Septic Tank and PTP upgrade: opportunity mapping & modelling

Natural England are exploring the use of replacing inefficient septic tanks and package treatment plants (PTPs) with PTPs that have a higher treatment efficiency for phosphorus and nitrogen to improve water quality in up to 27 catchments. The anticipated catchments are detailed in a table in the Annex.

For each catchment, we require estimates of the following:

Scale of opportunity: The scale of opportunity (in units) of upgrading inefficient septic tanks and PTPs in each catchment. This will need to be mapped using GI software.

Nutrient reduction: The potential nutrient reduction achieved (in kg/TP and kg/TN) for phosphorus and/or nitrogen depending on the NN catchment from replacing inefficient septic tanks and PTPs with more efficient PTPs.

Cost: The cost of delivering replacement PTPs and septic tanks at-scale.

In addition to the estimates above, the following deliverables are required:

Methodologies: Will need to be developed based on Natural England's existing methods and in consultation with Natural England and created using national datasets.

Datasets & code: Natural England will need the ability to run the model independently once the commission is complete. Any datasets and code used to create the methodology, estimates and mapping will need to be made available to NE upon completion.

Technical reports: The decided upon methodology will need to be written into a report to ensure it is reproducible by others. This should highlight any uncertainties where they arise.

These deliverables will need to be managed and administered by Natural England once the project is complete and are likely to be amended and updated over time.