Reviewing an existing coastal wastewater system for continued use

An existing wastewater discharge permit was approaching expiry for a residential property in the Marlborough Sounds.

The remote coastal site was not connected to public sewer and relied on a secondary treatment system with pump dosed drip irrigation across a steep, vegetated slope.

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RISEN was engaged to inspect the system, review its design against current standards and prepare the complete resource consent renewal application.

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The Task

The system had been installed more than a decade earlier to service a three bedroom dwelling. Before supporting its continued use, RISEN needed to confirm that the treatment unit, irrigation field and wider site conditions were still suitable.

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The assessment included a review of the original design, Council records and as built information, followed by a detailed site inspection.

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All treatment chambers were opened and checked. The blower, irrigation pump and high level alarm were tested and found to be operating correctly. The tanks were in good condition, with no signs of leakage, structural damage or infiltration.

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Testing the irrigation field

Several hundred litres of water were passed through the system to activate a dose cycle.

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The irrigation field was then walked in full, despite the steep terrain and dense vegetation. Distribution was even, with no ponding, leakage, surface seepage or odour observed.

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The established vegetation, sun exposure and coastal wind also provided good conditions for evapotranspiration and moisture recovery between doses.

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Updating the design assessment

RISEN completed new soil testing within the land application area using the current AS/NZS 1547:2012 method.

The testing supported a Category 5 light clay classification.

 

When reassessed under the current standard, the installed irrigation area remained closely aligned with the required area and was considered suitable for the dwelling and expected occupancy.

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The environmental risk assessment also considered slope, groundwater, coastal water, flood exposure, vegetation and setbacks. The system was assessed as presenting a low overall risk, provided regular servicing continued.

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The outcome

RISEN prepared the full consent renewal package, including:

• engineering review and site inspection

• Confirmed the soils are suitable.

• environmental risk and setback review

• wastewater loading certificate

• maintenance schedule

• assessment of environmental effects

• Council application documents

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The review confirmed that the existing system remained suitable for continued use without major modification.

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Need to renew an onsite wastewater system consent?

RISEN provides complete onsite wastewater resource consent renewal support across Marlborough, from inspection and engineering assessment through to the Council application.

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Or contact us to discuss further.

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