How Did Backflow Contaminate Corpus Christi Drinking Water?


Eric Roy, Ph.D.  |  Scientific Founder 

Today the City of Corpus Christi, TX alerted residents not to drink or bathe using tap water because a "backflow incident" had potentially contaminated the city's drinking water with Indulin AA-86, an emulsifier commonly used in the asphalt industry. As a result, we are getting a lot of questions about back-flow and Indulin AA-86 contamination from people in Corpus Christi, as well as the rest of the US.

What Is Backflow?

Backflow is a pretty simple concept. It simply means that the liquid in a plumbing line went in the opposite direction that it supposed to. In a residential setting, this happens if the pressure within the residential plumbing goes higher than the city's water pressure. This can happen if a water pump malfunctions, or if the city's water pressure unexpectedly drops (for example when a water main breaks). In an industrial setting, this typically happens as a result of operator error or when backflow devices are not installed properly.

When Is Backflow A Problem For Drinking Water?

Backflow becomes a problem when pipes used to transport drinkable water are connected to pipes that are carrying a solid, liquid, or gas that is not drinkable (also called a "cross-connection"). When backflow occurs, the non-drinkable substance flows into backwards into the potable water pipe, where it mixes with and contaminates the drinking water.

Cross Connection Backflow Corpus Christi Indulin AA-86

Difference between normal flow and backflow over a cross connection

What Is Indulin AA-86?

Indulin AA-86 is a trade name for an emulsifier commonly used in the asphalt industry. Because Indulin AA-86 is proprietary, the Material Safety Data Sheet (MSDS) is not required to disclose the chemical composition, so we can only look at clues. The MSDS does categorize the formulation as having fatty amine derivatives, and another MSDS for Indulin AA-86 discloses that several state regulatory agencies (including California Prop. 65) list ethyl acrylate as an ingredient. From this information, and other parts of the MSDS, we can assume that the substance as a whole is relatively insoluble in water, but because the specific formulation is disclosed, we do not know how soluble (if at all) the different components of Indulin AA-86 are.

How Did Indulin AA-86 Contamination Get Into Corpus Christi's Water?

At the time that this article was published, the details are pretty scarce. Corpus Christi estimates that between 3 and 24 gallons of Indulin AA-86 were flowed into the drinking water system, and that's about it. We'll keep you posted as more is learned.

***Update On 12/16: The disclosure that hydrochloric acid was backflowed gives us a huge clue into what happened. The presence of hydrochloric acid strongly suggests that already mixed emulsion solution, not the pure Indulin AA-86 chemical was backflowed. Indulin AA-86 is prepared in a 0.3% solution to form an emulsion. Therefore, for 24 gallons of Indulin AA-86 would be diluted with water into to 8,000 gallons, a volume that is a standard storage/mixing tank size in the industry. If I had to speculate, someone backflowed a full 8,000 gallon tank of prepared emulsion into the freshwater line that is used to fill the tank.

If this is what happened, it's a bad thing, because prepared emulsion will more readily mix with drinking water than the relatively insoluble Indulin AA-86 pure product.

What Now For Corpus Christi Residents?

As of the time of the publication, Corpus Christi is urging residents to drink, cook, and bathe with bottled water, while they learn more about the extent that the water supply has been contaminated.

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