AGGREGATE RESOURCE INVENTORY OF KITSAP COUNTY, WASHINGTON

Sand, gravel, and bedrock may be mined or quarried to produce raw materials known as aggregate. Aggregate resources are the building blocks of our communities as they are used in the manufacturing of critical materials for roads, bridges, and development. The Washington Geological Survey (WGS) is now regularly producing new county-scale aggregate resource inventory maps with the goal to have full state coverage. WGS chose to map Kitsap County’s aggregate resources in 2023 to provide data to the county that would benefit their land use decisions for their June 2024 comprehensive plan update.

The aggregate resource inventory of Kitsap County identifies potential sources of aggregate (both sand and gravel, and bedrock) using a combination of surficial and bedrock geologic mapping, subsurface records from boreholes and water wells, aggregate testing data, and records of past and present mining activity. Our aggregate resource classification scheme assesses both the quality and quantity of potential resources, and communicates that assessment using four classifications: Demonstrated, Inferred, Speculative, and Not a Resource. Our Kitsap County inventory classifies 64,396 acres of land as having the potential for economically significant aggregate resources, which is about 25 percent of the county’s land area. For sand and gravel resources mapped as Demonstrated and Inferred (our highest-certainty resource classifications), we estimate a range of 600 million to 1.3 billion cubic yards of aggregate (970 million to 2.3 billion tons). Results from our developed-lands analysis found that approximately 18 percent of areas we identify as potential sources of aggregate may be inaccessible for resource extraction because they are lands classified as developed according to the National Land Cover Database. A transportation-network analysis—aimed at understanding the distance-to-market relationship—reveals that 65 percent of inventoried resource is within a 10-mile drive from Bremerton, Port Orchard, Bainbridge Island, or Poulsbo. A second transportation-network analysis explores service areas of active aggregate mines in the county and identifies the northern tip of Kitsap County near Hansville and the southern half of Bainbridge Island as areas that are farthest from active aggregate mines.