Which material is typically NOT allowed for drain runs from a septic tank to a drainfield under paving?

The appropriate material that is typically not allowed for drain runs from a septic tank to a drainfield under paving is galvanized pipe. This is primarily due to the fact that galvanized pipe can corrode over time when exposed to the moist and chemically active environment of soil and wastewater. The lifespan of galvanized pipes can be significantly reduced in these conditions, leading to leaks or failures that jeopardize the integrity of the drainfield and the overall septic system.

In contrast, materials such as PVC schedule 80, cast iron, and HDPE (high-density polyethylene) are preferred for their durability and resistance to corrosion. PVC schedule 80 offers high pressure ratings and is lightweight, making it easy to install. Cast iron, while heavier and more expensive, has high durability and longevity. HDPE is flexible and resistant to many chemicals, making it an excellent choice for below-ground applications.

Thus, the use of galvanized pipe is typically prohibited in these scenarios due to the potential for deterioration and failure, highlighting the importance of selecting the right materials for septic systems.