Ever since AB 939 passed, there has been continuing debate about how to accurately quantify the amount of waste which is being generated and diverted from within each city and county in California. Originally, AB 939 required each jurisdiction to track and quantify the amount of all materials being diverted from the waste stream. This methodology proved unworkable for many reasons. The law was eventually changed to abandon this "diversion-based" method in favor of the "disposal-based" methodology currently used. Although the disposal-based method seems to be an improvement over the diversion-based method, there remains widespread concern from many jurisdictions about its accuracy because of the difficulties involved in reliably determining the jurisdictional origin every ton of waste being brought to a landfill for disposal.

Using the "disposal-based" accounting method, the annual amount of waste being landfilled from a particular jurisdiction is divided by that jurisdiction’s estimated waste generation tonnage for the corresponding year. If, for example, a jurisdiction had a waste generation tonnage of 100,000 tons and 60,000 tons of waste were landfilled, their calculated waste diversion rate would be 40%. As noted above, however, there are inherent problems in accurately determining the jurisdictional origin of many waste materials. Also, it is difficult to accurately determine the waste generation tonnage for any particular year since this is a mathematically derived number based on empirical relationships between waste generation and selected demographic factors. This is how it works. In 1990, all jurisdictions were required to quantify the amount of waste being landfilled and to estimate the amount of waste being diverted from landfills. This 1990 number (tons landfilled + tons diverted) has become the jurisdiction’s "base year" waste generation tonnage. This tonnage is then extrapolated to estimate waste generation in future years using factors based on changes in population, sales tax receipts, and unemployment rates.

A "worksheet" at this link demonstrates how selected demographic factors have been used to compute the 1998 waste diversion rates for the City of Angels and the County. Note that the worksheet calculations for both the County and City show a negative value for the "non-residential sector". This implies that the estimated "non-residential" waste generation rate for each jurisdiction has, according to CIWMB methodologies, decreased over the past ten years. Similarly, despite a 10-year cumulative population increase of around 20%, the amount of household waste increased, based on CIWMB methodologies, by only 7 or 8% over the past ten years. Additional information regarding the CIWMB's adjustment methodology is available at their website.

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