2312 W CASINO RD COMMUNITY TRANSIT Geotech Report 2022-10-25

TABLE 2. RECOMMENDED DESIGN PAVEMENT SECTIONS HMA ATB Crushed Surfacing Base PCC Plain Jointed Coarse L 1/2" PG64-22 Thickness Course with less than 5% Pavement Aggregate Thickness (inches)1 fines content(inches)2 Thickness(inches) Base(inches)3 (inches)1 Automobile Parking and Light Duty Service Vehicles 3 6 Heavy Duty Traffic and Limited Bus Traffic Alternative 1 2 4 6 Alternative 2 6 6 Bus Traffic and Parking 9 6 Notes: HMA Class 1/2-inch,PG 64-22 per WSDOT Standard Specifications 5-04 and 9-03. 2 Crushed Surfacing per WSDOT Standard Specification 9-03.9(3)compacted to 95 percent of MDD determined using ASTM D-1557, to be placed on subgrade compacted to 95 percent of the MDD. 3 Coarse aggregate base should be similar to AASHTO Grading No.57 as defined in WSDOT specification 9-03.1(4)C.The above pavement recommendations assume subgrade preparation and placement of structural fill as previously recommended. 4.9. Infiltration and Drainage Considerations Native soils at the site consist of very dense glacial till and are considered "hardpan." Infiltration is not recommended for these soils as defined in the 2014 Stormwater Management Manual for Western Washington Site Suitability Criteria SSC-5. SSC-5 requires the base of all infiltration basins or trench systems to be at least 5 feet above the seasonal high-water mark, bedrock or hardpan, or other low permeability layer. Very dense glacial till was encountered within 3 feet of the existing ground surface across the site with the exception of existing backfill around the existing facility. In addition, perched groundwater was observed at a depth of 71/2 feet below the pavement surface in the vicinity of the proposed stormwater facility. We recommend that pavement surfaces be sloped so that surface drainage flows away from the building. All areas should be graded to avoid concentration of runoff onto fill, cut slopes, natural slopes steeper than 10 percent or other erosion-sensitive areas. We recommend that all roof drainage be collected in tight lines for diversion into the storm drain system. Perched groundwater is anticipated at the site. We recommend footing drains be installed around new foundations.As recommended in the "Floor Slab Support"section, a vapor barrier should be utilized where control of moisture in the slab is critical. 5.0 LIMITATIONS We have prepared this report for use by Community Transit, Otak, Inc. and other members of the design team for use in the Casino Road Renovation Community Transit Kasch Park Base project in Everett, Washington. GEOENGINEERS November 14,2019 Page 11 File No.2095-019-07