Page 58 - Council Journal Winter 2019

FEATURE Development in Poor Soils the existing soil at a depth of 6-9
during dry weather periods;
• Facilitate plant nutrient uptake
drip dose and rest water balance procedures state “aerobic conditions optimise microbial breakdown of organic pollutants”. Clearly, this provides an excellent opportunity for drip to be used as a tertiary polishing solution.
inches (150- 200 mm) below the existing ground level using sub- surface pipe insertion machinery such as a mole plough attached to a farm tractor. Site disturbance is minimal and no aggregate or stone is required. Existing trees and shrubs can be retained with the dripline diverted around them or any obstacles. The dripline is pre-treated to prevent bacterial deposits building up
and prevent nitrate and phosphorous runoff to waterbodies;
on the tubing walls and also to prevent root intrusion from trees and shrubs.
• Allow the reuse of wastewater with its beneficial nutrients for irrigation purposes.
Dosing is time controlled from a large pump tank providing flow equalisation over a 24 hour period typically less than 10 minutes per dose cycle. The soil is rested between pumping events to optimise water infilltration and dispersal into the subsoil and allow the re-aeration of the subsoil.
The dripline has a series of emitters spaced at 600 mm intervals in the drip tubing which are moulded inline in the dripline.
Drip technology can optimise soil treatment in all site conditions. Drip distribution systems are
The uniform and time controlled dosing and resting cycles combined with the shallow placement of the dripline in the biologically active topsoil is designed to:
Once the EPA Code of Practice is revised to give guidance on the use of drip systems, it is likely that their use will provide an option for the development of sites with slowly permeable soils that were deemed unsuitable heretofore.
• Facilitate horizontal water movement in the unsaturated topsoil;
Tertiary polishing by drip distribution
Jow Walsh is An Environmental Engineer with Ash Environmental (www.ashtecs.ie)
A version of this article was originally printed in the Engineers Journal
• Retain air-filled soil pores to allow aerobic wastewater treatment in the topsoil;
The aerobic soil conditions below drip provide the best conditions for attenuation of most pollutants including pathogenic organisms. Additionally, the EPRI peer reviewed drip design guidelines referring to
• Encourage evapotranspiration
• Enhance the infilltration into subsoils;
• Minimise the impact of water mounding during periods of seasonal high water table;
This is not only true in low permeability soils but even more so in free draining and shallow soils where groundwater and receiving waters are at risk due to poor pollutant attenuation typical of free draining soils.
Each emitter releases very small quantities (0.03 litres/min) of water which commences to drip into the soil when the design pressure is reached. The PC tubing allows drip laterals of 90 -100 metre lengths to be run along site contours to encourage dispersal of the water along a long and narrow footprint.
already being used successfully on a range of domestic and non- domestic applications in this country.
Aerobic Treatment System
58 Council Journal