Skip to 0 minutes and 5 seconds As we have seen in the previous steps clean water and sanitation are a key part of sustainable development. In this video we going to look at a case study on site wastewater treatment i.e. sanitation for rural areas in Ireland. This will highlight some of the difficulties and challenges that are often faced in rural areas for improved sanitation. Over one third of the population of the Irish Republic live in rural areas without access to a sewer. This means that they need to treat and dispose of their waste water on site safely in order to protect public health and also to protect the environment. Many of these people also rely on their own private world for drinking water supply.
Skip to 0 minutes and 42 seconds What we will see in this case study is that developed countries such as Ireland still face challenges to achieving SDG 6, clean water, and sanitation. This slide shows typical pollutants in such a rural environment from agriculture. For example, the spreading of fertiliser, animals on the land, and then more point sources such as, slurry tanks, as well as domestic wastewater treatment systems known more generally as septic tanks, which are the main focus of this case study. Effluent from rural houses has the potential to pollute either the ground water, which may be used as a drinking water supply for houses in the area and also provides a baseline for rivers. Or it can directly pollute rivers if it travels over land.
Skip to 1 minute and 20 seconds Careful thought and design is needed for it to discharge safely onto the local land. This must be based on a particular site conditions and in particular, the nature of the soil. In Ireland and most other European countries, we use large quantities of water to remove and transport the waste from our houses. This includes faeces and urine from toilets, washwater from showers and baths, food waste in the sinks and dishwashers, and detergents from washing machines. Hence, the pollutants are diluted in a large amount of water, which needs to be considered in any subsequent disposal treatment process. In rural areas of Ireland, it doesn’t make economic sense to construct centralised sewerage networks and then treatment plants.
Skip to 1 minute and 58 seconds And so the wastewater effluent from such rural houses needs to be treated and disposed of on-site. This usually involves dispersing it over a large area of land so it can infiltrate into the soil. This soil can also provide excellent treatment of the pollutants if the system is designed properly. The first step is to provide a tank to receive the flows, which acts to damp out any hydraulic pulses, and then allow solids to settle out. This is usually a simple storage device called a septic tank, but sometimes it can be a more advanced level of treatment, which normally involves adding air to the sewerage by mechanical means, such as by pumps or blowers.
Skip to 2 minutes and 33 seconds Alternatively, more nature-based solutions can be used, such as constructed wetlands or tree-based evapotranspiration systems to provide additional treatment. The effluent from these units then needs to be discharged into the environment. However, despite these initial unit processes, it is not free from contaminants, and so not suitable for discharge directly into a stream. It should therefore be admitted into the soil through which it will percolate, thereby being treated to a safe level before it reaches the water table and the groundwater.
Skip to 3 minutes and 1 second In Ireland, the legislation defines how this is carried out, which is based upon a risk assessment that takes into account the level of pollution in the source, the pathway that the pollutants then travel once emitted into the environment, and then the potential target of such pollution. This is known as the so-called source-pathway-target concept. In this case, the source is the wastewater from the domestic dwelling, the pathway is the soil through which the effluent percolates, and the target is either the groundwater or the local surface water, for example streams, rivers, lakes. The risk assessment of any site first takes into account the quality of the groundwater beneath the site as a source of drinking water.
Skip to 3 minutes and 37 seconds This is primarily a function of different type of bedrock. For example, is it a limestone, a sandstone, a volcanic, et cetera, as different rocks can store and transmit different quantities of water, depending on how many voids are naturally present, or, more importantly for the older rocks, which cover most of Ireland, how many fractures or fissures are present. So if your site is sitting on an important groundwater resource, which may, for example, be being used by a large food processing industry, then you need to be more rigorous as to how you deal with the polluting activities at the surface compared to if the rock stores very limited amounts of water, just sufficient maybe for a single house supply.
Skip to 4 minutes and 14 seconds The protection of the groundwater is offered by the overlying soils. Soils naturally occur in many different forms, ranging from gravelly, sandy soils, which allow water to percolate quickly, through to silty clay soils, which have a much more limited capacity to allow water to percolate. In addition, soils occur in a range of depths, from nonexistence– for example, bare rock– through to tens of metres of depth. In general, the deeper the soil, the better the treatment and removal of any pollutants contained in the percolating effluent. Hence, soil can provide an excellent natural treatment against pollutants such as bacteria, viruses, and chemical compounds. So the longer it takes the effluent to infiltrate, the better, i.e., the more treatment.
Skip to 4 minutes and 54 seconds However, if the soil is too slow for the amount of effluent being added to it at any one point, then it will start to pond and flow overland, providing a risk to both public health and to the environment. So how is this assessed in practise, if somebody wants to build a new house in a location where there’s no access to a sewer? This brings up more challenges. A formal site assessment process is required, which involves geological maps, trial holes, and percolation tests. These enable the depth of the water table to be determined, as well as the nature of the soil. Is it sandy, clay, et cetera.
Skip to 5 minutes and 27 seconds A percolation test using clean water also gives an idea of how fast the water will percolate. All of this information then needs to be integrated to determine the optimal design of the on-site wastewater treatment system. This is guided in Ireland by a risk matrix that has been developed which takes into account the value and vulnerability of the underlying groundwater to pollution, which is the target, the nature of the pathway through which the pollutants must travel before reaching it, i.e. the depth and drainage characteristics of the overlying soil. This matrix then determines how big an area of soil the effluent needs to be spread across, and also what depth within the soil it should be discharged at.
Skip to 6 minutes and 3 seconds Once the design has been finalised, it is then submitted with all the other documents to the local authority to consider whether planning permission should or should not be granted for the construction of such a rural house at that particular location. If granted, then it is essential that the carefully considered design is actually constructed on-site. This includes ensuring that the correct pretreatment unit is installed, whether a septic tank or more advanced treatment system, or maybe a system constructed on-site, such as a sand filter or constructed wetland. The percolation trenches must then be dug to the correct depth, and the appropriate means of effluent distribution added.
Skip to 6 minutes and 38 seconds So to recap, what we have learned in this video is the approach taken in Ireland for appropriate sanitation for rural houses that lack access to centralised water infrastructure. What is interesting about this case study is that it links the understanding of how water-related diseases are spread using the source-pathway-target concept to a robust assessment of the natural conditions which can be used to ensure a sustainable approach to effective treatment of domestic wastewater on-site in order to protect both public health as well as the environment.
Skip to 7 minutes and 6 seconds If this approach is followed by all interested parties in the process, which starts with the site assessor and system designer, to the local authority who has the power to grant their planning permission, to the contractor constructing the system, and then finally to the homeowner with responsibility for ongoing maintenance, then this will promote the future sustainable development of people living in rural areas, particularly with respect to SDG 6 water and sanitation.
Challenges to Irish rural sanitation
Laurence has explored some of the challenges to Irish rural sanitation in this video.
Thinking about the environment around you:
- What type of soil surrounds where you live, work, or do recreation?
- How fast or slow does water run through this soil?
- How deep is the soil around you?
- Is there any evidence of rock around you?
- If effluent was discharged on the soil, how well would it be dispersed?
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