Sunnyside STP
1338 S 4th St, Sunnyside, WA 98944 · Yakima County · Publicly Owned Treatment Works
- Average flow
- 1.34 MGD
- Design flow
- 22.4 MGD
- NPDES permit
- WA0020991
- Administratively continued
- Permit expires
- January 2020
- Population served
- 18,327
- CWNS 2022
Sunnyside STP is a publicly owned wastewater treatment works in Sunnyside, Yakima County, Washington treating an average of 1.34 million gallons per day against a permitted design capacity of 22.4 MGD, serving about 18,327 residents. It discharges under NPDES permit WA0020991 (administratively continued), which expires in January 2020, with 1 recorded violation in the last three years.
Treatment technology
3 treatment structures and unit processes identified at Sunnyside STP.
Available with a free Klarifi account
See the full treatment train at Sunnyside STP: structures, unit processes and planned upgrades, with exact unit counts.
Compliance snapshot (last 3 years)
- Total violations
- 1
- Effluent violations
- 1
Based on NPDES Discharge Monitoring Reports. Full violation history, parameters and discharge data available in the Klarifi platform.
Key contacts
2 verified contacts for Sunnyside STP, with validated emails and direct phone numbers.
Unlock 2 verified contacts
Names, validated emails and direct phone numbers for decision-makers at Sunnyside STP, plus the full compliance history and discharge data.
Nearby wastewater treatment plants in Washington
Sunnyside · 1 mi away
1.64 MGD
Mabton · 6 mi away
0.15 MGD
Grandview · 9 mi away
0.93 MGD
Granger · 9 mi away
0.17 MGD
Zillah · 13 mi away
0.2 MGD
Toppenish · 13 mi away
0.66 MGD
Prosser · 14 mi away
0.74 MGD
Toppenish · 16 mi away
0.09 MGD
Sunnyside STP: 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 October 26, 2026; facility record last updated April 24, 2025.
Wastewater terms: POTW · MGD · NPDES permit · Inflow and infiltration · Significant industrial user · WWTP · all terms