Tuesday, April 16, 2024

Master plan for plant


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The South Coast Sewerage Project (SCSP) has been the subject of much national attention over the last year and, in particular, the last few months have witnessed a public health crisis unfold that has the potential to cause severe damage to the economy.

As the former project director of the Sewerage and Solid Waste Project Unit from 1994 to 1997, with responsibility for overseeing the construction of the SCSP during that period, please allow me to provide some background to the need for the project, its design and construction under the Ministry of Health, and its subsequent operation and maintenance under the Barbados Water Authority (BWA). I will also propose some suggestions to address the current difficulty.

The SCSP was conceptualised in the 1980s by the late Arthur Archer (former project director in the Ministry of Health) in response to two problems: (i) an overload of septage at the Bridgetown sewage treatment plant and (ii) deteriorating bathing beach water quality along the south coast. It should be noted that the Ministry of Health had responsibility for the construction of the plant, but its operation, management and maintenance, fell under the BWA, then located within the Ministry of Public Works, now within the Ministry of Agriculture.

The system was designed to collect approximately 9 000 m3/day (two million imperial gallons per day) of wastewater from about 3 000 properties from Bay Street to Oistins, along the coast and some distance inland. There was excess capacity to allow for property growth in the area.

The plant is designed to treat that waste water to advanced preliminary standards (screens with a mesh size of 2 mm (0.08 inches) at Graeme Hall, and then pump the treated wastewater through a 5-km (3.1 mile) force main to a marine outfall at Needham’s Point. 

A force main is a pipe through which waste water is pumped under pressure, instead of letting it flow by gravity. In this article, the terms wastewater and sewage are interchangeable, they mean the same thing – water discharged from toilets, sinks and baths in homes and businesses.

The outfall was designed to be 1.1 km (0.7 mile) long, ending outside the bank reef at a depth of 38 metres (125 feet). This outfall site was chosen after extensive studies had shown that there are strong, predominantly offshore currents in that area. The choice of the outfall site dictated the level of treatment required.

Construction of the sewerage system took place in four contract components. Contract 1, the Treatment Plant and Contract 3, the Outfall, were completed under my watch.  The sewage collection system, Contract 2, involved the construction of some 44 kilometers (~ 27 miles) of inter-connected sewers with 5 lift stations. The collection system and the individual property connections which comprised Contract 4, required the cooperation of property owners which was not always readily forthcoming. For a number of reasons, Contracts 2 and 4 of the project took longer than was originally projected.

The property connections component of the project was completed sometime around 2003, when the system would have been tested and commissioned and handed over to the BWA. Throughout the design and construction phase, the BWA assigned a senior engineer to the project unit to represent the utility’s interests and provide continuity into the operational phase.

The SCSP was designed and built to international specifications with IDB oversight and funding. It also went through several review stages which would have included Town Planning and the Coastal Zone Management Unit. There has recently been some discussion about whether a primary or tertiary treatment plant should have been chosen. The level of treatment required is dependent upon where the treated effluent will be discharged. Primary or advanced preliminary treatment is an acceptable international method, if linked to a long marine outfall that discharges the treated wastewater outside of sensitive areas. and that is what the IDB was prepared to fund at the time.

The plant was built with the capacity to upgrade to tertiary treatment. At tertiary level, the treated water is approaching potable standards.  Indeed, the technology now exists to turn sewage into safe drinking water. The barriers to implementing this approach are more cultural than technical.

That is the background, now to the current problems, as it appears that there are more than one.

It is my understanding that the two screw-lift pumps that carried the raw sewage into the plant at Graeme Hall for treatment, began to lose efficiency in 2014 and could no longer lift all of the incoming sewage to the top of the plant.  From 2014 onwards, some, if not all, of the sewage has been diverted around the treatment plant and discharged without treatment through the force main and outfall at Needham’s. 

Up to 100 per cent of the sewage continued to be diverted without treatment until 2016 when a partially successful attempt was made to fix one of the screw-lift pumps. However, apparently, no further maintenance work on the partially rehabilitated pump nor on the second damaged pump was conducted in 2017.

This has resulted in raw sewage continuing to move through the malfunctioning system and the outfall. Neither the force main nor the outfall, was designed to take raw sewage, only treated (screened) effluent with particles less than 2 mm in diameter. Treatment of all of the sewage has, apparently, not been taking place for three years.  It is quite possible that the force main and/or marine outfall has been damaged and is now, either partially blocked or has sprung a leak. A recent dye test by the BWA might have confirmed this, but I don’t have access to those data. I will come back to this force main when I get to my recommendations.

In addition to the damaged inlet pumps, it is my understanding that the screens at the plant have corroded and have not been replaced. Therefore, even the portion of wastewater that might be still going to the plant may not be receiving the treatment the plant was designed to provide.

After construction, the system was commissioned and handed over to the BWA within performance specifications.  As I have outlined, the system may have been operated, outside of its design specifications for the last several years and it was inevitable that it would fail if operated that way.

A second compounding problem appears to be what has been getting into and potentially blocking the sewers, which is everything that people could possibly throw down the sink or into the toilet. The BWA has responded with an education programme for connected residences and businesses. (HS)

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