The City of Portland Sanitation Department is responsible for the collection and disposal of all solid waste within the city limits. The city must collect and dispose of an average of 300 tons of garbage each day. The city is considering ways to improve the current solid-waste collection and disposal system.
€¢ The current system uses Dempster Dumpmaster frontend loaders for collection and incineration or landfill for disposal. Each collecting vehicle has a load capacity of 10 tons (or 24 cubic yards) and dumping is automatic. The incinerator in use was manufactured in 1942 and was designed to incinerate 150 tons per 24 hours. A natural-gas afterburner has been added in an effort to reduce air pollution. However, the incinerator still does not meet state air-pollution requirements, and it is operating under a permit from the Oregon State Air and Water Pollution Control Board. Prison-farm labor is used for the operation of the incinerator. Because the capacity of the incinerator is relatively low, some trash is not incinerated, but it is taken to the city landfill. The trash landfill is located approximately 11 miles, and the incinerator approximately 5 miles, from the center of the city. The mileage and costs in person-hours for delivery to the disposal sites are excessive; a high percentage of empty vehicle miles and person-hours is required, because separate methods of disposal are used and the destination sites are remote from the collection areas. The operating cost for the present system is $905,400, including $624,635 to operate the prison-farm incinerator, $222,928 to operate the existing landfill, and $57,837 to maintain the current incinerator.
€¢ The proposed system locates a number of portable incinerators, each with 100-ton-per-day capacity for the collection and disposal of refuse waste collected for three designated areas within the city. Collection vehicles will also be staged at these incineration-disposal sites together with the plant and support facilities that are required for incineration, fueling and washing of the vehicles, a support building for stores, and shower and locker rooms for collection and site crew personnel. The pickup-and-collection procedure remains essentially the same as in the existing system. The disposal-staging sites, however, are located strategically in the city on the basis of the volume and location of wastes collected, thus eliminating long hauls and reducing the number of miles the collection vehicles must retravel from pickup to disposal site.
Four variations of the proposed system are being considered, containing one, two, three, and four incinerator-staging areas, respectively. The type of incinerator is a modular prepackaged unit that can be installed at several sites in the city. Such units exceed all state and federal standards for exhaust emissions. The city of Portland needs 24 units, each with a rated capacity of 12.5 tons of garbage per 24 hours. The price per unit is $ 137,600, which means a capital investment of about $3,304,000. The plant facilities, such as housing and foundation, were estimated to cost $200,000 per facility based on a plan incorporating four incinerator plants strategically located around the city. Each plant would house eight units and be capable of handling 100 tons of garbage per day. Additional plant features, such as landscaping, were estimated to cost $60,000 for site 1 and other sites cost some additional expenses.
The annual operating cost of the proposed system would vary according to the type of system configuration. It takes about 1.5 to 1.7 million cubic feet (MCF) of fuel to incinerate 1 ton of garbage. The conservative 1.7-MCF figure was used for total cost. This means a fuel cost of $4.25 per ton of garbage at a cost of $2.50 per MCF. Electric requirements at each plant will be 230 kW per day, which means a $0.48-per-ton cost for electricity if the plant is operating at full capacity. The maintenance cost of each plant was estimated to be $1.19 per ton. Since three plants will require fewer transportation miles, it is necessary to consider the savings accruing from this operating advantage. Three plant locations will save 6.14 miles per truck per day on the average. At an estimated cost of $0.30 per mile, this would mean that an annual savings of $6,750 is realized on minimum trips to the landfill disposer for a total annual savings in transportation of $15,300. Savings in labor are also realized because of the shorter routes, which permit more pickups during the day. The annual savings from this source are $103,500. Table ST 16.2 summarizes all costs, in thousands of dollars, associated with the present and proposed systems.
A bond will be issued to provide the necessary capital investment at an interest rate of 8% with a maturity date 20 years in the future. The proposed systems are expected to last 20 years with negligible salvage values. If the current system is to be retained, the annual O&M costs would be expected to increase at an annual rate of 10%. The city will use the bond interest rate as the interest rate for any public-project evaluation.
(a) Determine the operating cost of the current system in terms of dollars per ton of solid waste.
(b) Determine the economics of each solid-waste disposal alternative in terms of dollars per ton of solid waste.
Table ST 16.2

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Costs for Proposed Systems Site Number Item Present System Capital costs: Incinerators Plant facilities Annex buildings Additional features $3,302 $3,302 $3.302 3,302 1,920 132 60 8 9100 $4,053 $4,384 $4,764 $5,454 $408 1.260 112 600 900 91 102 Total Annual O&M costs Annual savings: $905.4 $342 $480 $414 Pickup transportation Labor $13.2 $14.7 $15.3 $17.1 103.5 119.40 87.6 99.3