How are injection wells monitored to ensure safety and compliance with the law?

Monitoring conducted to verify the suitability of the well for continued injection of waste is essentially of two types: continuous and periodic. Continuous monitoring provides data regarding how the well is operated, and is used to document operational changes that could signal any change in the well condition. Periodic monitoring is used to validate the continuous monitoring, and to more thoroughly investigate well and disposal reservoir conditions to verify waste containment. 
Periodic mechanical integrity testing of well systems is conducted as required by regulations. Based on initial completion as a non-hazardous well, Part I annual testing will consist of standard one-hour static annulus pressure testing and an associated reservoir falloff test. The annulus pressure test measurements are recorded using a calibrated pressure gauge on the wellhead, witnessed by a regulatory inspector. A maximum change in pressure is allowed during the one-hour test. The gauges used to monitor pressure during the casing/tubing annular pressure tests are calibrated with a deadweight tester which is accurate to 0.1% of indicated pressure. Copies of gauge certifications are included with the pressure test records and reports. 
Part II periodic mechanical integrity testing is completed before wells become operational and thereafter on a five-year cycle or as required by permit. For wells used to inject non-hazardous waste, this testing consists of a radioactive tracer survey or equivalent acceptable method to verify the adequacy of the bottomhole cement at the base of the long-string casing. In addition, well logging designed to investigate vertical movement of fluids behind pipe will be conducted in the form of temperature, noise, oxygen activation logging or equivalent acceptable testing. Part II periodic mechanical integrity testing is required on an annual basis for wells used to dispose of hazardous wastes. 
Continuous monitoring will also be accomplished as required by regulation to record injection rate, injection pressure, annulus pressure and pressure differentials. Analysis of the waste stream for chemical and physical parameters is also completed on a case-by-case basis as required by permit.