Knowing When Your Wastewater Treatment Plant (WWTP) Needs to be Upgraded: A Guide for Rural Communities

A wastewater treatment plant upgrade is due when your own records start saying so: flow sitting close to your permitted capacity, wet weather peaks the plant can't pass, effluent results creeping toward your limits, equipment you can't keep running, or a planned change in what the plant treats. For a Texas plant, rural or not, the flow signal comes with hard triggers at 75 and 90 percent.

What flow numbers say your plant is running out of room?

Three straight months at 75 percent of your permitted flow. In Texas that is a rule, not a rule of thumb.

Under 30 TAC §305.126, when flow reaches 75 percent of the permitted average daily or annual average flow for three consecutive months, the permittee must start engineering and financial planning to expand or upgrade. When average daily or annual average flow reaches 90 percent of the permitted average daily flow for three consecutive months, the permittee must obtain TCEQ authorization to begin building the added facilities.

The rule asks for authorization at 90 percent, not construction, so the planning should be done by then.

Plot monthly flow against permitted flow, and you will see 75 percent coming.

Is the problem the plant or the pipes feeding it?

Check the pipes first. If rain and groundwater push your flow up, you may be treating water that should never reach the plant.

EPA New England's Guide for Estimating Infiltration and Inflow (June 2014) says excess I&I robs the system of capacity, burdens operation and maintenance, and shortens the life of the treatment facility. It recommends at least a year of influent flow data, and notes that steady I&I correction can help defer capacity expansion.

A plant that crosses 75 percent only in wet months may need a collection system fix more than a bigger plant. Our post on finding and fixing your worst I&I sections shows how to narrow it down.

Are your effluent results drifting toward your limits?

If the same parameter keeps landing near its limit, the plant has no margin left. One bad month is an operations question. A trend is a design question.

Unless your permit says otherwise, 30 TAC §319.7 requires a monthly discharge monitoring report by the 20th of the following month. Line up two or three years of them and look for a climbing parameter.

Under 30 TAC §305.125, the permittee must comply with every permit condition and properly operate and maintain its treatment facilities at all times. So a blower or clarifier drive that fails every few months is a compliance risk, not just a maintenance headache.

Will your next permit renewal change the target?

It might, so design for the permit you will have, not only the one you hold today.

A TPDES permit runs no more than five years under 30 TAC §305.127, and 30 TAC §305.65 makes the renewal application due at least 180 days before expiration. About two years out, ask your engineer whether the renewal could bring new limits or new monitoring.

Check for phases too. TCEQ's domestic technical report (TCEQ-10054) lists interim and final phases, each with its own design flow. If a larger phase is already authorized, the upgrade may fit inside it. On renewal, a phase not built within five years of authorization needs a justification of continued need, or the executive director may recommend denying it.

Which plant changes do you have to report to TCEQ?

Planned physical alterations or additions. Tell TCEQ as soon as possible, and before you build if the change would need a permit amendment.

Section 305.126(b) requires notice of planned alterations or additions, including any that could significantly change the nature or increase the quantity of pollutants discharged, or significantly change how sludge is used or disposed of. Section 305.125 requires notice before alterations that would need a permit amendment.

In a small town, a new commercial or industrial customer can prompt that kind of change. A food processor can change the strength of your wastewater as much as its volume, and the plant was designed around both.

Changing a permit term, such as raising permitted flow, takes an amendment. Under 30 TAC §305.62, one that changes a substantive term or limiting parameter is a major amendment. Our post on permit modification, renewal and amendment sorts out which path fits.

What data does the upgrade design need?

Years of flow records and at least a year of influent sampling. Start collecting before you need it.

For an existing plant that is altered or re-rated, 30 TAC §217.34 makes current operating data the design basis: five years of flow records from a totalizing meter (all of them if the plant is younger), and at least three influent composite samples a week for at least a year, through wet and dry weather.

Then TCEQ hears about the design. Under 30 TAC §217.6, the owner sends a summary transmittal letter for a treatment plant project, signed and sealed by the design engineer. If TCEQ does not say in writing within 30 business days that it will review the plans, the project is conditionally approved.

