WA Sewer-Connected Purchases: Ask What Happened to the Old Septic System

CHECK WHAT REMAINS BELOW THE BACKYARDWA purchase evidence for redundant septic systems

An older WA property can be connected to sewer and still have a redundant septic system beneath the garden. For a buyer planning a driveway, extension or subdivision, that history deserves a specific enquiry. The current water bill does not tell you whether every old tank, drain and associated component has been dealt with.

The purchase decision is whether the evidence is strong enough to accept the seller’s description of the land and the cost of preparing it. Start with records and specialist advice before assuming the former system has disappeared.

Connection and decommissioning are separate questions

WA Health’s guidance on disused septic systems explains that there is no legal obligation to decommission at the moment of sewer connection, but identifies sale, change of use and extensions encroaching on minimum setbacks as triggers. Ask the local environmental health team and your solicitor how those requirements apply to the property and transaction.

The important distinction is between evidence that sewage now goes to the reticulated network and evidence about the redundant system. Request both. A vendor may accurately say the property is sewer-connected without having provided a record that the former tanks and disposal components were decommissioned.

Request the whole system history

Ask for the original wastewater approval and location plan, any sewer connection documentation, contractor invoices and decommissioning records held by the vendor or council. Have the plumber compare the records with the site. Treat an old plan as a lead for investigation rather than a guaranteed record of everything underground.

Include leach drains, soakwells associated with the effluent system and relevant pipework in the enquiry. A receipt for pumping a tank should be read for exactly what work it records. It may be useful evidence, but your specialist needs to determine whether it demonstrates the complete decommissioning outcome.

Do not open tanks, enter a chamber or probe suspected structures yourself. Ask the contractor to assess access and safe investigation methods. A student’s useful contribution is an organised record request and a clear drawing of the proposed development.

Define the work before pricing the land preparation

The City of Swan wastewater guidance describes removal and backfilling options and recommends removal particularly where future development is planned. That is local guidance to discuss with the relevant council and your consultant, rather than a reason to order one treatment for every WA site.

Ask your engineer whether the proposed building or pavement needs further ground preparation or evidence after decommissioning. Keep that design question separate from the environmental health record. A contractor’s statement about the wastewater system is not automatically an engineering opinion about bearing conditions for a new structure.

Obtain a scope that identifies locating the system, waste removal, treatment of components, backfill, access constraints, reinstatement and required documentation. Request exclusions. If the complete extent cannot yet be established, carry a clearly labelled estimate and an investigation task instead of inventing a fixed removal price.

A practical retained-house scenario

Imagine a buyer intends to retain the front house and create a lot behind it. The property is already sewer-connected, and the proposed access crosses an area shown as a former leach drain on an old plan. The seller has no decommissioning record.

The next step is to ask the environmental health team what records exist and what evidence it will require. Give the plan and access concept to the plumber and civil engineer. Their advice may affect investigation access, excavation scope, the driveway design or the timing of works before the subdivision can progress.

Your solicitor should address responsibility and evidence under the actual sale contract. Do not assume that a seller’s promise, an adjustment at settlement or a buyer’s allowance automatically satisfies the statutory position. That is a transaction-specific question to resolve before committing.

TPC deal lens: evidence belongs in the completion scope

Local documentation can be quite specific. The City of Wanneroo certification form asks for a declaration that decommissioning complies with the named regulations. Use that as an example of why you should ask your own council what completion record it expects, rather than treating any invoice as sufficient.

Put the investigation and confirmed works in the feasibility, and identify who obtains the final record. If uncertainty remains, test the downside effect on access works and holding time. Keep all documents with the property file so the issue does not have to be reconstructed when you later build or sell.

Your next decision checklist

1. Request the council wastewater file and the vendor’s decommissioning records.
2. Give the proposed access and building layout to the plumber and engineer.
3. Ask the solicitor to resolve responsibility and required evidence before purchase.

Key Takeaway

Sewer-connected does not answer the old-system question. Establish the history, the physical scope and the required evidence before relying on a clear backyard in your feasibility. What document currently supports your assumption that the former effluent system has been dealt with?

Image credit: ANGIE BAONGOC / Unsplash. Illustrative photograph. Source · Licence Cropped and resized from the original; no content retouching.

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