Background
The project is a large earthworks scheme to facilitate the construction of a new road and junction off the M42 Junction 6. The new highway will alleviate traffic from the existing M42 junction and will eventually tie in with surrounding redevelopment including HS2.
In its current state the project is a large earthworks scheme that includes considerable excavations and fill profile restructuring. A number of sacrificial ponds and sumps have been created to temporarily store surface water run off and groundwater.
The ground conditions comprise mudstone and sandstone and as a result, waters are impacted with slow settling solids.
The Overall Objective
The overall objective is to treat all surface water run off prior to discharge to local surface water courses under permit by the EA.
It is important to discharge standing water and ground water so that earthworks can continue. As a considerable portion of the works involve a reduced dig it is crucial to be able to pump waters out of the excavations so that works can progress.
By reducing the volumes of water on site it is possible to retain the geotechnical properties of the earthworks materials so that they can be reused as structural backfill.
The only option for discharge is to a small drainage ditch that feeds a larger surface water course and as a result the highest discharge water quality is required.
Solution
Siltbuster initially specified and mobilised a single lift integrated HB40R unit for two stage flow proportional chemical dosing, capable of treating infeed flow rate of up to 40 m3/hr. The solution proved to be ideal as access for the HIAB vehicles was limited and the treatment system needed to be near to the discharge point.
Once installed it was established that the infeed waters did not provide sufficient pH buffering to allow the dosing chemicals to work efficiently. Siltbuster quickly upgraded the system to include a Sodium hydroxide dosing stage to maintain an optimum pH level.
Despite the current workload the system was installed within 3 days and once the third dosing stage was set up the system the system was producing a discharge water quality <40 mg/l.
