Wastewater Coalition Meeting 92500 Power Point

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Sewer System Issues Existing Today
Norman Utilities Authority
September 25, 2000
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Introduction

• Tonights presentation will review the following
• Development of Normans Sewer System
• Components of Wastewater Flow
• Wastewater Master Plan Development
• Development Ordinance Sec. 19-415(g)
• Wastewater System Defects - Public and Private
• Overview of Problems Faced
• General Comments

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Development of Normans Sewer System

• Normans first sewerlines were installed around
  statehood. Very few of these lines exist today.
• Normans sewer system has grown to include about
  two million feet of pipe ranging in size from 4
  inches to 42 inches in diameter.
• The majority of the lines installed since 1940
  are still in service.

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Development of Normans Sewer System

• The existing wastewater collection system today
  includes over 8,400 manholes.
• Manholes allow access for sewerline maintenance.
• Various materials have been used over time to
  construct manholes. Brick and cast concrete are
  the two most common materials historically used.

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Wastewater Flow Components

• Normans wastewater system carries unwanted
  stormwater (Inflow/Infiltration) following
  periods of rain due to defects existing in the
  public and private portions of the system.
• Stormwater inflow overloads our major
  interceptors.

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Master Plan Development

• The Wastewater Master Plan was initiated with
  prime objectives targeted
• Understand our current collection system capacity
  limitations
• Identify necessary improvements existing today in
  Norman
• Identify improvements necessary in Normans
  future
• A hydraulic model of Normans wastewater
  interceptor system was developed to identify
  existing and future infrastructure needs

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1998 Flow Monitoring Locations
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Master Plan Development - Flow Monitoring

• Flow monitoring occurred during 100 days of the
  spring and fall of 1998.
• Twenty-four meters collected data every 15
  minutes during this time.
• Four rain gauges were used in measuring rainfall
  rates during this period.
• Over 230,000 data readings occurred during this
  period.

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Master Plan Development - Design Conditions

• The Oklahoma Department of Environmental Quality
  requires Peak design flow must be based on an
  acceptable Infiltration/Inflow (I/I) study
• In Normans case, a 5-year storm has been
  historically accepted as representing conditions
  by which sanitary sewers are to be designed.

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Master Plan Development - Model Results

• Model results identified serious sewer capacity
  problems existing in many of the major
  interceptors serving the City of Norman

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Master Plan Development - Model Results
Ground Surface
Manhole
Pipe
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Master Plan Development - Model Results
Overflows Identified by Model Analysis
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Master Plan Development - Model Results
System Surcharges Identified by Model Analysis
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Master Plan Development - Critical Impacts

• Manhole surcharging can allow sewage to back up
  and cause damage to personal property.
• In Normans past, and occasionally today,
  significant storm events result in wastewater
  flows severe enough to create backups.

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Development Ordinance Sec. 19 - 415(g)
Whenever ninety-five (95) percent of the design
capacity of a wastewater collection system is
allocated through approval of final plats, as
determined by the City Engineer, no additional
plats shall be approved for that collection
system until such time as the capacity of said
waste water collection system is increased or
until the City Council has approved, as a part of
the program of improvements for a final plat, an
increase in the capacity of the collection
system. It is the intention of this section to
prohibit new plats until such time as the
capacity is increased or until said increase has
been approved as a condition for the filing of
the plat.
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Resolution Provisions - Current Platted Lots
Residential Industrial Commercial
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Questions Raised by the Public

• Why Not Repair the Aged Portion of Our System?
  Since 1990 Norman has performed the following
• Imhoff and Normandy Creek Interceptor
  Replacements, cost over 10 Million
• Annual Sewer Replacements by Fiscal Year, cost
  over 3 Million to date
• CDBG Funded Projects, cost over 550 Thousand to
  date
• Line Maintenance Annual Responsibility, cost over
  160 Thousand to date on materials alone

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Performance Problems?
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Wastewater System Performance

• During periods of heavy rain Normans sewer
  system experiences capacity limitations due to
  stormwater entering into the system from one of
  two sources.
• Public Sector Defects
• Private Sector Defects
• System performance is limited due to a dramatic
  increase in wastewater flow following a
  significant storm event.

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Wastewater System Performance
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Flow Depth (inch)
Typical Flow
15
10
5
012
157
342
527
712
857
1042
1227
1412
1557
1742
1927
2112
2257
Storm Flow
Average Day Flow
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System Defects Identification

• Since 1992 Norman has investigated and identified
  defects in our sewer system using Smoke Testing.
• Smoke Testing readily identifies defects where
  stormwater can enter into the sewer system.
  These defects are on both public and private
  properties.

