What is land-based disposal?
Land-based disposal involves either spraying treated wastewater onto land using an irrigation system, or drip-feeding it beneath the soil using irrigation pipes. The PMU has concluded that the sub-soil drip-feed option is more suitable for Rarotonga.
Land disposal enables plants to reuse the remaining nutrients in treated wastewater, and the soil has a natural ability to filter out pathogens. A well-designed system enables pathogens to decay within the ground, preventing them from getting into streams or aquifers. A wide range of plants can be grown on the land being fed by the treated wastewater. Land use options include golf courses, trees, and farming certain crops that absorb nutrients.
How much land does it use?
Land-based disposal for a new reticulated wastewater system for the developed Muri coastal area will need at least 18 hectares (44.5 acres) of land:
1. About 2 hectares (5 acres) for the treatment plant, and
2. 15 to 20 hectares for drip-feeding treated wastewater into the soil
If other areas around Rarotonga need to be connected to the system in future, more land would be needed.
What kind of land can be used?
Whether land is suitable or not depends on a combination of things such as slope, distance from the treatment system, soil type and rainfall. Initially, some land will be needed in the Muri area. The PMU is very keen to hear from anyone who has land they can offer to the project, and will assess any land offered to see if it is suitable.
How might it affect our environment and community?
· The system re-uses both nutrients and water, which support plant growth, so it could promote sustainable crop production
· Land disposal needs a large area of flat to rolling land, which would need to be acquired or leased. Once the system is running, the land can only be used for certain uses
· Public health risks are low for subsoil systems, and the land is even suitable for growing some food crops
· There is potential income from crop farming (if adopted), but also an ongoing need for local people to manage these crops
· If it’s not operated and maintained regularly and properly, the system could fail. This could cause unplanned discharges and/or unpleasant effects like odour
· Rarotonga may not be able to operate and maintain the system without support from overseas.