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Mater Dei High School October 20, 2023 Proposed Dance Studio, Santa Ana, California Project No. 3204.I 3204-I-01R (10/23) 13 4.4.5 Foundation Concrete Laboratory testing by Project X (Appendix B) indicates that the near surface soils exhibit a soluble sulfate content of 354 mg/kg (0.035 percent by weight). For the 2022 CBC, foundation concrete should conform to the requirements outlined in ACI 318, Section 4.3, for negligible levels of soluble sulfate exposure from the on-site soil (Category S0). Chloride levels in the samples of the upper soils ranged 14 mg/kg (.001 percent by weight). For concrete exposed to soil moisture, such as footings and floor slabs, we recommend a chloride Category C1. 4.4.6 Foundation Excavation Observation Prior to placement of concrete and steel, a representative of GPI should observe and approve all foundation excavations. 4.5 BUILDING FLOOR SLABS Slab-on-grade floors should be supported on at least 2 feet of granular, non-expansive (EI less than 20), compacted soils as discussed in the “Placement and compaction of Fills” section. The non-expansive soils should extend to at least 10 feet outside the building pad where flatwork is planned. Based on our explorations, granular, non- expansive soils are not readily available on-site in the near surface soils. The Structural Engineer should provide the final floor slab design. A mat foundation slab can be supported on the on-site soils with medium expansion potential provided that the soils are compacted as discussed in the “Placement and Compaction of Fills” section. A vapor/moisture retarder should be placed under slabs that are to be covered with moisture-sensitive floor coverings (parquet, vinyl tile, etc.). Currently, common practice is to use a 15-mil polyolefin product such as Stego Wrap for this purpose. Whether to place the concrete slab directly on the vapor barrier or place a clean sand layer between the slab and vapor barrier is a decision for the Project Architect, as it is not a geotechnical issue. If covered by sand, the sand layer should be about 2 inches thick and contain less than 5 percent by weight passing the No. 200 sieve. Based on our explorations and laboratory testing, the soils at the site are not suitable for this purpose. The function of the sand layer is to protect the vapor retarder during construction and to aid in the uniform curing of the concrete. This layer should be nominally compacted using light equipment. The sand placed over the vapor retarder should only be slightly moist. If the sand gets wet (for example as a result of rainfall or excessive moistening) it must be allowed to dry prior to placing concrete. Care should be taken to avoid infiltration of water into the sand layer after placement of the concrete slab, such as at slab cut-outs and other exposures. A sand layer is not required beneath the vapor retarder, but we take no exception if one is provided. It should be noted that the material used as a vapor retarder is only one of several factors affecting the prevention of moisture accumulation under floor coverings. Other factors include maintaining a low water to cement ratio for the concrete used for the floor slab, 1202 W Edinger Ave10/3/2024