick that was in this one and ones adjacent to it. This relates to infiltration which
will be discussed later.
107
The same manhole cover.
108
This shows the old brick that was in this manhole. This relates to infiltration which will
be discussed later.
109
Brick was used in manhole construction in Port Angeles as late as 1965. Historic
records indicate 927 manholes out of 1,797 that were built entirely or partially out of
brick.
110
A lot of the sewer pipes that were historically installed in Port Angeles were concrete. These
pipes are notoriously vulnerable to concrete corrosion as described below, particularly due to
their age. In addition, much of the piping is in four foot sections, with joints that have long ago
begun to leak due to such corrosion. Infiltration is a large portion of the CSO volume,
comprising about 41%.
Photos and figures from “The Problem of Hydrogen Sulphide in Sewers.” by Dr. Pomeroy.
Hydrogen sulfide gas combines with moisture and water condensation droplets on the pipe
crown to form sulfuric acid. Corrosion slowly, steadily eats the sewer crown and walls. The
pipe becomes thinner. Eventually, the pipe crown becomes completely eaten away. When it is
so thin it cannot support soil loads, the sewer collapses. Most sewer failures are collapse events
resulting from severe crown corrosion. Trunk sewers are prone to corrosion problems. They are
more likely to be constructed of concrete pipe, the sewage is older as it ravels down through
the collection system, and hydrogen sulfide release mechanism, such as turbulence, large
volume drop structures, pump stations, radical junctions, and thick debris buildup are more
frequent. (Wastewater Collection System Maintenance, Michael J. Parcher).
Fractures and wall thinness that leads to fractures or breaks is typically fixed as a total pipe
solution since it is usually a pervasive problem in its entire length. Typical solutions are cured-
in-place-pipe (CIPP), slip-lining, or replacement, depending on the specific deterioration and
situation.
111
Infiltration, corrosion, tree roots, breaks (from photo clips from video tapping). Various
locations.
112
Concrete, clay, and unknown piping received through annexations (probably clay or
concrete) are candidates for infiltration. There is a lot of this in the City.
113
April 2011. The above photograph was from the 2011 Bi-annual Sewer Main
Replacement Project. Grease is inundating an 8” sewer main. Note the loss of wall
thickness in lower area due to corrosion from hydrogen sulfide gas. The acronym FOG is
used in the industry for “Fats, Oil, and Grease.”
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Sewer pipe was laid at a depth of 7’ to 12’
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5,900’ of mains and 10,600’ of side sewers for $1.3M
88 parcels
More cost effective way to solve infiltration where no structural defects exist.
Cost comparison:
flood grouting (Sanipor): $1,275,000
joint grouting: $1,320,000
pipe bursting: $3,650,000
CIPP lining: $3,750,000
116
While OEC desires a LID based solution to eliminate the combined sewer overflow
problem, many other infrastructure issues would have to simultaneously be addressed
in order to approach a reduction in the number events to be within standards set by
Ecology. The following slide looks at all of those fixes, and for a variety of reasons,
what their effectiveness might be in reducing their part of combined sewer overflows.
The slide directs attention to the conclusion that all of the categories would have to be
fully implemented in order to even approach the reduction amount imposed for CSOs.
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The infiltration percent was determined from the B&C system flow model.
118
Proportions of CSOs are estimates only based on square footage calculations.
The infiltration percent was determined from the B&C system flow model.
Design and permitting cost is included in amounts above.
Marine Harbor Sewer Line Replacement would cost an additional $7+ million.
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Drawing showing Demand Management Approach construction impacts.
1.Downspout Disconnection – red dots, 41% of housing units
2.Eastern Corridor – magenta, two main lines
3.Alley Catch-basin/Grated Manhole Disconnection – yellow
4.Infiltration - turquoise
5.Stormwater Capacity Upgrades - purple
120
And the area just west is even harder, having numerous sewer catch-basins and grated
sewer manholes.
121
Mathematical improbability that you will be able to attain the required CSO compliance
levels, and even if you did, it would be difficult to maintain compliance. It would require
a lot of involuntary actions on the citizens and a lot of City staff to enforce it.
