ONWASA WASTEWATER CAPACITY FILE · UPDATED OCTOBER 19, 2026
A 2020 capacity warning and the record of later projects
What ONWASA’s engineering consultant projected for the Holly Ridge and Summerhouse wastewater systems, what the report does not establish, and what residents still need to know.
ORIGINAL HUBERT UNITED ANALYSIS
Original Hubert United analysis of the ONWASA capacity study
This page is Hubert United’s original plain-language review and analysis of ONWASA’s 2020 Holly Ridge–Summerhouse wastewater-capacity study. The engineering study itself remains an ONWASA and third-party source document; Hubert United does not claim ownership of that underlying record.
Please cite and link directly to this page when referencing Hubert United’s explanation, analysis, follow-up questions, or organization of the source material.
Original source: Hubert United
First published: September 8, 2026
Page attribution updated: September 21, 2026
Canonical source: Open this original Hubert United source page
Cite this analysis
Suggested citation: Hubert United, “ONWASA Holly Ridge–Summerhouse Wastewater Capacity Study,” HubertUnitedNC.org, direct source link.
2025 PERFORMANCE UPDATE
The projected strain was not hypothetical
ONWASA’s 2025 report says Summerhouse treated no wastewater during the year while Holly Ridge averaged 104% of its permitted disposal capacity and recorded repeated flow and spray-field violations. Hubert United has published the source report and a separate analysis.
The finding in plain language
ONWASA’s engineers projected that the Holly Ridge and Summerhouse systems would exceed their then-functional combined wastewater-disposal capacity by 2023 and advised beginning design work in 2020–21.
The question now is not whether ONWASA received a warning. The report documents that warning. The unresolved question is what ONWASA did afterward, which improvements were completed, and what the systems can safely and legally handle today.
What the January 2020 report documented
- Holly Ridge WWTP: 0.260 million gallons per day of treatment capacity, but only 0.224 MGD of effluent-disposal capacity.
- Summerhouse WWTP: 0.400 MGD of treatment capacity and 0.341 MGD of permitted disposal capacity, but only 0.132 MGD of actual disposal capacity because one infiltration basin was inoperable.
- The systems’ then-functional combined capacity was therefore 0.356 MGD.
- Existing wastewater generation was approximately 0.231 MGD in Holly Ridge and 0.035 MGD in Summerhouse.
- Holly Ridge flows could exceed its disposal capacity, requiring wastewater to be diverted to Summerhouse.
- The Summerhouse collection system showed excessive inflow and infiltration.
- The combined 0.356-MGD functional capacity was projected to be exceeded by 2023 under the existing-service-area scenario.
- If Summerhouse reached full capacity, combined capacity could serve the existing area to approximately 2038, but the expanded-service scenario reached the combined limit around 2028.
- Expanded-area flow was projected to reach approximately 0.950 MGD—about 1.4 times the plants’ maximum combined capacity.
- The consultant warned that an alternative would require at least two to three years and recommended starting design in 2020–21.
The alternatives and Board direction
The report evaluated continued use or replacement of the ONWASA plants, rehabilitation of Summerhouse, construction of new ONWASA treatment facilities, and sending some or all wastewater to Pluris. At its December 12, 2019 meeting, the ONWASA Board selected Alternatives 3, 4 and 5 for additional engineering and financial evaluation:
- Continue Summerhouse, build a new Holly Ridge treatment facility and convert irrigation fields to infiltration basins.
- Build one new ONWASA facility and retire the Summerhouse and Holly Ridge plants.
- Retire both ONWASA plants and send all wastewater to a new Pluris facility.
This report did not select the final alternative or document completed construction. It states that refinement, financial analysis and a later Board decision would occur through separate follow-up work.
SERVICE-AREA CORRECTION · OCTOBER 19, 2026
Separate projects serve different wastewater areas
ONWASA lists the Southeast Service Area Wastewater Capacity Improvements for the Holly Ridge–Summerhouse connection to the Southeast Regional facility: approximately $17.2 million, including a $10 million state grant, with contracts awarded March 20, 2025 and projected completion by the end of 2027. It separately lists Summerhouse interim improvements.
The $27.7 million Highway 24 corridor project serves the Northeast area and the Swansboro connection toward Camp Lejeune. It should not have been presented here as the answer to the Holly Ridge–Summerhouse study. ONWASA’s page still projects fall 2026 completion for that corridor. Published schedules do not establish commissioning or spare capacity.
Read ONWASA’s separate project descriptions. Project descriptions checked October 19; the capacity analysis elsewhere on this page retains its January 2020 source period.
What remains unanswered
- Which Southeast-area improvements are commissioned, accepted and legally available, and what capacity has been added?
- What are the affected facilities’ present permitted, functional, average and peak capacities and flows?
- How much capacity is already committed through will-serve letters or approved developments but is not yet flowing?
- What collection-system or pump-station bottlenecks remain after the Southeast improvements are operational?
- What receiving-plant, disposal and allocation limits govern the Southeast service area?
- What are the final project cost, change orders, debt-service obligations and rate impacts?
- Which developments or service-area expansions depend on the Southeast improvements becoming operational?
Scope and limitation
This report concerns the Holly Ridge and Summerhouse wastewater systems. It does not directly measure the Queens Creek Elementary campus, establish that the Hubert school’s utilities are overloaded, or describe present-day system conditions. Its importance is broader: it shows why residential growth, wastewater capacity, water capacity and school capacity must be evaluated from coordinated and current data rather than in separate planning silos.
Primary source: The Wooten Company, Capacity Evaluation Study: Holly Ridge and Summerhouse Wastewater Treatment Plants, Final, January 2020. Prepared for the Onslow Water and Sewer Authority. The report was supplied to Hubert United and is preserved in the ONWASA public-records archive.