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Our tests have now confirmed a source of these chemicals, and it is clear that forest fires are not the only flames threatening drinking water systems.

In a new study, we heated plastic water pipes commonly used in buildings and water systems to test how they would react to nearby fires.

The results, published on December 14th, show how easily forest fires can cause widespread drinking water pollution. They also show the risks if only part of a building catches fire and the rest is left in use. In some of our tests, more than 100 chemicals were leached from the damaged plastics by exposure to heat.

As environmental engineers, we advise communities on drinking water security and disaster recovery. The extreme wildfire seasons in the western United States are putting more communities at risk in ways they may not realize. That year alone, more than 52,000 fires destroyed more than 17,000 buildings – many of them houses connected to water systems. Heat damaged plastic pipe can continue to leach chemicals into water over time, and it can take months and millions of dollars to clear a water system of contamination.

A confusing source of contamination

The cause of drinking water pollution after forest fires has baffled authorities since it was discovered in 2017.

Following the 2017 Tubbs Fire and 2018 Camp Fire, chemicals were found in distributed water distribution networks, some in amounts comparable to hazardous waste. The water treatment plants or drinking water sources were not contaminated. Some homeowners found drinking water pollution in their pipelines.

Tests showed that volatile organic compounds had reached levels that posed imminent health risks in some areas, including benzene levels that exceeded the EPA’s 500 parts per billion hazardous waste threshold. Benzene has been found in amounts 8,000 times the federal drinking water limit and 200 times the amount that has immediate health effects. These effects can include dizziness, headache, skin and throat irritation, and even loss of consciousness, among others.

Plastic water pipes don’t have to burn to be a problem. Andrew Whelton / Purdue University, CC BY-ND

This year, forest fires caused drinking water pollution in at least two other California drinking water systems, and tests are still being conducted in other communities.

The problem with plastics

Plastics are ubiquitous in drinking water systems. They are often cheaper to install than metal alternatives that can withstand high heat but are prone to corrosion.

Water pipes under the street and those that deliver water to customers’ water meters are increasingly made of plastic. Pipes that transport the drinking water from the meter to the building are often made of plastic. Water meters sometimes also contain plastics. Private wells can have plastic well casings as well as buried plastic pipes that supply well water to plastic storage tanks and buildings.

Pipes in buildings that lead hot and cold water to taps can also be made of plastic, as can faucet fittings, immersion pipes for water heaters, refrigerators, and ice maker pipes.

Some common types of drinking water pipes: Black plastic is HDPE; White is PVC; yellow is CPVC; Red, maroon, orange, and blue are PEX; Green is PP; and gray is polybutylene. The metal pipes are lead, iron and copper. Andrew Whelton / Purdue University, CC BY-ND

To determine if plastic pipes could be responsible for drinking water pollution after forest fires, we exposed commonly available plastic pipes to heat. The temperatures were similar to the heat of wildfire radiating towards the building, but not enough to set the pipes on fire.

We tested several popular plastic drinking water pipes, including high density polyethylene (HDPE), crosslinked polyethylene (PEX), polyvinyl chloride (PVC), and chlorinated polyvinyl chloride (CPVC).

Benzene and other chemicals were created in the plastic pipes only by heating. After the plastics cooled, these chemicals were leached into the water. It happened at temperatures of only 392 degrees Fahrenheit. Fires can exceed 1,400 degrees.

While researchers previously discovered that plastics can release benzene and other chemicals into the air when heated, this new study shows that heat-damaged plastics can leach dozens of toxic chemicals directly into water.

What can be done against contamination?

A community can prevent water pollution from spreading if damaged pipes can be quickly insulated. Without insulation, the contaminated water can move to other parts of the water system in the city or within a building and cause further contamination.

During the fire at the CZU Lightning Complex near Santa Cruz, a water utility had valves on the water distribution system that appeared to contain the water contaminated with benzene.

Flushing heat damaged pipes does not always remove the contamination. While we were helping Paradise, California recover from the 2018 Camp Fire disaster, we and the U.S. Environmental Protection Agency estimated that some plastic pipes could have required more than 100 days of continuous water flushing to be safe. Instead, the officials decided to replace the pipes.

Different pipe types react differently to heating. Andrew Whelton / Purdue University, CC BY-ND

Even if a home is undamaged, we recommend testing the water in private wells and utility lines if there has been a fire on the property. If contamination is found, we recommend locating and removing the heat damaged plastic contamination sources. Some plastics can slowly leach chemicals such as benzene over time, and this can take months to years, depending on pollution levels and water usage. Boiling the water won’t help and can release benzene into the air.

Avoidance of widespread contamination

Municipalities can take measures to avoid contaminated drinking water in the event of fire. Water companies can install network shut-off valves and backflow preventer to prevent contaminated water from a damaged building from entering the utility network.

Insurance companies can use pricing to encourage property owners and cities to install refractory metal pipes instead of plastic. Rules to keep vegetation away from gauges and buildings can also reduce the likelihood of heat getting into the components of the plastic water system.

Homeowners and communities in rebuilding after a fire now have more information about the risks as they consider whether to use plastic pipe. Some, like the town of Paradise, have chosen to rebuild with plastic and accept the risks. In 2020 the city had another devastating fire and residents had to evacuate again.

Andrew J. Whelton is an Associate Professor of Civil, Environmental, and Ecological Engineering at Purdue University.

Amisha Shah is assistant professor for civil engineering as well as environmental and ecological engineering, Purdue University.

Kristofer P. Isaacson is a Ph.D. Student, Purdue University.

Disclosure Statement: Andrew J. Whelton has received funding from the Paradise Irrigation District and the Paradise Rotary Foundation. From January 2019 to May 2019, he also served on the Governor of California’s Fire of Fire Services Task Force. Amisha Shah has received funding from the Paradise Irrigation District. Kristofer P. Isaacson does not work for any company or organization that would benefit from this article, does not consult any stocks or companies that would benefit from this article, and has not disclosed any relevant affiliations beyond her academic appointment.

Republished with permission from The Conversation.

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