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The Demand Management Approact, that is, not doing a “bypass, storage, and treat” solution,
is hugely expensive to implement and would not ensure compliance with our CSO reduction
mandates. Even then, it must rely largely on our gray infrastructure (stormwater and
wastewater) to remain effective. And the most perplexing part is that it appears to allow for a
vulnerable pressurized sewer main to continue to operate in the harbor. This latter aspect
simply should not occur.
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The following slides represent the Phase 1 & 2 project proposed by the City and the
other routes considered that would have done the same storage and treatment.
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Quick Statistics:
Existing
- 10,000 ft continuous forcemain
- 21” & 27” diameter from PS4 to WWTP
-4,000 LF located offshore 30 – 40 ft in the harbor
-PS4: Two 1,150 gpm (8 MGD) pumps (16” main from Francis area pushes against
the force main)
New Project:
-30” & two 17” pipes inserted into an abandoned 48” industrial main then reverting
to a 30” and 24” east of Francis Park plus a separate 36” from Francis
-380% total increase in pipe conveyance
-PS4 upgraded to three 5,800 gpm pumps (25 MGD total)
-313% total increase in pump capacity at PS4
-5 MG tank
-Plant upgrades
-Bridge across Ennis Creek
Originally constructed in 1967-1968 timeframe. Main interceptor truck line tying the
west end along Hill Street, along Marine Drive eastward parallel to what is now is the
Olympic Discovery Trail, across the Rayonier Mill site and to the newly constructed
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primary wastewater treatment facility. Note that the main interceptor trunk line in the
harbor went in at this time. Pipeline was laid approximately 48’ due North of the
industrial water line in the harbor, typically buried to a depth of between 2 to 4 feet. In
the design drawings, pipe was to be either concrete cylinder pipe or welded steel pipe.
To date, pipe identified has been concrete cylinder. The typical closure section detail for
concrete cylinder pipe is shown on drawing C3701-2 of the drawing set, and shows a
normal dresser with gasket and anchor flange.
The Harbor Sewer Main presents a very serious environmental & health risk in the event
of its failure. Difficulty will pervade in effecting a timely repair on this system in an
underwater marine environment should such a rupture occur. It is crucial that this
pressurized sewer pipe be replaced outside of the harbor as soon as the City can
reasonably effect it. Nothing that the OEC has presented to date recognizes this
environmental risk nor the need to replace this line or how that might be accomplished
without using the Rayonier Mill site property.
The pipeline is now 44 years old. On May 18, 2011, Greg Zentner and Mahbub Alum of
the Department of Ecology were asked by Michael Puntenney about the possibility of
entertaining an alternate solution such as LID for solving the CSO overflow problem at
Port Angeles. It was stated that Ecology would always listen to proposals, but that this
would be difficult for them to accept for the Port Angeles situation . Additionally, they
would not consider State support for a higher cost solution. Lastly, they stated that the
City would still have to do something about removing the force main from the harbor.
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Harbor force main close-up.
126
This spill occurred on the pressured force main due to a rupture just east of
Pumpstation 4. This is the same line and type that the force main in the harbor is. Final
estimate of spill, 6 – 8 million gallons of sewage.
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It is intended that all plant effluent and CSOs from the storage tank be discharged
through the industrial outfall. However, at extreme high tides coincident with the
highest influent flows there may be insufficient industrial outfall capacity. Under these
rare events, flow will be spilled over a weir to the City outfall to control backups into
the WWTP.
A third overflow weir in the IDS wet well is provided for times of pump failure or
extremely high flow rates (flows greater than approx. 2.08 MGH) to divert excess flow
to the outfall (CSO). Normally, CSOs will only occur when the storage tank becomes full
from an overflow feature built in the tank.
When the influent flow rate drops below 10 MGD, the influent slide gate is opened
[automated] and the system is returned to “normal”. When the influent flow reaches a
flow that can accommodate the maximum possible return flow from the CSO tank, the
automated return sequence shall be initiated.
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This map shows the current routing of the proposed CSO Phase 1 & 2 projects. Note
the piping follows nearly where the existing pressurize pipeline including on the
Rayonier Mill Site.
