A compaction certificate is a formal document issued by a geotechnical testing laboratory confirming that the fill material placed in a former pool excavation has been compacted to a specified density standard. It matters because without it, no building certifier in NSW will approve a slab, footings, or structure over the filled pool area, and many real estate buyers, conveyancers, and councils will ask for it during property transactions.
This guide explains what testing is done, when you need a compaction certificate, what it costs, and what happens if your fill doesn’t meet standards. For a shorter, plain-English summary of exactly what the certificate document itself covers, see our pool fill compaction certificate guide.
Why Compaction Matters After Pool Fill-In
When a pool is filled in, the excavation void is filled with granular material, typically crushed concrete rubble from the demolition, gravel, or imported fill. This material does not naturally compact to the density of undisturbed ground. See our pool fill volume calculator guide for how to estimate how many cubic metres that void actually needs before fill is ordered. If it’s simply dumped into the hole without controlled compaction, it will settle unevenly over months and years as the fill consolidates.
Uneven settlement causes:
- Surface subsidence (dips and hollows appearing in the lawn or paving above the fill)
- Cracking of any structures built over the fill (sheds, slabs, decks)
- Damage to pipes or footings in the fill zone
- Long-term drainage issues as fill compresses and creates voids
Controlled compaction during fill placement, placing material in layers and compacting each layer with a vibrating compactor or the excavator bucket, dramatically reduces settlement. Compaction testing then verifies that the required density has been achieved throughout the fill depth.
What Does Compaction Testing Involve?
Compaction testing is performed by an accredited NATA geotechnical laboratory. The most common testing methods used in the Hunter region are:
Nuclear Density Gauge (NDG) Test: A probe is inserted into the fill and emits radiation, measuring the density and moisture content of the material around it. Fast, accurate, and non-destructive. The gauge provides an immediate reading of fill density compared to the maximum dry density established in the laboratory.
Sand Replacement Test (Sand Cone Method): A small hole is excavated in the compacted fill, the extracted material is weighed, and sand of known density is poured in to measure the volume. Used where nuclear density equipment isn’t available or as a verification method. More labour-intensive.
Dynamic Cone Penetrometer (DCP): A weighted cone is driven into the ground by a standard drop hammer. The rate of penetration indicates the strength and stiffness of the fill. Used as a quick index test and to profile compaction through depth.
For pool fill certification in the Hunter region, the NDG is the most common method. Testing is typically done at multiple depths, the fill is tested in layers as it’s placed, and a final series of tests at various depths confirms overall compliance.
What Compaction Standard Is Required?
The standard typically specified for pool fill compaction is 95% of Standard Maximum Dry Density (MDD) per AS 1289.5.4.1 or similar Australian standards. For areas where a building structure will be placed, 98% MDD is often required.
In plain language: the fill is compacted to at least 95% of the maximum density achievable under laboratory conditions. Below that threshold, the fill has too many air voids and will settle more than acceptable over time.
The fill specification should be agreed between the contractor and any future builder or certifier before the fill is placed. If you’re planning to build a slab, granny flat, or garage over the filled pool area, confirm the required compaction standard with your building certifier before the pool removal commences, it’s easier to specify this correctly at the start than to discover the wrong standard was used after the fact.
What Fill Material Is Used?
The fill material placed in the excavation affects compaction quality. Materials commonly used in Hunter region pool fill-ins:
| Material | Compaction Quality | Availability | Notes |
|---|---|---|---|
| Crushed concrete rubble (from pool demolition) | Good (with proper placement) | On-site | Most cost-effective; must be free of large voids |
| Road base (DGS20 or similar) | Excellent | Supplied; extra cost | Best material for building over |
| Clean fill (imported granular) | Good | Supplied; extra cost | Requires testing of source material |
| Gravel/drainage aggregate | Good | Supplied; extra cost | Good drainage properties |
| Mixed demolition fill | Variable | On-site | Less predictable; harder to certify |
Before any of this material is placed, it also has to be legitimately sourced and classified under NSW waste rules, see our guide on VENM vs ENM clean fill rules for pool backfill for what that classification means and why it’s a separate question to compaction quality. Occasionally the excavation itself hits rock beneath the pool’s original footprint before backfill placement even begins; see our guide on rock excavation surprises during pool removal for how that changes both the dig and the fill volume required. If you’re wondering where this material physically comes from and what it costs per cubic metre before compaction is even considered, our guide on pool backfill dirt cost covers that sourcing question directly.
For a standard pool fill-in where no future building is planned, crushed concrete rubble backfilled and compacted in layers is typically sufficient and cost-effective. For an area where a structure will be built, imported granular fill or road base may be specified by the engineer or certifier to achieve more reliable compaction results. See our dedicated guide on reusing crushed pool concrete as backfill for the NSW rules around asbestos testing and reuse, and the genuine cost savings on offer when a pool’s own rubble goes back in the hole.
