illustrates the point that future trends must be assessed carefully in long-term planning. Another important question is whether the quantities are actually changing or only the reporting system has improved Impacts of waste Diversion Programs As more states adopt legislation mandating the development of source reduction and recycling programs, the composition of the wastes collected will change. The impact of waste diversion programs on the composition of the wastes collected will vary depending on the other types of waste management programs that are in place. For example, a solid waste combustion facility. developed to the wast would be 6500 Btu/lb. Six years later when the facility went on line. the actual energy content of the waste was 4500 Btu/lb, owing to the extensive recvcling of cardboard that had developed in the intervening vears. To meet a contractual requirement to generate a firm amount of power, the numbe of truck loads of waste had to be increased, necessitating a change in the facility permit Future Changes in Waste Components In planning for future waste management systems, it will be important to consider the changes that may occur in the composition of solid waste with time. Four waste components that have an important influence on the composition of the wastes collected are food waste, paper and cardboard, yard waste, and plastics. Stable refuse has disappeared as a waste category in current classification systems, while plastics were nonexistent in the early 1900s Food Wastes. The quantity of residential food wastes collected has changed significantly over the years as a result of technical advances and changes in public attitude. Two technological advances that have had a significant effect are the development of the food processing and packaging industry and the use of kitchen food waste grinders. The percentage of food waste, by weight, has decreased from about 14 percent in the early 1960s to about 9 percent in 1992. Recently, because the public has ecome more environmentally aware and concerned, a trend has developed toward the use of more quantity of food wastes collected no firm data are available on this subjec s trend would increase the raw, rather than processed, vegetables. While it would appear that such Paper and Cardboard. The percentage of paper and cardboard (also known as paperboard and corrugated paper)found in solid wastes has increased greatly over the past half century, rising from about 20 percent in the early 1940s to about 40 percent in 1992. It is expected that use of paper and cardboard will remain stable for the next few years. If the U.S. postal rate for bulk mail were increased to that for first class mail, a significant reduction would occur in the amount of paper collected fo disposal Yard Wastes. The percentage of yard wastes in MSW has also increased significantly during the past quarter century, due primarily to passage of laws that prohibit burning of yard wastes. By weight, yard waste currently accounts for about 16 to 24 percent of the waste stream. Environmental conditions such as droughts have also affected the quantities of yard wastes collected in certain locations. For example, in Santa Barbara, CA, many areas that had lawns have been converted permanently to arid type landscaping with a concomitant decrease in the portion of yard wastes. Whether drought conditions in the south-western United States will continue to affect the quantity of yard wastes is unknown Plastics. The percentage of plastics in solid wastes has also increased significantly during the past 50 years. The use of plastic has increased from almost non-measurable quantities in the early 1940s to between 7 and 8 percent, by weight, in 1992. It is anticipated the use of plastics will continue to increase, but at a slower rate than during the past 25 years13-10 illustrates the point that future trends must be assessed carefully in long-term planning. Another important question is whether the quantities are actually changing or only the reporting system has improved. Impacts of Waste Diversion Programs As more states adopt legislation mandating the development of source reduction and recycling programs, the composition of the wastes collected will change. The impact of waste diversion programs on the composition of the wastes collected will vary depending on the other types of waste management programs that are in place. For example, a solid waste combustion facility, developed to serve a commercial area, was planned and designed on the basis that the energy content of the waste would be 6500 Btu/lb. Six years later when the facility went on line, the actual energy content of the waste was 4500 Btu/lb, owing to the extensive recycling of cardboard that had developed in the intervening years. To meet a contractual requirement to generate a firm amount of power, the number of truck loads of waste had to be increased, necessitating a change in the facility permit. Future Changes in Waste Components In planning for future waste management systems, it will be important to consider the changes that may occur in the composition of solid waste with time. Four waste components that have an important influence on the composition of the wastes collected are food waste, paper and cardboard, yard waste, and plastics. Stable refuse has disappeared as a waste category in current classification systems, while plastics were nonexistent in the early 1900s. Food Wastes. The quantity of residential food wastes collected has changed significantly over the years as a result of technical advances and changes in public attitude. Two technological advances that have had a significant effect are the development of the food processing and packaging industry and the use of kitchen food waste grinders. The percentage of food waste, by weight, has decreased from about 14 percent in the early 1960s to about 9 percent in 1992. Recently, because the public has become more environmentally aware and concerned, a trend has developed toward the use of more raw, rather than processed, vegetables. While it would appear that such a trend would increase the quantity of food wastes collected no firm data are available on this subject. Paper and Cardboard. The percentage of paper and cardboard (also known as paperboard and corrugated paper) found in solid wastes has increased greatly over the past half century, rising from about 20 percent in the early 1940s to about 40 percent in 1992. It is expected that use of paper and cardboard will remain stable for the next few years. If the U.S. postal rate for bulk mail were increased to that for first class mail, a significant reduction would occur in the amount of paper collected for disposal. Yard Wastes. The percentage of yard wastes in MSW has also increased significantly during the past quarter century, due primarily to passage of laws that prohibit burning of yard wastes. By weight, yard waste currently accounts for about 16 to 24 percent of the waste stream. Environmental conditions such as droughts have also affected the quantities of yard wastes collected in certain locations. For example, in Santa Barbara, CA, many areas that had lawns have been converted permanently to arid type landscaping with a concomitant decrease in the portion of yard wastes. Whether drought conditions in the south-western United States will continue to affect the quantity of yard wastes is unknown. Plastics. The percentage of plastics in solid wastes has also increased significantly during the past 50 years. The use of plastic has increased from almost non-measurable quantities in the early 1940s to between 7 and 8 percent, by weight, in 1992. It is anticipated the use of plastics will continue to increase, but at a slower rate than during the past 25 years