Review Article
Oil and Gas Production Wastewater: Soil Contamination and Pollution Prevention
Table 4
US EPA injection well classification system.
| Well class | Injection well description | Approximate inventory |
| Class I | Inject hazardous wastes beneath the lowermost USDW | 500 | Inject industrial nonhazardous liquid beneath the lowermost USDW | Inject municipal wastewater beneath the lowermost USDW |
| Class II | Dispose of fluids associated with the production of oil and natural gas | 147,000 | Inject fluids for enhanced oil recovery | Inject liquid hydrocarbons for storage |
| Class III | Inject fluids for the extraction of minerals | 17,000 |
| Class IV | Inject hazardous or radioactive waste into or above USDW, 40 sites | | This activity is banned. These wells can only inject as part of | | an authorized cleanup | |
| Class V | Wells not included in the other classes. Inject nonhazardous liquid into or above a USDW | 500,000 to >685,000 |
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