2211 GIBSON PL Geotech Report 2023-04-06

August 18, 2014 Gibson Bluff L&A Job No. 14-056 Page 23 below the top of trenches. The top of the gravel or crushed rock fill should also be covered with the filter fabric liner. The remaining trenches should then be backfilled with compacted onsite clean sandy soils. The gravel or crushed rock fill should be placed in lifts no more than 10 inches thick in loose state, with each lift compacted to a non- yielding state with a vibratory mechanical compactor. The compaction and densification of trench fill is critical if it is to support roadways or driveways. Stormwater captured over paved roadways/driveways should be routed into a catch basin equipped with an oil- water separator before being released into the infiltration trenches. If maintaining groundwater quality is critical, the bottom of trenches should be filled with a minimum 12-inch layer of uncompacted amended soil. The amended soil should contain 40 percent (by volume) of compost, mixed with clean, medium to coarse, sand, to achieve an organic content of at least 10% by dry weight. The trenches are then filled with clean 3/4 to 1-1/2 inch washed gravel or crushed rock as recommended above. The dispersion pipes, constructed of 4-inch rigid perforated PVC pipes, should be laid level and completely enclosed by the gravel or crushed rock fill at about 24 inches below the top of trenches. The top of the gravel or crushed rock fill should also be covered with the filter fabric liner. The remaining trenches may then be backfilled with compacted onsite clean sandy soil. RISK EVALUATION STATEMENT The site is underlain at shallow depth by medium-dense to dense, Esperance sand deposits. These competent soils have moderately-high to high shear strength, and are of LIU & ASSOCIATES, INC.