Abu Dhabi's deep sewer to be model for region

09 February 2015

The Strategic Tunnel Enhancement Programme has presented several challenges to Abu Dhabi due to its size and complexity, but it is on track to come online in 2015

The Middle East’s first deep-tunnel sewer network is set to become operational in 2015, with the completion of Abu Dhabi’s ground-breaking $1.6bn Strategic Tunnel Enhancement Programme (STEP).

The first construction tenders for the sewerage scheme were issued in late 2008, and, apart from some expected initial teething problems due to the complexity of the project, development of the tunnel programme has proceeded to plan.

“It’s scheduled to be complete by the end of 2015. Beyond that, there will be some finishing to be done to the buildings, but sewage is due to start going through the system in November,” says Alan Thomson, managing director of Abu Dhabi Sewerage Services Company (ADSSC), the body overseeing the STEP and the wastewater sector in the emirate.

Rising demand

The STEP was designed and procured to handle growing sewage levels in the emirate, which have increased steadily over the past 30 years in line with the population. Completion of the scheme will allow the emirate to focus on further advancements to its wastewater sector, such as boosting the utilisation of treated sewage effluent (TSE).

Key fact

Abu Dhabi’s raw sewage volumes are increasing by about 8 per cent a year

Source: ADSSC

“The deep-tunnel sewer is built for two reasons,” says Thomson. “It is built to increase capacity and allow for a trebling of the population. But it also relieves existing problems that the system has further upstream, which would not have enabled additional capacity to be built into the system in the future.”

Thomson says Abu Dhabi’s raw sewage volumes are increasing by about 8 per cent a year. “Most of that is correlated with population increase, so we are effectively building the system in line with the 2030 vision and a trebling of the population,” he says.

Long-lasting design

The technology used will ensure the infrastructure will benefit the emirate for the rest of the century.

“The design life of the sewer is 80 years – maintenance-free – so even if the population increase slows down and it doesn’t reach the treble [figure] until 2050 or whatever, the sewerage tunnel will still be serviceable and operating on a gravity system,” says Thomson. “So it is very easy to maintain and designed for long life.”

Developed to upgrade Abu Dhabi’s existing, strained sewage network, the majority of which was installed in the 1970s, the STEP consists of a 41-kilometre tunnel, starting on Abu Dhabi island and running south to the mainland, descending from 24 metres below ground level to a depth of 80 metres in some places.

Pumping station

A key component of the programme was the construction of a major new pumping station, which will enable the decommissioning of 35 existing pumping stations to improve the efficiency of the network.

“In many ways, it is a legacy system, unique for the region,” says Thomson. “And others now, such as Qatar, are beginning to follow.”

In addition to Qatar’s under-construction, $2.7bn Inner Doha Resewerage Implementation Strategy (Idris) project, MEED reported in January that Dubai was looking at building a deep-tunnel sewer network.

Challenging project

The unprecedented size and complexity of the project has resulted in several challenges that ADSSC has had to overcome, beginning with the tendering and procurement of the construction contracts.

“First of all, it was getting the right type of contract in place,” says Thomson. “We wanted to make sure we got construction companies and consultants that had the right experience behind them – which meant putting in a proper prequalification system to enable us to select those who could deliver.

“We set the bar very high to ensure we got good-quality consultants and contractors.”

It was the first time that the emirate utilised design-and-build deals for a major project, and the competitive tender resulted in ADSSC awarding six major contracts to firms from across the globe.

“We got CH2M Hill from the US [as programme manager], which had been heavily involved in building the Singaporean system, which was very similar to what we are doing,” says Thomson. “We selected contractors from Germany, South Korea, Brazil and India – international players with suitable experience with this type of contract.”

Construction work

The next challenge for the wastewater firm was to coordinate the complex construction work, while ensuring minimum disruption was caused to the UAE’s capital. Thomson gives the example of connecting existing and new link sewers as something that required careful planning and coordination.

