Over many years On-Site NewZ has been aware of the problem that arises when an apparently code complying on-site wastewater system shows symptoms of poor performance and/or failure. First, the owner is likely to blame the drainlayer, who will then question the adequacy of the design and blame the designer. The owner is also likely to blame the regulatory authority (usually a regional or district council) who approved the design and installation. Manufacturers of on-site domestic wastewater treatment units can also get caught up in this “blame game” when treatment quality deteriorates and irrigation lines or soakage fields become blocked.
Designs are usually developed around a dwelling capacity translated into an occupancy level and design flow, then configured in terms of sizing and location of the wastewater treatment and land application system to fit the on-lot site and soil conditions. If the design is appropriate to capacity requirements and site and soil conditions, and its integrity is ensured by high quality installation (certified by the designer as being in compliance with the design), verified by a regulatory authority through a certificate of compliance, and supported with detailed operation and maintenance instructions, and the system still performs poorly or fails, then questions arise as to when, how and why? Has the owner, through deliberate or inadvertent omission, or neglect, or overload, or misuse, contributed wholly or in part to the poor performance or failure?
Unwittingly (or in some cases deliberately) owners can contribute significantly to system failure through changing the loading or misusing the system beyond the design and operational parameters originally set and signed off on. Examples of detrimental owner actions are:
- Extending (without permit) the size of the dwelling with extra bedrooms to accommodate an increased family or occupancy size. It may well be a “granny flat” is added to the property, or an extra family moves in.
- Converting non-bedrooms or garages to sleeping areas to accommodate temporary or permanently increased occupancy.
- Erecting buildings (outhouses) over land application systems.
- Positioning tents, caravans or other holiday accommodation over land application areas for extended occupancy periods.
- Changing dietary habits (such as taking up vegan menus).
- Using medications detrimental to treatment unit operation and land application system performance.
- Developing medical conditions requiring higher than normal water use (such as extra baths).
- Installing high water use fixtures not allowed for in design (such as garbage grinders/food waste disposal units; dishwashers; high use washing machines; fish scaling and gutting sinks; spa baths and/or pools)
- Replacing flow restrictor fixtures and installing high water use fixtures.
- Changing from rainwater supply to bore water or reticulated community water supply.
- Switching off electricity to the aerated treatment unit in order to save on power costs.
- Overlooking or ignoring operation and maintenance instructions.
- Failing to carry out recommended operation and maintenance requirements.
- Failing to renew annual maintenance contract.
Another issue is when a property is sold and the new owner is unaware that the dwelling is serviced by an on-site wastewater system, or has received no information from the previous owner re the type, capacity and maintenance requirements of the system.
To deal with the matter of owner responsibility in use of their on-site wastewater system, the concept of a “loading certificate” was introduced into New Zealand design practice some years back and has now been incorporated into the latest version of the Australia/New Zealand Standard AS/NZS 1547:2012. The purpose of the loading certificate is to set out the design and operational limits of the installed system so that the owner/occupier and users of the dwelling have a clear indication of the limits to system use, and their operational and maintenance responsibilities. The clear message is, go beyond the capacity of the system and/or neglect its maintenance, and poor performance and/or failure may result.
Where diligent adherence to the provisions of a loading certificate can be demonstrated and a system has still failed, then the owner may quite rightly look for a reason to blame someone associated with design, manufacture, installation or regulatory oversight as the main contributor(s) to the performance/failure issues.
AS/NZS 1547:2012 covers the matter of a “loading certificate” in several sections:
- definitions – loading certificate is defined on page 15 of the Standard;
- designer’s role in providing a loading certificate in the design report and operating instructions (page 27);
- property owner/occupier role in adhering to the limits of the loading certificate (page 29);
- estate agents role in passing on the loading certificate to a new owner/occupier (page 29);
- content of a loading certificate as set out in the design report (page 70); and
- inclusion of a loading certificate within the operation and maintenance instructions (page 196).
Ideally the loading certificate should be also provided as a stand-alone document displayed in a prominent place in a dwelling – one suggestion received by On-Site NewZ is that it should be produced as a laminated A4 sheet and fixed to the inside of the door of the toilet compartment at knee height!
For an extract of the provisions in AS/NZS 1547:2012 relating to loading certificate and its content, go to ”Loading Certificate in On-site Domestic Wastewater System Design” in the pages sidebar of this blog.