Percolation Testing and On-Site Wastewater Assessments in NSW

What is a percolation test?

A percolation or infiltration test measures how water behaves at a selected location and depth under the agreed field-testing conditions. The results can help the relevant wastewater, hydraulic or civil designer understand whether ground conditions may influence a proposed absorption, infiltration or on-site wastewater arrangement.

The test does not, by itself, approve a wastewater system or establish that any design is suitable. System design, regulatory approval and interpretation of broader environmental requirements remain the responsibility of the appropriate project professionals and authorities.

When testing may be requested in Sydney and NSW

Percolation testing may be requested for residential or semi-rural projects where a designer, council or other project professional needs ground infiltration information. Relevant sites can occur around South West Sydney, Macarthur, Camden, Wollongong, the Illawarra and other parts of NSW, depending on the property and proposed system.

Requirements vary with the project, site characteristics, local conditions and the responsible approval authority. It is not correct to assume that every property or council requires the same test.

• Proposed on-site wastewater or effluent land-application areas.
• Stormwater infiltration or absorption concepts where testing is requested.
• Properties with shallow soil, weathered rock, clay or variable fill.
• Sites where groundwater, perched water or drainage may limit infiltration.
• Design reviews requiring location-specific field observations.

What the field assessment can and cannot establish

The agreed scope can include site observations, selected test locations and depths, ground descriptions and a record of relevant water behaviour under the test conditions. Shallow refusal, low-permeability material, perched water or groundwater can restrict the available test depth and should be documented.

AS/NZS 1547 may be relevant to on-site domestic wastewater management where applicable, but the appropriate designer and approval authority determine the full design and compliance requirements. Field results are one input, not a complete wastewater design or approval.

What to provide for a percolation testing quote

Send the site address, proposed development, survey, wastewater or stormwater concept drawings, likely disposal or infiltration area, access photographs and any written request from the designer, council or certifier. Mention known shallow rock, wet ground, previous reports or existing on-site systems.

Sydney Geotechnical confirms percolation-testing scope and pricing against the actual site and requested deliverables rather than advertising a generic price that may not match the project.