Explain the impact of large scale agriculture in the south western united states on our water supply

The southwestern part of the United States is mostly semi-arid region. There's relatively low amount of precipitation, so the water reserves are very sensitive to disruptions.

This region though, has been heavily used for agriculture in the past century. Also, the plants are the farmed are plants that require higher amounts of water, like the almonds for example. Because of that, most of the aquifers of this region started to be exploited. Because the demand for water for the crops was higher than what nature can replenish in the aquifers, their water levels started to shrink. Some smaller ones have already dried out, while the larger ones go in that direction.

This has led to abandoning of some farmlands as the water was spent. Most of the others are at a critical level. The clean freshwater from the aquifers that could have been used for drinking has been largely extracted, thus there's big problem, that will become even bigger, with water for drinking. The spaces that are left in the ground by the aquifers also cause problems because the ground on top either sinks or crumbles, causing lot of damage on the infrastructure.

i think its toxic gasses but i could be wrong