Project Background
There are approximately 83,000 cesspools in the State of Hawaii, releasing an estimated 50 million gallons per day (mgd) of wastewater into the environment. Cesspools can negatively impact human health, drinking water sources, water bodies, plants and animals, recreation, and the economy. In 2017, Act 125 was passed by the Hawaii State Legislature, setting a deadline of January 1, 2050, for all cesspools in the State to be upgraded, converted, or connected to a sewer system. A Hawaii Cesspool Prioritization Tool (HCPT) was subsequently developed by the University of Hawaii in collaboration with the State of Hawaii Department of Health (DOH) Wastewater Branch. The tool categorizes cesspools by Priority Levels 1, 2, or 3, with Priority 1 cesspools demonstrating the greatest contamination hazard.
Homeowners generally have three options for converting cesspools:
- Connect to an existing or new centralized sewer system.
- Connect to a community-scale, cluster or decentralized wastewater system.
- Convert to a State of Hawaii DOH-approved individual wastewater system (IWS).
This study focused on the second option, with the final report providing a basis of design for the conversion of existing cesspools within the Puako community (Hawaii Island) to a new decentralized wastewater system.
Basis of Design and Proposed Project
The Puako decentralized system’s basis of design considered regulatory requirements, local design standards, wastewater flows and loads, and water quality targets. Additionally, community engagement and outreach were conducted, consisting of public meetings to gather input on preferred methods of wastewater management, reuse, disposal, environmental protection, and funding options. These results were incorporated into the basis of design.
Two collection system options were considered: 1) a combination of gravity sewers, wastewater pump stations, and force mains; and 2) a low pressure sewer (LPS) system. A collection system hydraulic model was developed based on criteria from City and County of Honolulu and industry standards. Following the evaluation of available collection, treatment and disposal technologies, a gravity or low pressure collection system and a membrane bioreactor (MBR) treatment plant combination was selected for the project.
Proposals were obtained from various vendors to assist with developing the criteria for the MBR treatment plant, which includes fine screening, anoxic and aerobic biological treatment tanks, membrane filtration, sludge handling, and disinfection. The treatment process results in a high level of oxidation and biodegradation, nutrient removal, solids removal via membrane filtration, and pathogen disinfection using ultraviolet light.
The treated effluent would meet R-1 recycled standards, as defined by DOH Hawaii Administrative Rules , allowing for approved irrigation use. An R-1 storage basin would be used for irrigation within the Puako area, such as the fuel break that runs alongside the main road as an access lane for fire suppression. A percolation pond will be used as the backup method of disposal when irrigation is not practical.
Program Plan
Finally, a program plan was developed to integrate factors that typically impact project implementation, including:
- Project ownership
- Environmental approvals and permitting
- Funding options
- Project delivery alternatives
- Schedule
Project ownership alternatives for a decentralized wastewater system included the County of Hawaii or a homeowners’ association. Individual homeowners are not capable of funding such large projects and are typically only involved with ownership at the individual wastewater system level. Legal ownership type will play a role in determining what kind of local, state, and federal funding sources may be available. Environmental and permitting approvals and project delivery type can also affect project schedules and costs.