Slug Discharge Control Plans: What Texas Industrial Users Must Have on File

What counts as a slug discharge?

Anything non-routine and episodic that could hurt the plant. The federal rule defines a slug discharge as a discharge of a non-routine, episodic nature, such as an accidental spill or a non-customary batch discharge, with a reasonable potential to cause interference or pass through, or to violate the POTW's rules, local limits or permit conditions.

Your permit is written around a normal operating day. A tank cleanout drained at once, a caustic batch dumped instead of metered, a spill reaching a floor drain, or a production upset is not a normal day. A biological plant cannot absorb those spikes well.

Who decides whether my facility needs a plan?

The control authority, which is usually the city that owns the treatment plant. In Texas, cities with approved pretreatment programs make this call and write the result into your industrial user permit. TCEQ approves and audits those local programs, but you will deal with the city's pretreatment staff day to day.

The evaluation applies to significant industrial users. Our post on how a Texas facility gets classified as an SIU explains who that is. The rule requires the evaluation at least once, within one year of designation. The city may also reevaluate later.

The plan is not automatic. The rule says the plan's minimum contents apply if the POTW decides a plan is needed. Many SIUs with chemical storage or batch processes get one.

What must the plan contain?

Four elements at a minimum. Section 403.8(f)(2)(vi) lists them:

1. Discharge practices. A description of how you discharge, including non-routine batch discharges.
2. Stored chemicals. A description of what you store on site.
3. Notification. Procedures for notifying the POTW immediately of a slug discharge, including any discharge that would violate a specific prohibition under §403.5(b), with written follow-up within five days.
4. Spill prevention, if necessary. Procedures to prevent adverse impact from accidental spills.

The fourth element names its own topics: inspection and maintenance of storage areas, handling and transfer of materials, loading and unloading, control of plant site runoff, worker training, containment structures or equipment, measures for containing toxic organics including solvents, and emergency response equipment.

Cities can ask for more than the minimum. Read your permit and the city's sewer use ordinance before you write the plan.

What makes a plan hold up during an inspection?

It matches what the inspector sees on your floor. The control authority inspects and samples each SIU at least once a year. A template filled in from memory falls apart the moment an inspector finds a drum storage area next to a floor drain that the plan never mentions.

Build it from the facility outward:

• A process description showing where wastewater is made and where it goes
• Each point that could produce a slug, such as batch tanks, cleanout stations and chemical storage
• A chemical inventory with container sizes and the containment around each
• Shutdown steps an operator can take in minutes
• Who calls the city, what number, and what goes in the five-day letter
• Training records and a set review date

When does the plan have to change?

Whenever your facility changes in a way that affects slug risk. The rule requires SIUs to notify the POTW immediately of any changes at the facility affecting the potential for a slug discharge.

A new chemical, a new batch process, or a relocated storage area should trigger a plan update and a call to the city. A plan describing a facility that no longer exists is a finding waiting to happen.

How do I design the facility so the plan rarely gets used?

Put the controls in the drawings, not just in the binder. An equalization tank lets a batch or surge blend down before it reaches the sewer. Automated pH control with a hold or divert valve stops an off-spec stream from leaving the site.

Chemical feed interlocks shut dosing down on a fault. Flow alarms catch an abnormal discharge as it happens. Isolation valves and emergency storage give an operator somewhere to send a bad batch. Secondary containment around storage keeps a spill away from floor drains in the first place.

These items change pipe routing, slab layout and tank sizing. That is why the plan belongs in design development, before construction documents are final. Sizing the equipment is covered in our post on pretreatment equipment sizing.

What happens if the plan is missing or wrong?

It is a permit violation, and a real slug makes it worse. If your permit requires a plan, not having one or not following it violates the permit and the city's ordinance. The city's enforcement response plan sets how it escalates.

A real slug event without controls can upset the plant and cost far more to clean up than the controls would have. For a facility still in permitting, a rejected plan delays the connection.

This post explains the federal rule as general education. Your city's ordinance and your permit set what your plan must say, so confirm the requirements with its pretreatment staff.

Frequently asked questions

Is a slug discharge control plan the same as an SPCC plan?

No. An SPCC plan under 40 CFR Part 112 deals with oil reaching surface waters. A slug control plan deals with any non-routine discharge to the sewer that could harm the treatment plant. Some facilities need both, and the containment can serve both.

How fast do I have to report a slug discharge?

The plan must include procedures for notifying the POTW immediately and for written follow-up within five days. Your permit may set specific phone numbers and forms.

Does every SIU need a plan?

No. Every SIU must be evaluated. The plan is required where the POTW decides one is needed.

We run a food plant in Collin County and do large equipment washdowns that go to the sanitary sewer. Could those count as slug discharges, and what would reduce the risk?

A washdown that is non-customary or much stronger than your normal flow could fit the definition, so characterize what actually reaches the sewer. Equalization that meters the washdown out, containment around the wash area, and a written washdown procedure in the plan address both the engineering risk and what the city expects to read.

At what stage of a new industrial project should we write the plan?

During preliminary design, alongside the pretreatment permit application. Confirm your likely SIU status with the city first, then put the containment, equalization and isolation valves into the drawings so the plan describes what gets built.

Related resources

• Texas Wastewater Pretreatment Permits: What Industrial Facilities Discharging to a POTW Must Know
• Self-Monitoring and Reporting Requirements for Texas Significant Industrial Users
• Enforcement Response Plans: How Texas POTWs Escalate Pretreatment Violations
• Discharging to a Storm Drain vs. Sanitary Sewer: Why Texas Contractors Get It Wrong on Pipeline and Tank Projects

Does the city want a slug discharge control plan from your facility?

We write plans that match the facility, and we design the containment and controls the plan relies on. Bring us in during design and the two stay consistent.

We specialize in:

• Slug discharge control plans for significant industrial users
• Pretreatment permit applications and POTW coordination
• Equalization, pH control and divert system design
• Secondary containment and chemical storage layout
• Industrial wastewater characterization

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