29 July 2013: Due to the intense rainfall earlier this afternoon, the drainage system was unable to cope in the Dicq area and there was a diluted sewage spill into the sea for 30 minutes. As a precaution, Transport and Technical Services (TTS) is advising the public not swim or fish in the area of the Dicq slipway today (29 July 2013). TTS also advises not to take anything from the beach such as shells etc and to wash hands carefully if you’ve been in the area. The tide will refresh the beach overnight and swimming can resume tomorrow.
12 August 2019: Islanders are advised against swimming in the Havre des Pas beach area for the next 24 hours, following a sewage spill at the Dicq in the early hours of this morning. Lifeguards will close the bathing pool during the 24 hour period, during which there will be two tidal changes. Heavy rain during last night’s storm led to the spill from the Dicq pumping station at approximately 2.30am today. Teams from Growth, Housing and Environment have cleaned the spilled waste from the beach, and samples of the water have revealed high levels of E.coli and enterococci. The Dicq pumping station contains both foul sewage and surface water, and is connected to St Helier’s combined sewer system. When it rains heavily the surface water can overload the network.
12 August 2019: Islanders are advised against swimming in the Havre des Pas beach area for the next 24 hours, following a sewage spill at the Dicq in the early hours of this morning. Lifeguards will close the bathing pool during the 24 hour period, during which there will be two tidal changes. Heavy rain during last night’s storm led to the spill from the Dicq pumping station at approximately 2.30am today. Teams from Growth, Housing and Environment have cleaned the spilled waste from the beach, and samples of the water have revealed high levels of E.coli and enterococci. The Dicq pumping station contains both foul sewage and surface water, and is connected to St Helier’s combined sewer system. When it rains heavily the surface water can overload the network.
What is a Combined Sewer Overflow?
These events happen because most of that area has sewage and rainwater runoff water in the same pipes. Most of the time, all this wastewater is taken to the sewage treatment plant at Bellozanne, where it is treated and then purified and bacteria free water is discharged via an outfall to St Aubin’s Bay.
But, as the United States Environmental Protection Agency explains, there are circumstances when this breaks down:
“During periods of heavy rainfall or snowmelt, however, the wastewater volume in a combined sewer system can exceed the capacity of the sewer system or treatment plant. For this reason, combined sewer systems are designed to overflow occasionally and discharge excess wastewater directly to nearby streams, rivers, or other water bodies.”
A Legacy Issue
It’s not just Jersey which has this problem. It is part of the way in which most sewage systems were originally constructed. As John Tibbetts explains in “Combined Sewer Systems: Down, Dirty, and Out of Date”:
“When combined sewer systems were introduced in 1855, they were hailed as a vast improvement over urban cesspool ditches that ran along city streets and spilled over when it rained. These networks of underground pipes were designed to dry out streets by collecting rainwater runoff, domestic sewage from newly invented flush toilets, and industrial waste-water all in the same pipe. Waste- and storm water was then discharged directly into waterways; in the early twentieth century, sewage treatment plants were added to clean the wastewater before it hit streams. Combined sewer systems were—and still are—a great idea, with one catch: when too much storm water is added to the flow of raw sewage, the result is frequently an overflow.”
“The sewers have been specifically designed with escape overflow pipes so that the mixture of sewage and storm water doesn’t back up into buildings, including homes”
That’s why the Jersey overflow took place, to protect homes and drains from sewage bubbling back and coming out of toilets or roadside drains. When sewage overflows into homes and businesses, expensive remediation and decontamination is needed to make them safe again.
By far the safest option was to flush it into the sea, even if that meant environmental hazard.
As to those hazards, Tibbets comments:
“CSOs flood waterways with contaminants including microbial pathogens, suspended solids, chemicals, trash, and nutrients that deplete dissolved oxygen. Microbial pathogens and toxics can be present in CSOs at levels that pose risks to human health. CSOs can therefore lead to contamination of drinking water supplies, beaches, and shellfish beds.”
Why the Cavern didn't work?
Part of the problem caused by storm surges has been tacked in cities such as Boston, Chicago, and Atlanta with the building of deep storage tunnels to hold storm water overflows. Jersey has just such a one in the form of the cavern.
However, the overload was purely at the Dicq – too far down the chain to affect the cavern. It deals with, on average, about 12,000 tonnes of waste-water a day, but was overloaded.
Mr Duncan Berry, assistant director of liquid waste, said the Dicq deals with sewage from the east of the Island as well as a mixture of run-off water and sewage from town. He commented that:
“The Dicq deals with sewage and run-off water but because of the rainfall it was inundated with clear water and the pumps were going like crazy to get it to First Tower, but the maximum level was beaten and then it overflows and goes out to sea. We have an alarm system and we get an alert when that happens.”
The impact of Climate Change, Population Growth and Land Use
Experts say climate change is causing an increase in precipitation, flooding and high-intensity storms and combined sewer systems like Jersey’s could experience more overflows as result. Climate scientists predict that precipitation levels and the amount of rainfall from heavy downpours will increase over the next century.
