Guest Blog by Laurence Dolan
Laurence Dolan is a Waste Management Consultant based in Auckland.
You can contact Laurence by clicking here.
13,000 tons a day, over 130 million tons in total and the gates close in October this year. The closure of Los Angeles’ Puente Hills Landfill marks the end of an era for landfilling in the United States. It was big news even beyond the world of waste management, prompting a recent feature in The Atlantic magazine, “Touring the Largest Active Landfill in America”.
The article reminded me of my amazement at the scale of Puente Hills during a tour of the site back in April 1992. The site was several times bigger than anything I had seen in New Zealand.
I was at the landfill courtesy of a Local Government Study Award I received while Solid Waste Planner at Christchurch City Council. I spent a month travelling around the West Coast of the United States and Canada, with brief stop offs in Tahiti and Hawaii, visiting councils and looking at a variety of landfills, waste to energy plants, transfer stations, composting facilities, recycling plants and anaerobic digesters.
I was shown around Puente Hills by Operations Section Head Richard Lalkea. The first thing that struck me was the three weighbridges at the site entrance, each with several trucks queued up and a Geiger counter to check for radioactive loads.
The Puente Hills Landfill was the most popular landfill with waste haulers as it was the closest to the city of Los Angeles and had the lowest gate fee, $US16, when other landfills were charging up to $US24. The site opened at 6 am and was required to close once the 13,000 ton daily limit was reached. On the morning I visited the permitted tonnage was reached just after 10 am, signified by the raising of a blue flag on the hillside so that trucks knew to continue along the freeway to the next landfill site. In comparison the largest landfills in New Zealand (Redvale and Hampton Downs) receive around 2,000 tonnes in a day.
To make space for new cells for refuse, large sections of hillside were being removed and stockpiled for cover. New cells were then constructed with a compacted clay and HDPE composite liner and leachate collection system, at a time when we were yet to see a composite liner in New Zealand.
Operations differed from smaller sites. Because of the high tonnage of refuse arriving in a short time it was not feasible to use landfill compactors for initial compaction. Instead a number of Caterpillar D9N bulldozers were used to spread the refuse away from the tipping area as quickly as possible.
The accumulated weight of the refuse was used for compaction, with a 40 percent volume reduction in the first six months. The rapid settlement meant site roads quickly became like roller coaster rides and required rebuilding every six to nine months.
Having never seen them before, I asked what the stockpiles of green large-diameter non-perforated pipes were for. They were the landfill gas collection system. The pipes were laid in horizontal trenches and connected loosely using smaller diameter inner pipes with a lot of overlap. In this way the gas would be sucked into the pipes via the gaps left by the difference in diameter of the connectors and the loose fitting arrangement provided flexibility to allow for the high settlement rates.
In 1992, the landfill was producing over 500 cubic metres of gas per minute. This was converted into 40 megawatts of electricity using two boilers and a steam turbine generator set.
Seagulls were kept away from the refuse by use of numerous wires strung across 8 metre high poles approximately 10 metres apart. Following daily spreading operations all refuse was covered with 300 millimetres of soil.
What happens when Peunte Hills closes its gates in October, after 56 years? It will be replaced by the new Mesquite Regional Landfill in the Imperial Valley. Refuse will be loaded into containers and transported 320 kilometres by rail. The new landfill is permitted to accept 20,000 tonnes of waste per day and has a total capacity of 600 million tones, enough for 100 years.