Background
The location of an existing Affinity pumping station and pipeline in Hemel Hempstead is within an area undergoing significant development. It is understood that chalk based sediment from within the underlying aquifer had been mobilised as a result of drilling and piling works from adjacent construction sites. The mobilisation of sediment meant that the waters pumped, using the existing Affinity Water asset, were contaminated with slow settling suspended solids. Normally on this site, the clearance pumping is carried out and the washwater can be discharged directly to the adjacent watercourse.
The Overall Objective
Due to the local development work elevating the level of suspended solids in the aquifer, if this water had made its way to the nearby River Gade without treatment, it would unquestionably have harmed the aquatic ecosystem, and the discharge criteria within Affinity Water’s discharge permit would have been breached. It is for this reason the Siltbuster equipment was required to maintain site compliance and to protect the environment.
The water mains pipeline is part of a live water supply to nearby residents and businesses. So, it was critical that it could be cleaned and put back online as quickly as possible. Things were complicated further by the fact that space and access were very limited onsite. The only area suitable to set up a mobile water treatment solution was on the floor slab of a demolished building, located at the end of a busy sideroad.
Solution
Siltbuster designed and mobilised a 350m3/hr containerised two-stage flow proportional chemical dosing and solids removal system. The modular solution comprised of two 20ft customised dosing containers, two 30m3 dosing tanks complete with mixers, and five HB50M lamella clarifier units.
Due to the access restrictions onsite, a crane had to be used to manoeuvre our units into place. The system was installed within three days and it was operational for seven days a week, for three weeks, maintaining consistent compliance, while Affinity Water’s water main was pumped clean.
The pipeline washwater had to meet a discharge criteria of total suspended solids in a concentration of less than 50mg/l and a pH between 6 and 9. Siltbuster’s kit worked so well that the washwater produced had a total suspended solids concentration of less than 10mg/l.
