Soakage testing measures how fast stormwater drains into the ground on your site, so a soakage device can be sized and Auckland Council can approve disposal to ground. Chambers Consultants, a CPEng-led geotechnical practice in Auckland, carries out falling-head soakage testing in accordance with Auckland Council guideline GD07 and reports a factored design rate your drainage designer can use directly.
Request a soakage testing quote or call 09 278 1072.
When you need soakage testing in Auckland
Soakage testing is usually required where stormwater from roofs and paved areas is to be disposed of to ground rather than piped to the public network — commonly because no reticulated connection is available, or because the site is in an area where Auckland Council expects soakage, such as parts of the Auckland volcanic field. It is also used to assess stormwater retention and groundwater recharge devices for new dwellings, additions and subdivisions.
How we test
- Standard: falling-head (variable head) percolation testing in accordance with Auckland Council Guideline Document 2021/007 (GD07), Stormwater Soakage and Groundwater Recharge in the Auckland Region, with the rate also derived to NZ Building Code E1/VM1 as a cross-check.
- Test holes: typically 100 mm diameter hand-augered holes to about 1.0 m below ground level at the proposed device location, with topsoil or fill cased off so the natural soil is tested. Deeper holes are used where the device will be deeper.
- Pre-soaking: each hole is filled with water before testing so the result reflects saturated conditions.
- Test duration: water levels are recorded at short intervals at first and progressively longer intervals, typically over about 60 minutes, until the rate of fall has stabilised.
- Soil logging: the materials in each hole are logged so the result can be tied to the geology at the site.
What you get
A soakage testing memorandum with the test locations, soil logs, the measured percolation and soakage rates, the factors of safety applied under GD07 for consequence of failure and testing uncertainty, and the factored design soakage rate for sizing the device. We also flag when soakage is marginal and a piped connection or other approved outfall is likely to be needed.
Ground conditions matter
- Volcanic ground (scoria, fractured basalt) on the isthmus often soaks well.
- Waitematā Group clays on the North Shore, West and much of the city usually soak slowly; rates in the low single figures of mm/hr mean a large device footprint or an alternative outfall.
- Tauranga Group alluvium in southern and low-lying areas varies widely and can have shallow groundwater.
Soakage devices should never discharge near the crest or face of a slope or retaining wall, where added water can trigger instability. On sloping sites we assess soakage together with slope stability.
What Auckland clients say
“Sam and the team at Chambers Consultants are absolute professionals and provide excellent service and communication. They helped us recently with a complex pre purchase inspection and saved us from making a big mistake!”
Jeremy M., Google review
“The team was professional, reliable, and delivered high-quality results on time. Very responsive and easy to work with—I highly recommend them for any geotechnical needs.”
Hossein G., Google review
“Good reliable Consultant Engineers, technically sound.”
Shahid A., Google review
Read all reviews on Google · Geotechnical engineers in Auckland · What a geotechnical report costs
Frequently asked questions
How long does a soakage test take?
Fieldwork for a typical residential site with two test holes is usually completed in a single site visit, including pre-soaking and about an hour of testing per hole.
Can soakage testing be combined with my geotechnical report?
Yes. Combining soakage testing with the site investigation for a geotechnical report avoids a second site visit and reduces cost.
What if my site does not soak?
If the design rate is too low for a device to fit on the site, stormwater will need to go to the public network or another Auckland Council approved outfall. We will tell you this plainly in the report.
Does the season affect the result?
It can. Testing in wetter months is generally conservative, while summer testing can overstate long-term performance. We state the season tested and take it into account when interpreting the results.
Book soakage testing in Auckland: call 09 278 1072 or send us your site address. See also geotechnical engineers in Auckland.