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					Distribution
Application/Distribution Options
• Purpose:
  – Effluent must flow from one component to the
    next.
  – Effluent must then be distributed or applied to
    an infiltrative surface.
Application/Distribution Options
• Gravity-flow distribution
  – Description
    • Effluent flows out of one component and into the
      next downstream component and onto an
      infiltrative surface by gravity.
    • Flow will be dependent on when flow occurs.
    • Considered to be non-uniform over infiltrative
      surface.
    • Unless properly managed, the biomat may
      become too restrictive.
Application/Distribution Options
• Gravity-flow distribution
  – Other information
    • Inlet of downstream component must be at lower
      elevation than outlet of upstream component
    • Simplest and least expensive means of
      application
    • Results in least effective distribution of effluent
Application/Distribution Options

• Gravity-flow distribution – Parallel
  – Network of equal length laterals
     • Receive flow by gravity
     • Distribute flow by gravity
  – Typically 4-inch pipe
  – Need flow-splitting device
Application/Distribution Options
• Gravity-flow distribution - Parallel
  – Flow-splitting devices
     • Distribution box
     • Tees/wyes/header
Application/Distribution Options
• Gravity-flow distribution - Parallel
  – Distribution box
     • Two or more outlets
     • Objective: equal flows out of
                   each outlet
     • Each outlet to equal length lateral
     • Made of concrete or plastic
     • Frequently used
     • Need level installation
     • Needs periodic cleaning/pumping
Application/Distribution Options
• Gravity-flow distribution - Parallel
  – Distribution box
     • Problem with assuring outlets stay at same level
     • Tools exist to help assure this
Application/Distribution Options
• Gravity-flow distribution - Parallel
  – Distribution box
     • Needs to be watertight
     • Should be access to the surface to check flow
       distribution
     • Individual lines can be closed off
     • Flow can back-up from line into box and flow out
       other lines – operates like serial distribution
     • Many deficiencies – thus, not permitted in places
Application/Distribution Options

• Gravity-flow distribution - Parallel
  – Typically use 4 inch plastic pipe
  – Usually on slopes < 5%, but in some
    locations, each outlet feeds a lateral at a
    different elevation
Application/Distribution Options

• Gravity-flow distribution - Parallel
  – Each lateral should be parallel to a contour
  – Bottom of each lateral should be flat
  – Even if there are equal flows to each lateral,
    flows will not be uniform down length of
    laterals
  – Because of non-uniform distribution, this
    option is limited in some jurisdictions
Application/Distribution Options

• Gravity-flow distribution - Parallel
  – Many jurisdictions try to help distribution with
    a looped network
Application/Distribution Options
• Gravity-flow distribution - Sequential
  – Receives flow by gravity
  – Distributes flow by gravity
  – Sequentially loads laterals, forcing one to
    fully pond before a gravity flow to the next
    lateral
  – Typically uses 4 inch pipe
  – Needs device to force ponding and allow
    sequential loading of laterals
Application/Distribution Options
• Gravity-flow distribution - Sequential
  – Relief line
     • Simple overflow line from one trench to the next
       downslope trench
Application/Distribution Options
• Gravity-flow distribution - Serial
  – Relief line
     • Forces liquid to pond to predetermined level in
       upslope lateral before flowing to the next one




                  USEPA Manual, 1980
Application/Distribution Options
• Gravity-flow distribution - Serial
  – Relief line
     • Consists of a solid pipe that connects two
       perforated pipes, one in each trench
     • Installation must assure short-circuiting of effluent
       doesn’t occur
     • Trenches can be of unequal lengths
     • Can be located anywhere along lateral length
     • No access capability – it’s burried
 Application/Distribution Options
• Gravity-flow distribution - Sequential
  – Drop box
    • A box that forces liquid in a trench to pond fully
      prior to allowing it to spill over to the next
      downstream trench – sequential loading




