Subdividing a rural property in the Port Macquarie-Hastings Local Government Area is rarely straightforward, and on-site sewage management is one of the most common reasons rural subdivision proposals fail or require costly redesign. If your proposed lots won’t connect to town sewer, each lot must be able to accommodate a PMHC-approved OSSM system. Demonstrating this is a subdivision planning requirement, not an afterthought.
Quick answer (BLUF)
Every new lot created by subdivision in an unsewered area must demonstrate it can accommodate an approved on-site sewage management system that meets current standards. This means a soil assessment and preliminary system design for each proposed lot must be completed as part of the Development Application (DA) process, before subdivision can be approved. An existing septic system on the parent lot cannot be shared between new lots.
Why septic is a subdivision gatekeeper
Under the NSW Environmental Planning and Assessment Act 1979 and PMHC’s Local Environmental Plan (LEP), subdivision consent requires evidence that each new lot can be satisfactorily serviced for sewage management. This is not a bureaucratic formality, it’s a genuine technical constraint that determines whether subdivision is physically possible.
The Hastings region’s mix of high-rainfall climate, clay-dominant hinterland soils, sensitive waterways, and coastal water tables means that many rural blocks that appear to offer enough land for additional lots simply cannot support additional on-site sewage systems when setback requirements and soil permeability are considered.
What PMHC requires for subdivision approval
Preliminary OSSM assessment for each proposed lot
Each proposed new lot must be assessed for:
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Soil suitability: Percolation testing and soil profile assessment in the area intended for the OSSM system on each lot. If one lot in a proposed three-lot subdivision has unsuitable soils (too impermeable, too shallow, or high water table), that lot may not receive subdivision consent.
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Setback compliance: Each lot’s proposed building envelope, driveway, dam, bore, and the property boundary must all be compatible with a compliant OSSM system with all required setbacks.
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Available area: There must be sufficient clear, suitable land on each lot for the OSSM system plus its required setbacks from all constraints.
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System type: Based on the soil assessment, the preliminary design will specify what type of system is required, conventional trenches, mound, or AWTS.
Minimum lot size considerations
PMHC’s LEP specifies minimum lot sizes for rural subdivision in different zones. However, meeting the minimum lot size does not automatically mean the lot can support an OSSM system, the minimum lot size is a floor, not a guarantee of OSSM viability. Properties where the minimum lot size creates a lot that is too constrained for compliant OSSM may not receive consent regardless of compliance with minimum area requirements.
Connection to reticulated sewer
If the proposed lots are within reach of PMHC’s or Essential Water’s reticulated sewer network, Council may require connection as a condition of subdivision consent. This removes the OSSM constraint but adds infrastructure cost. Check servicing maps early in the subdivision planning process.
Subdivision scenarios and their challenges
Splitting a large rural block into two lots
The most common Hastings subdivision scenario. The existing system on the parent lot continues to serve the original dwelling. The new lot must demonstrate independent OSSM capacity. Key issues:
- The existing system cannot be located within the setback exclusion zone of the proposed new boundary
- If the existing system is close to the boundary, it may need to be relocated as a condition of subdivision, an expensive complication
- The new lot’s system must not conflict with the existing lot’s system
Splitting off a rural residential lot from a farming property
Common in the Hastings hinterland (Comboyne, Beechwood, King Creek areas). The farming use and its infrastructure (dams, fertiliser storage, vehicle access) create additional setback constraints for the new residential lot’s OSSM system.
Multiple lots subdivision
Creating three or more lots in an unsewered area significantly multiplies the OSSM assessment workload and costs. Each lot needs an independent assessment. In the Comboyne Plateau and other clay-soil areas, finding sufficient suitable land area on every proposed lot for independent systems can make the entire subdivision economically marginal.
OSSM assessment costs for subdivision
A preliminary OSSM assessment for one lot typically costs $1,500 to $3,500 (professional fees) plus PMHC application fees. For a three-lot subdivision, multiply accordingly. These costs should be factored into the feasibility assessment for any subdivision project before engaging a surveyor or lodging a DA.
Common reasons subdivision fails on OSSM grounds
- High water tables on all or part of the site: Particularly in coastal areas (Lake Cathie, Camden Haven) and parts of the Comboyne Plateau; mound systems may be required on all lots, significantly reducing feasibility
- Clay-dominant soils with very low percolation rates: In some areas of the Wauchope hinterland, soils percolate so slowly that the required absorption area exceeds what’s available on the lot
- Setback conflicts: The combination of required separations from boundaries, the proposed new property boundary, existing water sources, and vegetation leave insufficient clear area for the OSSM
- Undersized lots: Lots below approximately 1 ha can rarely support independent conventional OSSM systems in the Hastings region without AWTS
- Existing system non-compliance: If the parent lot’s existing system is non-compliant, PMHC may require rectification as a condition of subdivision consent
FAQs
Can the existing septic system be shared between two new lots?
No. Each lot in a subdivision must have its own independent OSSM system. Shared systems between lots are not permitted under NSW on-site sewage management regulations.
Does PMHC require the new system to be installed before subdivision is registered?
Typically, PMHC requires either that the system is installed before registration, or that the lot purchaser is required to install an approved system within a set timeframe post-settlement. The requirement varies, confirm with PMHC at the DA stage what conditions will be placed on the subdivision consent.
What if the soil assessment says my land isn’t suitable for conventional trenches?
AWTS with drip or subsurface irrigation is often viable on sites where conventional trenches are not, because the smaller absorption footprint is easier to accommodate. If the AWTS option can be demonstrated to be achievable with all required setbacks, the lot may still receive subdivision consent with the condition that an AWTS is installed.
How do I find a qualified person to do the OSSM assessment for subdivision?
You need an accredited OSSM designer or assessor, typically a licensed civil engineer, environmental scientist, or suitably experienced consultant registered with PMHC. Ask PMHC’s Development and Environment team for guidance, or ask your septic contractor for a referral to a qualified assessor they work with regularly.