The only location that the pipes come out of the existing industrial water line or out of
the ground is at the bridge. They are inside the bridge girder system and hidden. At the
inside edge of the bridge abutments, the natural ground elevation is currently about at
the 16 ft. elevation level, and ultimately the bottom of the girders of the bridge will be
two feet above that. The abutment top, which will be the road level, will be at about
elevation 24.5 ft for the west abutment, the higher of the two. So the top of the bridge
deck is only about 8.5 ft higher than the existing ground level . On top of the road is a
4' 8" pedestrian safety railing. The pipes are buried in the bridge approaches or hidden
underneath inside the girder system when directly transiting the bridge span. So, for all
intents, the only thing anyone would see is a bridge spanning Ennis Creek with gently
sloping approaches. All pipelines between the tank and wastewater treatment plant are
below ground
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The drawing is a profile of the overland route from Francis Park to Ennis Creek, which
were considered as design alternatives for this strategy. The routes predominantly
considered either Caroline St or Georgiana St and the alley in between. These were
ruled out due high cost for tunneling if a gravity main were considered. Note 40+ ft
excavation depth on the east end which had exceedingly high cost. Another option
would be a pressurized force main to pick up the Francis basin which would have
required the building of an additional pump station, also ruled due to cost. Other
alternatives were consider including a 12 ft storage tunnel in order to forego using the
Rayonier Tank. Volume would be 5 MG, the same as the Rayonier tank. It would
require a 12 ft diameter pipe, 4,000 ft long that would run from Albert St. to the west
Ennis Creek bank. It also was ruled out as being cost hugely cost prohibitive.
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Rayonier Sales Parcel. It has long term advantages to the City for future WWTP needs. It
is on the cleaner portion of the Rayonier Mill site, a MTCA site. The City purchased if for
just under $1 million. Considering the land and its tank, it was considered very
favorably priced for the City.
131
From B&C CSO Vunerability Assessment of 5/19/2011:
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133
Outfalls are restricted to less than one overflow per year based on a 5 year average.
After completion of the Phase 1 & 2 projects, average annual discharge volume from
CSO events will reduce to about 5 MG and be heavily diluted.
CSO outfall #7 and #8 will be eliminated. The CSO event analysis indicates 1.3 events
per year at the City's newly acquired industrial outfall that enters the harbor offshore
from the Rayonier property that will be put into operation as part of the CSO project.
Additionally, it will occur once in 8 years at CSO outfall #6 (Railroad & Oak) and once in
1.7 years at CSO outfall #10 (Francis St.). Both CSO outfalls #6 and #10 will be reset so
that overflows could only occur in very extreme storm events.
Statistics:
1.11/16 & 11/17 event:
- 2 days of continuous rain
- 22,290 gpm (32.1 MGD) instantaneous peak for CSOs’ occurred at 8:46
pm on 11/16
- 29,500 gpm (42.5 MGD) instantaneous peak flow was experienced for
the entire system (WWTP treatment plus CSOs)
- 2.25 inch rain event
- 8.4 MG of overflow volume occurred 11/16
- 6.7 MG of overflow volume occurred 11/17
2.12/12/2010 Event:
- 13.75 MG of overflow volume occurred 12/12
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Ranking criteria for State Revolving Fund (SRF) Water Quality loans.
135
The City’s CSO Phase 1 project loan request ranked 1st out of 82 requests for State
Revolving Funds loans for Water Quality Projects. It was the high scoring project for
fiscal year 2012 funding. This demonstrates its importance to the State for water
quality.
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Note: Approximately 11.3% for predesign, design, and permitting.
The Phase 1 and 2 CSO projects are estimated to cost approximately $40 million, the ensure
compliance, the eliminate overflows to the harbor, and it eliminates an environmental
vulnerability of having a force main in the harbor. Funding for it has been accumulating in the
rates. $26.40 per month (or $317 annually) per residence is what is anticipated rates will top
out at in 2015 for the CSO project cost. In 2005, the original rates was $2.00 monthly and
presently residential accounts are paying $15.75 a month (for less than 430 cubic feet of water)
or $17.60 (for more than 430 cubic feet of water). The total cost will probably be around
$5,000 per residence or in that range. It will be collected until such time as the amounts are
collected that are anticipated to be needed to pay off the low-interest loans that will be
incurred. How many more years into the future that will take is uncertain since it will depend
on the construction cost at time of award of the contracts and interest rates at the time the
loans are obtained. Currently, both are expected to be favorable.
Phase 1 & 2 CSO project ensures compliance while the alternative can only approach it and is
vulnerable to falling out of compliance. For downspout disconnection, parking drainage, and
infiltration, there will be some loss of attainment due to difficulties in locating all of the items.
