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A minimum organic content of 10%diy weight, and 5% organic matter content in turf areas. Incorporate organic amendments to a minimum 8-inch depth except where tree roots or other natural features limit the depth of incorporation. A pH between 6.0 and 8.0 or matching the pH of the undisturbed soil. • If blended topsoil is imported,then fines should be limited to 25 percent passing through a 200 sieve. • Accomplish the required organic content and pH by either returning native topsoil to the site and/or incorporating organic amendments. • To meet the organic content use compost that meets the definition of"composted materials" in WAC 173-350-220.This code is available online at: httL):HaLii)s.leg,wa.gov/WAC/default.asl)x?citc=l 73-350-220. p The compost must also have an organic matter content of 35% to 65%, and a carbon to nitrogen ratio below 25H:I V. The carbon to nitrogen ratio may be as high as 35H:IV for plantings composed entirely of plants native to the Puget Sound Lowlands region. For till soils use a mixture of approximately two parts soil to one part compost. This equates to 4 inches of compost mixed to a depth of 12 inches in till soils. Increasing the concentration of compost beyond this level can have negative effects on vegetal health, while decreasing the concentrations can reduce the benefits of amended soils. Gravel or cobble outwash soils, may require different approaches. Organics and fines easily migrate through the loose structure of these soils. Therefore,the importation of at least 6 inches of quality topsoil,underlain by some type of filter fabric to prevent the migration of fines,may be more appropriate for these soils. • The final composition and construction of the soil system will result in a natural selection or favoring of certain plant species over time. For example, incorporation of topsoil may favor grasses,while layering with mildly acidic,high-carbon amendments may favor more woody vegetation. • Allow sufficient time in scheduling for topsoil spreading prior to seeding, sodding, or planting. • Take care when applying top soil to subsoils with contrasting textures. Sandy topsoil over clayey subsoil is a particularly poor combination, as water creeps along the junction between the soil layers and causes the topsoil to slough. If topsoil and subsoil are not properly bonded, water will not infiltrate the soil profile evenly and it will be difficult to Vohiwe 1I—Construction Sioninvater Polhilion Pren,ention-August 2012 4-30