Improved Estimation of Waste Arisings Using Limited Sample Sizes

Abstract

Knowledge of the total tonnage of waste deposited at a landfill site is important if the site is to be effectively managed and appropriate plans made for the future. Unfortunately only at very large landfills is it economical to weight all the loads that are delivered. At present a number of methods for estimating the weight of wastes collected are in use. These are based on counts of bins emptied, number of properties from which waste is collected or of population served, together with knowledge of waste generated per appropriate unit based on nationally derived statistics. Experience shows, however, that the accuracy of such estimates founded on nationally derived statistics leaves much to be desired. Therefore accurate estimates of total waste deposited must be based on locally derived data. This paper describes how, in conjunction with the use of the tonnage estimation model, estimated can be made by weighing only a small, but representative, number of vehicle loads. The model is straightforward to use, requires little manpower to implement and represents a marked improvement on current techniques. The accuracy of the model was checked by using sample data from a waste disposal authority that weighed all its waste. Estimates obtained by the model were very close indeed to the actual figures. The paper gives a description of the model and how an appropriate sampling plan can be derived. A case study is then presented to illustrate how the model is used in practice.