2514 RAINIER AVE Geotech Report 2022-10-25

a ` 1 dtT1eC foster I wheeler However, appropriate inclinations will ultimately depend on the actual soil conditions exposed during 1 earthwork. Bedding Soils: Utility pipes should be bedded on an appropriate material that extends at least , 6 inches outward from the pipe in all directions. For level or gently sloping pipes, we recommend using a clean, uniform, well-rounded material, such as pea gravel or"Gravel Backfill for Pipe Bedding" I per WSDOT Standard Specification 9-03.12(3). Backfill Soils: The on-site soils will be difficult to compact as utility excavation backfill unless the , moisture content is kept within a narrow range of the optimum moisture content. During the wet season or during rainy periods, backfill material used for utility trenches and other excavations may , need to consist of clean, well-graded granular soils, such as "Gravel Borrow" per WSDOT Standard Specification 9-03.14, except with less than 5 percent passing the U.S. No. 200 sieve. Controlled-density fill (CDF) could be used as a more convenient, but also more expensive, alternative to backfill soil in any weather conditions. Backfill Compaction: We recommend utilitybackfill soils be compacted to a densitycommensurate 111 p p with surrounding fill or native soils, as well as with the requirements of any overlying structures. CDF backfill does not require compaction but should have a compressive strength commensurate with the application. 4.7 STORMWATER INFILTRATION We understand that ESD may desire to infiltrate stormwater into the underlying Advance Outwash sand and gravel, but preliminary design of stormwater infiltration facilities has not been completed at this time. We reviewed Volume III, Chapter 9—Infiltration Facilities of the City of Everett Stormwater Design Manual(2010) (referred to herein as the Everett Stormwater Manual) and are providing I preliminary comments relative to these criteria. Permeable soil layer: The depth to the permeable Advance Outwash sand and gravel across the site ranges from 10 to 19 feet below the ground surface. Table 4 summarizes the measured depth to relatively permeable soils. Groundwater was not encountered at time of drilling. I 1 Amec Foster Wheeler 16 Project No.6-917-18116-0 \\Sea-fs1\WordProc\ Projects\18000s\18116 Everett School District\Geotech Report\Revised\2017_10-19_Everett Middle School Geotech_Sx.docx