1920 MERRILL CREEK PKY 2018-01-01 MF Import

i i SHANNON F�WILSON,INC. scarp (see location on Figure 1) at the cent�al portion of the site. This area was excluded � from mitiga6on because of the limited height of the slope and the existing 60�egree � inclinadon of the scarp is relatively close to the recommended 1H:1V excavation face in the itill. Additionally, any attempt at regrading would disturb nadve vegetation upslope and possibly cause renewed erosion. I While the above slopes will prwide adequate facwrs of safety and masonable performance for cuts in the native soils (tills and outwash) and provide adequate factors of safety for the I upslope plateau development, the acisting 1.SH:1V to 1.75H:1V slopes in the Sil and colluvial soils on the slope azie marginaily shable. Those slopes may ezperience surface Iiavelling and mwement as induced by intense rainfall or seismic loading. Mwement in these slopes is liloely to resemble the existing surficial failure of the hillside slope located south of the project. Such potential surface mavements are not anticipated W affect the ' proposed structures on the upper plateau. These movements, however, would likely resutt I in the accumulation of debris at the toe of the existing slope. Such movements would requice local effort to restore and revegetate the slope and clean up debris at the toe. IAtter discussing several alternatives to mitigate poten6al instability of the 6ll/colluvial slopes on the subject site, we understand that the owner t�as elected to mitigate the on-site slope Iand not to attempt to stabilize the Sll/colluvium slopes. Disturbance to heavily vegetatod, marginally stable 811/colluvium slopes would incnease the potenGal for instability in the short term. 1'his is consistent with the City's conclusion in revised MDNS No. 37-89. I Although the design team felt that it was not feasible to stabilize the fill/colluvium to factors of safety corresponding to general embankment construction, thece are several measums that I couid be implemented to decrease the risk of fill/colluvium slope inslability, as discussed belaw. In order to reduce surface wdter flow wer the slope, the grading plan should be developed W include a ditch at the top of the slope to divert surface runoff away from the � slope. It should also be realized that unsafe actions by the adjacent property owner, over which the ' owner of this subject site may ha��e little control, could cause instability on the subject I property slope. These actions could include undercutting of the hillside, which could cause the slope to retreat and lead to instability in the fill and colluvium soils. Or it could include I W-6693-01 13