Wikipedia describes the modern transformation from tip to 'sanitary landfill':
Waste Not, Want Not
A landfill is a place to dispose of residual waste or rubbish from homess and businesses. However, from a zero waste point of view, a landfill is a waste of potential resources, so all other options should be considered first.
Environmental effects of landfills
Landfills are a source of liquid leachate, of global-warming landfill gas and a potential source of local health problems unless very well managed.
Groundwater pollution: When rainwater flows through landfills it dissolves chemicals producing a toxic liquid called Leachate . This leachate can contaminate groundwater and if it flows into rivers or the sea can kill aquatic life. A modern landfill diverts surface water away instead of letitng it soak in.
Air pollution: As organic matter breaks down in landfills it releases methane gas, a potent greenhouse gas that traps up to 20 times more heat in the atmosphere per molecule than carbon dioxide, although it is shorter-lived in the atmosphere. To avoid food and garden waste ending up in landfill you can set up a home compost or use a council composting servuce where available. Wood and paper in air-less landfills can also decay slowly into methane.
Soil Contamination: The chemical substances and decaying organic matter can decrease the soil fertility of the area around the landfill. This then affects the biodiversity potential in the area.
Social Impacts: Landfills are often unwanted by the surrounding communities due to the eyesore, smell and vermin (such as gulls and rats) associated with waste. This lowers land prices and can have detrimental health impacts on communities.
To encourage waste reduction, the Waste Minimisation Act 2008 placed a $10 levy on each tonne of waste disposed of at municipal landfills. in 2019 there is discussion within Government about raising this levy as an incentive to reduce waste to landfill.
The composition of New Zealand’s waste in the past decade shows top three categories: organics (23%), paper (15%) and timber (14%) adding up to 52% of the total volume. Most of these could be diverted from landfill.
By 2011 New Zealand was sending 2.461 million tonnes per year of solid waste to municipal landfills and more again to private landfills. The amount reaching landfills falls as diversion for reuse and recycling increases.
Modern, sanitary landfills are highly engineered sites with layers of storm water collection systems, clay and synthetic landfill liners with leachate collection systems to provide environmental protection from the effects of landfills. In information about Hampden Downs Landfill, Envirowaste outlines environmental management and monitoring, stormwater and groundwater monitoring and leachate control.
Many landfills are owned by local councils, while some are commercially owned and operated by companies, such as:
Side-benefits of landfills
Energy from gas: Redvale Landfill, owned by Waste Management NZ Ltd, has nine generators to produce electricity from the landfill gas it produces. Enough energy is produced to power the equivalent of 7,500 homes.
Shifting away from waste
The number of landfills is reducing, with more than 300 in 1995 reduced to less than 100 today. Resource consents for landfills are difficult and expensive to secure, and modern sanitary landfills with suitable protection for the environment are expensive to build and manage.
The Circular Economy
The circular economy may reduce waste to landfill as material flows are of two types, biological nutrients and technical nutrients.
In contrast to a traditional linear economy (of make -> use -> dispose) a circular economy aims to keep resources in use for as long as possible (make, use, reuse, upcycle and re-make)
Brief video from NZ Ministry for the Environment