3800 RIVERFRONT BLVD Geotech Report 2023-05-04

I March 26, 2019 HWA Project No. 2015-061-21 Task 600-7 I • HMA should not be placed when precipitation is anticipated before the pavement can be compacted, or before any other weather conditions which could prevent proper handling and compaction of HMA. I • HMA should not be placed when the average surface temperatures are less than 45° F. I • HMA temperature behind the paver should be in excess of 240° F. Compaction should be completed before the mix temperature drops below 180° F. Comprehensive temperature records should be kept during the HMA placement. I • For cold joints, tack coat should be applied to the edge to be joined and the paver screed should be set to overlap the first mat by 1 to 2 inches. I 4.5.9 Pavement Drainage IIt is essential to the satisfactory performance of the roadway that good drainage is provided to prevent water ponding on or alongside, or accumulating beneath, the pavement. Water ponding can cause saturation of the pavement and subgrade layers and lead to premature failure. The surface of the pavement should be sloped to convey water from the pavement to appropriate drainage facilities. I4.6 STORMWATER MANAGEMENT As Riverfront Boulevard will be constructed within the limits of the old Everett Landfill, the use Iof onsite infiltration will not be allowed. We understand that stormwater management will consist of treatment and discharge to a suitable outlet. I4.7 LANDFILL GAS The refuse along Riverfront Boulevard is expected to continue to generate landfill gasses I throughout the design life of the development. Landfill gas collection will likely be required along the roadway. It is our understanding that HMA pavement, PVC liner system, or possibly LPSB will be used as the landfill gas barrier along the various sections of Riverfront Boulevard Iand the surrounding corridor. Where used, each of these individual systems will function independently with connection details to ensure continuity at transitions between barrier types. I In addition to collection and disposal of landfill gas, measures should be implemented to prevent landfill gas from migrating along utility trench backfill and utilidors, and into manhole and vault structures. These measures could include placement of impermeable trench backfill at specific I locations and around manholes structures to prevent gas migration. Due to the anticipated low rate of flow through the more recently placed landfill cap materials, it may be necessary to install gas collections systems below these cap fill soils or extend vertical pipes below the cap fill ' materials, at regular intervals to facilitate gas removal. Further evaluations with respect to gas migration along utility trenches and gas collection in general is being completed by Herrera. I Geotechnical Report Revision 3 26 2019.doc 21 HWA GEOSCIENCES INC.