Base Year/Reporting Year Change Policy

Base-Year Inaccuracies

The California Waste Management Act of 1989 (Act) required local governments to prepare planning documents for achieving the 25 percent diversion goal of 1995 and the 50 percent diversion goal of 2000. These plans included a solid waste generation study that quantified the amounts and identified the types of solid waste disposed and diverted from each jurisdiction in its base year. After Board approval of their planning documents, jurisdictions are required to submit annual reports to the Board which demonstrate the progress being made toward achieving the established diversion goals. Originally, the Act required jurisdictions to measure the amount of waste generated (i.e., disposal plus diversion) in 1995 and 2000 to demonstrate compliance. But in 1992, Assembly Bill 2494 amended the Act, eliminating the need for future generation measurements by establishing a standard methodology for a disposal reduction measurement system.

The disposal reduction measurement system, as addressed in statute, estimates a reporting-year generation tonnage by adjusting the base-year generation for changes in population and economics between the base-year and reporting-year using the Board-approved adjustment method. The estimated reporting-year generation multiplied by 75 percent (i.e., the estimated maximum disposal amount) is then compared to the actual reporting-year disposal tonnage to determine the rate of diversion achieved based on the calculated disposal reduction.

In 1995, local governments were required to implement a state-mandated disposal reporting system to quantify the annual disposal tonnage for each jurisdiction. Prior to this time, there was no system for measuring waste disposal at the jurisdiction level. Instead, there were only state requirements for tracking quarterly disposal tonnage at the landfill level, which usually represented waste disposed from multiple jurisdictions. As a result, many inaccurate assumptions were made in the base-year waste generation studies to allocate tonnage down to the jurisdiction-specific level. For example, many counties used population ratios to allocate countywide tonnage.

Additionally, many landfills were not equipped with scales prior to 1995, so disposal tonnage had to be estimated. Methods to estimate the disposal tonnage included visual estimations, estimates based on aerial photos, the use of published volume-to-weight conversion factors, or actual measured volume-to-weight conversion factors. Further, many jurisdictions relied primarily on franchised hauler data to determine their base-year disposal data and omitted or understated self-haul or nonlicensed hauler tonnage. Thus, although based on the best available data at the time, the base-year data included inaccuracies due to estimation errors, misallocations of regional tonnage to individual jurisdictions, and/or omissions of significant portions of the nonfranchised waste stream. Many of the 1995 annual reports prepared-to-date include base-year revisions to correct for these types of errors.

As discussed above, the disposal reduction measurement system calculates a diversion rate based on the disposal reduction calculations. The disposal reduction calculations are based on a comparison of the adjusted base-year generation (an estimate of the reporting-year generation) with the actual reporting-year disposal. Large errors which understate base-year generation can result in exceedingly low diversion rates. Thus, inaccuracies in the base-year data can have a significant adverse impact on the calculated diversion rate. Therefore, base-year inaccuracies could negatively impact jurisdictions’ ability to quantitatively demonstrate their actual progress toward achieving the 25 percent diversion goal of 1995 and the 50 percent diversion goal of 2000.

Table of Contents | Reporting Inaccuracies

Last updated: October 26, 2007