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City of Arden Hills Project B2502087 June 13, 2025 Page 12 An OSHA-approved qualified person should review the soil classification in the field. Excavations must comply with the requirements of OSHA 29 CFR, Part 1926, Subpart P, “Excavations and Trenches.” This document states excavation safety is the responsibility of the contractor. The project specifications should reference these OSHA requirements. C.2.e. Excavation Dewatering We recommend removing groundwater that collects within excavations from rainfall events and/or surface runoff. Project planning should include temporary sumps and pumps for excavations in low- permeability soils, such as clays. Where granular soils are encountered at invert elevations, the design team may want to consider additional means and methods for removing groundwater, as sumps and pumps have the potential to loosen the granular soils at excavated bottoms. C.2.f. Engineered Fill Materials and Compaction Most on-site soils appear suitable for reuse as engineered fill within pavement subgrades and utility trenches, although some moisture conditioning may be required (drying or wetting of materials). If encountered, topsoil and soils with organic contents of greater than 5 percent by weight should not be reused as pavement subgrade or utility trench backfill anywhere on the project. Organic soils can be stockpiled for use as a component in topsoil dressing, side slopes or in other areas where loads are not supported. Any materials to be reused as engineered fill should be tested and approved by the engineer prior to reuse. We recommend that subgrade fill materials and compaction are in accordance with the MnDOT specifications presented in Table 6. Table 6. Engineered Fill Materials and Compaction Specifications Material Material Specification Compaction Specification Embankment fill, Utility trench backfill Common Embankment MnDOT 2106.2.B.1 MnDOT 2106.3.G.1 Pavement subbase Select Granular Material MnDOT 3149.2.B MnDOT 2106.3.G.3 Below landscaped surfaces, where subsidence is not a concern Non-Structural Grading Material MnDOT 2106.1.A.8 MnDOT 2106.3.G.2 We recommend spreading engineered fill in loose lifts of approximately 8 to 12 inches thick for granular soils and for cohesive soils, we recommend spreading in loose lifts of approximately 6 to 8 inches thick. We recommend performing moisture and density tests in engineered fill to evaluate if the contractors are effectively compacting the soil and meeting project requirements.