Type of System

The Solent Mitigation Partnership will upgrade householder current systems (septic tanks) that are over 10 years old.

The known tanks that meet the mitigation specification are from the manufacturers Graf, Klargester and Bio Bubble package treatment system, other equipment can be specified but must meet the nutrient reduction figures below.

The nutrient calculation for the existing dwellings served by septic tanks will be based on the Natural England default TN and TP discharge concentration figures 96.3 mg/l for TN and 11.6 mg/l for TP. These figures will be used as it is not possible to establish and evidence the actual discharge concentration and/or efficiencies of the existing septic tanks.

Many manufacturers have systems that meet efficient levels for TN and TP removal. To enable the installation of appropriate system for the property, the grant can be used to install any tank that has a TP under 3.5mg/l on the PIA certificate.

The nutrient credit calculations will be based on a precautionary methodology to enable the scheme to deliver a net environmental benefit to the protected sites. The precautionary performance figures used in our calculations are 20mg/l TN and 5mg/l TP.

Full details on the registration process and what we require of you will be released in March/ April 2026.

We hope you will consider joining the Solent Householder Septic Tank Upgrade Grant scheme. If you have any questions or require further information, please do not hesitate to contact us.