All about aquifers

 We also engaged with other activities to find out:

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• Between sand and gravel which holds more water?

We used two small cups, one filled with gravel and the other with sand. Water was filled in syringes and delivered to the two cups [until they were full]. The water left in the syringes was subtracted from the measurement before it was delivered and it was found that the sand held more water than the gravel.

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• How water in the aquifer is recharged: what is the speed of water passing through different materials?

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We watched an experiment testing different materials and how they allow the passage of water. [Materials were in buckets that had holes in the bottom for drainage] The materials were:

• Empty bucket

• Bucket with gravel

• Bucket with clean sand

• Bucket with garden soil

The bucket with gravel had the ability to pass water as fast as the empty bucket. This shows that gravel in the ground can allow water to move through it very quickly. [The bucket with sand passed water more slowly but all of the water did drain out. The bucket with soil passed some water quickly but not all of it. By the time the experiment ended a lot of the water still had not come out of the soil. This shows that soil can hold on to water, which is important for plants that grow in the soil and use the water that the soil retains.]

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• How water in the aquifer is polluted?

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The set up was in a clear plastic box where we put gravel and spread it to the sides of the box making a depression (to be a lake) in the middle and half filled it with clear water. Then we mixed a beaker of water with food dye and then poured it into the set up at one of the sides. It showed that the pollutant could easily pass through the gravel structure and mixed with the pure water.

 

• How water is cleaned using [activated] charcoal?

The challenge was how we could clean polluted water with charcoal. We added charcoal to a small cup and pumped [pink] water from the trough used in the above experiment to half fill the cup. We covered the top of the cup with filter paper and it was left [to allow the activated charcoal to absorb the impurities]. We then delivered the water [by pouring it through the filter paper] into another cup. The water that came out was clear.

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• How water is pumped out of an aquifer and how pollutants move around?

The set up was tested with two boxes whereby one had gravel at the bottom, a layer of clay to act as a confining layer that does not allow water to pass through, and a layer of sand at the top. Two holes were made at the sides where one hole had a handpump [a small plastic pump was used] and the other hole represented a latrine (a tube with a syringe that contains coloured water to act as a pollutant). [The handpump went into the bottom gravel layer and the latrine went only as deep as the top sand layer.] Clear water was rained on the top of the sand and it moved [through the sand and into the bottom gravel layer] through some spaces left in the layer of clay that act as fractures to the layer of gravel. Water was pumped out and the polluted water in the syringe was delivered in. The layer of clay has fractures and the layer of gravel has a lot of spaces so the pollutant water passes through easily and hence spread to the pump, when this happens in real aquifers it is dangerous for human consumption.

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