United Utilities are acting to end abstraction of raw water from Ennerdale Water, in order to protect the Freshwater Pearl Mussel population in the River Ehen and to ensure the security of future water supply for West Cumbria.
The project involves sourcing raw water from Thirlmere instead, and requires the construction of substantial new infrastructure including a 100km of pipeline, pumping stations, two new service reservoirs and a new water treatment works.
In preparation for obtaining planning consent, United Utilities identified that the construction of the infrastructure has the potential to impact on the water quality of the local rivers, including the River Derwent, designated as a Site of Special Scientific Interest for its salmonid populations.
United Utilities’ Construction Delivery Partner, Advance JV, are constructing the new Water Treatment Works.
During their preparations, Advance JV identified that the very fine particulates of the clay subsoil combined with anticipated heavy winter rainfall would cause a risk of silt pollution.
Passive, non-chemical-treatment mitigation measures, including lagoon settlement and filtration fencing were installed, but these were found to be inadequate, due to the volume of surface water requiring treatment and the very fine particle size of the suspended solids.
Advance JV, in partnership with United Utilities, initiated chemical-treatment silt control trials using WaterLynx™.
This bespoke system utilises a patented synthetic anionic polyacrylamide flocculant developed by Clearflow Group to bind together the fine clay particles, thereby aiding their separation from the water.
- Regulatory Stakeholders, including the Environment Agency, were engaged throughout the process to determine the legally-acceptable long-term chemical discharge parameters that would have no detriment to the environment.
- The WaterLynx™ flocculant is supplied in a gel block form, housed in a pipe reactor. Turbid water is pumped through this, mixing it with the flocculants, flows from which are then passed over both FlocMat™ and SiltMat, laid in a silt capture channel.
- These products provide further treatment and silt collection, allowing only the resulting clean, clear water to be discharged.
- The Total Suspended Solids were reduced from 310mg/l to 37mg/l and Turbidity levels from in >3000NTU to an average of 25NTU.
- There was also a reduction in Total Phosphorus from 0.1mg/l to 0.02mg/l and Biochemical Oxygen Demand from 69mg/l to <10mg/l, whilst achieving no change in pH.
- Laboratory analysis from Advance JV’s demonstrated that while the acrylamide monomer content increased from <0.008g/l to 0.017g/l within the treatment process, it consistently reduced to <0.008g/l prior to discharge to the watercourse. All these values are below the drinking water directive standard of 0.1g/l.
Glenn Entwistle, Senior Environmental Advisor at Advance JV was impressed with the outcome, stating
“frog environmental were knowledgeable, helping to establish a workable, cost-effective and low maintenance solution for site approved by the Regulator.
They really understood the water management issues we had on site and worked with us to develop a solution which works, as well as engaging with our operatives to ensure that they could effectively manage the system.
It was a long regulatory process, but we understand the risks associated with working in such sensitive areas, especially with new and different products and the concerns Stakeholders may have, and they were brilliant in helping provide the necessary data to satisfy Regulator requirements.
We are delighted to have found a solution that prevents pollution and protects the environment, and ultimately allows us to continue with construction.”
The set up on site is simple and easy to monitor, with no risk of overdosing, and none of the risks traditionally associated with storing liquid treatment chemicals.
The anionic WaterLynx™ flocculants have been scientifically proven to be safe for use on construction sites as they do not bioaccumulate, nor change the waste classification of the resulting sediments, which can be safely incorporated into the construction reinstatement, or taken off site as clean, inert soil.The results of Advance JV’s trial enabled them to obtain a bespoke permit from the Environment Agency to discharge treated site dewatering, upstream of the River Derwent SSSI, under some of the most stringent constraints.
The conditions of the bespoke permit are now administered by Advance JV, who confidently manage the treatment system independently of frog environmental, and continue their water quality monitoring obligations, required to confirm that the receiving stream is protected.