| Year (s) | Well construction and completion norms | Potential for pollution |
| 1830-1916 | Cable tool drilling, no cement isolation, wells vented | High |
| 1916-1970 | Cement isolation steadily improving | Moderate |
| 1930s | Rotary drilling replaces cable tool, pressure control systems developed | Moderate |
| 1952 | Hydraulic fracturing becomes commercial | Lower from frac aspects |
| 1960 | Gas-tight couplings and joint makeup improvements | Moderate |
| 1970 | Introduction of horizontal wells, cement improvements | Lower |
| 1988 | Multifrac, horizontal wells, pad drilling reduces environmental land footprint up to 90% | Lower |
| 2005 | Well integrity assessments, premium couplings, additional barriers, and cementing full strings | Lower after 2008-2010 |
| 2008 | Real-time well integrity needs being studied to achieve early warning and problem avoidance | Lowest yet |