Administered by State Water Resources Control Board (SWRCB) — Wastewater Operator Certification Program (WWOCP)
The Grade I exam runs 2 h 30 min with 80 items worth 135 points, and passing needs both 70% overall and at least half of the math points.
The certificate for operating a wastewater treatment plant in California, issued through the State Water Resources Control Board's Wastewater Operator Certification Program.
Equivalents and Formulas Sheet, Version 1 (opens in a new tab)State Water Resources Control Board, Wastewater Operator Certification Program · The program has announced that exams will include both sheets.
Equivalents and Formulas Sheet, Version 2 (opens in a new tab)State Water Resources Control Board, Wastewater Operator Certification Program · The program has announced that exams will include both sheets.
Grade I eligibility
Education and experience paths to Grade I
Education
Qualifying experience
High school diploma or equivalent + 6 educational points
1 year qualifying experience
The exam is taken before applying for certification; an operator-in-training (OIT) certificate lets a passer accrue the qualifying experience.
Experience is full-time qualifying experience (1,800 hours equals one year for operators-in-training).
Examination results are valid for four years from the date on the pass letter.
Subjects at Grade I: safety, sampling and simple analysis, preliminary and primary treatment, anaerobic digestion, disinfection, stabilization ponds, plant classification and operator certification rules.
Math topics at Grade I: chlorine demand and residual, overflow rate, removal efficiency, pumping rate, solids concentration, detention time, hydraulic and organic loading, volume and area.
How the Grade I exam is built
Item type
Count and points
true/false
45 items at 1 point each
multiple choice
25 items at 2 points each
math
10 items at 4 points each
Grade I exam format
Items: 80, worth 135 points
Time allowed: 2 h 30 min
Pass score: 94.5 points (70%) and at least 20 of 40 math points
Computer-based at Prometric centers year-round since February 2021; wastewater applications carry a 60-day filing period before the earliest test date.
Math: removal efficiency · an original practice item written only from publicly available sources, not a real exam question
Primary clarifier influent carries 220 mg/L of total suspended solids (TSS) and the effluent carries 121 mg/L. What is the removal efficiency?
45%
55%
82%
99%
Answer and working
A. 45%
Removal efficiency = (in − out) ÷ in × 100 = (220 − 121) ÷ 220 × 100 = 45%. 55% is the fraction remaining (121 ÷ 220); 82% divides the removal by the effluent (99 ÷ 121); 99 is the mg/L removed, not a percentage.
Grade I questions answered
How is the Grade I wastewater exam structured?
80 items worth 135 points in 2 h 30 min: true/false, 45 items at 1 point each; multiple choice, 25 items at 2 points each; math, 10 items at 4 points each. Passing takes 94.5 points (70%) and at least 20 of 40 math points.
What education and experience does Grade I require?
High school diploma or equivalent + 6 educational points, with 1 year qualifying experience. The exam is taken before applying for certification; an operator-in-training (OIT) certificate lets a passer accrue the qualifying experience.
What is the recent Grade I pass rate?
60%: 214 of 355 examinees passed from July 1, 2025 to June 30, 2026, summed from the agency's two half-year results tables.
What this exam covers
Preliminary & Primary
Activated Sludge
Secondary Clarification
Nutrient Removal
Disinfection
Biosolids & Digestion
Regulations & Effluent
Lab & Process Control
Operations & Safety
How to study for it here
Practice quizzes — filter to any topic above and work through it with explanations.
Flashcards — spaced repetition over terms, formulas and regulations.
Mock exam — a timed run at this grade, scored by points with the separate math minimum, as on the real exam.
Official formula sheet — a link to the sheet the certifying body publishes for this exam, where it publishes one, so you study from the real thing.
Free, no account, and progress stays in your browser.
Topic coverage follows WWTP Operator Examination Information (SWRCB Wastewater Operator Certification Program — per-grade documents).
Practice questions are written only from publicly available sources
(that outline and the regulations and references it cites); they are
not real exam questions, which are confidential.
Check current application requirements, fees and exam dates on the
certifying body's own page: official certification page.
Questions, flashcards, and explanations are AI-written from publicly available sources only: the exam content outlines and candidate materials each certifying body publishes without restriction, and the regulations and technical references they cite. No confidential material is used, including actual exam questions, recollections of any exam sat by the author, or any handbook or document released under a confidentiality agreement. Content is then put through repeated review — regulatory values checked against primary sources, every calculation recomputed, and errors corrected — plus spot checks by the author, who holds California water operator certifications and a California civil engineering licence. Those spot checks are sampling, not a professional review: nothing here is stamped, sealed, or offered as engineering advice, and not every item has been individually verified, so mistakes can still slip through.