Replacing or upgrading a septic system

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Signs your system may be failing

The QBCC's guide for homeowners says septic owners should keep an eye out for obvious signs of failure, such as saturated ground over the disposal area, and should check sludge levels so sludge doesn't reach the disposal area (QBCC Home Owners Guide to Plumbing Matters (opens in a new tab)). Other things that commonly prompt a call:

• sewage smells near the tank or trenches
• toilets and drains that are slow or gurgle
• lush, wet or spongy patches over the trenches
• a treatment plant alarm that keeps going off

A licensed plumber can tell you whether a pump-out, a repair or a full replacement is needed. Not every problem means a new system.

When an upgrade comes up

• Adding a granny flat, extension or more bedrooms: your system may need to be resized for the extra load. That's assessed through the plumbing approval process.
• Failed trenches: if the soil around the old trenches no longer absorbs, a new disposal area or a different system type may be required.
• Old or damaged tanks: cracked or collapsing tanks need replacing.

Any installation or alteration of an on-site sewerage facility needs a plumbing permit from Lockyer Valley Regional Council (Form 1), and new treatment plants must hold a Queensland treatment plant approval. See Business Queensland (opens in a new tab) and council forms (opens in a new tab).

What affects the cost

A repair, a like-for-like tank replacement and a full conversion to a treatment plant are very different jobs, so get an itemised quote after a site visit.

Cost factors: decommissioning the old tank, a new soil evaluation and design, new trenches or irrigation, power for a treatment plant, access for machinery around existing buildings and gardens, and council fees.

Questions to ask before you hire

1. Can the existing system be repaired, and what's the evidence it can't?
2. Will the old tank be pumped out, removed or filled, and is that in the price?
3. Will a new site and soil evaluation be needed?
4. How will you restore lawns, driveways or gardens disturbed by the work?
5. What's your QBCC licence number?