Onsite Wastewater Systems – Not the AlternativeUse worksheets for calculations
Requires designed GPM and designed head
pressure.
What are the benefits of a dosed volume over a
trickle?
Do you have any control over trickle distribution?
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effluent, whether by gravity or pressure?
Even distribution of effluent throughout
the field or mound.
system better than a gravity one, for the soil
component?
Soil organisms are fed evenly in unsaturated flow condition.
Gravity is more simple, but more affected by construction tolerances (ie. Water always flows to the low spot).
Gravity can overload the beginning of the trench, which causes saturated flow through the basal area.
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Flows by gravity through distribution boxes, gravity
pipe header, or drop boxes.
Can be used in Type 1 effluent fields only.
Total Gravity Distribution
treatment.
sand filters & the new
Potential for re-dosing before field can absorb last
dose of effluent, especially during high peak flow
periods.
Peak or high flow surges are controlled with a High
Water Alarm and Timer over-ride.
Better for field operation – allows for dosing during
off-peak times (night).
Requires larger dosing chamber.
change discharge rates from orifices.
Topography Matters:
effluent than high laterals.
requires a 3 foot squirt height.
1/8” and 5/32” orifices require
a squirt height of 5 feet.
Residual pressure (squirt height)
A variation of 20% in squirt
height = an approximate
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Considerations: There should not be large differences throughout the field. When checking pressure, watch the time that it takes for
liquid to get from the first orifice to the last orifice when discharging.
Implications: Small, short laterals. Small diameter pipe with evenly spaced orifices. Cleanouts should be installed at the end of each lateral.
SQUIRT HEIGHT
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Should orifices point up or down? What should you consider?
What kind of pipe can be used? ABS DWV NO! PVC Pipe, Sched. 40 or Series 160 or 200?
Pipe must be smooth, rigid, plastic piping. Should pipe be laying on sand layer of mound or on the trench
bottom or held up? How do you support pipe, and what spacing should you use
for supports? – 4 feet max. - CSA Standard
ORIFICES
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Are orifice shields necessary? What do orifice shields do? What kind are available? Where do you get orifice shields.
ORIFICES
Overview:
Smaller is better, to a point – if doses are too small, the effluent won’t reach the far end of laterals.
Dose volume should be a maximum of 20% of the expected average volume/day for fields and mounds.
Use approximately 5X volume of distribution lateral network piping.
In large fields, an option is to divide laterals into separate zones to minimize dose volume (and pump size).
DOSING VOLUME
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Did dose volumes work effectively on each lateral layout?
DISTRIBUTION HEADER LAYOUT
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Distribution Lateral Sizes: p. 17 to 21 of 24, PD Worksheet, SPM Appendices
Orifice Discharge Rates: p. 13 of 24, PD Worksheet, SPM Appendices
Pressure Loss through Piping: p. 14 of 24, PD Worksheet, SPM Appendices
Volume in Pipe: p. 16 of 24, PD Worksheet, SPM Appendices
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P. 22 & 23 of 24.
What diameter of lateral is needed for… A 60’ long lateral, with 16 x 1/8” orifices.
A 48’ long lateral, with 20 x 5/32” orifices.
We pick the number of orifices.
DIAMETER OF LATERALS
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How many orifices can be in a ¾” pipe, 60 feet long?
How many orifices can be in an 1 ¼” pipe, 60 feet long?
What typically happens with end-fed laterals?
What happens when changed to centre-fed? Table A.1.A
# OF ORIFICES & SIZE OF LATERAL
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Discharge rate changes with squirt height.
What discharge difference is there between a 1/8” orifice at 3’ and 6’?
What differences would you see on the laterals at different elevations?
What can you do to achieve even squirt height on laterals with varying
elevations?
Appendices.
at 5’ squirt?
total discharge?
affect the system requirements?
pipe size affect system pumping requirements?
Orifice size and spacing affects the volume required for a total system.
What size of pump is required by the system?
Should you design for a particular pump or just design and then buy the pump?
Or both?
Desired spacing on a mound is one orifice per each 4sq. ft. of sand.
If 24” or less wide, chamber is used.
In pipe and rock bed, 1 orifice per 6 sq.ft. of sand mound area.
Stagger orifices for better coverage.
DELIVERY PIPE FRICTION LOSS
distribution header.
loss is allowed in
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FRICTION LOSS
p. 14 of 24, PD Worksheet, SPM Appendices. How much friction loss in 1 ¼” pipe, 65’ long with 4 - 90° elbows, where 25
gallons/minute is discharged from all orifices? See step 6 in pressure distribution worksheets for minimum flow rates in pipe
sizes for delivery pipe – need to maintain velocities. How do you know what size to choose?
Somewhere in 5’ to 10’ head loss for the volume needed.
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FRICTION LOSS
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Number of doses per day.
How many should you have?
How large should each dose be? Volume needs to fill piping and deliver dose.
How much needs to be pumped to fill piping and deliver dose. How much has to be
pumped to put the desired dose on the soil?
Consider the 5X lateral pipe volume rule of thumb to put the desired dose on the
soil when designing the system.
EXAMPLE
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A mound is 100’ long, and 4.5 feet wide, with 6 laterals. It is centre fed.
Designer chose 1 ½” pipe for the laterals.
Peak flow design is 450 gallons for the 4-bedroom home.
4 people live in the home, at an average of 50 gallons/person.
Total average flow is 200 gallons.
Dosing should be 1/5 of average flow so that it equals 40 gallons per
dose.
Can each dose be 5X the volume of the piping? If not, what design
change can be made?
WHAT ARE THE PROBLEMS
DESIGN OF A PRESSURE
incorrectly?
Is a squirt test really needed?
Why?
Should you record the squirt height? Why?
What benefits do clean-outs provide at end of lateral?
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Determine lateral length
Determine lateral diameter
Choose delivery pipe size
Determine pressure head loss in delivery pipe based on GPM through all orifices
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Start with determining information needed and drawing out your
lateral layout.
Use appropriate tables and Pressure Distribution Worksheet to design pressure
system.
EXAMPLE 1
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A mound is 165’ long, and 4.5 feet wide. It is centre fed.
Choose 1 1/4” pipe for the laterals.
Peak flow design is 550 gallons for the 6-bedroom home.
6 people live in the home, at an average of 50 gallons/person.
Total average flow is 300 gallons.
EXAMPLE 2 A mound is 90’ long, and 5 feet wide. It is centre fed.
Choose 1 1/2” pipe for the laterals.
Peak flow design is 300 gallons for the 3-bedroom home.
5 people live in the home, at an average of 50 gallons/person.
Total average flow is 250 gallons.
EXAMPLE 3
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A mound is 180’ long, and 4 feet wide. It is centre fed.
Choose 3/4” pipe for the laterals.
Peak flow design is 450 gallons for the 5-bedroom home.
7 people live in the home, at an average of 350 gallons/person.
Total average flow is 350 gallons.
QUICK REVIEW
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Make choices regarding: piping, orifices, and volumes
Use worksheets for calculations