Sewer Authority Mid-Coastside
Half Moon Bay, CA · San Mateo County · Publicly Owned Treatment Works
- Average flow
- —
- Design flow
- 4 MGD
- NPDES permit
- CA0038598
- Effective
- Permit expires
- April 2028
- Population served
- 22,558
- CWNS 2022
Sewer Authority Mid-Coastside is a publicly owned wastewater treatment works in Half Moon Bay, San Mateo County, California, serving about 22,558 residents. Treatment on site includes clarifiers, biogas silos. It discharges under NPDES permit CA0038598 (effective), which expires in April 2028, with 3 recorded violations in the last three years.
Treatment technology
Treatment structures identified at this facility. Exact unit counts are available in Klarifi.
Compliance snapshot (last 3 years)
- Total violations
- 3
- Effluent violations
- 1
Based on NPDES Discharge Monitoring Reports. Full violation history, parameters and discharge data available in the Klarifi platform.
Key contacts
Decision-makers at Sewer Authority Mid-Coastside.
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Nearby wastewater treatment plants in California
Burlingame · 9 mi away
—
Pacifica · 10 mi away
1.91 MGD
San Mateo · 11 mi away
—
San Francisco · 12 mi away
—
San Francisco · 19 mi away
45.87 MGD
Union City · 21 mi away
—
San Leandro · 22 mi away
—
Sunnyvale · 24 mi away
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Sewer Authority Mid-Coastside: frequently asked questions
Sources and methodology
Flow, permit and violation figures come from the EPA's ICIS-NPDES discharge monitoring records. Population served comes from the Clean Watersheds Needs Survey 2022. Treatment structures are identified by Klarifi's review of aerial imagery, and capital improvement projects are extracted from published municipal budget documents. Violations are counted over the last three years of monitoring reports.
Data refreshed September 11, 2026; facility record last updated May 10, 2025.