Pollution Mitigation of Hobson's Brook and Coldham's Common

Cambridge City Council invites expressions of interest from suitably qualified organisations to provide pollution mitigation evidence integration, modelling and design support for the Hobson's Brook and Coldham's Common components of the Cambridge City chalk stream restoration programme.

At this stage, the Council is just undertaking a preliminary market engagement exercise. Interested parties are not required to submit detailed proposals; instead, suppliers are simply invited to register their interest via this portal. You may, however, choose to submit a brief summary of relevant previous experience or an outline of your suitability as a supplier for this project. The request for quote (RfQ) will follow shortly after and further details will be provided.

The commission will support the design of nature-based urban pollution mitigation systems, including forebays, wetland cells, swales, polishing stages and associated hydraulic and pollutant removal modelling.

Project Context and Evidence Base
The Greater Cambridge Chalk Stream Project has developed a substantial evidence base for urban chalk stream restoration and pollution mitigation. The Hobson's Brook Urban Chalk Stream Resilience Project identifies chronic urban runoff and diffuse pollution entering Hobson's Brook, including runoff conveyed by the North Ditch from the Cambridge Biomedical Campus. The project documentation identifies nutrients, sediments, hydrocarbons and salts as pollutants of concern and proposes treatment through a sequence of wetlands, infiltration swales and polishing ponds.
For Coldham's Common, the East Cambridge Main Drain and Coldham's Brook evidence base includes water quality snapshot sampling, mapping of the East Cambridge Main Drain and Coldham's Brook, and emerging nature-based solution proposals for wetlands and wider habitat restoration. Evidence includes field and laboratory measurements for dissolved oxygen, temperature, pH, electrical conductivity, turbidity, phosphate, ammonia, nitrate and faecal coliforms.
The wider project evidence base includes weekly water quality monitoring, laboratory nutrient analysis, high-resolution continuous data loggers, targeted snapshot surveys for heavy metals, hydrocarbons and other urban pollutant signatures, WHPT macroinvertebrate results, MTR macrophyte surveys, sediment research, geomorphological interpretation and restoration delivery records.

Purpose of the Commission
The purpose of this commission is to provide a specialist lead role for pollution mitigation evidence and design for Hobson's Brook and Coldham's Common. The commission must convert the available evidence into practical, defensible and measurable nature-based pollution mitigation designs capable of informing construction planning, consents, delivery sequencing and future performance validation.

The required outputs must support Cambridge City Council in moving from evidence and concept to delivery-ready technical design. The appointed supplier must provide a clear evidence trail from monitoring data and pollutant load analysis through to treatment train sizing, design assumptions, hydraulic performance, pollutant removal expectations, risks, uncertainties and monitoring validation requirements.

Strategic Role
• Provide specialist pollution mitigation leadership for Hobson's Brook and Coldham's Common.
• Integrate water quality, urban runoff, sediment, biological and habitat evidence into the design process.
• Develop pollutant load calculations and event-based design assumptions.
• Design or support the design of nature-based treatment systems for nutrients, fine sediment, metals, hydrocarbons and mixed urban runoff pressures.
• Support treatment train sizing, hydraulic performance and pollutant removal modelling.
• Provide technical input into consents, approvals, construction-ready plans and design validation.
• Work collaboratively with Cambridge City Council, ARU, Keele, contractors and other project partners.
• Support a monitoring and validation framework so that performance can be measured after delivery.