Flood Affected Sewer Systems

/0 Comments/in , , /by

Vacuum sewerage systems are ideal in areas that are subject to flooding

Nearly all vacuum sewerage systems are found in coastal area’s many of which are subject to flooding from rain/storms or rising sea levels. We all understand the problems that occur if I&I is present, we all know what causes it to occur.

We have operated a number of systems during major floods without the system going down. In one Sydney system major floods occurred every two years (see photo above), our operations contract stated that if any homeowner could not continue to use their plumbing they would be put up at a hotel at our cost. Happily we did not spend a cent on hotel costs.

For the vacuum valve to meet the European standard it must be able to operate under a full 10 inches of water. To meet the Australian standard it must operate without problem under 18 inches of water. By ensuring all hose clips are properly in place and the controller breather is clear of any water , the system will continue to operate.

In area’s where flooding is common we tend to put the controller and controller breather in a pillar besides the pit to ensure that the operator can still fire the valve without trying to access the pit through the flood water which might not always be possible.

Water infiltration from the homeowners property.

We have found that the main source of stormwater entering a system comes from the homeowners property. In some flood areas we have seen that certain sections of the town will regularly go under water. This usually means that residents have to be evacuated and in the past the water inundation from that area could risk the whole system. In this case we would install a remotely controlled division valve that would cut off that section of the town from the vacuum system. It is controlled from the operations base so that operators are not put at risk trying to isolate the area.

In some older towns we find that some houses, or more often camping grounds or caravan parks are set at ground levels

that are blow the legislated 100 year old flood levels that people can build at. If we find houses affected in this way, they must pump into the vacuum system rather than drain into it so that the system is not put at risk.

Candycanes/Gooseneck house breather vents when placed on properties will often be a source of infiltration, usually due them either being cut down by homeowners who object to them being in the middle of their yard or by gardeners knocking them over with their lawn mowers. At times they are placed too low to the ground, under the flood level. In these cases we would install a  Dedicated Pillar or think carefully about where the gooseneck vent is placed. Putting it in the middle of the yard risks it being cut down allowing water to enter the system. Putting it at the roof or garage top or against the house wall will limit water entering the system.

Smart Monitoring

As technology has improved, many asset managers have embraced the ability to locate exactly where and when I&I may be occurring. A sensor on a vacuum valve giving the open/close status will also be able to tell the operator the number of activations in a day. It is very easy for the operator to set up an alert to advise if any particular valve is operating more frequently than the general average, especially during wet weather events.

Once the operator has established which collection pit is activating more frequently than the other valves in the area, they can then troubleshoot the problem. The likely problems are that the homeowner has cut their house vent or inspection point to allow rainwater to enter the system or may have connected up their stormwater system to the sewer system or have a cracked gravity line feeding from the house to the pit. A letter to the homeowner to make the necessary rectifications is required.

There may also be groundwater or stormwater entering the collection pit due to incorrect pipework entering the pit allowing for water to enter. This is usually picked up at commissioning, if not should now be rectified.

You should also make sure that the pit lid is made for area’s that have flooding and has a seal and no holes to allow water to enter. the pit should not be located at a low point in the street.

The monitoring system makes it possible to identify these problems and fix them. this is not possible in a gravity system.

System Design

When designing a gravity sewer consideration must be made for Infiltration and Inflow on the pipes, the pump stations and the treatment plant.

Stormwater cannot enter the vacuum system via the vacuum pipework as it must remain tight for the vacuum pressure to hold tight. If a break occurs in a main it is immediately noticed and repaired.

An allowance is made for I&I but only for a small amount of the network, that being the homeowner gravity lines. So the system is not designed for infiltration and all steps must be taken to ensure that it does not occur. Luckily in a vacuum system the source of any I&I can be located.

If you have any leaks into your system, contact an expert for advice.

Frozen Vacuum Sewers and the Lessons from Europe

/0 Comments/in , , /by

Over the Northern winter we read with interest a number of stories related to frozen vacuum systems  which were caused by some of the worst winters seen in 100 years in the North East of America. These stories have increased in recent years with some commentators talking about the reality of climate change and its impact on many types of infrastructure, not just sewerage systems.

To understand some of the problems you need go no further than googling “Plum Island frozen sewers”. The main problems seemed to be related to frozen vacuum valves, water frozen in the pits, gooseneck vents submerged by snow, frozen sewage in the pipework, frozen gate valves and division valves and leaks in the line.

Does this  need to be the case every year that there is a big dump of snow or temperatures fall? Aren’t vacuum system supposed to be resilient?  We don’t have to  look as far afield as the vacuum systems in Alaska or even at the Arctic and Antarctic bases to get some solutions to the problems encountered in America. Germany, France, Poland the UK and some of the Nordic countries like Estonia have experienced very low temperatures and extreme snow falls from time to time with little impact on their vacuum systems.

