Emergency response when the lagoon nears freeboard

The gauge read 300 mm below freeboard on a Monday morning, and the forecast offered 60 mm by Wednesday. That is not yet an emergency. It becomes one somewhere around Tuesday lunchtime, and the decisions made in those six hours determine whether the week ends with a tanker bill or a prosecution.

Freeboard incidents are rarely caused by a single storm. They are caused by a lagoon that was already high, a plant that was already behind, and a forecast that was read as weather rather than as a deadline.

The first four hours

Three actions, in this order. Stop every avoidable inflow: recirculation off, washdown water diverted, any clean water that can be separated from the leachate system routed away. Then maximise outflow: check that all transfer pumps are running, that no valve is throttled, and that the treatment plant is at its rated capacity rather than its comfortable capacity.

Then call. The haulier, the contractor who can supply extra polymer, and the regulator if the trigger level in your permit has been reached. Calls made at 09:00 on Tuesday produce trucks on Wednesday. Calls made at 17:00 on Wednesday produce trucks on Friday.

Dosing at emergency rates

Emergency dosing is not normal dosing done faster. It is normal dosing with a different acceptance target. If the choice is between a cake that passes every test and a cake that is dry enough to haul but marginal on free liquid, the second is usually the right answer during a freeboard event, provided the receiving site has agreed in advance.

That agreement is the part sites forget to arrange. A receiving site that has never been asked will reject a marginal load at the gate, which turns a controlled emergency into an uncontrolled storage problem in the yard. Have the conversation in the dry season, in writing, with a named contact.

Who calls whom, and when

Write the notification thresholds down as levels, not as judgements. For example: 500 mm below freeboard, notify internally and place the haulier on standby. 300 mm, notify the regulator and start 24-hour manning. 150 mm, activate the emergency discharge plan, whatever that plan is.

Every person on the pad should know the first threshold and who to call. The second and third are for the site manager. If the thresholds live only in a permit document in the office, they will be discovered after the event.

Keep the contact list current. The haulier’s night number, the polymer supplier’s emergency line, the contractor who can lend a mixer, the regulator’s incident line — four numbers, checked at the start of every wet season, printed and taped inside the dosing cabin. During the event nobody has time to look up an extension.

The site that pumped to a field

A site in a high-rainfall region hit freeboard during a two-week storm and pumped 900 m³ of leachate onto an adjacent field at night. The field drained to a watercourse. The resulting investigation found the pumping was done by a contractor who had been told to “get the level down” without any instruction about where the water could go.

The fine was significant, but the larger cost was the remediation and the loss of the site’s operating licence for six weeks, during which waste was diverted to a competitor. The lagoon did not overflow. The response did.

What would have changed the outcome was not more storage. It was a written discharge plan with three named destinations, each with a capacity figure and a phone number, reviewed before each wet season. The site had storage capacity for another 400 m³. It used none of it because nobody had calculated it.

This week, find your freeboard trigger levels, confirm the lagoon’s usable volume above the sludge blanket, and check that the numbers add up to a plan. The polymer grades that set fastest are worth keeping in reserve for exactly this scenario, when throughput matters more than cost per kilogram.