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12. Criteria for selecting a wastewater servicing option

This handbook aims to provide sufficient information to enable communities and individuals to participate in making decisions about the best wastewater servicing option for their community. The options vary from a larger centralised wastewater servicing system to individual on-site wastewater systems. There are a variety of options for both the individual technological components of such systems and for the ways these different individual technologies can be fitted together to provide a total wastewater servicing system. There are also several options for the way these systems might be managed. All these factors can influence the decision on which is the best system to install.

This handbook emphasises that a wastewater servicing system can be linked to ecosystem services such as water supply, stormwater, and food and fibre production (via the nutrient cycles), as well as social and cultural services such as education and research. These factors are discussed in Section 1.

These various interrelated issues can make the process of selecting the best option very complex. To enable more holistic decision-making, and a better integration of services within these human and natural ecosystems, we have provided a framework for decision-making in this section. The basis of this framework is illustrated in Figure 12.1. From this is derived a series of criteria for evaluating the various options. The information required for these criteria has been provided in earlier sections of this handbook.

Scoping the options

Two levels of option assessment are offered to help you with your decision. Each site will have certain characteristics that will eliminate particular options.

The first level of evaluation, given in Tables 12.1 and 12.2, is an initial scoping exercise to eliminate the options that are clearly not suitable. The second level of evaluation, given in Table 12.3, provides more detailed criteria against which a reduced number of options can be assessed.

The detail of the criteria for evaluating the different options for wastewater technologies and wastewater system is extensive, complex and site-specific. As a result, it is strongly recommended that as a community you:

  • identify your own goals in relation to your need for wastewater systems
  • set your own criteria for evaluating the different wastewater system options
  • identify indicators that would enable ongoing monitoring of the chosen system.

Figure 12.1 Criteria for selecting options

Criteria for selecting optionsSee Figure 12.1 at its full size.

Table 12.1 Scoping the options: conventional systems – benefits and limitations

See Table 12.1 at its full size.

Table 12.2 Scoping the options: less common systems – benefits and limitations

See Table 12.2 at its full size.

Table 12.3 Examples of detailed criteria for assessment

Physical characteristics of the site:
  • limitation of site or area (eg, soils)
  • resilience to natural hazards.
Ecological:
  • effect on habitat
  • effect on ecosystem services
  • effect on waterways
  • effect on marine ecosystems
  • effect on overall natural systems
  • ecological restoration opportunities
  • resource efficiency – closing of ecological cycles.
Compatibility with Māori perspectives:
  • issue of passage onto land
  • protection of mauri.
Other cultural concerns:
  • sensitivity to other cultures
  • local stewardship/responsibility
  • potable re-use of treated water
  • inter-generational issues.
Public health:
  • operational safety
  • effects of failure on community health
  • residue and human proximity.
The technical system:
  • reliability
  • serviceability
  • engineering life of the system
  • resilience to acts of vandalism
  • linkages with other opportunities and services (eg, water supply).
Ability to be changed:
  • extendability
  • flexibility
  • adaptability.
Management:
  • convenience
  • operation and maintenance implications.
Economic factors:
  • capital costs
  • ongoing annual costs.
Community effects:
  • level of local control
  • need for external expertise/management.
Community change:
  • pressure for future growth
  • capacity to absorb growth
  • declining population
  • ageing population
  • visual and noise effects.
Other potential benefits:
  • leisure and recreation
  • education
  • research.
Formal processes:
  • familiarity to decision-makers
  • technical demands
  • differing demands
  • ease of the consent process.

An example of a matrix showing some of the above criteria evaluated against the broad wastewater services categories is given in Appendix 7.

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