Volume 2: Draft Gorst Planned Action Environmental Impact Statement

GORST PLANNED ACTION EIS | AFFECTED ENVIRONMENT, SIGNIFICANT IMPACTS, AND MITIGATION MEASURES3.1 Geology/SoilsAffected EnvironmentGEOLOGYWatershedThe study area lies within the Puget Trough physiographic province (Franklin and Dyrness 1988). The area wasinfluenced by glacial activity 13,000 to 15,000 years ago. Soil parent material is predominantly glacial till;compacted glacial till is covered by a thin layer of ablation till. It is underlain by sediments deposited duringprevious glacial or interglacial periods. In the northern portion of the watershed, thin deposits of till occur overbasalt bedrock associated with mountain slopes (United States Department of Agriculture [USDA] SoilConservation Service 1980). In the northern portion of the watershed, a large deposit of recessional outwashconsisting of fine-grained sand occurs, which has an important role in the recharge, storage, and discharge ofwater. The southern portion of the watershed consists primarily of Vashon Till, which has low permeability and lowrates of recharge and discharge (Sceva 1957 in City of Bremerton 2012).The following geologic units have been mapped within the study area (City of Bremerton 2011) (Figure 3.1-1 GorstCreek Watershed: Geology):• Qa – Alluvium• Qga – Advance continental glacial outwash, Fraser-age• Qgo – Continental glacial outwash, Fraser-age• Qgt – Continental glacial till, Fraser-age• Qp – Peat deposits• Qgd – Continental glacial drift, Fraser-age• Qgu – Glacial drift, undivided• Qf – Artificial fill, including modified land• Ev(c) – Basalt flows and flow breccias, Crescent FormationGorst UGAGeology in the northeast portion of the UGA is typified by basalt flows and flow breccias. The remainder of theUGA is typified by continental glacial outwash.Draft | June 2013 3-2