1710 W MARINE VIEW DR 2024-01-03

BMP C125: Topsoiling / Composting Purpose Topsoiling and composting provide a suitable growth medium for final site stabilization with veget- ation. While not a permanent cover practice in itself, topsoiling and composting are an integral com- ponent of providing permanent cover in those areas where there is an unsuitable soil surface for plant growth. Use this BMP in conjunction with other BMPs such as BMP C 120: Temporary and Per- manent Seeding, BMP C121: Mulching, or BMP C124: Sodding. Implementation of this BMP may meet the post -construction requirements of BMP T5.13: Post -Construction Soil Quality and Depth. Native soils and disturbed soils that have been organically amended not only retain much more stormwater, but also serve as effective biofilters for urban pollutants and, by supporting more vig- orous plant growth, reduce the water, fertilizer and pesticides needed to support installed land- scapes. Topsoil does not include any subsoils but only the material from the top several inches including organic debris. Conditions of Use . Permanent landscaped areas shall contain healthy topsoil that reduces the need for fertilizers, improves overall topsoil quality, provides for better vegetative health and vitality, improves hydrologic characteristics, and reduces the need for irrigation. . Leave native soils and the duff layer undisturbed to the maximum extent practicable. Stripping of existing, properly functioning soil system and vegetation for the purpose of topsoiling during construction is not acceptable. Preserve existing soil systems in undisturbed and uncom- pacted conditions if functioning properly. . Areas that already have good topsoil, such as undisturbed areas, do not require soil amend- ments. . Restore, to the maximum extent practical, native soils disturbed during clearing and grading to a condition equal to or better than the original site condition's moisture -holding capacity. Use on -site native topsoil, incorporate amendments into on -site soil, or import blended topsoil to meet this requirement. . Topsoiling is a required procedure when establishing vegetation on shallow soils, and soils of critically low pH (high acid) levels. . Beware of where the topsoil comes from, and what vegetation was on site before disturbance. Invasive plant seeds may be included and could cause problems for establishing native plants, landscaped areas, or grasses. . Topsoil from the site will contain mycorrhizal bacteria that are necessary for healthy root growth and nutrient transfer. These native mycorrhiza are acclimated to the site and will provide optimum conditions for establishing grasses. Use commercially available mycorrhiza products when using off -site topsoil. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 301