How do small communities pay for a plant upgrade?

State and federal programs: low-cost loans, some with principal forgiveness, and USDA loans and grants. The state cycle is annual, so get in line early.

The TWDB Clean Water State Revolving Fund funds planning, design and construction of wastewater projects, including treatment and collection upgrades, for cities, counties, districts and river authorities, among others. Its solicitation runs December to March, and you need a Project Information Form in by the deadline to be invited to apply under the initial Intended Use Plan. Principal forgiveness is limited, and covers groups such as small or rural disadvantaged communities and systems serving 1,000 or fewer people.

USDA Rural Development's Water and Waste Disposal program can fund work to construct, enlarge or improve rural sanitary sewage facilities under 7 CFR 1780.9. Under 7 CFR 1780.3, rural means outside any city or town of more than 10,000 people.

Is your plant ready for an upgrade decision?

Two or more no answers means you are not ready to choose an upgrade; close those gaps first.

1. Do you plot monthly average flow against permitted flow every month?
2. Do you know whether the plant has hit 75 percent for three consecutive months?
3. Do you have five years of metered flow records?
4. Do you have a year of influent composite sampling through wet and dry weather?
5. Do you know how far wet weather flow runs above dry weather flow?
6. Do you know which effluent parameters run closest to their limits?
7. Do you know your permit's expiration date and whether it has an unbuilt phase?

Then ask your engineer: Is our problem in the plant or the pipes? Which unit limits us first? Could the renewal change our limits? How we work with small systems is on our page for utilities and municipalities.

A note on limits: this is general education from public sources, current as of October 2026. The rules cited are Texas and federal; other states set their own. Your engineer and TCEQ have the final word on your plant.

Frequently asked questions

What is the 75/90 rule for Texas wastewater plants?

It is 30 TAC §305.126(a). At 75 percent of permitted average daily or annual average flow for three consecutive months, start engineering and financial planning. At 90 percent of permitted average daily flow for three consecutive months, obtain TCEQ authorization to begin construction.

Can TCEQ waive the 75 percent planning requirement?

Yes, on an engineering report showing the planned population or waste load stays within the design. The written waiver is reviewed when the permit expires and excuses no permit violation.

Does a growing town count as a new discharger?

Not for an existing permitted plant. Section 305.126(c) asks a new discharger for quantitative data within two years after discharge starts. Under 30 TAC §305.2, which matches 40 CFR 122.2, a new discharger has never received a finally effective permit for discharges at that site.

I'm the public works director for a small Texas city, and our plant just logged its third straight month above 75 percent of permitted flow. What do we do first?

Start the engineering and financial planning the rule requires. Compare a year of influent flow with rainfall to see whether I&I drives it, and check your permit for an authorized larger phase.

I sit on the board of a rural Texas water supply corporation that runs a small sewer plant, and our flow is fine but the blowers keep failing. Is that reason enough to upgrade?

It can be. The duty to properly operate and maintain in §305.125 makes unreliable equipment a compliance issue, though the fix may be replacement rather than more capacity. Under 7 CFR 1780.7, a not-for-profit corporation with broad local membership can be an eligible USDA applicant in a rural area.

Related resources

• Optimizing Collection Systems: Advanced Solutions for I&I Challenges in Rural Communities
• How TCEQ Sets Effluent Limits: Understanding Receiving Water Quality Standards and Permit Conditions
• Capital Improvement Planning for Small Municipalities
• Three Things You Need to Know for a Better Community Water and Sewer System

Not sure whether your plant needs an upgrade or a fix upstream?

Send us two or three years of flow records and monitoring reports, plus a copy of your permit. We will help you sort out whether the answer is in the plant, in the pipes or in the permit.

Modern Engineering Solutions, McKinney, Texas, with offices in Golden, Colorado and San Jose, California. 525+ projects completed.

Talk to an engineer about your plant or call (214) 833-6748.