Radon in Eastern Washington
Radon in Eastern Washington
Washington is divided into several distinctive regions: the Okanogan
Highlands, the Columbia Basin, the Blue Mountains, the Cascade Mountains,
the Puget Lowlands, the Coastal Mountains, the Columbia River Gorge, and the
Coastal Hills. Areas East of the Cascade Mountain Range are considered
part of Eastern Washington, and have higher rates of radon than the
Western part of the state. The Okanogan Highlands in Northeastern
Washington are dominated by the Columbia River valley and a few other
north-trending river valleys. Less than %20 of the area is characterized
as "gently sloping" and the local relief is 1000-3000 feet. The Columbia
Basin is in the southeastern portion of the state, bounded by the Cascade
Range on the west and by the Columbia and Spokane rivers to the North.
There are irregular plains of low relief (100-300 feet), and open hills
of moderate to high relief (300-3000 feet). The Blue Mountains lie in
the Southeastern portion of the state and are characterized by open low
mountains with 1000-3000 feet of relief. The Cascade Mountains divide
the state in Eastern and Western halves, and are high mountains where
relief exceeds 3,000 feet. East of the Cascades, rainfall is typically
between 9 and 15 inches per year.
The Cascade Mountains can be divided into two geologic terrains: a
northerly terrain of primarily Mesozoic metamorphic rocks intruded by
Mesozoic and Teritary granitic rocks, and a southerly terrain composed of
Tertiary and Holocene volcanic rocks. These Holocene volcanic centers are
responsible for thick volcanic ash deposits east of the Cascades. A layer of
Miocene basaltic volcanic rocks of the Columbia Basin are
underlain by an extensive glaciofluvial outwash and eolian and lacustrine
deposits. The mountainous northeast and north-central portion of the
state is underlain by Precambrian sedimentary rocks, Paleozoic
sedimentary rocks, and Mesozoic metamorphic rocks. Each layer is
intruded by Mesozoic and Tertiary granites in these these regions.
As ice from the glaciation of the late Pleistocene receded from
Northeastern Washington, large lakes formed behind ice dams along the
ancestoral Columbia River valley. Massive floods periodically carried
large quanities of alluvium along the entire river drainages, and in some
regions valleys were eroded all the way down to the underlying basalt
bedrock. Aerial radiometric data shows that in the Westernmost portions
of the Okanogan Highlands, mesozoic and Tertiary granites have low
equivalent Uranium (eU) signatures, while the eastern portions have
granites and some metamorphic rocks with eU signatures approaching 5 ppm eU.
Although much of the Columbia basin is underlain by basaltic rocks low in
uranium, most of this area showed eU signatures between 2 and 3 ppm
because of the extensive superficial cover of the Quaternatry and
Holocene glaciofluvial, lacustrin, and eolian deposits, derived from
rocks in NE Washington and Northern Idaho with higher Uranium content.
The east flank of the Southern Cascades and the Blue Mountains lack this
superficial cover, and show eU reading between 0.5 ppm and 1.5 ppm.
Uranium occurances and deposits in Washington are largely associated with
granitic and metamorphic rocks in the Okanogan Highland region north of
Spokane and with Tertiary sedimentary rocks. Alluvium along stream
valleys of the granitic terrains of the Okanogan Highlands are sites of
potential superficial uranium deposits.Because of their relative youth, these Holocene uranium
deposits are low in radioactivity, and moreover, they are found in the
floodplains of streams or in wetlands, where construction is unlikely.
In 1987, the Bonneville Power Administration's Residential Standards
Demonstration Program (RSDP) completed three and twelve-month studies of
radon concentrations of indoor air for homes in the Pacific Northwest. Homes
constructed under Model Conservation Standards (MCS) were tested as well
as control dwellings that met construction codes and were recently
built. The study showed that there was no significant difference in radon
levels between homes built to MCS standards and other homes. These
homes were both single and multifamily site-built dwellings. Of the 331
three month test sites, 155 were MCS and 176 were
control. Of the 343 sites in the twelve month group, 161 were MCS and
182 were controls. Measurements were made with The Findings of the EPA
