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Is Idaho Causing Arsenic Woes For Ontario's Water?

August 8, 2016

Five years ago, Oregon’s Department of Environmental Quality developed new health standards for arsenic in drinking water. But the community of Ontario in eastern Oregon has not been able to meet those standards.

One big reason could be because Ontario’s drinking water supply comes from Idaho. Ontario withdraws its water from the Snake River, which flows across Idaho and the Oregon border. Idaho allows 10 parts per billion of dissolved inorganic arsenic.

But Oregon’s standard is nearly five times stricter — it  allows 2.1 parts per billion of inorganic arsenic. Arsenic levels in the Snake River already exceed Oregon’s standards by the time the water reaches Ontario, so to meet standards, the city has to very aggressively treat the water.

Arsenic is a known carcinogen and in high concentrations can be the source of cardiovascular, kidney and central nervous system damage. It can also accumulate in aquatic insects and fish, just like mercury, so people must be careful of how much fish they eat from water bodies with high arsenic standards.

Arsenic is both a naturally-occurring and an industrially-generated element. It’s used in many pesticides and for other agricultural purposes, but is also present in volcanic soil and basalt terrain.

Ontario’s problem with arsenic is in its second water treatment process. Drinking water is treated before it enters people’s homes and faucets and again after it goes down the drain and into the system as wastewater.

Where the water doesn’t meet state standards is in that second treatment. After the water is used by homes and industries, it seems to collect more arsenic, potentially through leaks in the collection surface pipes or surface water leakage. 

“The water that they’ve treated and then has gotten flushed down toilets is getting arsenic re-introduced to it,” said Don Butcher with DEQ. “So they’re fighting a losing battle in that regard.”

So people in Ontario don’t necessarily need to worry about the water coming out of their faucets, but those arsenic levels might be a problem for fish in the Snake River, where the city puts its wastewater.

In order to meet state standards, Ontario can either install a very expensive treatment system or the city can apply for a variance from the state — essentially, ask the state for permission for lenience as long as they do everything they can to reduce arsenic levels. No other community has been granted an exception for arsenic, according to the DEQ, but it seems likely that the agency could approve the exception. The city is in the process of conducting a facility plan to better understand the arsenic infiltration into the wastewater collection system.

“The chemistry is complex, and it’s not fully understood," said Jerry Elliott, water and wastewater supervisor for the city of Ontario. “Each wastewater system will have a different way of handling arsenic molecules.”

For its part, Idaho may soon have to change its arsenic standards. The EPA was recently sued by the Northwest Environmental Advocates over its approval of Idaho’s arsenic standards, which the group said are far too lax.

“It was legally incorrect and not protective of human health,” said Nina Bell, executive director of Northwest Environmental Advocates. “It was also obviously inconsistent with what Oregon was doing and with what the EPA was requiring Oregon to do.”

In a legal settlement, the EPA agreed to reverse its approval of Idaho’s arsenic levels, which means the state could be forced to develop new standards in the near future.


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Ontario is able to effectively treat its water for arsenic as it goes into people's homes. But on second treatment, when wastewater flows back to the Snake River, the city has trouble meeting standards.

Amanda Peacher

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