California WWTP Classification, CPO & DOIC Requirements

California classifies wastewater treatment plants from Class I through Class V. Plant classification is separate from an individual operator's certification grade, although the two are connected through staffing requirements for the Chief Plant Operator and Designated Operator-in-Charge.

For exam preparation, this distinction is critical: a Class III wastewater treatment plant is a facility classification, while a Grade III operator certificate is an individual operator qualification.

Who Classifies California Wastewater Treatment Plants?

The California State Water Resources Control Board Wastewater Operator Certification Program, or WWOCP, is responsible for classifying wastewater treatment plants that fall within the program's statutory authority.

Plant owners do not assign their own official classification, and a Regional Water Quality Control Board does not independently substitute its own plant classification for the WWOCP classification.

Five WWTP Classification Levels

California uses five wastewater treatment plant classification levels:

• Class I;
• Class II;
• Class III;
• Class IV;
• Class V.

Classification reflects the treatment processes used and the amount of wastewater the plant is designed to treat under the WWOCP classification framework.

Plant Classification and Operator Grade Are Different

The terms Class I through Class V refer to the wastewater treatment plant.

The terms Grade I through Grade V refer to an individual wastewater operator certificate.

These terms are related but not interchangeable.

Chief Plant Operator

The Chief Plant Operator, commonly called the CPO, is responsible for the overall operation of the wastewater treatment plant.

The CPO also has responsibility for ensuring that plant operations comply with applicable waste discharge requirements and for carrying out important supervisory duties required by the operator-certification program.

CPO Minimum Certification Grade

The CPO must hold a valid wastewater operator certificate at a grade equal to or higher than the classification of the wastewater treatment plant.

The minimum CPO relationship is:

• Class I WWTP - minimum CPO Grade I;
• Class II WWTP - minimum CPO Grade II;
• Class III WWTP - minimum CPO Grade III;
• Class IV WWTP - minimum CPO Grade IV;
• Class V WWTP - minimum CPO Grade V.

Designated Operator-in-Charge

The Designated Operator-in-Charge, commonly called the DOIC, is a certified operator appointed by the CPO to be responsible for the overall operation of the wastewater treatment plant when the CPO is unable to carry out the responsibilities of the position.

The DOIC reports directly to the CPO.

DOIC Minimum Certification Grade

The minimum DOIC certification grade depends on plant classification.

• Class I WWTP - minimum DOIC Grade I;
• Class II WWTP - minimum DOIC Grade I;
• Class III WWTP - minimum DOIC Grade II;
• Class IV WWTP - minimum DOIC Grade III;
• Class V WWTP - minimum DOIC Grade III.

CPO and DOIC Table

• Class I: CPO Grade I minimum; DOIC Grade I minimum.
• Class II: CPO Grade II minimum; DOIC Grade I minimum.
• Class III: CPO Grade III minimum; DOIC Grade II minimum.
• Class IV: CPO Grade IV minimum; DOIC Grade III minimum.
• Class V: CPO Grade V minimum; DOIC Grade III minimum.

The DOIC Does Not Always Match the Plant Class

A common exam trap is assuming that the DOIC must always hold a certificate equal to the plant classification.

That is not correct under the current California table. For example:

• a Class II plant requires at least a Grade II CPO but only a Grade I DOIC;
• a Class III plant requires at least a Grade III CPO but only a Grade II DOIC;
• a Class V plant requires at least a Grade V CPO but only a Grade III DOIC.

Classification Submittal Before Operation

The owner, or the CPO acting on behalf of the owner, must submit wastewater treatment plant classification information before the plant begins operation.

Current WWOCP guidance requires the classification form to be submitted at least 60 days before the plant begins operations.

Reporting Changes to the Plant

Changes to a wastewater treatment plant can affect its classification information.

Current WWOCP guidance requires classification information to be submitted within 30 days of changes to the plant, including closure.

Information Submitted for Classification

The classification package includes supporting information that helps WWOCP understand the facility and its staffing structure.

Current WWOCP guidance identifies materials such as:

• the wastewater plant classification form;
• an organization chart;
• a plant flow diagram;
• job descriptions for personnel classifications;
• duty rosters.

WWOCP Assigns the Classification

After reviewing the submitted information, WWOCP determines the plant classification and communicates the classification and applicable operator-grade requirements.

A utility should therefore not assume that a planned or historical classification remains correct after major treatment-process or plant changes.

Number of Operators Versus Minimum Grades

WWOCP specifies minimum certification grade relationships for the CPO and DOIC, but current WWOCP classification guidance states that it does not specify the number of operators that must be employed at each grade.

This is another important exam distinction:

• minimum certification grade is specified for CPO and DOIC roles;
• the classification table does not by itself establish a fixed number of operators at each grade.

Why Plant Classification Matters

Plant classification affects the minimum certification grade required for key operator roles.

It also provides a structured way to relate plant complexity and design characteristics to operator qualifications.

Treatment Processes and Classification

California classification criteria consider treatment processes and design treatment capacity.

Depending on the class, treatment processes can include combinations of:

• primary treatment;
• treatment ponds;
• biofiltration;
• activated sludge;
• sequencing batch reactors;
• tertiary treatment.

Operators should use the official WWOCP classification determination rather than try to assign a class based only on one process name.

