Question 4 (a) If, after a rain storm, you found pools of water with a yellow-br

Question

Question 4 (a) If, after a rain storm, you found pools of water with a yellow-brown discoloration caused by clay, what would you suspect about the soil in the vicinity of these pools? Would this soil bea good material to form the impermeable zone of an earth dam? Explain your answers to both questions above. (3 mark) b) What causes "Acid Sulphate Soils"? What potential impacts could they have to the natural and built environments? Soils? What measures can we take to minimize the impacts of Acid Sulphate (c) Explain why a sand castle is most stable when the sand is kept moist but would collapse when the sand is dried under the sun or when the sand is saturated by rain. (3 mark)

Explanation / Answer

(a) The pools are found with water which is yellow - brown in colour caused by clay therefore the soil around the vicinity of pools is Acid sulfate soils, which contain microscopic crystals of iron sulfide minerals (commonly pyrite).

Construction projects like dams in acid sulfate soils areas are difficult to manage even when the soil is not acidified. As many acid sulfate soils are unconsolidated estuarine muds and clays with gel-like properties and low load-bearing capacity, foundations or earthworks built on these materials may settle or subside unevenly and slowly. Careful engineering is required to avoid problems with subsidence, which can cause roadways to slump and foundations to crack.

(b) Causes of Acid sulfate soils are:

1. Sulfate-reducing bacteria: They produce pyrite crystals by the process of their metabolism.

2. Iron, in its reduced form (Fe2+), reacts with the hydrogen sulfide (H2S) produced by the sulfate-reducing bacteria, to form pyrite (FeS2).

3. Water movement (like tidal flushing of the system) will remove bicarbonate and leave the pyrite behind, allowing it to accumulate.

Impacts of Acid sulfate soils on natural and built environments:

1. Acid sulfate soils is responsible for acid rain which is harmful for natural agents like it can weaken and kill aquatic creatures likes fishes apart and it is also responsible for chemical degradation of human built infrastructures.

2. The iron produced by the breakdown of pyrite can clog pipes and other metallic utilities.

3. Construction projects in acid sulfate soils areas can be difficult to manage even when the soil is not acidified as mentioned previously.

Measures:

The most easy and economical way of protection from acid sulphate soil is to treat it with mix an alkaline material into the soil, where it can react with acidity and neutralise it. Agricultural lime (powdered calcium carbonate—CaCO3) is the most common neutralising material in use. Apart from this other measures can be like aligning and designing linear infrastructure in tidal areas so that natural water flows (both surface and groundwater) are not blocked, making farm and urban drains broad and shallow so they don't dig into buried acid sulfate soil layers, but can still remove excess surface water efficiently.

(c) Sand rich soils can absorb large quantities of water, becoming sticky and heavy. Conversely, they can also become very hard when dry, resulting in shrinking and cracking of the ground. This softening, is used to keep the sand castle stable when the sand is kept moist and shrinking and cracking will make it to collapse.

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