12728 19TH AVE SE BASE FILE Geotech Report 2025-07-29

May 28, 2007 Proposed Office Building L&A Job No. 7A053 Page 15 ' We recommend that a 4-inch-thick minimum, compacted, crushed rock base (CRB), consisting of 7/8-inch-minus crushed rock, be used for the parking lot and driveways. The crushed rock ' base should be topped by 3-inch-thick Class B asphalt concrete(AC. ' DRAINAGE CONTROL Site and Roadway Grading The on-site surficial fine-grained soils can be saturated quickly and heavy runoff and near- surface groundwater may be encountered during periods of heavy rain. To minimize,potential difficulties for site grading work due to storm runoff and groundwater seepage during construction, one or more lines of ditches or interceptor trench drains should be installed, as �. required, along the uphill side of the site to intercept storm runoff and near-surface groundwater flow. Water thus collected should be direct into a nearby storm inlet covered with a filter sock. I Excavation of Vault Pit and Building Footprint wExcavation of detention vault pit and building footprint, if encountering groundwater, should have the bottom of excavation sloped and ditches excavated along the bases of cut banks to direct groundwater seepage to flow into a sump pit from which water can be pumped out of the pits into a nearby storm inlet. A layer of 2-inch crushed rocks should be placed over firm subgrade soils under footings, as required, to protect the soils from disturbance by construction equipment and foot traffic. This crushed rock base should be built to a few inches above groundwater level, but not less than 6 inches thick. The crush rock base should be compacted in 12-inch lifts to a non- yielding state with a vibratory mechanical compactor. Runoff over Impervious Surfaces Storm runoff over impervious surfaces, such as roofs and paved parking lot and driveways, should be collected by underground drain line systems connected to downspouts and by catch 111 LIU & ASS OCIATES, INC. . I