Marlborough Sounds Resource Management Plan 10 M arch 2006 This situation is made worse by the fact that many on-site systems are inaccessible for servicing; (d) Stormwater is entering the treatment unit or land application area, increasing the hydraulic loading on the site soils; and (e) Given the age of some systems, and the rate of property ownership change in the Sounds, present owners may know little about the on-site wastewater management system on their property. The Council’s ability to respond to poorly performing or failing systems under the Resource Management Act is limited to instances of non-compliance with permitted activity rules and resource consents. It is considered that a more proactive and integrated programme is required to resolve the issues. Secondly, it is important that the existing situation is not made worse by future residential subdivision and development. There is still undeveloped land zoned for residential purposes by this Plan, and many of the sites are more difficult to develop and service than those already built upon. It is important that any on-site wastewater management system installed is appropriate to the site, given the nature of the discharge and the site conditions. A demand for further residential properties throughout the Sounds is reflected in resource consent applications to subdivide land. It is important that the density of future properties does not exceed the ability of the surrounding environment to assimilate domestic wastewater. This may mean that existing and future subdivisions are better serviced by off-site systems. It will be important to continue monitoring the performance of on-site systems, and their potential effects on the surrounding environment, to determine whether the various initiatives identified in this Plan are effective. 14.4 Issue The use of inappropriate on-site wastewater management systems to service buildings producing domestic wastewater, and/or the poor management and maintenance of on-site wastewater management systems, can result in adverse effects on the surrounding environment. If the discharge of domestic wastewater to land exceeds the capacity of the soil to assimilate it, then the wastewater will not be contained within the land application area (commonly referred to as “failure”) and will adversely affect the surrounding environment. Such effects may include the contamination of water, particularly given the proximity of many on-site systems to streams, to coastal water or, in some cases, to underlying aquifers. Amenity values enjoyed on neighbouring properties can also be adversely affected by the runoff of mismanaged domestic wastewater or from odour associated with the operation of the on-site system. By increasing the hydraulic load on the site soils, the discharge of domestic wastewater may result in the degradation of the soils, or may initiate instability or make existing instability worse. The Marlborough Sounds present unique constraints for the successful on-site management of domestic wastewater, including poorly drained soils, thin soils, steep slopes, unstable geology, periods of heavy rainfall and the potential for low evapo-transpiration. If the method of treating the wastewater and/ or the nature of the land application area does not take into account and reflect the site conditions, system failure, and adverse effects on the surrounding environment, are more likely. 14 - 8