There’s an additional effect from population growth and more houses and flats. With continued population growth, the demands on Jersey’s combined sewer systems have increased.
Moreover, houses and flats on Brownfield sites make more paved surfaces which can increase the volume of runoff when it does rain.
What are the options?
What can be done? As far as engineering is concerned, there are a number of options available.
Upgrades can include improvements like larger and newer pipes, even converting combined sewage systems to separate sewer systems, where storm water runs through a completely separate set of pipes. But these will be costly, even if they do help offset the impacts of heavy downpours.
“Treatment Techniques for Combined Sewer Overflows” by S.M. Scherrenberg looks at other solutions.
In Jersey’s recent overflow, some sanitary products and larger matter went through the outfall to the beaches. But there are solutions for that, such as the Netting TrashTrapTM System of Fresh Creek Technologies Inc. This is a modular floatable collection system located at the CSO outfall. Using nets is an inexpensive and simple way of removing trash and floatables without using electrical or mechanical power.
What can be done? As far as engineering is concerned, there are a number of options available.
Upgrades can include improvements like larger and newer pipes, even converting combined sewage systems to separate sewer systems, where storm water runs through a completely separate set of pipes. But these will be costly, even if they do help offset the impacts of heavy downpours.
“Treatment Techniques for Combined Sewer Overflows” by S.M. Scherrenberg looks at other solutions.
In Jersey’s recent overflow, some sanitary products and larger matter went through the outfall to the beaches. But there are solutions for that, such as the Netting TrashTrapTM System of Fresh Creek Technologies Inc. This is a modular floatable collection system located at the CSO outfall. Using nets is an inexpensive and simple way of removing trash and floatables without using electrical or mechanical power.
As Scherrenberg notes:
“In general the nets need to be replaced regularly to prevent odour annoyance to the surroundings and visual pollution. Replacement of the nets will take about 30 minutes.”
But they are efficient at removing larger floatable materials from storm surges and overflows.Maybe those fatbergs would have been trapped.
Another solution he looks at is Hydrodynamic Vortex separation:
“In the USA hydrodynamic vortex separation (HDVS) devices are applied for the removal of suspended solids and other easy settable particles.”
“The system is self-inducing so there are no moving parts. Because of the gravity the solids will be pulled down. The floor of the vortex is under a slope to sweep the solids towards a central drain. Vortex separators can be applied when dealing with extremely high flows”
“In the past years more advanced vortex separators were developed. The Swirl Concentrator, the Fluidsep® and the Storm King® (illustrated in Figure 3-1) are examples of these advanced vortex systems, which are used for treatment of CSO water. In these systems inorganic chemicals (coagulants) can be dosed for coagulation and flocculation. In this way removal efficiencies increase dramatically (Averill et al., 1997) and colloidal matter, which will not settle by gravity, will also be removed (Helliwell and Harper, 1993).”
It should be noted that will not remove all the problem, only larger solid material. Disinfecting the water is a challenge, as UV systems cannot cope with storm surges.
So perhaps it is also time to address new buildings for the increased population, and more permeable surfaces. I hope to examine that in a later blog.
References
https://www3.epa.gov/region1/eco/uep/cso.html
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1257666/
https://pdfs.semanticscholar.org/d5cd/609c8dc11d7cf5b478d154cc43ef9c1186c6.pdf
“In general the nets need to be replaced regularly to prevent odour annoyance to the surroundings and visual pollution. Replacement of the nets will take about 30 minutes.”
But they are efficient at removing larger floatable materials from storm surges and overflows.Maybe those fatbergs would have been trapped.
Another solution he looks at is Hydrodynamic Vortex separation:
“In the USA hydrodynamic vortex separation (HDVS) devices are applied for the removal of suspended solids and other easy settable particles.”
“The system is self-inducing so there are no moving parts. Because of the gravity the solids will be pulled down. The floor of the vortex is under a slope to sweep the solids towards a central drain. Vortex separators can be applied when dealing with extremely high flows”
“In the past years more advanced vortex separators were developed. The Swirl Concentrator, the Fluidsep® and the Storm King® (illustrated in Figure 3-1) are examples of these advanced vortex systems, which are used for treatment of CSO water. In these systems inorganic chemicals (coagulants) can be dosed for coagulation and flocculation. In this way removal efficiencies increase dramatically (Averill et al., 1997) and colloidal matter, which will not settle by gravity, will also be removed (Helliwell and Harper, 1993).”
It should be noted that will not remove all the problem, only larger solid material. Disinfecting the water is a challenge, as UV systems cannot cope with storm surges.
So perhaps it is also time to address new buildings for the increased population, and more permeable surfaces. I hope to examine that in a later blog.
References
https://www3.epa.gov/region1/eco/uep/cso.html
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1257666/
https://pdfs.semanticscholar.org/d5cd/609c8dc11d7cf5b478d154cc43ef9c1186c6.pdf
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