Appendix 3: Sand Sieve Analysis - CAWST

Biosand Filter Manual Appendix 3
12. Determine the Percent Passing Through the #150 Sieve. This is the measure of
the very fine sand (also called rock flour) that can plug the filtration sand and cause
turbid water to come out of the biosand filter. CAWST recommends that the sand is
washed sufficiently so that not more than 4% of the sand will pass through the #150
sieve.
Recommended Value for Percent Passing Through the #150 Sieve = < 4%
Instructions to Determine % Rejected
To determine what percentage of a sand source will be too large to use as filtration sand:
1. Place only the #24 sieve on to the catch pan. Take a representative of a dry sand
sample.
2. Fill the graduated cylinder with 100 ml of the dry sand sample.
3. Pour the entire 100 ml sample from the graduated cylinder onto the top sieve (#24)
and place the lid on top of the sieve.
4. Shake the #24 sieve, including the bottom catch pan and top lid, for about 20
seconds. Shake both sideways and up and down to ensure the sand falls through the
screen.
5. Remove the top lid and pour the sand from the #24 sieve into the graduated cylinder.
Use a piece of paper as a funnel to help pour the sand into the cylinder. Read the
amount of sand in the graduated cylinder. This value is the % Rejected – Too
Coarse.
6. Empty the graduated cylinder and pour in the sand from the catch pan. Read the
amount of sand in the graduated cylinder. This is the portion of the sand that will
remain after sieving with the #24 screen. Note that this portion may have a
considerable amount of very fine sand in it. To determine the amount of very fine
sand, follow the previous instructions using all 5 sieves to determine the % passing
through #150 sieve – this is approximately the % Rejected – Too Fine and will need
to be removed by washing.
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