Environmental Techniques

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Overview: Scheme undertaken in Dublin City Centre including CCTV and Sonar Surveying of pipes, manhole surveys, pumping station surveys and jetting of sewers.

 Location: Various locations around Dublin City Centre

Operations:  CCTV Survey, Sonar Surveys, Manhole Survey, CSO Survey, Pumping Station Survey
Clients: Atkins Ltd, Irish Water, Dublin City Council


The scope of the contract was to carry out a comprehensive survey to assess the structural condition of the ageing and complex drainage system at various locations within the south-side of the Dublin City Centre catchment and also to assist the build and verification of the hydraulic model.

Some of the constraints faced during this project

 Large diameter, irregular shaped pipes

 Semi-surcharged and surcharge pipelines

 Heavily silted sewers which had never been cleaned or surveyed before

 Working in busy city centre environment

 Requirement to avoid disruption to vehicular traffic and LUAS flows



Assessment and recording of condition of approximately 26km of foul/combined/storm sewers varying in size from 100mm to 2700mm and varying in shape (circular, egg, arch and rectangular)



Initial inspections found that major sewers adjacent to the River Liffey were in a constant surcharged / semi-surcharged state. In order to obtain a survey of adequate use to the client, Sonar surveys were carried out on these sewers using a sonar profiling system mounted on a float. In conjunction with CCTV footage, the sonar data provided much needed information on the condition of the pipe and amount of debris below the water level.


Initially, a total of 1km of sonar surveys were completed in this location ranging from 900mm diameter to1350mm. The use of sonar and CCTV on a float system allowed sewers to be surveyed for which no information had been previously collected. Due to heavy infiltration from the River Liffey, overpumping the line was virtually impossible and setting up traffic management to get the overpumping equipment, in addition to the jetting equipment, would have caused major traffic disruptions in an extremely busy location at the centre of Dublin City Centre.


A further 4km of sonar surveys were completed along Dublin’s South Quays and Ringsend area as data provided by the initial survey contractor was insufficient for assisting in the build of the hydraulic model due to the pipes being in a surcharged/semi surcharged state. Environmental Techniques were tasked by Dublin City Council and Atkins to survey these sewers with sonar following the success of the initial sonar surveys. To improve productivity, guide ropes for the sonar survey were installed at each location by a man entry team working ahead of the sonar survey squad.


The sonar survey proved invaluable for collecting information in the surcharge/semi-surcharged sewers and its utilisation in this situation led to the project being awarded “Innovative Scheme” at the 2015 UKSTT Annual Dinner and Awards Ceremony.



Many of the sewers identified for survey were brick, egg shaped culverts, with narrow inverts. Due to the size of the sewers, the narrow inverts and the irregularity of the bricks, it was not possible to undertake the survey of these sewers with a CCTV camera. Instead, man entry surveys were carried out for 1.8km of sewers ranging in diameters 1600x700mm to 2600x800mm (egg shaped). Each survey team consisted of 7 personnel all of whom were confined space trained. Video footage of the tunnels were recorded by the operative who noted defects and inspected them using the camera system.



An internal condition and dimensional survey along with a GPS/Total Station survey was undertaken for 179No. critical manholes. The position, diameter, material and invert level of every pipe entering and leaving each manhole was recorded along with the manhole construction details, condition and internal dimensions. Detailed plan and cross sections were completed for the critical manhole and CSOs.



Surveys were completed for 8No. pumping stations throughout the catchment. The surveys involved recording dimensions and levels of the pipework and assets within the pumping station chamber and a topographical survey of the pumping station site.



Through abandonment of initial CCTV Surveys, approximately 4.5km of sewers were identified for jetting to facilitate completion of the CCTV inspections. Sewer diameters varied in diameter from 150mm to 1200mm diameter. All jetting/desilting carried out on the instructions of the Client’s representative and CCTV inspections were undertaken immediately upon completion of the cleaning operations.


Environmental Techniques undertook a large majority of the works at night to minimise disruption to the vehicular traffic and the LUAS line. Through the use of sonar profiling systems and man entry tunnel surveys, the majority of the lines presented in the scope of this project were able to be surveyed providing network engineers with critical information for their models. These models were further enhanced with the detailed surveys undertaken on pumping stations and combined sewer overflow chambers, allowing critical network scenarios to be modelled.

