Having been involved in several small tire fires (estimated 2000-10,000 tires) simply burying the pile is often the most effective way, both in terms of cost and enviromental management, of handling the incident.
The fact is pouring water on the incident for days generally does not solve the fire problem but does create tremendous runoff and water management issues that are more daunting than the fire itself.
It seems like they have selected the best tactics for the situation.