Leach-Field / Trench Drainrock Volume
Washed drainrock for a septic leach field from the trench layout: stone = trenches x length x width x depth / 27; tons = stone x ~1.4 ton/cy. Three 60 ft trenches, 24 in wide with 12 in of stone, is 14.7 cy (about 20 tons) at 10% waste; a deeper 18 in bed is 22 cy. The trench count, width, and stone depth come from the AHJ-approved septic design (the required length is septic-drainfield); the geotextile over the stone is taken off separately.
Formula and source
stone_cf = num_trenches x trench_length_ft x (trench_width_in/12) x (stone_depth_in/12); stone_cy = stone_cf / 27 x (1 + waste_pct/100); stone_tons = stone_cy x 1.4.
Leach-field drainrock identity by name (trench box volume to cubic yards with waste, then tonnage); first-principles volume arithmetic.
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