As an engineering firm we need to be aware of local conditions where ever we install a system whether it is in the arid desert of Australia, tropical conditions in Malaysia, remote islands in the Cocos Islands. All systems should be designed to suit the local conditions..

When dealing in area’s subject to extreme cold we need to take care of how deep the vacuum mains are laid, what type of division valves are used, how the collection pit is designed, where the air intake vent should be for the operation of the valve. Many of these things can be adjusted in existing systems.

One of the important developments in how Flovac vacuum systems are managed is in the use of monitoring systems at the valve and pit. As a standard in cold conditions we monitor the temperature in the pit via our monitoring system.

This would have helped a lot in the Plum island project as any valve failures would have been easily and quickly located due to freezing ensuring no loss of service for residents or sewage overflows into their basements.

The monitoring system also makes it very easy for operators to locate the exact location of collection pits. This is also true in coastal area’s where pits can often be covered by sand during the summer months.

Many communities in the US are fretting over what will happen next winter with their vacuum systems. Will the Fire station chief need to allow residents to use their showers and toilets. Will portable toilets be sold out early, or will everyone just head for Florida.

Maybe one solution is to contact us here at Flovac and we would  bring a team of experts from Europe to look at ways to ensure that your Happy Holiday season is truly Happy.

Flovac Vacuum Sewerage Systems are experts in solving difficult wastewater engineering problems in unique geographic areas with Global Knowledge and Local Solutions.

High Flow Projects – Reef Island Bahrain

/0 Comments/in , /by

Over the last five years building work has continued at Reef Island in Bahrain and this year Flovac has added its proprietary wireless monitoring system to assist the operations group with troubleshooting the system.

Concept Design for Reef Island Bahrain. Shows 55 story building, 32, 16 and 8 story apartments.

When design work commenced on the Reef Island project in 2008 many engineers suggested that vacuum systems could not be designed to handle flows coming from high rise buildings such as those being planned at Reef Island.

The developer at Reef island was planning a number of high rise apartment blocks which included 8, 16 and 32 story blocks. There was also a plan for a 55 story building on the reclaimed land site.

As Flovac had previously done a number of high flow projects including the world’s first in Bangkok, Thailand; ( See Thailand Project details)  there had also been a number of other high flow projects including oil refineries, industrial area’s , schools, hotels, shopping centres and hospitals.

Ensuring that the flows do not steal vacuum from other lots upstream and sticking to a limited flow per valve has ensured that the Reef Island project has run smoothly and handled the flows easily.

For more details on Reef Island

Preston’s Housing Development in Christchurch

/in , /by

It’s a case of one down and 2599 to go at the biggest subdivision in Christchurch.

The single house under construction in the Prestons housing development in Christchurch will not be alone for long.

The milestone of Prestons’ first house was marked by a visit from Prime Minister John Key this week, five years after the giant housing development was first launched. That first house is owned by 87-year-old Cliff Mitten. Since sections in the Marshland subdivision first went on sale last year, about 330 have been sold.

Of the 200 sections in the first stage, known as Korowai, only four remain unsold. Those buyers now have titles to their sections and more construction is due to get underway soon.

In the second stage, Harakeke, 130 of the 230 sections have sold without being officially released to the market. Titles in that stage will be ready for buyers in June next year.

Prestons is the city’s biggest subdivision, designed for 2600 homes and 8000 residents. It is being developed by CDL Land NZ, Ngai Tahu and Foodstuffs South Island.

Section sizes are from 450sqm to 650sqm, and those in stage two are priced at $210,000 to $244,000.

The developers first released their plans for Prestons in 2008.

They were in the process of trying to get the farmland rezoned for housing, in the face of opposition from Environment Canterbury and other parties, when the earthquakes hit.

The decision was put on hold and then the project was given the green light in 2011 under the Canterbury Earthquake Recovery Act.

At 203 hectares, Prestons is on a site bigger than Hagley Park. It is next to the Bottle Lake Forest reserve, and the Waitikiri and Windsor Golf Courses.

The development has been designed to include a shopping area with cafes and restaurants, a New World supermarket, a primary school and parks. David Schwartfeger, development manager for Ngai Tahu Property, says the section buyers so far have come from across the board in both age and location.

He believes the geotechnical report that comes with each section is helping attract buyers.

Most of the land in the development has been classed as TC1, the least earthquake damage- prone of the government’s technical categories, while the remaining TC2 land has been brought up to TC1 level.

As part of that work, the developers did a soil swap with the Waitikiri Golf Club, removing and giving the club 70,000 cubic metres of peat in exchange for 70,000 cubic metres of sand. The subdivision was then stabilised with a 40-tonne elliptical roller which has been used overseas for mining work.

The Flovac vacuum sewerage system was chosen due to concerns about future earthquakes and due to the high water table in the area. This is Flovac’s second project in Christchurch, which is at Shirley.