text: the consumption of cubic yards of available airspace. These costs include all costs to acquire and construct a 
  site including excavation, natural and synthetic liners, construction of leachate collection systems, installation 
  of methane gas collection and monitoring systems, installation of groundwater monitoring wells, and other 
  costs associated with the acquisition and development of the site. Obligations associated with Ñnal capping, 
  closure and post-closure are capitalized, and amortized on a units-of-consumption basis as airspace is 
  consumed. 
  
  Cost and airspace estimates are developed annually by engineers. These estimates are used by our 
  operating and accounting personnel to annually adjust our rates used to expense capitalized costs. Changes in 
  these estimates primarily relate to changes in available airspace, inÖation and applicable regulations. Changes 
  in available airspace include changes in design and changes due to the addition of airspace lying in expansion 
  areas that we believe have a probable likelihood of being permitted. 
  
  Our operations are managed and reviewed through Ñve regions which we designate as our reportable 
  segments. From 2003 to 2004, operating income increased in our Eastern, Southern and Western regions due 
  to an overall increase in revenue resulting from the successful execution of our growth strategy. In the Central 
  region, increased revenue was oÅset by weak economic conditions and an increase in costs related to the long- 
  haul transport of waste by third-party vendors. In the Southwestern region, revenue growth was impeded by 
  the closure of a landÑll and the completion of a special waste contract during 2003. The decrease in costs for 
  Corporate Entities from 2003 to 2004 is primarily due to a decrease in self-insurance expense. 