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Municipal 2 > 10.0 Sanitary Sewer System 1 > Flashcards

10.0 Sanitary Sewer System 1 Flashcards

1
Q

Sanitary Sewer Sytems

Purpose

A
  • designed to bring sanitary flow
  • typically by gravity to water treatment plants
  • should be failsafe
  • need to consider all flow sources such as residential, infiltration, industrial and extraneous flow
  • design for the worst case
  • check for other conditions to make sure sanitary water is in suitable motion
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2
Q

Regional (Metro Van) Sewage Service Areas

A

Every lot with a sanitary connection in region is interconnected all the way to one of the 5 Metro Vancouver WWTP’s

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3
Q

Basics of Sanitary flow

A
  • Gravity controlled
  • laid at a slope
  • to avoid pumping b/c particulate matter in wastewater can easily damage pumping equipment
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4
Q

Velocities

A
  • velocity of the flow is a limiting factor of the design of the piping system
  • high flow cause erosion
  • low flow cause the particulate matter in the water to settle in the pipe (causing clogs)
  • Ideal range = 1-3 m/s
  • acceptable range = 0.5-3.5 m/s
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5
Q

Hydraulic Analysis

A
  • unpressurized
  • not flowing full (most times)
  • Manning’s equation is used
  • Assuming steady state gravity flow conditions with the pipe flowing full or less than full
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6
Q

Manning’s Equation

A
  • For open channel flow
  • unpressurized flow
  • For storm and sanitary systems
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7
Q

Demand and Flows

A
  • Considering the residential and industrial demand, infiltration, and extraneous flows
  • find average flow rate and multiply by a peaking factor
  • In pressurized systems, when there is a crack in the pipe, water bleeds out. This avoids contaminating the water supply
  • In UNpressurized systems, groundwater leaks into the pipe (infiltration). Extraneous flow operates in the same way, from clean water sources
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8
Q

Inflow and Infiltration

A
  • I&I flow is used as an allowance to account for any infiltration and inflow into the sanitary sewer
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9
Q

Minimum size

A
  • 200mm diameter: single family residential zones
  • 250mm diameter: all other zones
  • shall not be less than 200mm unless in a residential area where it cannot be extended
  • no less than 150mm
  • downstream pipe size reduction may only be used in special circumstances
  • A downstream pipe must not be reduced in size unless
    1. it has increased slope to provide sufficient capacity
    2. it is greater than or equal to 525mm
    3. it is not reduced by more than 2 pipe sizes
    4. a detailed hydraulic analysis has been done
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10
Q

design of sanitary sewer components

A
  • size and material
  • alignment
  • depth
  • curvlinear sewers
  • velocities and slopes
  • structural design
  • maintenance and holes
  • service connections
  • inspection chambers
  • odour mitigation
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11
Q

Material

A
  1. Vitrified Clay extra strength
  2. Non-reinforced concrete Cl.3
  3. PVC SDR35
  4. PVC C900
  5. HDPE DR21
  6. Reinforced concrete Cl. III, IV, V
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12
Q

Alignment

A
  • sewers should be located based on the elevations of the adjacent properties
  • when both sides of the street are serviced by a sewer, the sewer shall be located on the lower elevation side
  • the sewer shall be at a constant offset from the property line
  • minimize crossing conflicts
  • meet clearance and separation requirements
  • minimize contruction, public, and traffic impacts
  • minimize construction costs
  • maximize maintenence access
  • consider long term plans for separated and traditional sewer routing
  • avoid trees and other surface features
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13
Q

Clearance and Separation requirements

A
  • minimum 3m horizontal separation (pipe center to center)
  • minimum 1.5m horizontal separation to large structures (outside of the utility to the outside of the structure
    1m minimum horizontal utility separation between watermains, sanitary and storm sewers to a property line (outside of the utility to property line)
  • Where a water main crosses a sanitary sewer or storm sewer:
    1. Install the water main above the sewer with a minimum clearance of 0.5m
    2. wrap the joints of the water main over a length extending 3m either side of the sewer crossing
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14
Q

Depth

trench

A
  • minimum depth cover is 1m
  • generally the max. depth of trench depth is 6m. greater than 6m or poor soil conditions require design by a professional engineer
  • The sanitary sewer must also be sufficiently deep to
    1. service basements by gravity
    2. allow for tie-ins of other mains and services
    3. structurally withstand surface loading
    4. avoid conflicts with other utilities
    5. prevent freezing
    6. accomodate future sewer separations and consider long term plans for separated sewer routing
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15
Q

Curvlinear Sewers

A
  • horizontal and vertical curves will be permitted under special circumstances
  • vertical curves may be required where excessive rock cuts are to be avoided and where energy dissipation is required
  • the rate of curvature must be uniform throughout the curve
  • only 1 curve (v or h) is allowed between consecutive maintenance holes
  • curves must be formed through joint deflection or bends and not by bending of the pipe
  • the joint deflection must not be greater than 50% of the recommended max. by the pipe manufacturer
  • the radius must also meet min. requirements
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16
Q

Structural Design

A
  • ensure that the pipe is sufficiently designed to withstand loading that will be applied to it without deflection or damage as per manufacture specifications
  • the calculations shall be completed using the manufacturers recommendations and submitted to the municipality
17
Q

Maintenance Holes

Must be placed at the following locations:

A
  • at terminal ends
  • at all grade changes
  • at all size changes
  • at all alignment changes (except curved sewers)
  • every pipe intersection except for 100mm and 150mm service connections
  • upstream end of every sewer line
  • every future pipe intersection
  • max. spacing of 150m
  • at the downstream end of a curved sewer
18
Q

Service connections

A

Each lot will have:
* a gravity connection to the frontage sewer
* a gravity connection to the sewer located in an open lane, walkway or service corridor with an access road
* or a gravity connection through a registered private easement

The size of a service connection will be selected to accomodate the PWWF generated on the property being served and shall be:
* a min. 100mm diameter for all single-family residential lots
* a min. 150mm for all other zonings

  1. the preferred connection depth to invert at the property line shall be 1.5m below the centreline of the street or lane
  2. the sanitary connection must be installed at the same elevation as the storm connection at the property line
  3. the service slope shall not be less than 2%
19
Q

Inspection Chamber

A

required on all new services and are to be located at 0.3m outside of property line

20
Q

Odour Mitigation

A

To reduce the effect of odour caused by the presence of Hydrogen Sulphide (H2S):
* steeper sewers should be used when possible
* larger pipe sizes reduce the depth of flow
* maintenance hole drop structures should be avoided since turbulence release odours

21
Q

Slopes

A
  • min. slope is 0.5%
  • designed with a pipe slope which provides the min. velocity at max. flows
  • anchors will be required when lateral forces are excessive to unseat pipe joints (steep slopes)
22
Q

Maintenance Hole covers

A
  • for safety reasons, all maintenance hole covers in playgrounds, schoolyards, and other areas that pose a safety hazard shall be buried 150mm below grade and secured (bolt-down cover and frame)
23
Q

Maintenance Holes

Rules

A
  1. the min. size of standard maintenance hole is based on the largest pipe diameter entering the maintenance hole
  2. the angles, elevation and the number of incoming pipes must also be considered to ensure safe entry and structural integrity of the maintenance hole
  3. drop strucutres should be avoided by adjusting the grade of the sewer
  4. where drop structure cannot be avoided, the MH structure type depends on the difference in invert

Municipal 2 (7 decks)

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