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System Defects Identification
Phase 1 Phase 2 Phase 3 Phase 4
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System Defects

• The four phases have identified 13,782 defects
  within Normans sewer system.
• 12,552 of the defects identified were from Public
  Sources.
• 1,230 of the defects identified were from Private
  Sources.

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System Defects - Public and Private Sources
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System Defects - Public Sources

• To date over 4,866 manholes have been inspected
  for defects.
• Many manholes have been repaired or replaced as
  necessary.

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System Defects - Public Sources

• Over 1,200,000 linear feet of sewerline have been
  tested for defects.
• Numerous line replacements and point repairs have
  occurred.
• City of Norman Line Maintenance Crews clean
  and/or replace lines systematically.

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System Defects - Public Sources

• To date, four phases of investigation have been
  completed. Only three phases have been
  constructed.
• It is projected that 79 of the public defects
  will have been addressed upon completion of the
  fourth phase of construction.
• Remaining items are not considered critical and
  will be systematically addressed in the Capital
  Budget in future years.

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System Defects - Private Sources

• Private sources of stormwater entering into
  Normans wastewater system were also identified
  during the smoke testing investigations.
• Each defect was categorized
• Uncapped Sewer Cleanouts
• Defective Service Lines
• Roof Downspouts
• Area Drains

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System Defects - Private Sources (Cleanouts)

• A cleanout is an access point into the property
  owners service line which connects to Normans
  wastewater system. It provides access for
  cleaning if the service line becomes obstructed
  or blocked.
• Over 840 cleanouts have been identified as
  defective.

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System Defects - Private Sources (Service Line)

• Over time many different materials have been used
  to connect buildings to the City of Normans
  sewer system.
• Some of the materials have withstood the test of
  time and some have not.
• Defective service lines contribute to the amount
  of stormwater entering the system and are costly
  to correct.

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System Defects - Private Sources (Downspout)

• In some cases a buildings rain gutter is
  connected directly to the sanitary sewer system.
• In the past this was an accepted practice. Today
  it is not allowed.
• This defect is not common. To date only eight
  have been identified, with some being corrected
  shortly after discovery.

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System Defects - Private Sources (Area Drains)

• In some locations, inappropriate drains have been
  connected to Normans wastewater system.
• A total of 37 locations have been identified at
  which area, driveway, or basement drains have
  been connected to the sewer.

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Private Defects - System Performance Impact?

• In the past it has been reported that 16 of the
  stormwater entering into the system is from
  private sources.
• This value was derived in 1994 during the Phase 1
  Sewer Study.
• The data reviewed in developing this number
  considered only the most severe problem areas in
  town, as identified by the initial flow
  monitoring efforts.
• The consideration that all of Norman contributes
  flow equal to most severe locations is an
  erroneous assumption.

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Private Defects - System Performance Impact?

• Considering that the initial study reported that,
  in a worst case scenario, a defective or broken
  cleanout would contribute 1 gallon per minute
  (1440 gallons per day).
• The initial report stated that a defective
  service line contribute 2 gallons per minute
  (2880 gallons per day).
• The initial report stated that a roof or area
  drain contributed a maximum of 6.4 gallons per
  minute (9,200 gallons per day).

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Private Defects - System Performance Impact?

• Assuming that all defects known to exist at this
  time contribute at the average rate reported in
  the initial study then the flow from these
  locations would total 1.06 Million Gallons during
  a design storm event.
• This rate equates to 2.8 of the maximum
  wastewater flows recorded at Normans wastewater
  treatment plant.
• If the defect numbers are projected to represent
  all of Norman a total of 1.7 Million Gallons
  would result. This total equals 4.5 of the
  maximum flows observed.

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Private Defects - System Performance Impact?

• The removal of any percentage of stormwater is
  important, but a reduction of the magnitude
  discussed will not solve the capacity issues
  existing today.
• 16 of the maximum daily flow of 38 Million
  Gallons per Day would represent over 6 Million
  Gallons of flow originating from private sources.
• This large amount is not believed to be practical
  and it is certainly not believed to represent our
  system during storm events.

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Summary

• Past efforts to eliminate defects where
  stormwater enters the system have effectively
  reduced capacity related problems.
• The sewer interceptors serving Norman today are
  still beyond capacity during a 5-year storm.
• Improvements will continue to be made to remove
  defects from the sewer system.
• Line maintenance activities will continue to
  address items that allow stormwater to enter into
  the sewer system.

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Sewer System Issues Existing Today
Norman Utilities Authority
September 25, 2000