25 Pa. Code § 299.211 – General requirements.

(a) Residual waste shall be completely enclosed or covered during transportation, including parking, unless the waste cannot be dispersed.
(b) A person or municipality that transports residual waste may not mix the waste with:
1. (1) Hazardous waste that is regulated under Article VII (relating to hazardous waste management).
2. (2) Other solid waste to create a risk of fire or explosion, or a risk of the accumulation of poisonous or otherwise harmful vapors or gases.

This section cited in 25 Pa. Code § 299.201 (relating to scope).