Additionally, there is a recidivism factor for re-emergent infiltration due to continued
settlement and aging of infrastructure or for trauma to the sewer system. Additionally, there
will be some unidentifiable reconnection by residents for the disconnection effort (e.g.
dissatisfation with swampy lawns) or deliberate and approved reconnection due to
unanticipated consequences to neighboring properties.
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This drawing shows what the CSO Phase 1 & 2 construction impacts might look like.
Infiltration improvement projects are shown spread across a number of years even
though they would really be done in a variety of locations throughout the City. Many
are already programmed in the City’s CFP program with others being added in the 2011
cycle. Through year 2023, identified for the CFP is $7 million on infiltration and pipe
replacement related projects for the sewer system. This can be an appropriate target
year to change weir plates in the influent diversion structure should measurements of
outfalls indicate a sufficient drop in flow rates due to I&I reduction in order to ensure
everything from the combined sewer receives secondary treatment. Additionally,
through the stormwater fund, promoting LID could facilitate getting to this goal earlier.
CSO pipeline upgrade and removal from the harbor – blue.
Infiltration restoration – turquoise
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The City’s CSO projects are the least cost and most feasible solution for the City of Port
Angeles to truly solve their CSO problem. No other course of action can do this as well.
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Final thoughts and acknowledgements. The City’s CSO project is the least cost and most
feasible solution for the City of Port Angeles to truly solve our CSO problem. No other
course of action can guarantee that this will occur to the level that these projects do.
No other set of projects will be as helpful to the environment. These projects do
protect the harbor environment and the public health. When coupled with future
infiltration projects, particularly those that are in the vicinity of our streams, even
greater environmental benefit will be realized.
It is not to say that well-targeted LID projects would not be helpful. They do, and
restoring water to the groundwater system is beneficial in lot of ways. Where they
make sense, they provide a significant benefit. But we must remember, that there is
only so much that our soils can sustain for certain areas within the City. So we should
be deliberate in our choices. LID projects should be undertaken by the City and
continue to be encouraged and supported wherever possibly for the public.
Much of this research was brought on by questions brought forth by the Olympic
Environmental Council. My thanks go out to them for pushing us. Also, to my staff and
to Jack Warburton and Mike O’Neal from Brown & Caldwell, who were instrumental in
the data gathering and validating. It was a lot of work.
We must continue on this path. Our dollars are dear to us, so we must choose to spend
them wisely and get the most from them, both for the public and for the environment.
Like I said, we only have one earth and also one Port Angeles.
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M. C. Puntenney
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Table indicates different treatment levels dependent on flow rate.
Adaptability. System set-points and weirs can be readily replaced as treatment and
flow parameters change. The primary flow management control concept is the
proportion of flow diverted to storage versus flow through treatment plant. As flow
exceeds 11,100 gpm, the current weir design is based on flow from 0 to 20,800 gpm
diversion to storage while the plant will only increase from 11,100 gpm to 13,900 gpm
during the same time. If this proportional relationship is required to be changed in the
future, the weirs are simple steel plates bolted to the concrete walls in the Influent
Diversion Structure that can be changed. Conceivably, if CSO flow rate can be reduced
and maintained sufficiently, e.g., infiltration reductions, downspout disconnections,
etc., then the need to bypass secondary treatment might be eliminated. Modification
of the weir plates could be done readily to effect this.
142
Table indicates different treatment levels dependent on flow rate.
Adaptability. System set-points and weirs can be readily replaced as treatment and
flow parameters change. The primary flow management control concept is the
proportion of flow diverted to storage versus flow through treatment plant. As flow
exceeds 16 MGD, the current weir design is based on flow from 0 to 30 MGD diversion
to storage while the plant will only increase from 16 MGD to 20 MGD during the same
time. If this proportional relationship is required to be changed in the future, the weirs
are simple steel plates bolted to the concrete walls in the Influent Diversion Structure
that can be changed. Conceivably, if CSO flow rate can be reduced and maintained
sufficiently, e.g., infiltration reductions, downspout disconnections, etc., then the need
to bypass secondary treatment might be eliminated. Modification of the weir plates
could be done readily to effect this.
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Concept to eliminate the bypassing of secondary treatment at certain flows by 2024 .
