Final answer:
Underground gas piping systems typically require a minimum cover of 12 inches under lawns and 18 inches under streets and parking lots, but local codes may vary.
Step-by-step explanation:
The depth at which underground gas piping systems must be installed varies based on local codes and regulations. However, a common standard found in many codes is that the piping should be installed with a minimum cover of 12 inches if the piping is beneath a lawn or landscaped area and 18 inches if it is beneath streets, parking lots, and similar areas where it may be subjected to additional loads. It is always essential to reference the local codes and regulations for specific requirements as these can differ from one location to another. Additionally, when dealing with gas lines, it is crucial to follow these regulations to ensure safety and compliance.