In the rural hinterland around Wauchope, Comboyne, King Creek and Beechwood, it’s common for properties to rely on both a groundwater bore for water supply and a septic system for sewage management. When these two systems are correctly sited, they coexist safely. When they’re too close, or on the wrong side of each other, the health risks are serious.
Quick answer (BLUF)
NSW guidelines require a minimum 50-metre separation between the absorption area of a septic system and any bore used for drinking water, measured from the edge of the absorption area to the bore casing. The septic tank itself must be at least 20 metres from a bore. On sandy, permeable, or fractured rock aquifer soils common in parts of the Hastings region, 50 metres may not be sufficient, a greater separation or a hydrogeological assessment may be needed.
How septic systems can contaminate bore water
Groundwater contamination from septic systems follows a subsurface pathway. Effluent from absorption trenches percolates through the soil, which provides biological and physical treatment. If the treatment distance, the path from the absorption area to the bore, is insufficient, contaminants reach the groundwater before adequate treatment occurs.
The primary contaminants of concern:
Pathogens: Faecal bacteria (E. coli, coliforms), viruses (Hepatitis A, norovirus, rotavirus), and protozoa (Cryptosporidium, Giardia) can survive in soil and groundwater for days to months. Their travel distance depends on soil type and groundwater flow.
Nitrate: Converted from nitrogen in wastewater by soil bacteria. Nitrate is highly mobile in groundwater and travels further than most pathogens. High nitrate in bore water is a known risk factor for “blue baby syndrome” (methaemoglobinaemia) in infants and is associated with other health effects in adults. NSW Health’s drinking water guideline is 50 mg/L nitrate.
Pharmaceuticals and personal care products: A growing concern in groundwater near septic systems, but less acutely regulated than pathogens and nitrate.
The 50-metre rule: where it applies and where it doesn’t
The 50-metre minimum setback from absorption area to bore is a risk-based minimum, not a guaranteed safe distance. Its adequacy depends on:
Soil permeability: Sandy soils and gravel allow rapid lateral groundwater movement. Bacteria and viruses travel further in these conditions. Clay-dominant soils (common around Wauchope) slow movement significantly but also slow treatment.
Fractured rock aquifers: Parts of the Hastings hinterland, particularly around the Comboyne Plateau and areas with exposed basalt or sandstone, have fractured rock aquifers where water (and contaminants) can travel very quickly through cracks in the rock, effectively bypassing the soil treatment distance entirely. In these settings, 50 metres may provide very little protection.
Groundwater gradient: Water flows downhill underground, following the hydraulic gradient. The 50-metre separation should always be measured upslope from the bore to the absorption area, the bore must be uphill of the septic absorption area. A bore that is downslope is at greater risk even at the same physical distance.
Aquifer depth: Deep confined aquifers are far less vulnerable to surface contamination than shallow unconfined aquifers. If your bore taps a deep, confined aquifer with an impermeable clay or rock cap, contamination risk from a surface septic system is much lower.
What to do if your bore and septic system are too close
Step 1: Have your bore water tested
The first priority is knowing whether contamination has already occurred. A water quality test for faecal coliforms, E. coli, and nitrate will confirm current safety. NSW Health recommends bore water used for drinking is tested at least annually; if you suspect a proximity problem, test immediately.
Testing can be arranged through a NATA-accredited laboratory, collect samples using sterile containers provided by the lab.
Step 2: Don’t drink the bore water until tested
If you haven’t had the water tested recently and your bore is within 50 metres of your septic system’s absorption area, treat bore water for drinking purposes (boiling, UV treatment, or filtration) until you have confirmed results.
Step 3: Get a professional assessment
A licensed septic contractor can assess your system condition and layout. A hydrogeologist (if the situation is complex) can model groundwater flow and estimate contamination risk given your specific soil and aquifer conditions.
Step 4: Consider your options
- Relocate the absorption area: If alternative suitable land is available, moving the absorption area further from the bore (or upslope of it) may resolve the setback issue. Requires PMHC OSSM approval.
- Upgrade to AWTS: AWTS produces higher-quality effluent with lower pathogen loading, reducing (but not eliminating) groundwater contamination risk. The absorption area for AWTS can also be smaller, making it easier to achieve setback compliance.
- Bore relocation or deepening: If the bore is tapping a shallow unconfined aquifer, deepening it to access a confined aquifer may significantly reduce contamination risk. Requires WaterNSW approval.
- Alternative water supply: If safe bore distances cannot be achieved, switching to rainwater harvesting or town water supply (if available) may be the most practical solution.
Neighbouring bores: your responsibility extends to the property line
The 50-metre setback applies to your own bores, but you also have an obligation not to contaminate your neighbour’s water supply. If your neighbour’s bore is within 50 metres of your absorption area, even on their property, this is a compliance issue. PMHC can require system relocation or upgrade in these circumstances.
This is a not uncommon situation in the Wauchope and Beechwood hinterland where rural-residential lots are 1-5 ha and bores are often sited near shared boundaries.
The Comboyne Plateau: a special case
The Comboyne Plateau’s basaltic geology creates fractured rock aquifers with high permeability. Septic system effluent can potentially travel faster and further through this geology than through the clay soils lower in the catchment. If you’re on the Comboyne Plateau with a bore, extra care in septic system siting, and regular bore water testing, is warranted.
FAQs
Does the 50-metre rule apply to the septic tank or to the absorption trenches?
The 50-metre minimum applies to the absorption area (trenches, mound, or irrigation area). The tank itself must be at least 20 metres from a bore. The absorption area is where effluent enters the soil, so it’s the higher-risk component for groundwater contamination.
How do I find out the direction my groundwater flows?
A hydrogeological assessment or water table survey can determine groundwater flow direction on your property. As a rough guide, groundwater generally follows surface topography, flowing in the same direction as the slope. However, in fractured rock aquifers or areas with complex geology, this may not hold.
Is bore water near a septic system always unsafe?
Not necessarily. Proper separation, suitable soils, and a well-functioning modern AWTS system can produce conditions where groundwater quality is maintained. Regular bore water testing is the best way to confirm safety. Many rural properties in the Hastings region operate safely with bore water when systems are correctly sited and maintained.
What if I’m buying a property and the bore appears too close to the septic?
Make a water quality test a condition of purchase. Have a licensed septic contractor assess the separation distance and system condition. If the system is non-compliant, negotiate a price adjustment or require rectification before settlement, the cost of a system upgrade or bore relocation should be factored into your offer.