6624 BROADWAY 2018-01-02 MF Import

We reviewed a publishc.l geologic map titled Distribution and Description of the Geologic Units in the Everett Quadranole, Washington, By James P. Minard, 1981, United States I Geological Survey Open File Report 81-248. This published map indicates that the site is characterized by lodgment till sediments, with advance outwash sediments also mapped in 1 close proximity. In our opinion it is not unusual for site -specific explorations to disagree with published regional geologic maps. Site -specific explorations should be used as a basis for design. CONCLUSIONS AND RECOMMENDATIONS Existing Fill - Site Layout Implications Exploration boring HA -I encountered existing fill greater than 5 feet thick that is unsuitable for foundaEon support. It would be possible to remove the existing fill and replace it with compacted, imported structural fill; however, the resulting costs would be significant. It would also be possible to support new structures in this area using a system of rock -filled trenches, as summarized in this report. The most cost effective alternative would be to site the new buildings in such a way that they will not be underlain by existing fill. We are available to answer questions that may arise during planning of the site layout. Site Preparation Site preparation should begin with installation of temporary erosion and sedimentation 1 controls. The existing structures, foundations, utilities, and any other existing site improvements in the planned development area should be removed. We are not aware of any existing septic systems on -site, but if any septic systems exist they should be decommissioned in accordance with ^.ounty Health Department regilations and removed from structural areas. If demolition creates areas of excavation or disturbed soils below foundation grades, these areas should be backfillcd with structural fill, as discussed under the "Structural Fill" section. J Because: the existing structure includes a partial basement, we anticipate that there will be excavations below planned foundation grades that will require structural fill placement. Site preparation of planned building and driveway areas should include removal of all trees, brush, debris, and any other deleterious material. Additionally, the upper organic topsoil should be removed and the remaining roots grubbed. Areas where loose surficial soils exist due to grubbing operations should be considered as fill to the depth of disturbance and treated as subsequently recommended for structural fill placement. In our opinion, stable construction slopes should be the responsibility of the contractor and should be determined during construction. For estimating purposes, however, we anticipate that temporary, unsupported cut slopes in the existing fill can be planned at a maximum slope of 211:1V (Horizontal:Vcrtical). Temporary cut slopes in ice contact sediments can be planned at 1.511:IV. As is typical with earthwork operations, some sloughing and raveling may occur, 3