Many projects are already programmed in the City’s CFP program with others being
added in the 2011 cycle. Through year 2023, identified for the CFP is $7 million on
infiltration and pipe replacement related projects for the sewer system. This can be an
appropriate target year to change weir plates in the influent diversion structure should
measurements of outfalls indicate a sufficient drop in flow rates due to I&I reduction in
order to ensure everything from the combined sewer receives secondary treatment.
Additionally, through the stormwater fund, promoting LID could facilitate getting to
this goal earlier.
The current operating strategy has all flow going through both primary and secondary
treatment up to a flow rate of 0.56 MGH. When the flow rate exceeds a flow rate of
0.56 MGH, that portion above 0.56 MGH bypasses secondary treatment, receiving only
primary treatment and full chlorination for disinfection. When the flow rate exceeds
0.67 MGH, that flow above this flow rate is split between the tank and receiving only
primary treatment (including chlorination). When flows exceeds 0.83 MGH, that
portion that exceeds this flow rate goes to the storage tank. For the “all secondary
option,’” that is, 100% of flows in excess of 0.56 MGH being transferred directly to the
tank to prevent an overflow, a volume of the flow equivalent to that receiving just
primary treatment would have to be removed from the system. For the one year event
this translates to approximately 1.0MG of volume. Based on the input hydrograph for
the one-year event, peak flow would have to be reduced by approximately 0.31
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MGH. For the one-year event, peak infiltration was estimated at 1.05 MGH. Thus, if
assuming just a focus on infiltration, the required reduction in infiltration is 0.31/1.05 =
29.6% to move to an “all secondary” option for the 1- year storm event.
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This map was prepared as part of the National Tsunami Hazard Mitigation Program
(NTHMP) to aid local governments in designing evacuation plans for areas at risk from
potentially damaging tsunamis.The landward limit of tsunami inundation is based on a
computer model of waves generated by two different scenario earthquakes, both
moment magnitude 9.1, on the Cascadia subduction zone.
The model used is a finite element model called ADCIRC.
The model runs do not include the influences of changes in tides but use a tide height
of four feet. The tide stage and tidal currents can amplify or reduce the impact of a
tsunami on a specific community.
Note that the first wave crest is predicted to arrive 90 minutes after the earthquake,
but significant flooding occurs before the crest, rendering evacuation time even shorter.
Actual flooding depth and extent will depend on the tide height at the time of tsunami
arrival.
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Roof Drains. Most of the roof drains in the pilot test area were not smoke sources. Only
48 of the houses proved to have roof drains connected directly to a sanitary sewer. In
some of those 48 cases, all downspouts were connected to the sewer, but for most of
the homes, only some of the downspouts were connected to the sewer and the rest
were routed to the driveway or lawn. To assist the construction team that would
perform the disconnection and allow it to focus only on the downspouts needing
removal, Brown and Caldwell prepared a set of figures with aerial photos of the pilot
basin and the approximate location of the connected roof drains.
Rain Barrel: Connection of a rain barrel simply requires saw cutting the existing
downspout for reconnection to the rain barrel. The cost of the rain barrel varies
depending upon manufacturer or self- construction; costs range from approximately
$20 - $130 dollars. The City of Bremerton estimated the minimum materials cost for
construction of a rain barrel on the order of $20 dollars. The purchase price of a rain
barrel can vary from as low as $85 up to $130 dollars. Variation in purchase price is
based on materials of construction ranging from 50 -gallon plastic barrels to 211-gallon
wooden barrels, with the majority of barrels above $100 having overflow connections.
Consideration of this option allows for potential overflows during heavy periods of
rainfall. An overflow bypass needs to be considered where this option is applicable.
(Page 36,
146
http://water.me.vccs.edu/courses/ENV149/advanced.htm
Tertiary treatment is the next wastewater treatment process after secondary treatment. This step removes stubborn
contaminants that secondary treatment was not able to clean up. Tertiary treatment technologies can be extensions
of conventional secondary biological treatment to further stabilize oxygen-demanding substances in the
wastewater, or to remove nitrogen and phosphorus. Tertiary treatment may also involve physical-chemical
separation techniques such as carbon adsorption. One methodology is to create lagoons and/or aeration basins.
