California Industrial Discharge Permits: What the Sewer Connection Process Really Looks Like

Who issues an industrial discharge permit in California?

Usually the agency that owns the treatment plant. Federal pretreatment rules call it the control authority. Under 40 CFR 403.3, that is the publicly owned treatment works (POTW) when its pretreatment program has been approved, and the approval authority when it has not.

California took over the national pretreatment program from EPA under a memorandum of agreement dated September 22, 1989. The State Water Board's pretreatment program SOP says so, and names the Regional Water Board as the approval authority that reviews and approves POTW programs.

In practice, your permit, your local limits and your reporting dates come from the sewer use ordinance of the city or sanitation district that treats your water. That may not be the city whose pipe you tie into.

Why doesn't a finished sewer connection mean you can discharge?

Because the two approvals answer different questions. The connection asks whether your lateral is sized right, the fees are paid and the inspections passed. That is a construction milestone, and most developers know it well.

The discharge authorization asks whether what you will actually put in the sewer, at your real flow and pollutant load, is something the treatment plant can take. A facility can pass every connection inspection and still have no authority to discharge process wastewater.

What does the process look like from first call to first discharge?

It is a sequence, and most steps can run alongside design and construction. A typical path for a new industrial user looks like this:

1. Confirm which agency treats your wastewater, and get its sewer use ordinance, local limits and application forms.
2. File the industrial user questionnaire or permit application: processes, chemicals, expected flows and wastewater character.
3. The control authority classifies the facility: significant industrial user (SIU), categorical user, or a smaller user under local rules.
4. Characterize the expected discharge against every standard that applies.
5. Design and install pretreatment where the characterization says you need it.
6. For a new categorical source, file the baseline monitoring report at least 90 days before discharge. Our post on the 90-day rule for California industrial discharge walks through those dates.
7. Receive the permit or control mechanism, then start discharging and start reporting.

Each POTW orders and names these steps its own way. The list is the shape, not the form set.

What makes a facility a significant industrial user?

A categorical standard, a flow or capacity threshold, or the control authority's judgment. Under 40 CFR 403.3(v), an SIU is any user subject to a federal categorical pretreatment standard, plus any other user that:

• discharges an average of 25,000 gallons per day or more of process wastewater, not counting sanitary, noncontact cooling and boiler blowdown wastewater;
• contributes a process stream that makes up 5 percent or more of the plant's average dry weather hydraulic or organic capacity; or
• is designated by the control authority as having a reasonable potential to upset the plant or violate a standard.

The same section lets the control authority treat a very small categorical user, one that never discharges more than 100 gallons per day of categorical wastewater and meets other conditions, as non-significant. You do not pick your own classification. Ask early, in writing, because it drives everything after it.

What do local limits check, and why can't you borrow another city's?

Local limits are set for one plant, so they only fit that plant. A POTW develops them to protect its treatment process, its workers and collection system, its sludge quality and its own discharge permit. They depend on that plant's capacity, its existing industrial users and its receiving water.

A limit that worked for a similar plant in another California city tells you little. Get the actual numbers for your POTW, compare your expected discharge to them, and only then decide whether you need treatment. If the discharge exceeds a limit untreated, it cannot be authorized as proposed, however far along construction is.

When is pretreatment required, and when must it be running?

It is required when your untreated discharge fails a standard, and it has to work before you discharge. Pretreatment ranges from a grease interceptor at a food operation to a full treatment train for metals or high-strength process water. The design follows from your characterization, not from your industry label.

For a new categorical source, 40 CFR 403.6(b) requires the equipment to be installed and started up before discharge begins. For other users the permit sets the terms. Either way, pretreatment is not something you bolt on after production starts. If you need it and do not have it, the process water has nowhere lawful to go while equipment is bought and built. Sizing is its own topic; our post on pretreatment equipment sizing against local limits covers the method.

What keeps going after the permit is issued?

The permit is the start of a reporting life, not the end of a project. Under 40 CFR 403.8, an SIU's permit or equivalent control mechanism runs no more than five years, and the POTW must evaluate within a year of designation whether the SIU needs a slug discharge control plan.

The reporting rules in 40 CFR 403.12 add more. A non-categorical SIU reports at least every six months. A categorical user reports each June and December unless the control authority sets other months. Any user must give notice before a substantial change in the volume or character of its discharge.

That last one catches facilities that add a product line years later. Build the sampling and reporting duties into operations, with a named owner, before the first sample is due.

Limits of this article: it covers the federal pretreatment framework and how California oversees it, as of October 2026. Your POTW's ordinance can be stricter, and its forms, fees and review times vary. Confirm the requirements with your control authority before you set a production date.

Frequently asked questions

Does connecting to a California sewer authorize industrial discharge?

No. The physical connection and the discharge authorization are separate approvals. Process wastewater needs review under the POTW's pretreatment program, and an SIU needs an individual permit or equivalent control mechanism, before it discharges.

Who sets the local limits my facility must meet?

The POTW that treats your wastewater, through its sewer use ordinance and approved pretreatment program. In California, the Regional Water Board approves and oversees those programs.

I manage a food processing plant expansion in California, and our city's sewer flows to a regional sanitation district. Who issues our discharge permit?

Usually the agency whose pretreatment program covers the treatment plant, but agreements between cities and districts vary. Ask both agencies who your control authority is, which ordinance applies and which forms to file, and get the answer in writing before design is final.

I'm developing a spec industrial building in California with no tenant yet. Can I get the discharge permit before we know what the tenant will make?

Generally not, because the permit is written for a specific user and a specific discharge. What you can do is plan for it: a lateral with room for growth, space and access for a future pretreatment system and a sampling point, and a clear note to tenants that they must apply before they discharge process water.

Can production start before the discharge permit is issued?

Not if production creates process wastewater that needs authorization to go to the sewer. Without it, that water has no lawful path to the POTW, so the permit has to be in hand before the production date.

Related resources

• Local Sewer Connection vs. State Permit: When a California SIU Permit Is the Faster Path
• Significant Industrial User Designation: How a Texas Facility Gets Classified and What Changes
• Slug Discharge Control Plans: What Texas Industrial Users Must Have on File
• Wastewater engineering in California

Planning an industrial sewer discharge in California?

We help facilities line up the POTW review, the pretreatment design and the construction schedule so the discharge permit is ready when production is. Tell us about your facility.

We specialize in:

• Industrial wastewater and pretreatment system design
• Wastewater characterization and POTW permit applications
• Sewer connection and utility design
• Site civil engineering for industrial development
• Wastewater engineering in California and eight other states
• Construction administration

Modern Engineering Solutions, McKinney, Texas. Contact: (214) 833-6748 or mod-eng.com