Black Lane WTW Refurbishment

As part of Wessex Water’s GRID resilience project, Sweco designed works to provide improved nitrate removal at Black Lane Water Treatment Works.


Client: Wessex Water

Location: Blandford Forum, Dorset

Date: 2014 - 2017

Value: £7.5 million 


In order to resolve nitrate issues and improve security of supply within the southern water resource zone, it was decided to provide a low nitrate transfer from Black Lane to Sturminster Marshall via Snowsdown Reservoir. The existing ISEP® nitrate removal plant would be replaced and measures taken to secure the works output in the event of flooding or loss of power. The works would be refurbished in line with current standards.

Sweco were commissioned by Wessex Water in March 2014, initially to undertake the outline design for the scheme, including a detailed process assessment to identify the most appropriate nitrate removal system for the site. The scheme progressed to detailed design leading to a construction start in October 2015.


The works based on a design horizon of 2035 involved the refurbishment of the boreholes and their pumps and the provision of a new nitrate treatment plant together with a flow balancing tank and extensive ancillary works.

The GRID, a £230M resilience scheme, which includes 200km of new pipelines, 24 new or refurbished pumping stations and 12 new Service Reservoirs, will provide the facility to utilise the full 10.5 Ml/d output from Black Lane.

Primary services:

• Process Design
• Outline Design
• Detailed Design
• Flood Risk Assessment
• Geotechnical Investigations
• Environmental Surveys
• Environmental permit applications
• Stakeholder Management
• Hydraulic Analysis
• Civil & Structural Engineering Design
• Geotechnical Design
• MEICA Design
• Construction Support

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Sweco’s project team covered process, civil, mechanical, electrical, ICA, geotechnical, structural and hydraulic design components.

The key elements of the design solution were as follows:

• Replacement of existing pipe culvert in Pimperne Brook with new rectangular culvert to carry site roadway
• Construction of 3nr. outfalls to Pimperne Brook
• Replacement of 3nr. borehole pumps and ancillaries, including raising headplates above flood level
• Provision of auto divert facilities from boreholes (based on high turbidity)
• New nitrate removal plant (Ovivo Nitrasep® Advanced Amberpack® process) in the new building
• Nitrate building to house nitrate plant and MCC. Steel portal frame with blockwork walls to half height and timber hit-and-miss boarding above. Pitched steel panel roof, piled foundations and reinforced concrete floor
• Lighting and ventilation to the new building
• Demolition of existing GAC building superstructure and installation of new salt saturators, brine waste tanks in existing bund
• New chlorine dosing facilities
• Replacement of existing balancing tank with new RC tank
• LCPB4 rated security doors to all buildings
• MCCs and distribution boards, control PLCs and telemetry
• Refurbishment of existing standby generator and associated diesel tanks
• Construction of shallow earth bund and diversion channel for overland flow
• Site works and ancillaries