Water Recycling Treatment Plants

Current WWOCP materials state that water recycling treatment plants are wastewater treatment plants for purposes of the operator-certification program.

This is important because recycled-water treatment can still fall within WWTP classification and operator-certification requirements.

Class I Exemption

California provides a possible exemption pathway for certain Class I wastewater treatment plants.

Current WWOCP guidance states that an owner of a Class I plant may apply for an exemption if the plant has been classified as Class I and the plant could not, due to operator error, violate water quality objectives.

An exemption is not automatic merely because a plant is Class I.

CPO Supervisory Responsibilities

The CPO has broader responsibilities than simply holding the correct certificate grade.

Current WWOCP materials describe the CPO as responsible for overall plant operation, regulatory compliance, and supervision of operator activities required by the certification program.

OIT Supervision

The CPO has responsibilities related to Operators-in-Training, including appropriate supervision and documentation of qualifying wastewater operating experience.

This connects plant staffing requirements with the operator-certification pathway.

When the CPO Is Unavailable

The DOIC role exists to provide qualified responsibility for overall plant operation when the CPO cannot carry out the position's responsibilities.

The DOIC is therefore not simply another shift operator title. It is a designated responsibility with a minimum certification-grade requirement based on plant class.

Valid Certificates Are Required

CPO and DOIC grade requirements refer to valid operator certificates.

An expired certificate should not be treated as satisfying the required minimum operator grade.

Higher Grades Can Satisfy a Minimum

A minimum grade means that an equal or higher valid certificate can satisfy the grade requirement.

For example, a Grade IV operator can satisfy a minimum Grade III requirement, assuming all other applicable requirements are met.

Example: Class II Plant

A Class II wastewater treatment plant requires:

• a CPO with at least a Grade II certificate;
• a DOIC with at least a Grade I certificate.

A Grade I operator cannot serve as the CPO solely on the basis of holding a valid Grade I certificate because the plant requires a minimum Grade II CPO.

Example: Class IV Plant

A Class IV wastewater treatment plant requires:

• a CPO with at least a Grade IV certificate;
• a DOIC with at least a Grade III certificate.

The DOIC is not required by the classification table to hold Grade IV merely because the plant is Class IV.

Example: Class V Plant

A Class V wastewater treatment plant requires:

• a CPO with at least a Grade V certificate;
• a DOIC with at least a Grade III certificate.

This difference between the CPO and DOIC minimum grade is especially important to remember.

Classification Changes

A plant modification can change treatment processes, capacity, or other classification-relevant information.

The owner or CPO should not wait until the next certification cycle to address a plant-classification change. Current WWOCP reporting requirements apply when classification-relevant plant changes occur.

Facility Records

Utilities should maintain clear records related to plant classification and operator staffing.

Useful records can include:

• WWOCP classification correspondence;
• current organization chart;
• operator certificates;
• CPO designation;
• DOIC designation;
• duty rosters;
• job descriptions;
• plant process and flow diagrams.

Common Exam Mistakes

• Confusing plant Class with operator Grade.
• Assuming the utility assigns its own official WWTP classification.
• Assuming the DOIC minimum grade always equals the plant class.
• Assuming a Class V plant requires a Grade V DOIC.
• Assuming WWOCP specifies an exact number of operators at every grade through the classification table.
• Ignoring the 60-day pre-operation classification submittal requirement.
• Ignoring the 30-day reporting requirement for plant changes.
• Assuming a Class I exemption is automatic.
• Assuming an expired certificate satisfies a CPO or DOIC minimum-grade requirement.

A Practical Classification Review

1. Confirm the official WWOCP wastewater treatment plant classification.
2. Confirm the minimum CPO grade for that plant class.
3. Confirm the minimum DOIC grade for that plant class.
4. Verify that the designated operators hold current valid certificates.
5. Maintain current classification records and staffing documentation.
6. Submit required classification information before a new plant begins operation.
7. Report classification-relevant plant changes within the required period.
8. Reevaluate staffing implications when plant classification changes.

What to Remember for the Exam

• California WWOCP classifies wastewater treatment plants from Class I through Class V.
• Plant Class and operator Grade are different concepts.
• The CPO is responsible for the overall operation of the wastewater treatment plant.
• The CPO must hold a valid certificate at a grade equal to or higher than the plant classification.
• The DOIC is appointed to assume overall plant responsibility when the CPO cannot carry out the position's responsibilities.
• Minimum DOIC grades are I, I, II, III, and III for Classes I through V respectively.
• A Class II plant requires at least a Grade II CPO and Grade I DOIC.
• A Class III plant requires at least a Grade III CPO and Grade II DOIC.
• A Class IV plant requires at least a Grade IV CPO and Grade III DOIC.
• A Class V plant requires at least a Grade V CPO and Grade III DOIC.
• Current WWOCP guidance requires classification information at least 60 days before a plant begins operation.
• Current WWOCP guidance requires classification information within 30 days of plant changes, including closure.
• WWOCP determines the official classification after reviewing submitted facility information.
• The classification table establishes minimum CPO and DOIC grades but does not itself specify a fixed number of operators at each grade.
• A Class I plant exemption is not automatic and requires meeting the applicable exemption conditions.