Overview: Removal of debris that had accumulated in Trash Basket which is used for preventing debris in the Belfast Tunnel from reaching the Terminal Pumping Station


Location: Pollock Dock, Belfast
Operations:  Chamber Cleaning, Silt Removal


To help alleviate flooding issues in Belfast during high periods of rainfall, a large storm water tunnel was constructed underneath Belfast running from Glenmachan Street and Ormeau Park to a Terminal Pumping Station at the docks. The project, which started in 2006, was one of the biggest and most important infrastructure investments in the city involving work to upgrade the existing sewer network and to increase stormwater capacity.

At Whitla Street, before the tunnel reaches the Terminal Pumping Station, a large ‘trash basket’ is installed in the sump of one of the shafts. When storm water flows through the chamber, any large debris transported by the flow is designed to fall into the basket and is prevented from reaching the Terminal Pumping Station.

Environmental Techniques were contracted to clean out the trash basket. The procedure had not been attempted since the initial construction of the sewer, and there was no understanding of how much debris had accumulated in the basket.

After numerous planning visits to the site, trial lifts and several revisions of method statements, lifting of the basket was attempted. Compacted debris in the basket caused the force exerted by the crane to exceed the safe working load of the basket and manual removal of debris at sump level had to be undertaken first. 

Difficult access restrictions; the base of the Trash Basket chamber lies approximately 32m below ground level. Entry was undertaken using cranes and man-riding baskets.

As the basket was marginally larger than the access opening, the basket could not be lifted above ground level to be emptied. The basket was held just below the opening whilst the sucking hose of the Jet-Vac unit was lowered into place to lift out the debris.

Photographs taken by operatives from within the shaft provided information on the condition of the walls and benching inside the shaft.

With the basket emptied, the sump would continue to remove heavier debris from the flow and prevent it causing issues further downstream at the Terminal Pumping Station.


Management of Health and Safety of this project was especially important as the environment and method of work posed unique hazards which required safe and efficient solutions. Rigorous escape plans were put together which involved input from the Fire Department. Personnel entering into the Trash Basket chamber were fully trained in the use of breathing apparatus and escape sets and this equipment was provided to each operative.

During reasonably dry weather, little flow is expected within the tunnel. The Met Office forecast was consulted on a daily basis to ensure there was little chance of rain. There was however an added risk of large flows should any of the major pumping stations along the route fail and discharge into the tunnel. To reduce the severity of this risk, lookouts were placed along the tunnel with direct radio communication with personnel at the Trash Basket site. Should any dangerous flows occur into the tunnel, this would be noticed further upstream, allowing personnel within the Trash Basket shaft ample time to evacuate safely. Throughout the Trash Basket cleaning, the weather remained dry and no flows were reported by the lookouts, allowing the work to be undertaken in safe conditions.

The cleaning of the Trash Basket supplemented surveys undertaken by Environmental Techniques on other shafts along the network. Despite some unforeseen problems, the cleaning of the Trash Basket was a success and was completed in a shorter time period than expected. 


Overview: Jetting twin 1448mm siphons to remove silt, debris and grease which had been impacting the rate of flow passing through the siphons.


Location: Queen’s Bridge, Belfast Lough
Operations:  Sewer Cleaning, Grease Removal, CCTV Survey


Sewage from East Belfast is carried under the River Lagan by twin inverted 1448mm cast iron siphons located just south of the Queens Bridge in Belfast.  Constructed in the 1960s, the siphons are capable of passing forward 571l/s to the Low Level Sewer, which gravitates to Belfast WWTW

Environmental Techniques were contracted to undertake CCTV surveys to determine the structural integrity of the twin siphons. The project involved;

Undertaking traffic and pedestrian management in a busy city centre environment

Installation of a gantry system to support the pumps used to drain down the isolated siphon. The pumps remained running throughout the project to overcome infiltration and leakage through the penstocks.

Removal of 120 tonnes of silt, debris and grease from the lines.

Successful completion of CCTV survey along each of siphon.

The removal of the silt, debris and grease from the siphons improved the capacity of the siphons and reduced the likelihood of problems upstream.


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