Which of the following is/are the possible consequence/s of heavy sand mining in river beds?<br/>1. Decreased salinity in the river<br/>2. Pollution of groundwater<br/>3. Lowering of the water-table<br/><br/>Select the correct answer using the code given below:

1. Decreased salinity in the river — Incorrect. Heavy sand mining does not decrease river salinity; in coastal rivers it can actually promote saline water intrusion by deepening the channel and disturbing the river-aquifer balance.

2. Pollution of groundwater — Correct. Excessive sand removal disturbs the natural filtration function of riverbeds and can allow contaminants/turbidity to affect adjoining groundwater.

3. Lowering of the water-table — Correct. Sand mining deepens the riverbed, increases drainage from nearby aquifers, and commonly lowers the local groundwater table.

Therefore, 2 and 3 only are correct.