Advanced Wastewater Treatment may be broken into three major categories by the type of process flow scheme
utilized:
1. Tertiary Treatment
2. Physical-Chemical Treatment
3. Combined Biological-Physical Treatment
Tertiary treatment may be defined as any treatment process in which unit operations are added to the flow scheme
following conventional secondary treatment. Additions to conventional secondary treatment could be as simple as
the addition of a filter for suspended solids removal or as complex as the addition of many unit processes for
organic, suspended solids, nitrogen and phosphorous removal. Physical-chemical treatment is defined as a
treatment process in which biological and physical-chemical processes are intermixed to achieve the desired
effluent. Combined biological-physical-chemical treatment is differentiated from tertiary treatment in that in
tertiary treatment any unit processes are added after conventional biological treatment, while in combined
treatment, biological and physical-chemical treatment are mixed.
Another way to classify advanced wastewater treatment is to differentiate on the basis of desired treatment
goals. Advanced wastewater treatment is used for:
1. Additional organic and suspended solids removal
2. Removal of nitrogenous oxygen demand (NOD)
3. Nutrient removal
4. Removal of toxic materials
In many, if not most instances today, conventional secondary treatment gives adequate BOD and suspended solids
removals. Why, then, is additional organic and suspended solids removal by advanced treatment necessary? There
are a number of good answers to this question.
1. Advanced wastewater treatment plant effluents may be recycled directly or
indirectly to increase the available domestic water supply.
147
2. Advanced wastewater treatment effluents may be used for
industrial process or cooling water supplies.
3. Some receiving waters are not capable of withstanding the
pollutional loads from the discharge of secondary effluents.
4. Secondary treatment does not remove as much of the organic
pollution in wastewater as may be assumed.
The first three reasons for additional organic removal through advanced wastewater
treatment are simple. The fourth requires some explanation. The performance of
secondary treatment plants is almost always measured in terms of BOD and SS
removals. A well designed and operated secondary plant will remove from 85 to 95% of
the influent BOD and SS. However, the BOD test does not measure all of the organic
material present in the wastewater. An average secondary effluent may have a BOD of
20 mg/L and a COD of 60 to 100 mg/L. The average secondary plant removes
approximately 65% of the influent COD. Thus, when high quality effluents are required,
additional organic removals must be accomplished. In addition to the organic materials
remaining in most secondary effluents, there is an additional oxygen demand resulting
from the nitrogen present in the wastewater.
In wastewaters, much of the nitrogen is found in the form of ammonia. When
secondary treatment is used, a great deal of this ammonia is discharged in the
effluent. Bacteria can utilize this ammonia as an energy source and convert ammonia to
nitrite and nitrate.
NH3 + O2 + Bacteria ® NO2 + O2 + Bacteria ®NO3
Another reason for advanced wastewater treatment may be to remove nutrients
contained in discharges from secondary treatment plants. The effluents from secondary
treatment plants contain both nitrogen (N) and phosphorous (P). N and P are
ingredients in all fertilizers. When excess amounts of N and P are discharged, plant
growth in the receiving waters may be accelerated. Algae growth may be stimulated
causing blooms which are toxic to fish life as well as aesthetically unpleasing. Fixed
plant growth may also be accelerated causing the eventual process of a lake becoming a
swamp to be speeded up. Therefore, it has become necessary to remove nitrogen and
phosphorous prior to discharge in some cases
Toxic materials, both organic and inorganic are discharged into many sewage collections
systems. When these materials are present in sufficient quantities to be toxic to
bacteria, it will be necessary to remove them prior to biological treatment. In other
cases, it is necessary to remove even small amounts of these materials prior to
discharge to protect receiving waters or drinking water supplies. Thus, advanced
wastewater treatment processes have been used in cases where conventional
147
secondary treatment was not possible due to materials toxic to bacteria entering the
plant as well as in cases where even trace amounts of toxic materials were
unacceptable in plant effluents.
