Almost all houses, holiday homes, buildings used for visitor accommodation and rural industries outside of Marlborough's major towns rely on on-site systems to manage domestic wastewater. This means that domestic wastewater generated in the building receives initial treatment in some form of treatment unit, such as a septic tank, and is then discharged into or onto a land application area on the property. Contaminants present in the wastewater, such as bacteria and nutrients, are then further treated or absorbed as the wastewater passes through the soil.
In the Marlborough area, domestic wastewater is discharged into soils of low permeability, into thin soils with limited ability to treat contaminants or into extremely permeable alluvial soils. In all cases, there is the potential for contaminants to travel beyond the land application area and into the surrounding environment, through runoff or infiltration.
Many buildings are located in close proximity to streams, creeks, underlying ground water or coastal water. This means that, if the on-site wastewater management system servicing the building performs poorly, there is a risk that the subsequent discharge will contaminate water. For example, Council's monitoring has established that there are elevated levels of bacteria in some coastal waters in the Marlborough Sounds over the summer months. Yet there is a community expectation that water quality is to be maintained or enhanced. It is therefore clear that the risk of contamination needs to be managed. This involves two key steps.
Firstly, it is important to improve the performance of existing on-site systems over time. The following links contain useful information on appropriate operation and maintenance of on-site wastewater management systems. Secondly, it is important that the existing situation is not made worse by future residential subdivision and development.
The following contains guidelines for the design, installation and management of new on-site wastewater management systems.
Change to the Marlborough Sounds Resource Management Plan
Council has introduced new plan provisions to reduce the impact of on-site domestic wastewater discharges on water quality in the Marlborough Sounds. The provisions contained in Plan Change 7 affect both existing and new wastewater management systems. Plan Change 7 became operative on 10 March 2006. A copy of the plan change can be downloaded below.