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represent flood and alluvial plain environments, and the gravelly sand lenses are channel
deposits from the river. These lenses interfinger and interlayer in a complex pattern. They
are generally loose and soft, though some lenses (especially the gravelly channel beds)
are dense. Gradation analysis of samples of sand or sandy silt lenses from several of the
borings show that the individual lenses are generally poorly graded. A gradation analysis
of a sandy gravel tense from B-8 (25 feet bgs) shows a reasonably well graded material.
Post -Glacial Alluvial Saud: At depth, the interbedded materials grade to fairly
continuous thick lenses of alluvial sand and sandy gravel. These lenses are dark gray to
gray brown, medium dense to dense, with massive bedding. The dark gray color is
indicative of a high content of volcanic lithic fragments, indicating the material is non -
glacial in origin. The grains are sub -angular, which suggests a relatively short distance of
travel and supporting the idea that the lenses are past -glacial alluvial from the Cedar
River system and other local streams. The depth at which the continuous sand is
encountered varies greatly across the site, from 37 feet bgs in B-6 to 58 feet bgs it. B-7.
In some areas the contact is sharp. with a peat or silt -clay bed immediately above a dense
sand bed. In other portions of the site, the contact is more gradual, with silty sand giving
way to sand, which may be loose in the top few feet. No strong pattern in the depth of the
top of the sand layer could be identified, though the top of the sand appeared to generally
get deeper to the south and west.
Glacial Silt: Glacial sediments were found in only one boring, B-9. The tense consists of,
hard silt that is characteristic of the glaciolacustrine silt of the Lawton Formation. This
lens %vas penetrated at 56 feet bgs.
2.4 GROUNDWATER
Groundwater'A as encountered in all borings that were advanced within the building footprint (13-
1 through B-10). The depth at which groundwater was encountered during drilling varies from
5.0 feet bgs in B-6 to 19.5 feet bgs in B-4.
Piezometers were installed in B-1, B-3, B-7, and B-9. These borings were located at the corners
of the proposed building. The piezometers were screened between 5 and 15 feet bgs and were
constructed in accordance with Washington State regulations. The water level was subsequently
measured on February 4 and February 23, 2001. The water level measurements are summarized
in the table below.
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