EPA/TCD Research into Wastewater Disposal Options
Project Overview
Trinity College Dublin undertook a research project on behalf of the Irish Environmental Protection Agency (EPA) to assess wastewater disposal solutions for sites with low permeability soils throughout Ireland i.e. greater than T-90.
As part of the research project two sites located on low-permeability soil were upgraded by installing 2 pressure-dosed distribution systems, a Low-Pressure Pipe (LPP) and Drip Distribution system.
Both systems performed well and the drip system performed particularly well. The report concluded:
““This resulted in a decrease in the faecal contamination of groundwater, as well as the prevention of surface ponding of effluent, at both sites”.”
The report recommended introducing Drip Distribution and LPP Distribution into EPA Code of Practice (2009), prompting the current revision of the COP.
Drip Distribution System
Ashtecs designed and supervised installation of a Drip Distribution system using Geoflow wastewater drip tubing.
Key findings:
Uniform and unsaturated soil below drip
Overloading trials (infiltration rate doubled) detected no adverse impacts
No surface water ponding
Effluent was evenly distributed
Favourable conditions for denitrification
Reduced nitrate to groundwater likely
Decrease in faecal contamination of groundwater
Can provide solution in low permeability soils up to T-120 with 600mm unsaturated subsoil
As a result of the successful research evaluation of drip as a solution to low permeability soils drip is the only solution recommended to be used in soils from T-90 to T-120. An additional benefit is only 600mm of unsaturated soil is required beneath, which is a 33% reduction in depth.
Low-Pressure Pipe Distribution System
Key findings:
Overloading trials (infiltration rate doubled) detected no adverse impacts
No surface water ponding even during overloading trials and heavy rainfall
Effluent was evenly distributed
Favourable conditions for denitrification
Reduced nitrate to groundwater likely
Decrease in faecal contamination of groundwater
Can provide a solution for low permeability soils up to T-90 with 900mm unsaturated subsoil.
As a result of the successful research evaluation of drip as a solution to low permeability soils the LPP system is recommended as a solution for sites with T-values of less than 90 with 900mm of unsaturated soil above water table.
