WAC 246-272B-06700. Sand-lined trenches and beds

(1) Sand-lined trenches or beds may be used to meet Treatment Level B. (2) The minimum dosing frequency is: (a) Twelve equally spaced timed doses per day for coarse sand; or (b) Six equally spaced timed doses per day for ASTM C-33 sand. (3) The maximum allowable hydraulic loading rate is one gallon per square foot per day. (4) The design engineer shall: (a) Use coarse sand that meets the following specifications: (i) Particle size distribution per Table 8 of this section; (ii) Effective particle size from 0.3 to 0.5 mm; and (iii) Uniformity coefficient less than four; or (b) Use sand that meets the ASTM-33 specification, Table 9 of this section and: (i) Has no more than forty-five percent passing any one sieve and retained on the next consecutive sieve, of those listed in Table 9 of this section; and (ii) Has a fineness modulus of not less than 2.3 or more than 3.1. The fineness modulus is calculated by adding the cumulative percents of samples retained on the sieves listed in Table 9 and dividing the sum by 100; or (c) Verify that the sand material meets the desired specification and provide to the department a particle size analysis of the sand material. (5) The minimum depth of sand media is twenty-four inches. (6) The design engineer shall: (a) Design the LOSS to meet the drainfield requirements in Table 3 in WAC 246-272B-06050 for the minimum horizontal setback from the edge of the sand-lined trench or bed; (b) Specify that for installations in type 1 soil, trench and bed widths be increased by one foot from the calculated minimum absorption area based on design flow; the additional volume must be filled with sand media in order to prevent effluent from bypassing filter media by flowing out the sidewalls; and (c) Specify monitoring ports as required in WAC 246-272B-06400 . Table 8: Coarse Sand—Required Particle Size Distribution Sieve Particle Diameter, mm Percent Passing by Weight 3/8 inch 9.50 100 No. 4 4.75 95 to 100 No. 8 2.36 80 to 100 No. 16 1.18 45 to 85 No. 30 0.6 15 to 60 No. 50 0.3 3 to 15 No. 100 0.15 0 to 4 Sieve Particle Diameter, mm Percent Passing by Weight 3/8 inch 9.50 100 No. 4 4.75 95 to 100 No. 8 2.36 80 to 100 No. 16 1.18 45 to 85 No. 30 0.6 15 to 60 No. 50 0.3 3 to 15 No. 100 0.15 0 to 4 Table 9: Fine Aggregate—ASTM C-33 Sand—Particle Size Distribution Sieve Particle Diameter, mm Percent Passing by Weight 3/8 inch 9.50 100 No. 4 4.75 95 to 100 No. 8 2.36 80 to 100 No. 16 1.18 50 to 85 No. 30 0.6 25 to 60 No. 50 0.3 5 to 30 No. 100 0.15 0 to 10; prefer < 4 No. 200 0.075 0 - 3; prefer 0 Sieve Particle Diameter, mm Percent Passing by Weight 3/8 inch 9.50 100 No. 4 4.75 95 to 100 No. 8 2.36 80 to 100 No. 16 1.18 50 to 85 No. 30 0.6 25 to 60 No. 50 0.3 5 to 30 No. 100 0.15 0 to 10; prefer < 4 No. 200 0.075 0 - 3; prefer 0