The masterplan not only plans volumes, but also what the treatment capacity needs to be in the future

Alan Thomson, ADSSC

“We had to implement 300 openings of the ground on the island and mainland of Abu Dhabi – all within a relatively short period of time,” he says. “We had to get the municipality and other stakeholders on board to understand what we were doing and how we were selecting the methods of construction to enable the least disruption of the day-to-day operating of the city.”

Thomson says it was important the route for the sewer tunnel was planned and constructed in a way that would not affect future planned development projects, such as the proposed metro, and effective coordination with the various government agencies and clients was vital.

“We spent a lot of effort trying to bring everyone on board with the concept of what we were doing, and managed to build up very good relationships and support,” he says. “Now, all the openings are in place and all of the permits were given in advance of when we needed them; the construction has gone well with minimal disruption.”

Long-term forecasting

The careful planning of the STEP is in line with Abu Dhabi’s commitment to long-term forecasting. In addition to the Vision 2030, which maps out all of the major areas of the emirate’s medium-term development, ADSSC is currently updating its masterplan for the wastewater sector.

In May 2014, the utility appointed US consultancy MWH Global to update the masterplan, and this is scheduled to be completed by October this year. Thomson says ADSSC is assisting efforts through a testing programme to ensure the plan is as comprehensive as possible.

“We are doing some physical tests and calibrations of the system so that what [MWH] runs in respect of the future of the system will be as accurate as possible – not just theoretical, but some of the physical aspects of the system are being taken onboard with the masterplan as well,” he says.

Planning critical

Thomson says long-term planning is an imperative part of ensuring wastewater infrastructure meets the needs of the emirate’s population for generations to come.

“Masterplanning enables us to look as far ahead as we possibly can, and look at where Abu Dhabi is going to expand, and what the likely type of demand will be, either residential or commercial in one area or industrial in another, and allow us to predict flows in catchment areas,” says Thomson. “Then we can hydraulically model the flow on our computers to see how it affects the downstream system.”

Long-term planning also enables ADSSC to prepare for the next phase of development of its wastewater network.

“The masterplan not only plans volumes, but also what the treatment capacity needs to be in the future, as well,” says Thomson. “This includes the qualitative elements of our sewage –how can we best treat it to ensure what comes out of the other end is good-quality TSE for irrigation services? We can then plan where to pipe the TSE and pump it towards the end-users.”

Treated sewage

Water reuse will play an increasingly important role in the Gulf in the coming years as governments seek to meet rapidly growing demand for water for irrigation and industrial purposes. Thomson says ADSSC has managed to achieve a 100 per cent reuse rate in the city of Al-Ain, and the next step is to meet this target for the rest of the emirate.

“In Abu Dhabi city, we have a current reuse rate of about 50 per cent, so that is the next target,” he says. “We have reports from the government on plans to build infrastructure to take this water to where it can replace groundwater for irrigation.”

Projects to enhance and expand the emirate’s effluent infrastructure form part of ADSSC’s AED6.1bn ($435.6m), five-year capital expenditure plan until 2019. While there are currently no plans to scale back the investment programme due to the recent fall in oil prices, Thomson says the utility will be able to rationalise if required.

Oil prices

“I think we are just really looking at what our priorities would be for our future investment programme. It may mean some of our investment programmes have to be deferred if we are asked to make cutbacks… in terms of capital investment,” says Thomson.

“There are options [for alternative funding] in wastewater treatment. Previously, we have used BOOT [build, own, operate, transfer] to get investment from private investors; this is a possibility if we need to press forward with further construction of more sewage treatment plants, or expand existing plants.”

However, while the new era of lower-priced oil may have a significant impact on some of the Gulf’s industrial sectors, Thomson says the demand dynamics of the wastewater sector will ensure investments proceed.

Demand dynamics

“The population is still increasing in the region significantly,” he says. “The population growth rate and the [sewage] flow [growth] rate are almost identical, and since 2005, both have doubled and have driven infrastructure investment.

“Historically, I’ve looked back to 1982, at figures in terms of growth [in the sewage sector]. They’ve continued to average between 6 and 8 per cent.”

While 2015 will bring the end of construction work on one of the region’s largest and most innovative wastewater projects to date, it is clear ADSSC and its managing director will be kept busy for many years to come.

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