Five Checks at the Gate Before You Accept a Solidified Leachate Load

The load arrived at 07:40 with a paper trail saying 1.12 t/m3 and a surface that looked dry. By 09:15 there were 30 mm of dark liquid in the unloading bay and a phone call from the site manager. Nothing on the paperwork was false — the material had been solid enough when it was loaded, six hours and one warm night earlier.

Why a Load Can Pass at Loading and Fail at the Gate

Gel held under pressure in a sealed drum behaves differently from gel spread on a tipping floor. Free liquid migrates to the bottom during transport, and the vibration of a 40 km haul consolidates the mass and squeezes out what the batch test called bound. A batch that showed no free liquid in a jar at 08:00 can show a 20 mm pool in an IBC at 14:00. The gate check exists because of that gap, not because anyone distrusts the producer.

The Five Checks

Check one is free liquid, and it is measured rather than eyeballed. Tip or sample the load and let it stand 15 minutes in a shallow tray. Anything more than a thin film is a problem. The formal version is a paint filter test: 100 g of material in a 400 µm mesh cone for five minutes, no more than a few drops passing. In practice a 24-hour drain test on a 2 L sample in a graduated cylinder is more informative — under 0.5 mL of collected liquid is a comfortable pass, 0.5-5 mL is a conditional accept that needs a note, and above 5 mL is a rejection.

Check two is resistance, not appearance. A gloved thumb press tells you almost nothing. Drop a 5 kg cone or a 2 kg steel ball from 300 mm and look at the crater. A well-solidified load deforms but holds; a marginal one splashes. This is crude, but it is consistent between operators once they have seen ten loads together, and consistency is worth more than precision at a gate.

Check three is weight against declared density. Weigh the vehicle, weigh it out, and divide by the declared volume. Solidified leachate normally lands between 1.05 and 1.15 t/m3. A load at 1.00 is carrying water you were told was bound; a load at 1.25 has probably been bulked with soil or ash, which is a different problem and a different price. A variance over 2% is worth a conversation before tipping.

Check four is temperature and smell. An infrared gun on the load face, two readings, one at the centre. Above 40 °C, the batch is still reacting and free liquid may appear as it cools. A sharp sulphidic smell at the gate means the material is still anaerobic and wet enough to release gas, and it will be a problem in the bay even if the free-liquid test passes.

Check five is the paperwork: batch number, polymer grade, dose rate, tonnage, and the name of the person who signed the batch off. If the hauler cannot name the dose, the load is unauditable and should not be accepted on trust.

How Often to Test

Test every load from a new hauler for the first 20 loads. After that, one in five, plus every load from a vehicle that has previously failed, plus the first load after any rain event over 20 mm at the producing site. Keep the records for the period your permit requires — usually three years, sometimes longer for material going to a hazardous cell.

The limit to be clear about: none of this measures leaching. A load can pass every gate check and still fail a leachability test in a laboratory, because free liquid and chemical mobility are different questions. Gate testing protects your bay and your haulage contract; it does not replace analytical testing of the stabilized material, and anyone who claims otherwise is selling you something.

The polymer specification behind the batch record — absorption range, particle size, gel strength — is the part we can help fix, and it is set out on our landfill leachate solidification grades page.