902 PINE ST NORTH SOUND BEHAVIORAL HEALTH TREATMENT CENTER 2025-11-04

rGeoTest Services, Inc. November 16,2018 North Puget Sound Behavioral Health—Treatment Center Addition Job No. 18-0770 Dewatering Considerations Typically, groundwater elevations are highest in the late winter and early spring months, and lowest in late summer or early fall. Based on our previous experience with native soils in the project area, we consider the glacial till to be a restrictive layer that will not provide adequate vertical drainage in trenches or open cut areas during site excavation. Shallow groundwater during the wet season or storm events can perch on these surfaces and create temporary ponding that may need to be addressed during construction. We anticipate this condition will be present in the winter season and under storm conditions if trenches or similar excavations are left open for long periods of time. We recommend localized pumping and removal of accumulated water as needed during earthwork. Collected water should be disposed of in an approved location. GeoTest does not anticipate that dewatering will be necessary at a large scale at the project unless excavations of greater than 10 to 15 feet BGS are planned. It is, however, the Contractor's responsibility to provide a suitable dewatering plan based on the type and depth of the excavation and the ground water elevation during construction. Temporary and Permanent Slopes Actual construction slope configurations and maintenance of safe working conditions, including temporary excavation stability, should be the responsibility of the contractor,who ' is able to monitor the construction activities and has direct control over the means and methods of construction. All applicable local, state, and federal safety codes should be followed. All open cuts should be monitored during and after excavation for any evidence ' of instability. If instability is detected, the contractor should flatten the side slopes or install temporary shoring. Temporary excavations in excess of 4 ft should be shored or sloped in accordance with Safety Standards for Construction Work Part N, WAC 296-155-66403. Temporary unsupported excavations in the native glacial till soils encountered onsite should be classified as a Type B soil according to WAC 296-155-66401 and may be sloped as steep as 1 H:1 V (Horizontal: Vertical). All soils encountered are classified as Type C soil in the presence of groundwater seepage and should be sloped 1.5H:1V. Flatter slopes or temporary shoring may be required in areas where perched water flow is present and unstable conditions develop. The contractor should be prepared to address difficult excavation conditions during utility construction and deep foundations if required. We recommend that permanent cut or fill slopes be designed for inclinations of 2H:1V or flatter. Permanent cuts or fills used in detention ponds, retention ponds, or earth slopes intended to hold water should be 3H:1V or flatter. All permanent cut slopes should be vegetated or otherwise protected to limit the potential for erosion as soon as practical after construction. Permanent slopes requiring immediate protection from the effects of erosion should be covered with either mulch or erosion control netting/blankets. Areas requiring permanent stabilization should be seeded with an approved grass seed mixture, or hydroseeded with an approved seed-mulch-fertilizer mixture. Pavement Subgrade Preparation Selection of a pavement section is typically a compromise between higher initial cost and lower maintenance on one side, and lower initial cost, with more frequent maintenance on Page 13 of 17