Under the Building Act 2004 if there is a Council reticulated sewage system adjacent or within reasonable proximity to your property, then you must connect to it. If there is no reticulated sewage, then the owner is required to provide for on-site disposal of wastewater via a Septic Tank and an effluent disposal field. Any discharge to ground is under the authority of either Otago Regional Council or Environment Canterbury. As this rule is reasonably complex, it will require the owner to engage the services of a registered Drain Layer conversant with the requirements of the regional plan, or a registered Drainage Engineer, who will conduct a full assessment of the site, the proposed dwelling, the numbers of occupants and the projected volumes of wastewater to be produced.
This qualified, registered person will provide a report and their design of the system. Depending on a number of factors, the report may achieve an acceptable solution, in which case the assessment can be processed via a Building Consent Application either separately or in conjunction with a dwelling.
If the report indicates that the proposal cannot achieve an acceptable solution, then the application for the system must be processed by Regional Council as a Land-use or Resource Consent.
Some basic rules that would determine the requirement to have the application processed by the regional council:
The discharge of wastewater from a new, modified or upgraded on-site wastewater treatment system onto or into land in circumstances where a contaminant may enter water is a permitted activity, provided the following conditions are met:
1. The discharge volume does not exceed 2 m3 per day; and
2. The discharge is onto or into a site that is equal to or greater than 4 hectares in area; and
2a. The discharge is not located within an area where residential density exceeds 1.5 dwellings per hectare and the total population is greater than 1000 persons: and
3. The discharge is not onto or into land:
a. where there is an available sewerage network; or
b. that is contaminated or potentially contaminated; or
c. that is listed as an archaeological site; or
d. in circumstances where the discharge would enter any surface waterbody; or
e. within 20 m of any surface waterbody or the Coastal Marine Area; or
f. within 50 m of a bore used for water abstraction: or
g. within a Community Drinking-water Protection Zone as set out in Schedule 1; or
h. where there is, at any time, less than 1 m of vertical separation between the discharge point and groundwater: and
4. The treatment and disposal system are designed and installed in accordance with Sections 5 and 6 of New Zealand Standard AS/NZS 1547:2012 – On-site Domestic Wastewater Management; and
5. The treatment and disposal system is operated and maintained in accordance with the system’s design specification for maintenance or, if there is no design specification for maintenance, Section 6.3 of New Zealand Standard AS/NZS 1547:2012 - On-site Domestic Wastewater Management; and
6. The discharge does not result in wastewater being visible on the ground surface; and
7. The discharge does not contain any hazardous substance.
12.A.1.4 The discharge of human sewage through any on-site wastewater treatment system, installed after 28 February 1998, onto or into land is a permitted activity, providing:
(a) The discharge does not exceed 2000 litres per day (calculated as a weekly average); and
(b) The discharge does not occur within the A zone of any Groundwater Protection Zone, as identified on the C-series maps, nor in the area of the Lake Hayes catchment, as identified on Map B6; and
(c) The system’s disposal field is sited more than 50 metres from any surface water body or mean high water springs: and
(d) The system’s disposal field is sited more than 50 metres from any bore which:
(i) Existed before the commencement of the discharge activity; and
(ii) Is used to supply water for domestic needs or drinking water for livestock; and
(e) There is no direct discharge of human sewage, or effluent derived from it, to water in any drain or water race, or to groundwater; and
(f) Effluent from the system does not run off to any other person’s property; and 12-32 Regional Plan: Water for Otago, updated to 1 September 2015 RULES: WATER TAKE, USE AND MANAGEMENT
(g) The discharge does not cause flooding of any other person’s property, erosion, land instability, sedimentation, or property damage.
Your Drainage Engineer or other suitably qualified professional will be able to advise you further.