“RISK-BASED SELECTION OF ONSITE TREATMENT TECHNOLOGIES FOR PACIFIC ISLAND ENVIRONMENTS”

Pacific Islands range from low-lying atolls (Kiribati and Majuro) to limestone plateaus (Tonga and Niue) to high volcanic islands (American Samoa and PNG). Wastewater treatment in these Pacific Islands is provided primarily by individual onsite systems. Because of limited land area for housing, less than ideal soil and site conditions, restricted availability of construction materials and equipment, low household incomes, and cultural traditions, strict enforcement of onsite treatment rules are not always practical. With few practical options available for use where traditional systems are inappropriate and because the ability to prohibit unsewered development is limited, local authorities must strive to ensure that systems installed present the lowest risk under the given site conditions. However, common guidance for the siting, design, and construction of onsite treatment systems is not helpful in assessing the risks that are associated with different courses of action. Local authorities need to be able to assess the relative risks of different system technologies and designs so that the best management practices are used for the given site characteristics.An onsite wastewater treatment manual is under development for American Samoa that includes a decision process to select the lowest relative risk method of treatment for particular site conditions. This approach acknowledges that all systems constructed will not present the same risk to public health and the environment; but under the conditions they are implemented, each system presents the lowest risk relative to the options available.This decision method establishes a hierarchical ranking of treatment technologies and household plumbing options. Within each of these categories, specific technologies or practices are ranked according to their relative risks. Plumbing options are ranked as well, from conventional plumbing to segregated wastes to severe water conservation. The selection process is modified by availability of construction materials and equipment, and affordability. By using this decision process, remaining risks are better understood, and they may be dealt with using other control measures.