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Snohomish County Area, Washington <br /> 5—Alderwood-Urban land complex, 2 to 8 percent slopes <br /> Map Unit Setting <br /> • National map unit symbol: 2hz9 <br /> • Elevation: 50 to 800 feet <br /> ' • Mean annual precipitation: 25 to 60 inches <br /> • Mean annual air temperature: 48 to 52 degrees F <br /> ' • Frost-free period: 180 to 220 days <br /> • Farmland classification: Not prime farmland <br /> Map Unit Composition <br /> ' • Alderwood and similar soils: 60 percent <br /> • Urban land: 25 percent <br /> • Minor components: 15 percent <br /> • Estimates are based on observations, descriptions, and transects of the <br /> ' mapunit. <br /> Description of Alderwood <br /> ' Setting <br /> • Landform: Till plains <br /> • Parent material: Basal till <br /> Typical profile <br /> ' • H1 - 0 to 7 inches: gravelly ashy sandy loam <br /> • H2 - 7 to 35 inches: very gravelly ashy sandy loam <br /> • H3 - 35 to 60 inches: gravelly sandy loam <br /> ' Properties and qualities <br /> • Slope: 2 to 8 percent <br /> ' • Depth to restrictive feature: 20 to 40 inches to densic material <br /> • Natural drainage class: Moderately well drained <br /> ' • Capacity of the most limiting layer to transmit water (Ksat): Very low to <br /> moderately low (0.00 to 0.06 in/hr) <br /> ' • Depth to water table: About 18 to 36 inches <br /> • Frequency of flooding: None <br /> ' • Frequency of ponding: None <br /> • Available water storage in profile: Low (about 3.0 inches) <br /> Insight Engineering Co. -Stormwater Site Plan 12/30/20 <br /> - 10- <br /> 1 <br />