Rapid sand filters, micro straining and fluidized bed systems are commonly used in
tertiary treatment. Activated carbon and sand are typically used. Beds of aquatic
macrophytes and reed bed systesm (artificial wetlands) are also used in tertiary
treatment. The biomass should be harvested frequently to maintain the productivity of
the system for efficient functioning. A macrophyte is an aquatic plant that grows in or
near water and is either emergent, submergent, or floating.
http://en.wikipedia.org/wiki/Sewage_treatment
Constructed wetlands
Constructed wetlands (can either be surface flow or subsurface flow, horizontal or
vertical flow), include engineered reedbeds and belong to the family of phytorestoration
and ecotechnologies; they provide a high degree of biological improvement and
depending on design, act as a primary, secondary and sometimes tertiary treatment,
also see phytoremediation. One example is a small reedbed used to clean the drainage
from the elephants' enclosure at Chester Zoo in England; numerous CWs are used to
recycle the water of the city of Honfleur in France and numerous other towns in Europe,
the US, Asia and Australia. They are known to be highly productive systems as they copy
natural wetlands, called the "Kidneys of the earth" for their fundamental recycling
capacity of the hydrological cycle in the biosphere. Robust and reliable, their treatment
capacities improve as time go by, at the opposite of conventional treatment plants
whose machinery age with time. They are being increasingly used, although adequate
and experienced design are more fundamental than for other systems and space
limitation may impede their use.
Lagooning
Lagooning provides settlement and further biological improvement through storage in
large man-made ponds or lagoons. These lagoons are highly aerobic and colonization by
native macrophytes, especially reeds, is often encouraged. Small filter feeding
invertebrates such as Daphnia and species of Rotifera greatly assist in treatment by
removing fine particulates.
Another Alternative for Tertiary Treatment - Mechanical treatment plants
Typically 2 to 3 times as expensive to construct as lagoons
Full time, trained operators required
High maintenance and energy costs
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Continual sludge handling and disposal
Poor performance record in small communities
Aerobic stabilization ponds or lagoons are very shallow. They are only about 3 feet
deep.
They are most often the final cells in a multi-staged lagoon system. They are also used
as
polishing ponds for tertiary treatment of trickling filter plant effluent. Their shallow
depth
allows sunlight to penetrate to the bottom of the pond to encourage algae growth and
aerobic
conditions throughout the pond. The low solids loadings found in these tertiary
treatment
applications means that these ponds normally have no sludge zone. These ponds may
be
mechanically aerated. Sunlight penetration can also help dechlorinate treated effluents.
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From NPDES Permit
S12.B. Technology-based Requirements for CSOs
The Permittee must comply with the following technology-based requirements:
1. The Permittee must implement proper operation and maintenance programs for the
sewer system and all CSO outfalls to reduce the magnitude, frequency, and duration of
CSOs. The program must consider regular sewer inspections; sewer, catch basin, and
regulator cleaning; equipment and sewer collection system repair or replacement,
where necessary; and disconnection of illegal connections.
2. The Permittee must implement procedures that will maximize use of the collection
system for wastewater storage that can be accommodated by the storage capacity of
the collection system in order to reduce the magnitude, frequency, and duration of
CSOs.
3. The Permittee must review and modify, as appropriate, its existing pretreatment
program to minimize CSO impacts from the discharges from nondomestic users.
4. The Permittee must operate the wastewater treatment plant at maximum treatable
flow during all wet weather flow conditions to reduce the magnitude, frequency, and
duration of CSOs. The Permittee must deliver all flows to the treatment plant within the
constraints of the treatment capacity of the POTW.
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5. Dry weather overflows from CSO outfalls are prohibited. The Permittee must report a
dry weather overtlow to the Depm1ment as soon as the Pemittee becomes aware of
such an overtlow. When the Permittee detects a dry weather overflow, the Permittee
must begin corrective action immediately. The Permittee must inspect the dry weather
overflow each subsequent day until the overflow has been eliminated.
6. The Permittee must implement measures to control solid and floatable materials in
CSOs.
7. The Permittee must implement a pollution prevention program focused on reducing
the impact of CSOs on receiving waters.
8. The Permittee must implement a public notification process to inform citizens of
when and where CSOs occur. The process must include (a) a mechanism to alert
persons of the occurrence of CSOs and (b) a system to determine the nature and
duration of conditions that are potentially harmful for users of receiving waters due to
CSOs.
9. The Permittee must monitor CSO outfalls to characterize CSO impacts and the
efficacy of CSO controls. This must include collection of data that will be used to
evaluate the efficacy of the technology-based controls., These data shall include:
Total number of CSO events and frequency and duration of CSOs for a representative
number of events;
Locations and designated uses of receiving water bodies; and
Water quality impacts directly related to CSOs (e.g., beach closings, floatables wash-up
episodes, fish kills).
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