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Groundwater

The uppermost hydrologic unit for most of the subwatershed is the unconsolidated sedimentary aquifer. The groundwater level is generally greater than 150 feet above msl. The aquifer thickness is less than 200 feet. In the northeastern portion of the subwatershed, around Mt. Tabor, the Troutdale Gravel aquifer is the uppermost hydrologic unit. The groundwater level of the Troutdale Gravel aquifer ranges from 100 to 150 feet. above msl; and the aquifer thickness ranges from 400 to 1,200 feet. (McFarland and Morgan, Plate 2, 1996).

Underlying the unconsolidated sedimentary aquifer is the Troutdale gravel aquifer, which begins less than 20 feet above msl in the western portion of the watershed and increases to 150 feet above msl in the west. Aquifer thickness is generally between 200 feet and 400 feet in the western two-thirds of the subwatershed, and increases up to 1,200 feet thick around Mt. Tabor (McFarland and Morgan, Plate 3, 1996).

Generally, depth to groundwater is less than 100 feet. throughout most of the subwatershed. However, in the northeastern corner between 60th and 76th Streets, depth to groundwater increases, reaching 490 feet. in one area.
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