Yesterday, I talked about the structure and parts of a landfill and how it affects the Earth. If you haven’t already, read to catch up. Today I’ll be talking about how it affects our water supply. And stay tuned because tomorrow, I’ll be talking about it affects our air supply. Read how landfills affect our air for more information.
Landfills and Groundwater
All sanitary landfills should have systems for collecting and monitoring groundwater to ensure against contamination. They also have systems for collecting leachate, a liquid that filters down through the landfill with rainwater and could contain harmful chemicals. The water can become acidic and eat into the waste of containers. The system for collecting groundwater and leachate does not breach the lining systems of the landfill. Engineers line the quarry with clay or synthetic materials and the leachate cannot as easily pass through those materials. Pipes then collect the leachate for storage in tanks and special treatment. Old landfills do not have a leachate collecting system, so it flows to pollute and contaminate the drinking water in the ground.
Storm Water Drainage
It is important to keep the landfill as dry as possible to reduce the amount of leachate. This can be done in two ways:
- Exclude liquids from the solid waste. Solid waste must be tested for liquids before entering the landfill. This is done by passing samples of the waste through standard paint filters. If no liquid comes through the sample after 10 minutes, then the trash is accepted into the landfill.
- Keep rainwater out of the landfill. To exclude rainwater, the landfill has a storm drainage system. Plastic drainage pipes and storm liners collect water from areas of the landfill and channel it to drainage ditches surrounding the landfill’s base.
The ditches are either concrete or gravel-lined and carry water to collection ponds to the side of the landfill. In the collection ponds, suspended soil particles are allowed to settle and the water is tested for leachate chemicals. Once settling has occurred and the water has passed tests, it is then pumped or allowed to flow off-site.
Leachate Collection System
No system to exclude water from the landfill is perfect and water does get into the landfill. The water percolates through the cells and soil in the landfill much as water percolates through ground coffee in a drip coffee maker. As the water percolates through the trash, it picks up contaminants (organic and inorganic chemicals, metals, biological waste products of decomposition) just as water picks up coffee in the coffee maker. This water with the dissolved contaminants is called leachate and is typically acidic.
To collect leachate, perforated pipes run throughout the landfill. These pipes then drain into a leachate pipe, which carries leachate to a leachate collection pond. Leachate can be pumped to the collection pond or flow to it by gravity, as it does in the North Wake County Landfill.
The leachate in the pond is tested for acceptable levels of various chemicals (biological and chemical oxygen demands, organic chemicals, pH, calcium, magnesium, iron, sulfate and chloride) and allowed to settle. After testing, the leachate must be treated like any other sewage/wastewater; the treatment may occur on-site or off-site. Some landfills recirculate the leachate and later treat it. This method reduces the volume of leachate from the landfill, but increases the concentrations of contaminants in the leachate.
Occasionally, leachate may seep through weak point in the covering and come out on to the surface. It appears black and bubbly. Later, it will stain the ground red. Leachate seepages are promptly repaired by excavating the area around the seepage and filling it with well-compacted soil to divert the flow of leachate back into the landfill.
At many points surrounding the landfill are groundwater monitoring stations. These are pipes that are sunk into the groundwater so water can be sampled and tested for the presence of leachate chemicals. The temperature of the groundwater is measured. Because the temperature rises when solid waste decomposes, an increase in groundwater temperature could indicate that leachate is seeping into the groundwater. Also, if the pH of the groundwater becomes acidic, that could indicate seeping leachate.