4620 SEAHURST AVE 2020-05-20 - Laserfiche WebLink

March 7, 2011 Mr. Paul Thompson/Kolbear, Inc. L&A Job No. 11-001 Page 13 We recommend that a minimum 4-inch-thick layer of compacted, 3/4-inch crushed rock base (CRB)be used for the driveway. The crushed rock base should be topped with a 4-inch concrete pavement reinforced with a layer of welded wire fabric at mid-depth of the pavement. If pervious pavement is to be used for the driveway and to allow runoff to disperse into the ground, the pervious pavement should be constructed over at least 36 inches of free-draining material, including a 24-inch subbase course of clean gravelly sand (WSDOT No. 17 soil) and a 12-inch rock base course of 1-1/2-inch-minus crushed rock (WSDOT No. 57 crushed rock), topped by a 2-inch bedding course of 3/8-inch-minus crushed rock (WSDOT No. 8 material). The sand and crushed rock fill should be placed in lifts no more than 8 inches thick with lift compacted to a non-yielding state with a vibratory compactor. The pervious pavement may then be constructed on the crushed rock base. ONSITE STORMWATER DISPOSAL Surface Dispersion The very-dense fresh till soil underlying the southern half of the Lot 3 at shallow depth is very stable and surface dispersion may be achieved for onsite disposal of roof runoff for the residence on Lot 3. Stormwater should be directed into a distribution trench and overflow the trench in sheet flow onto a vegetated area call "vegetated flowpath segment" over which water would evaporate into the ambience, be absorbed by the root system of vegetation and infiltrate into the ground. The vegetated flowpath segment in the southern half of Lot 3 may required some grading so that sheet flow over the segment can be assured. This would require cutting down the northern portion of LIU & ASSOCIATES, INC.