The client was part-way through construction work required to accommodate a new production facility in one of its existing buildings. The method of construction required a series of well points to be installed around the periphery of sheet piles so as to lower the water table and prevent the base of the excavation from heaving.
Soon after dewatering commenced, the dissolved iron concentration in the groundwater started to increase rapidly, to a point where it could compromise compliance with the discharge consent limit. At that point Tata stopped the dewatering process and put the project on hold whilst a suitable method of removing the dissolved iron was sourced.
The Overall Objective
Tata required a solution that could be rapidly deployed and that could treat 120m³/hr of groundwater containing 70mg/l of dissolved iron 24 hrs per day without interruption for the full 10 week construction period, whist ensuring compliance with the 10mg/l Iron limit.
The process deployed on site involved a combination of pH adjustment and aeration to precipitate the dissolved iron and then to separate the precipitate from the water using DAF technology. Because of the large volume water to be treated, the solids recovered by the DAF plant were then dewatered using a mobile filter press mounted on an articulated lorry.
During the whole 10 week project duration some 180,000m3 of groundwater was treated and over 10 tonnes of dissolved iron was prevented from contaminating the River Dee.
Tata’s Senior Project Engineer Simon McCormick commented “without the expertise and swift response from Siltbuster, the project could have been delayed for several months with significant additional costs incurred whilst an alternative method of construction was developed and implemented.”