Shannon Dininny Associated Press

The aquifers under the Columbia Plateau – a 44,000-square-mile area roughly the size of Ohio – serve nearly 1.3 million people in the three states and provide irrigation water for an agriculture industry valued at about $6 billion.

YAKIMA – Groundwater levels in wells that have been drilled in a vast, arid plateau crossing Washington, Idaho and Oregon are declining nearly 2 feet per year on average, according to a new report published Tuesday by the U.S. Geological Survey.

The aquifers under the Columbia Plateau – a 44,000-square-mile area roughly the size of Ohio – serve nearly 1.3 million people in the three states and provide irrigation water for an agriculture industry valued at about $6 billion.

Scientists compiled data about water levels in 60,000 wells in the region. The report concludes that nearly three-fourths of all wells, or 72 percent, declined from 1968 to 2009. The average rate of change for all wells was 1.9 feet per year of decline.

Declining groundwater levels in several aquifers in the region have long been a source of concern, highlighted by climate change and periodic droughts.

Last year, Washington state officials warned that 25 communities in the arid Columbia River basin could have their municipal wells go dry in as soon as a decade. The communities draw their water from the rapidly declining Odessa aquifer, the same aquifer that serves thousands of acres of farmland in a region that has become a driving economic force of agricultural production.

State officials have said the problem is not an immediate crisis but a looming one.

Scientists examined two large areas that have been of particular concern to state and local agencies: the four-county region that draws water from the Odessa aquifer, and the Umatilla area in northeast Oregon.

In these areas, groundwater levels have declined hundreds of feet, the report found. Both groundwater pumping – for municipal, residential and agricultural use – and well leakage between aquifers may be contributing.

At the same time, geologic barriers such as basalt that impede the flow of groundwater may also protect some areas from decline, while making the decline more severe in other areas, the report concluded.

Groundwater levels were rising in some areas – generally in shallow ground – though the groundwater levels deep beneath layers of basalt in the same spot were often declining, the report concluded.

The report marked the most complete compilation of data in the region to date, according to researcher Erick Burns of the U.S. Geological Survey.

“This area is the size of the state of Ohio. We can’t deal with every small-scale feature, but hopefully, it’ll give a really good foundation for people who want to zoom in and do a more focused study.”