CITY PROJECT - 1821 & 1823 E Chestnut Ave - Plan

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ASSOCIATED SOILS ENGINEERING, INC. Project No.: 7160.23 2860 Walnut Avenue, Signal Hill CA 90755 January 23, 2024 Tel: (562) 426 -7990 * Fax: (562) 426 -1842 Page 9 approximately 40 feet below grade. Additionally, the groundwater levels in groundwater monitoring wells closest to the Site were in excess of 60 feet below well grades, as per reviewed from the State Geotracker well records. Considering that: 1) site subsurface soils have been classified as Holocene-age younger fan deposits consisting of dense to very dense granular, sandy soils within the maximum explored depth of 26 feet and likely beyond; 2) a PGAM of 0.592g from 2022 CBC seismic design criteria; 3) the historic high groundwater level is 40 feet deep per CGS and likely exceeding 60 feet deep per nearby groundwater monitoring well data; and 4) an earthquake magnitude of 6.6 Mw derived per EQFAULT software, the potential for the occurrence of seismically-induced liquefaction at the Site has been assessed to be nil, per the criteria stipulated in SP 117A (Reference 2). 4.2.2 Seismic Settlements: Ground accelerations emitted from a seismic event can cause densification of loose soils both above and below the groundwater table that may result in settlements on ground surface due to volumetric compression of soil mass. This phenomenon is often referred to as seismic settlement and commonly takes place in relatively clean sands, as well as soils with low plasticity and less fines. Although the earth materials on site include medium dense to very dense granular, sandy soils within the maximum depth explored, and are considered non-liquefiable as per stated in Section 4.2.1 above, they may still undergo minor seismically- induced volumetric densification above groundwater level upon a MCE event. The settlement of site granular, sandy materials in their present state as a result of seismically- induced densification (i.e. “dry” seismic settlement) is estimated to be less than one-half (1/2) inch. Such magnitude of seismically-induced dry soil settlement is expected to affect relatively large area. Thus, the corresponding differential settlement over short distances is likely to be negligible. 4.2.3 Earthquake-Induced Landslides: As evidenced in Figure 3, the Site is not located within an area identified as having a potential for earthquake-induced landslides. There is lack of significant relief on or adjacent to the Site. During ASE’s field investigation, there was no indication that recent landslides or unstable slope conditions exist on or adjacent to the Site that would otherwise result in a landslide hazard to the Building or adjacent properties. The potential for earthquake-induced landslides at the Site is considered nil. 4.2.4 Lateral Spreading: Lateral spreading, a phenomenon associated with seismically-induced soil liquefaction, is a display of lateral displacement of soils due to inertial motion and lack of lateral support during or post