2207 GIBSON PL 2022-10-28 - Laserfiche WebLink

August 18,2014 • Gibson Bluff L&A Job No. 14-056 Page 22 deposits underlying the site at shallow depth are capable of supporting infiltration trenches or galleries to be used for onsite stormwater disposal. infiltration trenches/galleries should be set back at least 5 feet from property lines, 10 feet from adjacent building footing foundations or utility trenches, and 30 feet from the top of slopes of 40% grade or more. The bottom of infiltration trenches er galleries should be at least one foot lower than adjacent building footing foundations or utility trenches. • Infiltration trenches/galleries should be scattered throughout the site to spread water over the entire site and, thus, minimize potential problems from disposed stormwater. Infiltration trenches/galleries installed underneath the access road would a suitable choice. • • Infiltration Trench/Gallery Construction The trenches should be cut at least 6 inches into the Esperance sand deposits of clean, fine to medium sand. To reach this target soil stratum the trenches would have to be -- excavated- to--about 5.0 to 9.0 feet deep or more, depending on the locations= of-the --- infiltration trenches/galleries. The condition of the soil unit at bottom of trenches should be verified by a geotechnical engineer. The stability of the trench cut banks should also • be verified by a geotechnical engineer during excavation. The trenches should be at least 24 inches wide. The side walls of the trenches should be lined with a layer of non-woven filter fabric, such as MIRAFI 140NS. The trenches are then filled with clean washed 3/4 to 1-1/2 inch gravel or crushed rock to within about 12 inches of the finish grade. The dispersion pipes should be constructed of 4-inch rigid PVC pipes and laid level in the gravel or crushed rock filled trenches at about 24 inches • LIU & ASSOCIATES, INC.