System and method for monitoring the location of fractures in earth formations

A system and method for the real-time monitoring of the location (e.g. vertical extent) of a fracture within a waste disposal formation as that fracture is being formed. Acoustical-energy sensors (e.g. geophones) are isolated within the annulus of the well through which the waste material is injected into the formation. This eliminates the need for expensive, dedicated monitor wells while protecting the sensors from the abrasive effects of the injected waste material.