SPECIAL REPORT SR-2022-02
2021 Hawai‘i Cesspool Hazard Assessment & Prioritization Tool
202l Report & Technical Appendices
Michael Mezzacapo
August 2021, 97 pp.
Prepared For:
State of Hawai‘i Department of Health Wastewater Branch
State of Hawai‘i Cesspool Conversion Working Group
ABSTRACT
Cesspools are a substandard sewage disposal method and widely recognized to harm human health and the environment. The state of Hawai‘i has an estimated 82,000 cesspools. To address pollution concerns, the Hawai‘i State Legislature mandated replacement of all cesspools by 2050. A major step in achieving this goal is to categorize cesspools based on potential or realized harm to humans and the environment. This report details a comprehensive tool designed for this purpose. After researching similar efforts, methods and datasets were chosen that met the needs of state government, cultural values, and environmental sensitivities. The Hawai‘i Cesspool Prioritization Tool (HCPT) was developed by integrating fifteen risk-factors that either control or relate to how cesspool impacts are distributed across communities and the environment. These factors were processed with a geospatial model to calculate a single prioritization score for every cesspool in Hawai‘i. Because sewage pollution impacts are cumulative, individual scores were consolidated by census boundary areas. Results from the HCPT prioritization were validated through comparison with a statewide assessment of nearshore wastewater impacts funded by Hawai‘i Act 132. Future data, organized within census area frameworks, can be layered onto the results to address equity and outreach challenges.
The HCPT was designed to be as objective as possible with prioritization based solely on the relationships between datasets, thereby reducing human bias as much as possible. All data used in the HCPT is at the statewide scale, normalized, and based on regulatory rules or modeling outputs. The total number of cesspools in the state categorized as Priority Level 1 was 13,885, with 13,482 and 54,058 as Priority Level 2 and Priority Level 3, respectively. Approximately 35%, 7%, 21%, and 37% of cesspools in the Priority Level 1 group are located on O‘ahu, Maui, Kaua‘i, and Hawai‘i Island respectively.