    University of Minnesota      NSFC
Application/Distribution Options
• Gravity-flow distribution - Serial
  – Drop box
     • Concrete or plastic box
          – One inlet
          – One or two outlets near bottom to laterals
          – One outlet, higher than the others, to next downslope
            lateral
     •   Like relief lines, used on sloping sites
     •   Must be watertight
     •   Can block off one or more outlets allowing resting
     •   Outlet to next lateral must be lower than inlet
Application/Distribution Options
• Gravity-flow distribution - Serial
  – Drop box
     • Can block off one or more outlets allowing
       trenches to rest
     • Outlet to next lateral must be lower than inlet
     • Access to surface possible with a riser
Application/Distribution Options
• Gravity-flow distribution - Serial
     • Uses all infiltrative surface – bottom &
       sidewall
     • Forces biomat to quickly form
     • Overloading of upslope laterals reduces
       loading on downslope laterals
     • Laterals must be at different elevations –
       thus, usually on sloped sites
     • “Spill-over” level must be lower than outlet of
       preceding component
Application/Distribution Options
• Gravity-flow distribution - Serial
     • Because of trench surfaces in portions of
       network remain wet, there are concerns for
       failure
     • Installation elevations are critical
     • Each lateral can be of different lengths
     • Requires same infiltrative surface area as
       parallel
     • Non-uniform distribution to entire infiltrative
       surface area
Application/Distribution Options
• Dosed-flow distribution
  – Description
    • Predetermined volumes of effluent are held in a
      chamber and dosed to the next component.
    • This provides:
       – More uniform loading to next component
       – Resting times between doses
Application/Distribution Options
• Dosed-flow distribution
  – Other information
    • Can be used to distribute effluent in almost any
      situation
    • Cost more and is more complex than gravity flow
    • For many has become the method of choice
    • On-going monitoring & maintenance are important
  Application/Distribution Options
• Dosed-flow distribution
  – Dosing methods - Demand
       – Dose occurs when sufficient volume of effluent has
         been collected.
       – Dosing frequency depends on how much
         wastewater is being generated.
       – There is no control on how much effluent is being
         dosed daily.
  Application/Distribution Options
• Dosed-flow distribution
  – Dosing methods - Demand
       – Pump controlled directly by floats
Application/Distribution Options
• Dosed-flow distribution
  – Dosing methods - Timed
       – A timer controls the number of doses per day
         and the dose volume.
       – Will allow only a certain amount of effluent to be
         dosed daily.
       – Is more costly and complicated.
       – Protects downstream components from
         overloading.
Application/Distribution Options
• Dosed-flow distribution
  – Dosing methods - Timed
       – A timer controls the dosing device.
Application/Distribution Options
• Dosed-flow distribution
  – Dosing devices - Pump
Application/Distribution Options
• Dosed-flow distribution
  – Dosing devices – Pump
    • In pump tank




                     NSFC
Application/Distribution Options
• Dosed-flow distribution
  – Dosing devices – Pump
    • In 2nd compartment




                      NSFC
Application/Distribution Options
• Dosed-flow distribution
  – Dosing devices – Pump
    • In pump vault
Application/Distribution Options

• Dosed-flow distribution
  – Dosing devices
    • Siphon
Application/Distribution Options
• Dosed-flow distribution
  – Options – Dose to gravity




     NSFC
Application/Distribution Options
• Dosed-flow distribution
  – Options – Dose to gravity
    • Does not result in uniform distribution in laterals
    • Can discharge to either parallel or serial network
    • Parallel network may be looped.
Application/Distribution Options
• Dosed-flow distribution
  – Options – Pressure manifold
Application/Distribution Options
• Dosed-flow distribution
  – Options – Pressure distribution
    • Designed to distribute effluent uniformly over
      infiltrative surfaces of receiving component.
   Application/Distribution Options

• Pressure distribution
  – Uses a network of small diameter pipe and
    small orifices
Application/Distribution Options
 – Pressure distribution
   • Objectives:
     – Pressurize network as fast as possible
     – Be fully pressurized for most of dose
     – Minimize draining into lower laterals
     – To have about the same amount of effluent
       reach each square foot of trench bottom
Application/Distribution Options
• Pressure distribution
  – Used when uniformity of distribution is critical
    to achieving unsaturated flow in the receiving
    medium.
  – Laterals are typically 1-2 inches in diameter
  – Orifices are typically 1/8 to 3/16 inches in
    diameter
  – Depending on specific site, there is usually
    one orifice every 4-15 square feet
  – Orifices can face 6 o’clock or 12 o’clock
  – Low pressures in network are typically
    between 2 and 5 feet of head
Application/Distribution Options
• Pressure distribution
  – The smaller the orifice diameter, the greater
    the potential for plugging.
  – Orifices at 12 o’clock will help network
    pressurize faster but are more subject to
    plugging.
  – Allowable lateral lengths can be several
    hundred feet
  – Laterals can be of different lengths and be
    located in different places
  – On-going monitoring & maintenance are
    important
  – Typically, $1,000 to $2,500 more than gravity
    network
Application/Distribution Options
• Pressure distribution
  – May use flow-splitting devices to minimize
    pump size

				
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posted:11/30/2011
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