Leukocyte Esterase. Leukocyte esterase is an enzyme present in most white blood cells (WBCs). A few white blood cells are normally present in urine and usually give a negative chemical test result. When the number of WBCs in urine increases significantly, this screening test will become positive.
Land subsidence occurs when large amounts of groundwater have been withdrawn from certain types of rocks, such as fine-grained sediments. The rock compacts because the water is partly responsible for holding the ground up. When the water is withdrawn, the rocks falls in on itself.
By definition, subsidence is the very slow to rapid sinking or settling of the land surface. Subsidence can be the result of natural causes. Some types of carbonate rock underlies topography containing numerous natural depressions, known as sinkholes. The topography is known as karst topography.