7710 EVERGREEN WAY NEW CINGULAR WIRELESS ANTENNA 2016-09-26

• Adapt Engineering Evergreen Way. The proposed lease area is covered with asphalt surfacing material and is currently utilized as vehicle parking far the adjacent commercial building. Subsurface Conditions At the exploration location designated B-1, the near-surface soil conditions below the 2 to 3-inch thick asphalt surfacing material consist of roughly 3 to 6-inches of fine to coarse sand with gravel, interpreted to be fill material used as a grading course, mantling crushed rock and rock spalls, also interpreted to be fill material. Below these surficial soils, at a depth of approximately 5.0-ft bgs, we encountered alternating zones of very dense fine to coarse sand with silt and cobbles and very dense silty gravel with sand and cobbles, which generally extended to the full explored depth of approximately 35.5-feet bgs. Perched groundwater seepage was encountered within the test boring near 25.0-ft bgs, at the time of drilling. Please note, throughout the year, groundwater levels may likely fluctuate in response to changing precipitation patterns, off-site construction activities, and changes in site utilization. Seisinic Conditions Based on our analysis of subsurface exploration logs and a review of published geologic maps, we interpret the on-site soil conditions to correspond to Site Class C, as defined by Table 203-1 within Chapter 20 of ASCE 7 in accordance with the 2012 International Building Code (IBC). The soil profile type for this site classification is characterized by very dense/hard soils with an average blowcount above 50 blows-per-foot within the upper 100 feet bgs. Current (2003) National Seismic Hazard Maps prepared by the U.S. Geological Survey indicate that peak bedrock site acceleration coefficients of about 0.293 and 0.539 are appropriate for an earthquake having a 10-percent and 2-percent probabi]ity of exceedance in 50 years (corresponding to return intervals of 475 and 2,475 years, respectively). The IBC mapped spectral accelerations for short periods at the subject site (SS and S�; Site Class B) are 121.5 and 42.8 (expressed in percent of gravity) at 0.2 and 1.0-second periods, respectively with 2 percent probability of exceedance in 50 years. In accordance with Tables 1613.5.3(1) and 1613.5.3(2), Site Coefficients, Fa and F,,, are 1.0 and 1372, respectively for a Site Class C. Therefore the adjusted MCE ground motions are SMS=1.215g and SM�-0.587g. For purposes of seismic site characterization, the observed soil conditions were extrapolated below the exploration termination depth, based on a review of geologic maps and our knowledge of regional geology. CONCLUSIONS AND RECOMMENDATIONS Current development plans call for the construction of a new steel telecom�nunication tower and associated equipment building or cabinet pad within the proposed lease area. Based on the subsurface conditions revealed by our field exploration, we recommend that the proposed tower be supported on either a drilled pier or concrete mat foundation. Typically, a drilled pier design provides a cost-effective foundation design for communication tower structures, provided that adequate embedment depths can be achieved with the drilled pier augering equipment, that the site is accessible to the drill rig, and that drilled pier contractors are available within a reasonable distance from the site. Alternatively, a reinforced concrete mat foundation may be selected if difficult drilling conditions are anticipated due to the presence of shallow bedrock or boulders, provided that the proposed lease area can accommodate the generally larger excavation area required for a mat foundation. We recommend that both of these AT&T Mobility c/o Ryka Consulting May 5, 2014 Adapt Project No. WA14-18929-GEO Page 3