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Project No. 364 571 Page 3 CONCLUSIONS AND RECOMMENDATIONS The conclusions and recommendations presented in this report are based on the information provided to us, results of the field investigation, analyses, and professional judgment. We have observed only a very small portion of the pertinent soil, rock and groundwater conditions. The recommendations made are based on the assumption that site conditions do not deviate appreciably from those found during the field investigation. If the plans for site development are changed, or if variations or undesirable geotechnical conditions are encountered during construction, we should be consulted for further recommendations. Site Characteristics The site is mantled with approximately 2 to 4 feet of brown, firm to stiff silt. This silt contains root hairs and trace imported basalt gravels, and is underlain to depths of at least 311/2 feet by firm to hard silty to sandy silt soil formed from the alluvial sediments of the Willamette Silt. Portions of the underlying silty softs contain up to 40% wood and wood fiber debris. Groundwater is anticipated at depths greater than 30 feet at this site. Monopole Foundation We recommend that the monopole be supported by a drilled pier foundation. Significant groundwater does not appear to be present within 30 feet of the ground surface. A structural mat foundation is not recommended on this site due to the presense of highly compressible peat layers below a depth of about 12V2 feet. The drilled pier should be at least 5 feet in diameter and extend at least 30 feet below the ground surface into the hard silt. We anticipate that the silt on the site can be drilled with conventional, heavy-duty large-diameter drilling equipment. Since the drilled pier will need to resist downward loads in end-bearing, we recommend that the bottom of the excavation be cleaned of loose soil cuttings prior to placing the rebar cage or concrete. The bottom of the excavation should contain less than 2 inches of soft, loose soil after cleaning w/th a fiat-bottom cleaning bucket. The maximum bending moment and deflection of the drilled piers during lateral loading were evaluated using the computer program LPILE1 (Ensoft Inc., 1989), which models the behavior of laterally loaded piles in layered soils. The calculations are attached as Appendix B. For our analysis, we assumed that the top of the drilled pier is located one foot above the ground surface.