4620 SEAHURST AVE 2020-05-20 - Laserfiche WebLink

March 7, 2011 Mr. Paul Thompson/Kolbear, Inc. L&A Job No. 11-001 • Page 14 the area. Cut bank along the north side of the southern half of the lot may be lined by a rockery or precast concrete block wall. The vegetated segment should have well-established vegetation, be landscaped with well- established groundcover, or be with native vegetation natural ground cover. The groundcover should be dense enough to help disperse and infiltrate flow and prevent erosion. The flowpath segment should be in areas reserved for such surface dispersion use. The slope of the flowpath segment should be no steeper than 20% for any 20-foot reach of the flowpath segment. The length of vegetated flowpath segment should be at least 25 feet long in the direction of water flow. The distribution trench should be about 24-inch wide by 24-inch deep. The length of the distribution trench should be 10 feet for every 700 square feet of impervious area served, but need not to be more than 50 lineal feet. The distribution trench should be located at least 10 feet from nearby buildings and at least 5 feet away from property lines, and should be outside of areas more than 20% slope. The distribution trench, to be filled with clean, 3/4 to 1-1/2 inch, wash gravel or crushed rock, should be equipped with a notched board to distribute stormwater in sheet flow onto the vegetated flowpath segment. Infiltration Trenches Test Pits 5 and 6, located along the common lot line of Lots 1 and 2, encountered a gravelly fine to coarse sand deposit at about 3.0 to 5.5 feet deep. Infiltration trenches installed into this gravelly sand deposit may be used to dispose roof runoff for the residences to be constructed on these two lots. This gravelly sand can be classified as sand to slightly loamy sand. The infiltration rate of this type of soil is normally in the range of 10 to 20 inches per hour. We LIU & ASSOCIATES, INC.