Nutrient Neutrality - Feasibility assessment for a constructed wetland located on land near Lyscombe and Highdon SSSI in the Poole Harbour catchment area in Dorset

To create a feasibility assessment for a constructed wetland located on land near Lyscombe and Highdon SSSI in the Poole Harbour catchment area in Dorset. Nature recovery is a key focus for stakeholders, therefore naturalised solutions or those in keeping with the natural landscape should be included within the optioneering process.

The output for the site assessment would be a brief report to identify the opportunities for developing a treatment wetland to treat historical nutrient loads from a groundwater-fed natural spring.

Key outputs would include:

• a map of the holding and the area(s) of interest (including an estimation of the amount land required in hectares required to build a treatment wetland). • an options assessment of wetland types or design that identifies opportunities for the development of a treatment wetland working with natural processes to achieve nutrient reduction and habitat improvement. • a description of the potential of the site, including barriers or potential 'show-stoppers' to the development of a treatment wetland. • an initial broad assessment of the potential nutrient credit yield range and the financial cost of delivery. Including appraisal against the wetland mitigation framework confidence matrix.

1. Desk-based feasibility assessment

• A desk-based feasibility assessment guided by stage 2 of the wetland framework. This assessment should review: o Topography;  o Soil; o Geology & Hydrogeology; o Groundwater protection; o Hydrology & drainage; o Flood risk; o Protected sites & species;  o Land use, Historic landfill & Contaminated Land

2. Site assessment

• The pre-feasibility assessment will require a visit from a treatment wetland engineer. To provide an overview of the land and associated hydraulic pathways through the site, then focusing on the areas with the greatest potential in terms of both credit nutrient yield and any business objectives for the land.

• A soil sample(s) to be taken from prospective areas identified for wetland to determine: o Potential for groundwater interaction o Whether the wetland requires a clay or artificial liner o If soil nutrient levels pose a risk of 'treatment liability' in terms of nutrient leaching

• A water sample(s) to be taken from potential source of influent to the wetland to identify nutrient concentrations of Total Nitrogen and Total Phosphorus. o Water sample(s) should be analysed against the time of year, flow conditions and recent rainfall patterns for potential variability. o Identification of prospective water sampling points on-site to measure flows and loads to the wetland.

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3. Options assessment & nutrient credit yield

• Conduct an options assessment of wetland types/design to identify opportunities for the development of a treatment wetland working with natural processes to achieve nutrient reduction and habitat improvement. Options could include, but are not limited to: o Free surface water or integrated constructed wetlands o Floating vegetation wetlands o Hybrid systems o Other approaches to river restoration (e.g., Stage zero or reconnection to floodplain) that could deliver nutrient reductions.

• Within the options assessment, identify the possible range, i.e., minimum and maximum, for nutrient reduction capacity for wetland types or design proposed. o One of the following methods should be used with a supporting narrative:  P-k-C* model  k-C* model  Regression equation

• Nutrient credit yield (reduction) calculations must show the input data and methodology used to reach the nutrient yield potential. The calculation(s) should be supported by detailed workings. o On-site samples should influence/support the calculations  Water sample(s) should be analysed against the time of year, flow conditions and recent rainfall patterns for potential variability.  Soil sample(s) should be analysed to confirm soil type. o Consideration of long-term water quality:  Consideration of the effects of surrounding land use change to deliver nutrient mitigation.  Consideration of the effects of changing groundwater quality. o Any uncertainties in the data or calculations should be highlighted.

Suggested baseline datasets to support assessments:

• BGS - Geology Viewer (bedrock and superficial geology) - https://geologyviewer.bgs.ac.uk/?_ga=2.118364809.1498923974.1682338991-1042246947.1682338991 • Risk of Flooding from Surface Water Extent: 3.3 percent annual chance

Any dataset, or surrogate data used should be accompanied by a supporting rationale for their use.

To apply for this opportunity you must submit your quotation meeting the requirements detailed in the Request for Quotation (RFQ) attached. Your response must be sent to [email protected] by 17:00 on 14th November 2023

If you have any clarification questions linked to this opportunity or the procurement process please submit these via email to [email protected]. Please note that, unless commercially sensitive, both the question and the response will be circulated to all tenderers.