Why Is Selecting Sand Type Important For A Septic Dispersal Field?

By Tobias Moser
Elementary Category (Grades 4-6)
Experiment | Environment

My science project is a study of percolation for three different types of sand filters. Percolation is the rate at which a liquid passes through a filter. The filters are fine, medium and coarse sand.

My interest in this project was because my parents are building a septic system for our new home and there was a lot of talks about sand. I wanted to understand why selecting the right sand types was so important, for a septic dispersal field.

Two different experiments setups were conducted. The materials used were simple items that I found around the house, pop bottles, mesh cloth, measuring jugs and food coloring. The sand I collected was from Robinson creek in Mesachie Lake summer of 2019.

Experiment 1 looks at the percolation rate of washed and dried sand. Experiment 2 looks at the percolation rate of washed sand that is dosed at an interval of 10 minutes. This is a more realistic  scenario of what happens in a septic dispersal field.

Experiment 1, when 250ml of blue water was poured into 250ml of sand filter. Fine sand, about 50% of the water filtered through and took the longest time as compared to medium and coarse sand. All or nearly all water was drained through the medium and coarse sand. The average percolation rates were 2ml/sec for fine sand, 7ml/sec for medium and 17ml/sec for coarse sand.

Experiment 2, when 250ml of blue water was poured into 250ml of sand filter at 10 minutes intervals. Nearly all or all liquid was drained through all three sand filters. The percolation rate was 1ml/sec for fine sand, 4ml/sec for medium sand and 16ml/sec for coarse sand.

In fine sand whether it is dried or wet as in the interval dosing set up. It was observed that the water pooled on the surface. In a septic dispersal field this can cause big puddles to form. The pooled water will result in stinky odors and may pose a health hazard due to the bacteria forming in the puddles.

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