Environmental Impact Statement for the
Sand Island Wastewater Treatment Plant
Secondary Treatment Phase 2
Protecting human and ecological health from waterborne diseases through the development, operation and maintenance of the Sand Island Wastewater Treatment Plant
UPCOMING
Publications
REPUBLICATION - Environmental Impact Statement Preparation Notice (EISPN) Public Comment Period
What: EISPN public review and comment period
Republication Date: March 8, 2026
Comment Deadline: April 7, 2026
Submit Comments: See comment form below.
Document Link: View EISPN
Invitation Letter: View PDF
Note: The EISPN was originally published on Jan 23, 2026, however, the accompanying EISPN public scoping meeting was cancelled due to severe storm conditions. The EISPN is being republished and the public scoping meeting rescheduled to meet public notification requirements. All previously submitted EISPN comments will be addressed in the Draft EIS.
Meetings
EISPN Public Scoping Meeting
Description: In-person and virtual public meeting to obtain scoping input for the EIS process.
Date / Time: March 19, 2026 @ 6:00 p.m.
Location: Mission Memorial Building (550 South King Street, Honolulu, Hawai‘i 96813)
Virtual Participation: Access Link
Invitation Letter: View PDF
PROJECT OVERVIEW
Who
The City and County of Honolulu (CCH), Department of Environmental Services (ENV) (“Applicant”) proposes to undertake the project.
What
The Sand Island Wastewater Treatment Plant (SIWWTP) began operations in 1978 as an advanced primary treatment plant responsible for treating all wastewater flows generated in urban Honolulu, from Niu Valley in the east to Salt Lake/Āliamanu in the west. It currently has capacity to treat an average daily flow of 90 million gallons per day (mgd). Current treatment methods at the facility include screening wastewater flows into the plant, using primary clarifier tanks to separate solids from liquid streams, using chemicals to enhance primary treatment, and disinfecting flows using ultraviolet light before discharging treated liquid flows through a pipe that extends approximately 2 miles offshore.
The City is in the process of expanding and upgrading the SIWWTP to provide secondary treatment to all 90 mgd incoming average daily wastewater flows by December 2035 as required by the Clean Water Act of 1972 and Consent Decree Civil No. 94-00765DAE-KSC (“2010 Consent Decree”, Amended in 2012) between the City, Hawai‘i Department of Health, U.S. Environmental Protection Agency, and the “Intervenors” (The Sierra Club, Hawai‘i’s Thousand Friends, and Our Children’s Earth Foundation).
In compliance with the Consent Decree, the City is currently constructing Secondary Treatment Phase 1 facilities at SIWWTP, using membrane bioreactor treatment technology, to treat 20 mgd of the 90 mgd average daily flow.
The Secondary Treatment Phase 2 project that is the subject of the current EIS process will provide secondary treatment to the remaining 70 mgd average daily flows. For the Phase 2 project, the City proposes to construct new secondary treatment facilities at SIWWTP using aerobic granular sludge technology. The Phase 2 project upgrades at SIWWTP will improve water quality by further reducing contaminants in the treated wastewater flows before they are discharged to the ocean in compliance with secondary treatment requirements established by the CWA of 1972.
Where
SIWWTP is located on Sand Island in Honolulu, Island of O'ahu, Hawai'i. The SIWWTP is located on an approximately 64-acre land area identified by Tax Map Key (TMK) parcels 1-5-041: 005 and 022 (portion). For the Phase 2 project, an additional, contiguous 9.6-acre area identified by TMK parcel 1-5-041: 351 is being considered for temporary use for project construction staging and stockpiling.
Why
The purpose of the project is to:
Protect public and environmental health and safety through the development and maintenance of municipal wastewater treatment facilities;
Meet secondary treatment requirements set by the EPA under the Clean Water Act, in accordance with the 2010 Consent Decree, Amended in 2012;
Accommodate projected wastewater flows from the Sand Island Sewer Basin through 2055;
Upgrade existing process and non-process facilities to meet wastewater management needs; and
Implement certain requirements of federal and state permits and mandates.
PUBLIC PARTICIPATION
ENV invites the public to provide input on issues of concern that should be assessed in the Draft EIS being prepared for the SIWWTP Secondary Treatment Phase 2 project. The deadline for receiving comments is February 23, 2026.
EIS Process
The EIS process is governed by Hawai‘i Revised Statutes (HRS) Chapter 343 and Hawai‘i Administrative Rules (HAR) Chapter 11-200.1.
Public participation is a key part of the EIS process to identify environmental concerns and develop mitigation measures to reduce, minimize or eliminate project impacts.
Opportunities for public participation include reviewing and commenting on the EIS Preparation Notice and Draft EIS documents and participating in public meetings for the project. Additional opportunities for public participation, including public hearings, will occur during the environmental permitting process after completion of the EIS.