When Is a Compaction Certificate Required?
A compaction certificate is specifically required when:
- You plan to build over the filled pool area, any DA or CDC-approved structure will require evidence that the fill meets the required standard before the certifier approves the slab or footings
- Your building certifier requests it, private certifiers often require compaction certification as a condition of a construction certificate
- You are selling the property, while not always legally required, providing a compaction certificate gives buyers and their solicitors confidence that the pool fill was done properly
- Council requires it, some councils impose this as a condition of pool removal approvals
If none of the above apply, for example, you’re just creating a backyard lawn area with no future building planned, a compaction certificate may not be strictly necessary, though it’s still good practice.
How Long Does Testing Take?
Compaction testing is conducted on-site during and after fill placement. Individual NDG tests take minutes to perform. The laboratory turns around results within 24-72 hours typically. If testing reveals that fill in a particular zone doesn’t meet the standard, the contractor must additional compact or replace that section, and re-test.
The geotechnical testing firm issues the compaction report and certificate once all required tests pass. Allow 3-7 days from completion of fill placement for certificate issue in the Hunter region.
Cost of Compaction Testing and Certification
Compaction testing costs in the Newcastle/Hunter region (2026):
| Service | Typical Cost |
|---|---|
| Single NDG test point | $180 to $300 |
| Full pool fill compaction testing (6-12 test points) | $1,200 to $3,000 |
| Compaction certificate issue | Included in testing cost |
| Geotechnical report (if required) | $800 to $2,500 (additional) |
These costs are separate from the pool removal contractor’s quote, they’re fees charged by the geotechnical testing firm. Some pool removal contractors include testing coordination in their project management; others leave it to the homeowner to arrange.
Clarify with your contractor: “Will compaction testing be arranged as part of this job, and is the testing cost included in the quote?”
The Relationship Between Compaction Certification and Geotechnical Reports
A compaction certificate confirms that fill already placed has been compacted correctly. A geotechnical report (or site investigation report) is a broader analysis that assesses the soil conditions of the site, including the fill zone, and provides recommendations for foundation design.
These are two different documents:
- Compaction certificate: Issues after fill is placed and tested; confirms compliance
- Geotechnical report: Usually prepared before or after building design; informs how footings should be designed for the site conditions
If you’re planning to build a structure over a filled pool area, you’ll typically need both, the compaction certificate to confirm the fill is acceptable, and a geotechnical report to guide the footing design. See our dedicated guide on geotechnical reports after pool fill-in.
What Happens If Fill Doesn’t Pass?
If compaction testing reveals zones that don’t meet the required standard, the remediation options are:
- Additional compaction passes on the affected zone (viable if the fill is still accessible and not over-compacted on one side)
- Excavation and re-fill of the failing zone (more expensive but sometimes necessary)
- Acceptance at a reduced standard with amended building design (only if the building designer/certifier agrees to modified footing specifications)
Failure to meet compaction standards is most common when fill is placed too quickly without layer-by-layer compaction, when fill material contains organic matter or large voids, or when fill is placed in wet conditions. See our wet weather pool removal guide for how weather affects compaction.
Practical Steps for Homeowners
- Decide before the job starts whether you’ll need to build over the fill area, this determines what compaction standard to specify
- Tell your contractor the intended end use of the filled area (lawn, slab, garden, etc.)
- Confirm testing responsibility, who arranges and pays for the geotechnical testing firm
- Request a copy of the compaction certificate for your records, even if you don’t need it immediately, you’ll likely need it when you sell
Frequently Asked Questions
Is a compaction certificate the same as a geotechnical report? No. A compaction certificate confirms that fill already placed has been compacted to the specified density. A geotechnical report is a broader soil investigation that informs foundation design. You may need both if you’re planning to build over the filled area.
My contractor says they don’t need to do compaction testing. Is this OK? For simple lawn or garden areas with no future building planned, formal testing may not be strictly required. For any area where a structure will be placed, formal testing is necessary and should be specified upfront. Don’t let a contractor skip testing if you have building plans for the area.
How many test points are needed for a pool fill-in? As a guide, testing at multiple depths and across the plan area of the fill is needed. For a standard 50-70sqm pool, expect six to twelve test points at multiple depths. Your geotechnical consultant will determine the testing plan based on the depth and extent of fill.
Can I get a compaction certificate for a partial pool fill-in? Yes. The same testing methods apply to partial fill-ins. The certificate covers the fill zone that was placed, which in a partial fill-in is the interior of the pool shell.
How long do I need to wait after fill placement before testing? For granular fill, testing can begin immediately after compaction is complete, there is no required waiting period. For fill containing any organic or highly plastic materials, there may be waiting periods, but standard pool fill materials can be tested immediately.
Need a pool fill-in with proper compaction and certification? Contact Hunter Pool Removals for a free quote, we coordinate geotechnical testing and compaction certification across Newcastle, Lake Macquarie, and Maitland.