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1 <br /> Su6swJuce Erplorntton, Gco(ogic Hazard, and <br /> r Neuring Hopt Phuse!! Freliminary Geaechnicd Enginetring Repon <br /> � Eti rrrrr. Wnr/u'ngron Geologic Hazards and Mirigations <br /> ' iI. GEOLOGIC I�+►ZARDS AND :�IITIGATIONS <br /> rThe foUowing discussion of potential geologic hazards is based on the geologic conditions as <br /> observed and discusseci herein. <br /> � 5.0 SLOPE STABILITY HAZARDS AND RECOMb1ENDED MITIGATION <br /> ( 12econnaissance of this site was limi[ed to the area shown on Figure 1. 'The northeast site <br /> corner topography is relatively flat to slightly hummocky. However, steep slopes inclined at <br /> � up to 50 pe�cent exist along the west boundary of the proposed development area. These <br /> slopes have been oversteepened by past gra�ing activities during development of building pads <br /> for the adjacent duplexes to the west. Up to 4 feet of fill was present at the toe of this slope in <br /> � EP-3 and EP=3. It is expec[ed that at least this much fill is also present on the slope face and <br /> possibly near the crest of the slope. Abundant construction debris and trash was noted within <br /> the shallow surficial fill soils on the slope face. The slope shows signs of shallow instability <br /> ! and erosion. `fany of the [rees are severely bowed at their base from downslope loose soil <br /> movement. <br /> ( The north-facine slope along the south property line is inclined at approximately 30 percent <br /> a�d is comprised of native soils. In our opinion, this slope appears considerably more stable <br /> with respect to shallow surficial landsliding and erosion potential than the western slope. � <br /> ! . h <br /> Given the area proposed for development is exvemely :imited, and the on-site slopes have been <br /> 1� artificially s[eepened by past grading and filling activities, it is our opinion that imposing <br /> � setbacks from the toe of these slopes is not practical or sufficient to effectively reduce the <br /> po[ential landslide hazard. Therefore, we recommend retaining, buttressing, or otherwise <br /> � reinforcing these slopes. Construction of retairing walls along the west site margin and along <br /> [he south property line, if grades are significantly lowered in chis area, will not only protect the <br /> new structures, but will provide protection and additional founda:ion stabiliry for the duplexes <br /> � to the wes[ nf the proposed buildin� area. Sevcral options aze available for retaining wall <br /> design depending on the intended building design and finished floor elevations. These options <br /> � are discussed in �etad in thP Design Recommendations section of this repoR. <br /> I6.0 SEIS�IIC HAZARDS AND RECOM:�IENDED MITIGATION <br /> Earthquakes occur in the Puget Sound Lowland with great regulariry. The vast majority of <br /> I these events are small and are usually not felt by people. However, large earthquakes do occur <br /> as evidenced by the most recen[ 6.8-magnitude event on February 28, 2001 near Olympia <br /> Washington, the 1965, 6.5-magnitude event, and the 1949, 7.2-magnitude eveat. The 1949 <br /> � February 11. 2002 ASSOCIATED F1R77f SC/ENCES, INC. <br /> SrlliL!.KE017�9A3�Pm�rar'.�l��PKf.'FlWP-W2X Page 6 <br /> i %a� <br />