Page 57 - Council Journal Winter 2019

and length of pump line or rising main. As a result, the choice of pump and the volume of the pump tank or pump compartment are critical design elements.
recognised as the most effective method of distributing wastewater to subsurface soils. The suitability of soil types ranges from fast free draining soils to the low permeability in textured clay soils. It has now been used in more than one third of the counties in Ireland.
FEATURE Development in Poor Soils at sites where point source discharges
So to be effective, designs for pressure pipe networks require these calculated design values and should be provided with the pipe network:
There are many strong endorsements of drip distribution from the US two of which come from the US EPA and the US Electric Power Research Institute (EPRI)’s peer reviewed guidelines. The US EPA wastewater design manual 2002 describes drip as “the most effcient of all distribution methods and is well suited for all types of subsurface wastewater infiltration systems”.
and National Pollutant Discharge Elimination System (NPDES) permits are not appropriate due to the environmental sensitivity of receiving streams. It is also commonly used at sites where conventional systems are not appropriate due to site constraints such as shallow soils above a restrictive layer (e.g. rock, groundwater, hardpan, etc.), steep slopes, or clay soils with low permeability.”
• The minimum operating pump capacity for the specific pipe network at the site TDH head in litres/minute;
• The minimum recommended network dose volume in litres per dose i.e. per pumping event.
The drip system disperses the filltered effluent uniformly over the percolation area using pressure compensating drip tubing. High head submersible pumps pressurise the dripline network while taking account of the site total dynamic head including network friction losses. The drip emitters which are moulded into the drip tubing are designed to restrict the flow typically to 1⁄2 US gallons per hour (0.03 Litres/min) during operation.
Drip distribution of wastewater to soil percolation areas evolved from the development of drip irrigation in Israel in the 1960’s. Later technology improvements and root inhibiting modifications allowed the drip irrigation to be subsurface. The demands of water shortages meant the reuse of wastewater via drip irrigation soon followed.
The US Electric Power Research Institute (EPRI) and Tennessee Valley Authority Peer reviewed Drip guidelines 2004 state: “Subsurface drip irrigation, or more appropriately for wastewater applications, subsurface drip distribution (SDD) is the most efficient method currently available for application and subsurface dispersal of wastewater to soil. Because it is so effective, drip distribution represents a viable option for wastewater disposal for all soil types.
Drip distribution systems
Drip distribution involves the controlled dripping of minute quantities of water about 6-9 inches below ground at the biologically active root zone of the ground surface vegetation. It is increasingly
“The technology is commonly used
With approximately 2.4 emitters per square metre throughout the percolation area, each square metre of soil consistently receives the same volume of water. Low permeability soils are dosed less frequently than more permeable soil types.
Drip distribution system
The dripline is usually inserted into
Council Journal 57