Hydrostatic Testing on Elevated Storage Tanks vs. Buried Pipelines: Why They Need Different Compliance Plans

Does a tank need a different permit than a pipeline?

Usually not. TPDES General Permit TXG670000 defines a vessel as pipelines, tanks and other similar containers. Part II, Section A authorizes discharges from new vessels and from existing vessels that held raw or potable water, among others.

Under Part II, Section C.4, those vessels need no NOI if the discharger complies with all applicable permit conditions. A new elevated tank, a rehabilitated ground storage tank and a new distribution main can all sit in that no-NOI group. A tank or line that held petroleum or natural gas substances is a different category, with more effluent limits and an NOI unless the water is land applied under Part III, Section C.

Why does a tank change the sampling?

Sampling is counted per discharge, not per gallon. When the test water has been hyperchlorinated, Part III, Section A.1 sets a daily maximum of 0.10 mg/L total residual chlorine, sampled by grab two times per discharge. One sample is taken in the first hour. If the discharge runs longer than an hour, the second is taken of the last 10% of the effluent.

For a pipeline program, that means two samples for every segment you drain, which adds up across a long job. For a tank, it means one long event where the last 10% matters. Water from the bottom of a tank can look different from the first hour's sample, so the dechlorination dose has to hold to the end.

Samples go at a point right after the vessel or after treatment, before the water mixes with stormwater or other flows. On a tank, that means sampling below the dechlorination point on the drain line, not from the overflow or a hatch.

How do drawdown rate and elevation change the outlet?

A tank drain delivers more water, faster, with more head. Part III, Section B.1 requires discharge to a splash pad, a paved area or another surface that prevents erosion, with the rate controlled through best management practices. On a pipeline segment that is often a rock pad and a diffuser at the blowoff.

On an elevated tank the same rule applies, but the water arrives with the energy of the tank's height. The drain line routing, the throttling valve and the energy dissipater carry real load. A crew that opens the drain fully and lets the tank empty at its own rate is not controlling the rate.

A practical tank rule is that someone owns the valve for the whole drawdown and has authority to slow it when the outlet or the flow path starts to show stress.

What tank-specific water quality issues come up?

Coatings, sediment and cleaning water. Texas public water system rules in 30 TAC §290.43(c) require potable storage to be tested and disinfected under current AWWA standards. Paragraph (c)(8) bars coatings containing lead and requires new coatings to meet ANSI/NSF Standard 61.

Those rules shape the water in a tank after rehabilitation. Two things to watch in the discharge plan:

• Cleaning and rinse water is not test water. Part II, Section B.11 of TXG670000 says cleaning or rinsing wastewater generated before filling a vessel for testing, and material from pressure washing or other cleaning, is not authorized under the general permit. Handle tank washout as its own waste stream.
• Floor sediment and coating debris. Part III, Section B.7 prohibits discharging floating solids or visible foam other than in trace amounts, and visible oil. Plan for filter bags or settling if the tank floor has not been cleaned out.

Section 290.43(c) also says tank drains shall not be connected to any waste or sewage disposal system. Confirm where the drain goes before the test, not during it.

What is different about a pipeline program?

Repetition. A water main job may drain dozens of test sections at different blowoffs over several weeks. Each drain needs a stable landing surface, its own two chlorine samples when hyperchlorinated, and its own record.

The permit gives one break. Under Part III, Section A.3, if a vessel fails its test and needs another one, no additional analyses are required when the retest is within 30 days of the first test, the first discharge had no exceedances, and nothing was added to the vessel. That applies to tanks too, but it comes up far more on pipelines.

On a pipeline, the discharge points move with the work. Each one should be checked for distance from wells and drinking water intakes: Part III, Sections B.2 and B.3 require 300 feet from a domestic drinking water intake and 500 feet from any water well. Our water distribution design work picks blowoff locations with those distances in mind.

How should the records differ?

Pipelines need a clean index; tanks need a detailed log. For a pipeline, the risk is losing track of which segment was drained where, so organize records by segment and outlet. For a tank, the risk is one long event without enough detail, so log flow rate, valve changes, sample times and outlet condition through the drawdown.

Either way, Part IV.9 requires keeping records for three years from the date of the record.

Limits: this article summarizes TXG670000 and 30 TAC §290.43 as of October 2026 for general education. Petroleum and natural gas vessels, Railroad Commission jurisdiction, the Edwards Aquifer rules and local utility requirements are outside its scope. Confirm your discharge plan with your engineer and the system operator.

Frequently asked questions

Does an elevated tank need an NOI for hydrostatic test discharge?

Not if it is a new tank or one that held raw or potable water and the discharge meets all applicable TXG670000 conditions. Part II, Section C.4 exempts those vessels from the NOI requirement.

How many chlorine samples does a tank discharge need?

If the water was hyperchlorinated, two grab samples per discharge: one in the first hour and, if the discharge lasts over an hour, one of the last 10% of the effluent, under Part III, Section A.1.

Can we discharge the tank washout under the same permit?

No. Part II, Section B.11 excludes cleaning and rinse water generated before the vessel is filled for testing, and material from pressure washing or other cleaning.

I manage capital projects for a small Texas water supply corporation and we're testing a new elevated tank and 3 miles of main in the same contract. Can one discharge plan cover both?

One document can, but it needs two sections. The tank section should cover drawdown rate, the drain line outlet and the last-10% sample. The main section should cover segment-by-segment outlets, well and intake distances, and a record index by segment.

We're a contractor in Texas and the tank we're recoating had sediment on the floor. What should we do before the hydrostatic test?

Clean the floor and handle that washout as its own waste, since TXG670000 does not cover it. Then plan filter bags or settling at the outlet, because the permit bars floating solids and visible oil in the test discharge.

Related resources

• New Water Main Disinfection and Test Water Discharge: How to Coordinate AWWA Standards with TCEQ Rules
• Does Test Water Volume Trigger a Different Permit Tier? What TXG670000 Actually Requires for Pipeline Tests
• Erosion and Sedimentation Control at the Discharge Point: What Inspectors Check When Test Water Hits Open Ground
• Chlorine Neutralization Before Discharge: The Field Step Contractors Skip Until It Becomes a Compliance Problem

Testing a tank and a pipeline on the same project?

We write discharge plans sized for the asset being tested, with outlets, sampling and records that match how each one drains.

We specialize in:

• Water storage and distribution design
• Public water system design
• Hydrostatic test water discharge planning
• SWPPPs and erosion and sediment control plans
• Construction administration

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