If you’re digging out soil on a building site, sooner or later someone will ask for WAC results. WAC stands for Waste Acceptance Criteria. It’s a set of lab tests that tells a landfill whether it’s allowed to take your waste, and at which type of site.
Getting WAC right can make a large difference to your disposal bill. This guide explains what the test is, when you need it, and how to avoid paying non-inert rates for soil that could have gone somewhere cheaper.
WAC testing and waste classification are different tests
People often mix these up, but they answer two separate questions.
- Waste classification (WM3) asks whether the soil is hazardous or non-hazardous. It looks at the total amount of contaminants in the soil.
- WAC testing asks which type of landfill can accept it. It mainly looks at what leaches out of the soil when it gets wet.
WAC testing doesn’t tell you whether waste is hazardous. You always classify first, then use WAC to confirm the landfill route. If you haven’t classified your soil yet, start with our guide to whether your waste is hazardous.
The three types of landfill
| Landfill type | What it takes | WAC needed? |
|---|---|---|
| Inert | Clean soils, stones, concrete, brick and other waste that won’t react or break down | Yes, in most cases |
| Non-hazardous | Non-hazardous waste that doesn’t meet inert limits | Not usually, if it’s classified as non-hazardous |
| Hazardous | Hazardous waste, including some asbestos contaminated soils in special cells | Yes |
In short, you need WAC when non-hazardous soil is heading for an inert landfill, or when hazardous soil is going to a hazardous landfill. Non-hazardous soil going to a non-hazardous landfill usually doesn’t need it.
What does a WAC test measure?
A WAC suite has two parts.
Solid analysis of the soil itself, including total organic carbon (TOC), loss on ignition, pH, acid neutralising capacity and some organic contaminants such as mineral oil and PAHs.
Leachate analysis, where the soil is mixed with water in the lab and the liquid is tested for metals, chloride, sulphate, fluoride, phenols and dissolved organic carbon. The Environment Agency accepts a single stage leaching test, but some landfill operators ask for a two stage test, so check before you book.
Each result is compared with the limits for inert, non-hazardous and hazardous landfill. Fail one inert limit and the soil can’t go to an inert site.
Why the result matters for cost
The route your soil takes decides the landfill tax charged on it. In England from April 2026:
- inert material that qualifies for the lower rate is taxed at under £9 a tonne
- everything else pays the standard rate of £130.75 a tonne
Scotland and Wales set their own rates. On a job with a few hundred tonnes of muck away, the difference between inert and non-inert can run into tens of thousands of pounds, before gate fees and haulage.
Can soil go to inert landfill without testing?
Sometimes. Clean, natural soil and stones from a site with no history of contamination can be accepted at some inert landfills without WAC testing. Topsoil and peat are normally excluded. The landfill operator makes the decision, and will usually want evidence such as a site history or desk study.
If the site was previously used for industry, fuel storage or a garage, or it’s made ground, expect to test.
How to get soil tested
- Keep stockpiles separate. Don’t mix clean natural ground with made ground or anything that looks or smells contaminated. Test each stockpile on its own.
- Take enough samples. One sample rarely represents a whole site. More samples give a truer picture and reduce the risk of a whole load failing on one bad result.
- Use an accredited lab. The lab will supply the containers, usually a plastic tub plus glass jars for organic tests.
- Allow time. Standard turnaround is around 10 working days. Faster results are available at extra cost.
- Send results to the landfill before you haul. Many sites won’t book in loads until they’ve approved the results.
Can you avoid landfill altogether?
Often, yes. Clean excavated soil can sometimes be reused on the same site or another site under the CL:AIRE Definition of Waste Code of Practice, so it never becomes waste. Suitable material can also go to soil recycling or restoration projects under an exemption or permit. Both are usually cheaper than landfill and better for your recycling figures.
Contaminated soil and hazardous results
If classification shows your soil is hazardous, it needs a hazardous waste consignment note, a carrier licensed for hazardous waste and a hazardous landfill or treatment site. WAC testing is then used to confirm the soil meets that landfill’s limits. Soil that fails can sometimes be treated first to bring it within limits.
Our contaminated soil disposal service can arrange sampling, interpret the results and book the right route.
Frequently asked questions
How much does WAC testing cost?
It depends on the lab and the number of samples. Ask for a price per sample and check whether the classification suite is included.
How long are WAC results valid for?
There’s no fixed expiry, but the results must represent the material you’re sending. If the stockpile changes or you dig into a new area, test again.
Does my grab lorry company need the results?
Yes. The haulier and the receiving site both need to know what they’re carrying. See our grab lorry and muck away guides.
Need soil taken away?
Select A Skip arranges muck away, grab lorries and soils and aggregates across the UK, with testing and paperwork handled for you. Get a quote or call 01743 341 000.
Sources: Southern Testing, Understanding waste classification and WAC; Ground & Water, Guide to waste classification; letsrecycle.com, landfill tax rates from April 2026.