[ Target Science: Waste Not, Want Not. ]
LANDFILLS
Landfills are probably the oldest method of disposal. When people were done with something they threw it on the ground. Eventually they threw debris into a central location. Until the population increased drastically and land prices rose to recent levels, landfills were convenient and cheap. Now inexpensive landfill space is disappearing. Of the nine present landfills
(see map) that accept at least 100 tons per day, as many as four might close in the next six years. One of the largest, the B.K.K. which accepted 10,000 tons per day in Covina, closed in September 1996. Facing a budget crisis, Orange County landfills are now accepting some on L.A. County's trash.
The present cost of disposing of one ton of trash will probably quadruple from $25 to $100 per ton in the next 4-5 years. Many east coast cities are already paying over $100 per ton for trash disposal. For an update on local rates, check these landfills which are operated by the Sanitation Districts of Los Angeles County (LACSD); Calabasas, Puente Hills, Scholl Canyon, and Spadra.
The Puente Hills landfill seen here has accepted over 80 million tons of trash. Presently it accepts about 1/3 of L.A. Counties trash, or 72,000 tons per week, from over 200 trash haulers in the L.A. basin. Some trucks come from as far as Palos Verdes. It will probably reach its capacity in the year 2,003.
The anticipated landfill crisis of the 1990s has been averted for two reasons. First, the recession has caused a reduction in construction and demolition refuse which contributed a large percentage to the landfill solid waste during the 1980s. Second, cities have responded to the state law which required them to attain a 25% recycling rate by 1995, and a 50% recycling rate by 2,000.
Due to the closing of local landfills, it is expected that in 10 to 15 years that trash will be put on trains and hauled 80 to 100 miles to outlying dessert landfills.
Managing a Landfill
Managing a landfill so that it produces as little pollution, odor, and inconvenience as possible while still accepting thousands of tons of trash daily, and produce 6MW of electricity is challenging.
Two important tasks are to keep it very dry and sealing off the material from the ground water table. A 6 ft. thick system of plastic liners, sand, and clay cover the bottom the the Puent Hills landfill. Water is not added to the landfill as this reduces the leachate of landfill fluids that sinks to the bottom of the basin. Also, A series of wells and underground dams are installed to collect the leachate, sometimes called new oil. The leachate is pumped out of the wells to before it reaches the ground water.
Waste to Energy
As the organic material in the landfill decomposes, it produces methane gas. Usually this combustable gas is allowed to naturally vent, or is tapped with large pipes and burned off. At the Puente Hills landfill, however, a series of pipes is buried into the ground to collect the methane. Here a large green pipe is visible in the foreground.
A network of these pipes feeds the methane to a 6 MW powerplant where it is burned to create steam, turn a turbine, and generate electricity. In this way the landfill captures the waste gas and produces enough enough electricity for 10,000 homes. Many of the tractors and trucks at the landfill run on this methane too.
The world's largest electric wood-chipper (left) is used to reduce branches to mulch. The landfill also grinds up old tires for use as a fuel or road covering. Appliances such are refrigerators and stoves are dissasembled and recycled.
To deter the thousands of sea gulls that normally would blanket this landfill, a thin nylon line has been stretched between poles over 100 yards apart. This nylon line extends around the perimeter and appears to spook the birds so that they do not fly into the landfill. This experiment was attempted after local residents complained about the droppings from an estimated 5,000 gulls who used to visit the landfill daily.
At the end of every day the bulldozers spread 1 foot of soil over the refuse to control odors. Also, wind-blown trash has been a problem. A low fence has been extended around the facility to catch the most common nusiance, wind-blown plastic bags.
Related Web Sites
Puente Hills Landfill Tour
National Parks Service Calabasas Landfill Report
(KCRW) Which Way, L.A.? Landfill Space
Landfill Gas
Student Landfill Project
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Project Home: Waste Not, Want Not. Copyright © 1996 Target Science
Two important tasks are to keep it very dry and sealing off the material from the ground water table. A 6 ft. thick system of plastic liners, sand, and clay cover the bottom the the Puent Hills landfill. Water is not added to the landfill as this reduces the leachate of landfill fluids that sinks to the bottom of the basin. Also, A series of wells and underground dams are installed to collect the leachate, sometimes called new oil. The leachate is pumped out of the wells to before it reaches the ground water.
