The well that takes the water
EPA's Underground Injection Control program regulates Class II wells, which are used only to inject fluids associated with oil and natural gas production. The fluids are primarily brines, salt water brought to the surface while producing oil and gas, and the EPA estimates that over 2 billion gallons of fluids are injected in the United States every day. Approximately 180,000 Class II wells are in operation, and disposal wells, the ones that take produced water and fracturing wastewater, make up about 20 percent of them. Most are in Texas, California, Oklahoma, and Kansas, which is where most of the produced water comes from.
The permit and the testing that go with it
States have the option of running their own UIC programs for Class II wells under Section 1422 or 1425 of the Safe Drinking Water Act. Under Section 1422, disposal wells are issued permits, and the owners and operators must meet construction, operation, monitoring and testing, reporting, and closure requirements. The core prohibition sits in 40 CFR Part 144: no owner or operator may construct, operate, maintain, convert, plug, abandon, or conduct any other injection activity in a manner that allows the movement of fluid containing any contaminant into underground sources of drinking water. The permit, the mechanical integrity testing, and the inspection records are the evidence that the well is doing its job.
The truck record is part of the well's file
Produced water reaches the disposal well by truck or pipeline, and the trucked volume is the number that has to reconcile with the well's injection records. A hauler that drops a load without a ticket, or a disposal operator who logs the barrel count from memory, creates a gap between what the state sees and what actually went downhole. The same field ticket that pays the hauler is the compliance record for the disposal well, and the same discipline that prevents billing disputes prevents reporting gaps. Load counts, well numbers, and injection totals should match at the end of every month.
Disposal operations sit beside the rest of the water cycle: produced water hauling, drill cuttings and waste management, and annular pressure monitoring. If truck tickets and injection reports are reconciled by hand at month end, an operations audit will show which volumes are verified and which are assumed.