There had been demand for Soil for Making level of your plot high or Making Bricks, Historically this soil had been digged from Agricultural fields Like making them 2,3 feet deep. Like this this farmer would take rest for one year, new fertile land would be recovered from beneath, and because f low level Land it was easy to irrigate.
Now because of increasing cost and time of transportaion and lack of free agri Land near bigger cities, A different method is being employed. With newr machinery they countinue digging small plot deeper and deeper, Like upto 30 Feet or deeper, sell the soil much costlier than cost of actual Land. And later this pit becomes Deep Dirty water pound, I guess this method is full of hazard spoling underwater resource. As polluted water gets chance to touch 30 to 40 feet depth. Pls look arround in your society before making purchase. 
