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Ireland's Group Water Schemes
A mid-century deficit between urban and rural drinking water in Ireland prompted the development of a government programme to support local communities in developing their own drinking water infrastructure. People came together, often with the encouragement of the Country Women's Association or the local priest, and formed co-operatives to allow them to access state funding. Water supplies were identified. Pipes and pumps were purchased and installed. And for the first time for many, water flowed directly into the home.
Group Water Schemes have had a significant impact on rural life in Ireland, affecting domestic, agricultural and industrial practices. But the sector has itself changed significantly over the past 50 years. Using an interactive diagram of a GWS treatment facility as its point of departure, this blog post discusses various issues, pressures and threats that Group Water Schemes have had to overcome, and the technical and social means that they have used to do so.
Abstracting from Pollacat Springs
Pollacat Springs is a cluster of naturally-occurring fresh water springs near the village of Elphin in County Roscommon. Springs are a common feature of the karstic landscapes west of the River Shannon. They occur where water, travelling underground through cracks, gaps and caves in the limestone, is forced above ground by hydrological pressure. Although the Pollacat Springs provide a consistent source of raw water, the rapid rate at which water flows underground leaves the source susceptible to contamination and periods of low rainfall.
The GWS abstracting from this site serves around 400 homes. It is an amalgamation of three schemes, Aughrim, Boheroe/Corbally and Creeve, all of which were installed in the 1980s. These had relatively simple treatment procedures in which chlorine was added, often by hand, to kill bacteria.
Upgrading the treatment process
Pollacat Springs GWS has undergone significant changes over the past 15 years. Leveraging successive waves of state funding they have expanded and upgraded their treatment plant, responding to demands for higher drinking water quality as well as challenges brought on by agricultural intensification.
In the late 1990s, sampling by the national Environmental Protection Agency indicated that more that 40% of GWSs were failing to meet safe drinking water standards. Simultaneously, the 1998 European Union Drinking Water Directive placed pressure on the Irish state to improve regulatory compliance for both public and private supplies.
Due to the relative autonomy and independence of Group Water Schemes, there are often significant managerial and logistical difficulties to improving their drinking water. The Rural Water Programme has provided the funding to upgrade GWS facilities, and the National Federation of Group Water Schemes has been pivotal in co-ordinating local responses.
Design, Build & Operate
In 2003, Pollacat Springs GWS entered into a service contract with the environmental management company Veolia. This was part of a series of Design, Build and Operate contracts that continue to be rolled out in the sector.
Under the first phase of development the Pollacat Springs GWS moved to a new source, a different spring some 50 meters up the road from the abstraction point of Creeve GWS. A pump house was constructed, with one pump for abstraction and flow around the treatment plant, and another for pumping water to the scheme's reservoir.
Before water is pumped around the treatment plant, however, it passes through a sump. This is intended to prevent aquatic life, such as fish and frogs, from being pulled into the treatment process. While usually effective, the caretaker occasionally has to pull frogs from the top of the very grates designed to keep them out.
Filter Control Unit
The filter control unit reduces the turbidity of the water by filtering out organic material. It was installed in striking 20 foot blue container by a Dublin-based engineering firm, and is referred to by the caretaker as Morris's blue container.
As a simple and relatively inexpensive unit, the filter control unit was ultimately unsuited to the fluctuations in turbidity and colour at Pollacat Springs. Even though its function has been usurped by a more sophisticated process of flocculation and clarification, water continues to pass through Morris's blue container.
Following filtration the water is piped into a holding tank. It is then chlorinated as it passes into another tank. The water is now considered potable and ready to be pumped on to the reservoir.
Chlorination kills bacteria and certain microbes. While chlorine is perfectly safe in small doses there is a balancing act to chlorine treatment. If there are too many organic compounds in the water, the chlorine will react with them to form trihalomethanes and haloacetic acids, which can have adverse health affects. Too little chlorine and the water may contain microbacteria. Too much and the risk is from THMs.
Pollacat Springs GWS was allocated €35,000 under the 2017 Rural Water Programme to address THMs in its network.
Cleaning and overflow
Every few hours, the plant's tanks and rotors are automatically cleaned. They are flushed with water and the rotors are spun quickly, generating a turbulence that resuspends sediment stuck to the inside of the tank. This unwanted matter is then flushed into an overflow tank, whereupon it becomes wastewater and is discharged from the facility.
