Pollution Liability Coverage under Truckers Policy

Our insured has a truckers policy with endorsement CA 99 48 attached; this endorsement provides broadened coverage for pollution liability. The insured carries hazardous material and has contracts in which he releases the other party from any liability that arises from spillage and clean up costs. However, CA 99 48 indicates that coverage does not apply to liability assumed under any contract or agreement. So, our insured is confused as to whether he has any coverage for a pollution spill. Can you clarify this issue?

New Mexico Subscriber