Four Campaigns a Year: Solidifying Leachate at a Closed Site With No Plant

A landfill closed in 1996 still generates 240 m³ of leachate a year from a 60 m³ sump with no power, no operator and no treatment plant. Four times a year a three-person crew arrives with a trailer, spends two days, and leaves with 60 m³ converted to about 72 m³ of cake in four skips. Polymer consumption runs 1.44 tonnes per campaign. The alternative, a permanent installation, was quoted at $340,000 and would have sat idle for 360 days a year.

Closed and orphaned sites are the clearest case for campaign-based solidification, and they need a different design logic from a continuously operating plant. This article covers how to size a campaign rather than a plant, the trailer kit that covers the whole job, an hour-by-hour sequence for campaign day, and what changes by year three.

Sizing a Campaign Instead of a Plant

Start with the sump, not the annual volume. A 60 m³ sump with 1.2 m of freeboard holds 45 m³ usable, and the campaign has to clear that before the wet season refills it. Four campaigns a year at 45 m³ each gives 180 m³ of capacity, which is less than the 240 m³ generated, so either the sump is larger than stated or the campaign frequency is wrong. This arithmetic is worth doing first, because it is the most common reason a closed-site programme fails in year two.

Then size the batch. A 2 m³ batch tank in a trailer allows 15 batches over two days with time for mixing, discharge and cleaning. At 24 kg/m³ that is 48 kg per batch, or two 25 kg sacks. Total for the campaign: 30 sacks, 750 kg, comfortably inside a tonne pallet.

Dose on a closed site usually runs higher than on an active one, because the leachate is old, ammoniacal and saline. Budget 24 to 30 kg/m³ and confirm with a jar test on arrival rather than relying on last year’s number.

The Trailer Kit That Covers the Whole Job

One trailer, loaded the same way every time, removes most of the failure modes. The list that works: a 2 m³ HDPE batch tank with a 1.5 kW paddle, a 6 kVA generator, a 2 inch diaphragm pump with 20 m of layflat, a 500 kg electronic scale or a certified flowmeter, a Jar test kit with six beakers and a portable stirrer, a paint filter kit, PPE for three, a spill kit, and a weatherproof clipboard with the batch sheets.

Two items get left off and should not. A dipstick calibrated in litres for the sump, because estimating volume from depth is where most campaign records go wrong. And a folding table, because the bench work happens outdoors and a jar test on the tailgate in the wind produces numbers nobody trusts.

Campaign Day, Hour by Hour

Day one starts with sampling at three depths and a jar test that takes two hours. Nothing is dosed before the curve is read, even if the crew has done the site ten times. By mid-morning the first batch is mixing, and the pattern settles into a 90-minute cycle: 20 minutes to fill, 25 to dose and mix, 20 to discharge and 15 to clean and record.

Discharge goes into skips lined with a 500 micron liner, filled to no more than 1.2 m depth so the cake can be tested and re-worked if needed. Each skip gets a batch sheet taped inside the lid. Day two repeats the cycle, with the last batch finishing by 14:00 so there is time to test, re-work and close the skips before the haulier arrives.

Rain stops the job. A campaign run in drizzle produces a cake that gains two points of moisture from the air and loses the paint filter, and there is no cover on a closed site. Build two weather contingency days into the schedule rather than pushing through.

What Changes by Year Three

Three things drift and each has a fix. Sump silt accumulates at 100 to 200 mm a year, reducing usable volume and raising the solids load on the first batch of each campaign, so plan a suction dredge every third year. Dose creeps upward by 4 to 8 percent a year as the waste stabilises and ammonia accumulates, which is normal and should be forecast rather than treated as a supplier problem. And the liner, if the sump has one, develops seams that need inspection; a campaign is the only time anyone sees the sump empty.

Keep a single running file per site with every campaign’s volume, dose, moisture results and disposal tickets. After four campaigns it becomes the strongest argument you have at permit review, because it shows a site being actively managed rather than slowly abandoned. SAP in 25 kg sacks with a two-year shelf life suits a site that buys once and doses four times a year.