Bespoke Water Treatment Solution Ensured Compliance with The Environment Agency During Repairs of a Leaking Sewer
Project Overview
Sewer repairs were required for Thames Water, on a HS2 site, where the Colne Valley viaduct carries train tracks over a series of lakes and waterways at Hillingdon. The repair project was being carried out by J Browne Utilities Services, and it was due to take place over a number of weeks. There is an ever-expanding awareness of the need for sustainable environmental business practice, including in the area of water management during construction works. Bodies such as the Environment Agency have increasing powers to fine polluters, with decreasing tolerance for offenders. It was imperative that while this project took place, water was discharged responsibly.Challenge
J Browne had to access a section of the leaking sewer in order to make repairs. Due to the proximity of several lakes, the excavation took them significantly below the water table, and despite the installation of a cofferdam, it required continuous dewatering at a rate of 20-30m3/h to keep the area dry.
This volume was too high to tanker off-site and it was not possible to discharge water into the foul sewer.
Water from the excavation was highly turbid as it was being pumped from the bottom of an active work area. This water needed to be treated to produce visually clear and safe water before being discharged, including reducing the pH if required.
J Browne called upon RVT Group to survey, recommend, and install a water treatment solution that would help them to meet their project timescales. It was also essential that the solution would deliver water quality that was in line with what the Environment Agency identified as the discharge parameters at this location.
Solution
After surveying the project, RVT installed a full chemical dosing system. This consisted of an agitated mix tank, dosing stand, and lamella settlement tank. The system provided flow-proportional chemical dosing and pH adjustment. The dosing skid automatically added flocculant and coagulant as required to make fine suspended solids easier to remove when discharging the water.
Silt laden contaminated water was fed into the back chamber of the Lamella Plate Settlement Tank, where it flowed around into the base of the lamella plate section of the tank. The water stream flowed upwards between the inclined Lamella plates. With the reduced flow, the solids fell to the plate surface, where it slid by gravity, down the plate, to the sludge collection chamber at the bottom. The sludge was then periodically drained using the valve at the bottom of the hopper.
Given the environmental impacts of discharging polluted water, along with the risk of associated financial and reputational damage, it is not recommended to rely on periodic manual water quality checks. So a real-time monitor was installed on site. This water monitoring unit gave the team the ability to assess water quality levels in real-time. The results could be used as evidence to show compliance should the Environment Agency request it, and it also gave the site team peace of mind that discharge water was being managed responsibly.
Contact RVT Group
This case study was produced and originally issued by RVT Group - construction industry partners for EnviroHub. To contact them directly, please call 0808 178 3286 (7:30am to 4:30pm Mon-Fri).
Gallery
Above: EnviroHub Lamella Plate Settlement Tank removing suspended solid particles from water (50m² volume).
Above: The water settlement tank is a simple but effective way of separating solids from water on site.
Above: RVT’s water treatment solution on site.
Above: Water samples before and after being treated by RVT’s bespoke water treatment solution.