As a furious moment in what is otherwise a calm and relatively quiet process, the caretaker will sometimes trigger the cleaning process manually for visitors to Pollacat Springs GWS.
Pump to reservoir
Finally, the potable water is pumped away from the plant to a reservoir, from which it is distributed through the pipes that serve the scheme's members. Treated water cannot remain in a reservoir for long without becoming unsafe to drink. It is therefore necessary to maintain a regular throughput of potable water.
In instances of peak use, such as during the drought of Summer 2018, increased demand for water can overwhelm the capacity of the reservoir, treatment facility or raw water source. There are various ways to address this and ensure network resiliency. The simplest is to reduce leaks on the distribution pipes through continuous repairs and upgrades.
Since 2011, Pollacat GWS have reduced total water usage on their network by more than a third through a combination of metering and pipe upgrades.
During the formation of the DBO in 2003, insufficient testing was carried out on the raw water at Pollacat Springs. As a result, the treatment plant was unable to cope with seasonal variations in water quality.
In 2010, the build up of silt in the bottom of the reservoir lead to difficulties maintaining sufficient chlorine levels at the end of the network. The GWS was placed on a boil water notice (due to the presence of Cryptosporidium) and received ongoing complaints about water colour. Despite being aware of these issues and initiating a plan for their remediation, the scheme faced continuous setbacks and delays, both in terms of council permission and national-level funding.
It was not until 2016 that the upgrades to the plant were finally finished. This included remedial works around the spring to limit organic growth and the purchase of adjacent land for source protection and plant expansion. Due to these incremental upgrades, water follows idiosyncratic circuit of pipes through the plant. The diagram simplifies this in order to achieve clarity rather than accuracy.
As part of upgrades to the facility, Veolia installed a multi-stage tank capable of removing considerable organic material from the raw water. This is composed of two main steps: flocculation and clarification.
Flocculation is the process of floc formation. It is initiated by adding an aluminium-based coagulant to the raw water. Powerful rotars are used to rapidly mix in the coagulant throughout the water, before a longer period of gentler mixing encourages the formation of the floc.
After flocculation, the water passes into a second area for clarification. Here, the floc is separated from the water and passed on to a sludge tank, while the purified water continues to the next stage of treatment. Sludge is composed of sediment, organic matter and agricultural run-off. While a small amount is returned to the area for flocculation in order to ensure that the process operates correctly, the vast majority is considered waste and must be regularly removed from the site.
Try clicking on the tree beside the spring.
UV treatment kills biological contaminants by exposing them to ultra-violet rays emanating from specially made light bulbs. This was installed at Pollacat Springs because of the presence of Cryptosporidium in the source water.
Cryptosporidium is a parasite that can cause severe illness if ingested by humans. Contamination most often occurs when animal effluent enters into the karst aquifer, especially during slurry spreading season and after heavy rainfall. Due to the speed, seasonality and uncertainty of groundwater movements in County Roscommon, the exact source of Cryptosporidium contamination is difficult to pin down.
Pollacat Springs GWS is currently involved in a project with the Geological Survey of Ireland to map the local karst features and determine how water flows beneath ground using dye tracing. This has on occasion lead to upwellings of dark red water from the spring. The plant is now more than capable of ensuring that this dye does not reach its customers.
An overlooking tree
A tree overlooks Pollacat Springs. In Autumn, its leaves blow into the open clarification tank. This upsets the treatment process, clogging up the lines and reintroducing organic material to already-treated water.
As the tree is not on land owned by the GWS it cannot be removed. As the scheme is already in a long-term contract, it is not so simple to fundamentally alter the facilities. To address the issue, the GWS caretaker has contructed an ad hoc cover from timber and chicken wire, which has been fitted on top of the clarification tank. While this prevents most of the leaves from entering the tank, it is still necessary to have a fishing net handy in case any leaves slip through.
Various chemicals are added to water at different stages of treatment. Poly-aluminium chloride is a coagulant used to remove organic material from raw water. Sulphuric acid is used to balance the water's pH level. And sodium chloride is used as a source of chlorine to kill bacteria and microbes. These chemicals can be dangerous in high quantities, so their use necessitates that care be taken in their use and storage.