HomeMy WebLinkAbout42M KLEIN FELDER
2.2 REGIONAL GEOLOGY"
The Puget Sound regional topography cansisu of a series of rolling ridges and valleys produced
by the movement of the large valley glaciers that occupied the basin during the glacial ages, the
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last episode of which was about 13,000 years ago. The ridges and valleys are generally oriented
north-northwest to south-southeast. The project site is located in one of the valley areas, which
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separates the upland ridge of the Renton Highlands (to the east) and the Skyway area to the west.
The Renton Valley is contiguous with the large Kent valley trough to the south. In the post -
glacial period the lowlands were inundated by the seawater of Puget Sound. ErosiJn on the
uplands to the east by such rivers and the Cedar River filled the Renton -Kent valle_ with loose,
fine siltv sediments until the Lake Washington basin became physiographically isolated from
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r Puget Sound and developed into a fresh water lake. Marshes grew in areas throughout the
Renton -Kent valley and along the lakeshore. Prior to the construction of the Lake Washington
Ship Canal, the Cedar River entered Lake Washington from the southeast, depositing sand and
silt deltaic sedimer-s. The lake drained throu_eh the Black River, located approximately where
the Renton Airport is now situated. This stream was eliminated when the lake drainage was
diverted through the ship canal.
The geology of the project site is covered in the Geologic Map of the Renton quadrangle, King
County, Washington, 1965, by D.R. MulIineaux (U.S. Geological Survey Geologic Quadrangle
Map GQ-405). More recently, the south portion of the project site is described in Liquefaction
Susceptibility of the Renton Quadrangle, Washington, by S.P. Palmer, H.W. Schasse and D.K.
r Norman (Washington Division of Geology and Earth Resources Geologic 'tap GM-41, 1994).
23 SUBSURFACE
Our field exploration p-ogram consisted of 9 borings (B-1 through B-9) that were advanced
within the superstore building footprint. Boring depths varied from 61.5 feet to 76.5 feet below
ground surface (bgs). Boring locations are show-n in Figure 2. We installed 2-inch diameter
piezometers for groundwater monitoring in each of the four comer borings. A flush -mounted
steel well box (locked -monument) was place-3 over each piezometer to allow periodic
measurement of groundwater levels.
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