Slug Discharge Control Plans: When Your POTW Requires One
A slug discharge control plan is the written procedure your facility submits to a Publicly Owned Treatment Works (POTW) showing how you handle the chemicals stored on site and what happens if something accidentally hits the sewer. It is almost always a condition of an industrial wastewater discharge permit, not an optional add-on. Some districts call the same document a slug discharge prevention plan or an Industrial User (IU) slug plan. The requirements are the same.
A slug discharge control plan is the written procedure your facility submits to a Publicly Owned Treatment Works (POTW) showing how you handle the chemicals stored on site and what happens if something accidentally hits the sewer. It is almost always a condition of an industrial wastewater discharge permit, not an optional add-on. Some districts call the same document a slug discharge prevention plan or an Industrial User (IU) slug plan. The requirements are the same.
Most facilities we help with a slug plan didn’t go looking for one. A notice arrived from the local sanitation district, or the permit came back with a new condition, and someone in the office had to figure out what the term meant before the deadline. That’s the reader this page is written for.
When a Slug Plan Is Required
The slug plan requirement comes from the federal pretreatment program (40 CFR Part 403), which is enforced locally by your POTW or sanitation district. Federal rules set the floor. California POTWs (San José-Santa Clara, Livermore, EBMUD, OC San, LA County Sanitation Districts, and others) decide who has to file one and what it has to look like.
The triggers we typically see:
- A wastewater discharge permit was issued or renewed. The plan is listed as a permit condition, often alongside a Toxic Organic Management Plan (TOMP). The district expects both.
- The facility was classified as a Significant Industrial User (SIU) or as a Categorical Industrial User under a federal pretreatment standard. Once a facility hits that classification, the POTW evaluates whether a slug plan is needed and often requires one as a permit condition.
- The district sent a notice. Sometimes this arrives as a standalone request after an inspection. Sometimes it follows a process change the district noticed in your last self-monitoring report.
- An operation change. New tanks, new chemicals, new processes, a building addition, or a layout change that affects floor drains. The existing plan needs to be updated.
- A startup or expansion. New facilities that will discharge process water typically file the permit, the plan, and a baseline monitoring report at the same time.
If your operation doesn’t discharge process water to the sewer at all (a truly dry machine shop, an assembly facility with only sanitary drains), a slug plan generally won’t apply. The plan attaches to facilities that have, or will have, a discharge connection to the sanitation system.
What’s Inside a Slug Discharge Control Plan
Districts vary in format, but the content the federal pretreatment program requires is consistent. The plan documents both your normal operation and what the facility will do when something goes wrong.
| Section | What it covers |
|---|---|
| Discharge practices | Routine and non-routine discharges, where they go, what’s in them, and what volumes you handle |
| Stored chemicals and tanks | Inventory of chemicals on site, tank schedule (size, contents, location), and how containers and totes are kept |
| Site mapping | Facility map showing process areas, floor drains, storm drains, tank locations, and the connection to the sewer |
| Spill prevention measures | Inspections, maintenance, handling, loading and unloading practices, employee training, secondary containment, and emergency response |
| Notification procedures | The chain you will follow if a slug discharge actually happens |
When we walk a facility for a slug plan, the first thing we look at is the gap between the chemicals listed on the Hazardous Materials Business Plan and what is physically on the floor. The second is where the drains go: which ones connect to the sanitary sewer, which connect to storm, and which (often the surprise) connect to nothing the staff can point to with certainty. Those answers shape the spill-prevention section more than anything else.
The Notification Chain
The notification procedures are the section that gets used in a real incident. If a slug discharge actually reaches the sewer, the typical sequence written into the plan is:
Immediate response.
Stop the source if it can be done safely. Call 911 if the discharge poses a risk to people, the environment, or the treatment plant.
Verbal report to the POTW within 24 hours.
Most districts require the facility to notify the agency by phone within one business day, with the time, volume, material involved, and corrective action taken.
Written follow-up within five days.
A written report covering cause, response, and steps to prevent recurrence.
Federal rules require immediate notification to the POTW for discharges that could cause problems (40 CFR 403.12(f)). The specific deadlines above are common in California POTW permits and ordinances. Some districts shorten the verbal-notification window or require specific reporting forms. The plan should reflect the version your district actually enforces, not a generic template.
Slug Plan vs. SPCC Plan
Clients regularly ask whether the SPCC plan they already have covers this. It doesn’t.
- A Spill Prevention, Control, and Countermeasure (SPCC) plan addresses oil discharges to navigable waters under 40 CFR Part 112. It is a federal EPA program, inspected in California by the local CUPA (often a fire department, county environmental health agency, or other local agency) under the Aboveground Petroleum Storage Act (APSA).
- A slug discharge control plan addresses non-oil discharges that reach the sanitary sewer system, under the local POTW’s pretreatment program.
Many facilities need both. They overlap in subject matter (storage, containment, training, response), but they are written to different agencies, under different rules, and enforced by different inspectors. Reusing SPCC text inside a slug plan without rewriting it to the POTW’s outline is one of the most common findings we see. For the SPCC side, see our SPCC plan guide.
Updating an Existing Plan
A slug plan isn’t a one-time document. The federal pretreatment program assumes the plan tracks the facility as it changes. We update existing plans when:
A process, chemical, or tank changes
A new building, process line, or floor drain layout is added
The wastewater discharge permit is renewed or modified
The district issues new pretreatment standards or a TOMP requirement
An inspection finding flags the plan as outdated
If your facility files quarterly Self-Monitoring Reports (SMRs), as Livermore and Santa Clara dischargers typically do, those reports often surface the conditions that should trigger a plan update. Our piece on self-monitoring and baseline monitoring reports for wastewater permits covers the reporting cadence and what districts look for.
For the broader picture of how the slug plan fits into the permit package itself, see our industrial wastewater discharge permit guide and the companion piece on what’s inside a wastewater discharge permit application.
How CDMS Handles the Work
We come to your facility, walk the process areas and tank locations with your operations lead, and document the discharge practices, stored chemicals, drain layout, and spill-response procedures. We then draft the plan against the format your specific district requires. San José-Santa Clara WPCP, for example, publishes its own IU Slug Plan Outline; other districts have their own variants. We update the facility diagrams as part of the deliverable, run an internal review for completeness, and submit the plan to the district per the permit conditions.
For facilities on an ongoing compliance arrangement with us, plan maintenance, quarterly SMRs where required, and updates triggered by process changes are folded into the regular scope. The plan stays current without a new project each time the facility changes.
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Trusted throughout California
BSY started working with CDMS last year after our in-house EHS person departed the company. CDMS reviewed our existing operational permits as well as any additional Federal, State and Local regulations that could apply and helped us to create a comprehensive compliance calendar to track regulatory deadlines and submittal due dates. The CDMS team does an excellent job of tracking everything and can be relied upon to complete the forms accurately and assist with submittals, allowing me to focus on our business.
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