Washington Administrative Code
Title 246 - Health, Department of
SEWER SYSTEMS
Chapter 246-272B - Large on-site sewage system regulations
Part 6 - DESIGN AND TECHNICAL STANDARDS
Subpart B - Specific Technologies
Section 246-272B-06700 - Sand-lined trenches and beds

Universal Citation: WA Admin Code 246-272B-06700

Current through Register Vol. 24-18, September 15, 2024

(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

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

Statutory Authority: RCW 70.118B.020. 11-12-035, § 246-272B-06700, filed 5/25/11, effective 7/1/11.

Disclaimer: These regulations may not be the most recent version. Washington may have more current or accurate information. We make no warranties or guarantees about the accuracy, completeness, or adequacy of the information contained on this site or the information linked to on the state site. Please check official sources.
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