Officials review secondary treatment at Sand Island, EPA rules and health data

City officials and council members discussed secondary wastewater treatment, regulatory requirements and scientific monitoring for the Sand Island Treatment Plant during the Committee on Executive Management meeting May 28.

Roger Babcock, director of the Department of Environmental Services (ENV), explained the federal framework that sets minimum wastewater treatment standards under the Clean Water Act and described why secondary treatment is prescribed to remove suspended solids and biochemical oxygen demand (BOD). "Secondary treatment requires 85% removal" of BOD compared with lower removal at primary treatment, Babcock said, adding that requirements can vary by discharge location and sensitivity.

Council members and ENV staff reviewed the current status of Sand Island: the plant historically operated under primary treatment for much of its capacity, and a phased upgrade to secondary treatment is underway. Babcock said Phase 1 is about 80% complete and will bring roughly 20 million gallons per day of a 90 million gallon per day capacity onto secondary treatment when finished (projected by end of next year). He described monitoring programs conducted under past waivers and referenced the Mamala Bay study and ongoing ocean monitoring that inform permit and rulemaking decisions.

Why secondary treatment matters

Babcock described the technical reasons for secondary treatment: suspended solids can settle and degrade receiving waters and BOD reflects organic material that reduces dissolved oxygen when consumed by bacteria, which can harm aquatic life. He said pH requirements (typically between 6 and 9) are also federal standards. The Clean Water Act and the federal rulemaking process establish these minimum standards through risk, economic and public‑comment analysis.

Questions, data and alternatives

Council members pressed for health-impact data tied to Sand Island's current level of treatment. When asked whether there have been health cases directly linked to not having secondary treatment at Sand Island, Babcock said, "No. Not that I know of." He noted that the city conducts ocean monitoring around outfalls as part of past waiver agreements and that modeling and monitoring studies — including a 1996 Mamala Bay study — have informed past decisions such as installing UV disinfection at Sand Island to reduce the chance of treated effluent reaching recreational areas under some conditions.

Members also discussed alternative technical approaches that have been proposed in prior reviews and the Environmental Impact Statement (EIS) process. The chair referenced proposals to retrofit existing primary clarifiers to trickling filters and to extend outfall locations farther offshore as potential alternatives explored in past planning documents. Committee members raised concerns about greenhouse gas implications: the EIS (2019 RMTAL EIS) and subsequent discussion include estimates of carbon emissions associated with various upgrade options, and one slide cited that membrane bioreactor technology could increase CO2 emissions substantially compared with current operations.

Process and next steps

Babcock said federal standards and rulemaking are national processes that incorporate scientific study, economic analysis and public comment, and that the city has been working within that regulatory framework while completing upgrades at Sand Island. The committee did not adopt any policy change regarding secondary treatment at the May 28 meeting; council members requested additional information and peer‑reviewed studies and flagged the need to ground future discussions in the available monitoring data and health analyses.